// Copyright 2023 Greptime Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Mito region.

pub mod catchup;
pub mod opener;
pub mod options;
pub mod utils;
pub(crate) mod version;

use std::collections::hash_map::Entry;
use std::collections::{HashMap, HashSet};
use std::sync::atomic::{AtomicI64, AtomicU64, Ordering};
use std::sync::{Arc, Mutex, RwLock};

use common_base::hash::partition_expr_version;
use common_recordbatch::adapter::RegionQueryStatCounters;
use common_telemetry::{error, info, warn};
use crossbeam_utils::atomic::AtomicCell;
use partition::expr::PartitionExpr;
use snafu::{OptionExt, ResultExt, ensure};
use store_api::ManifestVersion;
use store_api::codec::PrimaryKeyEncoding;
use store_api::logstore::provider::Provider;
use store_api::metadata::RegionMetadataRef;
use store_api::metrics::{REGION_QUERY_CPU_TIME, REGION_QUERY_SCANNED_BYTES};
use store_api::region_engine::{
    RegionManifestInfo, RegionRole, RegionStatistic, SettableRegionRoleState,
};
use store_api::region_info::RegionInfoEntry;
use store_api::region_request::{PathType, StagingPartitionDirective};
use store_api::sst_entry::ManifestSstEntry;
use store_api::storage::{FileId, RegionId, SequenceNumber};
use tokio::sync::RwLockWriteGuard;
pub use utils::*;

use crate::access_layer::AccessLayerRef;
use crate::engine::region_hook::{PendingManifestHook, RegionHookRef};
use crate::error::{
    FlushableRegionStateSnafu, InvalidPartitionExprSnafu, RegionNotFoundSnafu, RegionStateSnafu,
    RegionTruncatedSnafu, Result, UnexpectedSnafu, UpdateManifestSnafu,
};
use crate::manifest::action::{
    RegionChange, RegionManifest, RegionMetaAction, RegionMetaActionList,
};
use crate::manifest::manager::RegionManifestManager;
use crate::region::version::{VersionControlRef, VersionRef};
use crate::request::{OnFailure, OptionOutputTx};
use crate::sst::file::FileMeta;
use crate::sst::file_purger::FilePurgerRef;
use crate::sst::location::{index_file_path, sst_file_path};
use crate::time_provider::TimeProviderRef;

/// This is the approximate factor to estimate the size of wal.
const ESTIMATED_WAL_FACTOR: f32 = 0.42825;

/// Region status include region id, memtable usage, sst usage, wal usage and manifest usage.
#[derive(Debug)]
pub struct RegionUsage {
    pub region_id: RegionId,
    pub wal_usage: u64,
    pub sst_usage: u64,
    pub manifest_usage: u64,
}

impl RegionUsage {
    pub fn disk_usage(&self) -> u64 {
        self.wal_usage + self.sst_usage + self.manifest_usage
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RegionLeaderState {
    /// The region is opened and is writable.
    Writable,
    /// The region is in staging mode - writable but no checkpoint/compaction.
    Staging,
    /// The region is entering staging mode. - write requests will be stalled.
    EnteringStaging,
    /// The region is altering.
    Altering,
    /// The region is dropping.
    Dropping,
    /// The region is truncating.
    Truncating,
    /// The region is handling a region edit.
    Editing,
    /// The region is stepping down.
    Downgrading,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RegionRoleState {
    Leader(RegionLeaderState),
    Follower,
}

impl RegionRoleState {
    /// Converts the region role state to leader state if it is a leader state.
    pub fn into_leader_state(self) -> Option<RegionLeaderState> {
        match self {
            RegionRoleState::Leader(leader_state) => Some(leader_state),
            RegionRoleState::Follower => None,
        }
    }

    pub(crate) fn as_str(&self) -> &'static str {
        match self {
            RegionRoleState::Follower => "Follower",
            RegionRoleState::Leader(RegionLeaderState::Writable) => "Leader(Writable)",
            RegionRoleState::Leader(RegionLeaderState::Staging) => "Leader(Staging)",
            RegionRoleState::Leader(RegionLeaderState::EnteringStaging) => {
                "Leader(EnteringStaging)"
            }
            RegionRoleState::Leader(RegionLeaderState::Altering) => "Leader(Altering)",
            RegionRoleState::Leader(RegionLeaderState::Dropping) => "Leader(Dropping)",
            RegionRoleState::Leader(RegionLeaderState::Truncating) => "Leader(Truncating)",
            RegionRoleState::Leader(RegionLeaderState::Editing) => "Leader(Editing)",
            RegionRoleState::Leader(RegionLeaderState::Downgrading) => "Leader(Downgrading)",
        }
    }
}

/// Metadata and runtime status of a region.
///
/// Writing and reading a region follow a single-writer-multi-reader rule:
/// - Only the region worker thread this region belongs to can modify the metadata.
/// - Multiple reader threads are allowed to read a specific `version` of a region.
#[derive(Debug)]
pub struct MitoRegion {
    /// Id of this region.
    ///
    /// Accessing region id from the version control is inconvenient so
    /// we also store it here.
    pub(crate) region_id: RegionId,

    /// Version controller for this region.
    ///
    /// We MUST update the version control inside the write lock of the region manifest manager.
    pub(crate) version_control: VersionControlRef,
    /// SSTs accessor for this region.
    pub(crate) access_layer: AccessLayerRef,
    /// Context to maintain manifest for this region.
    pub(crate) manifest_ctx: ManifestContextRef,
    /// SST file purger.
    pub(crate) file_purger: FilePurgerRef,
    /// The provider of log store.
    pub(crate) provider: Provider,
    /// Last flush time in millis.
    last_flush_millis: AtomicI64,
    /// Last schedule compaction time in millis.
    last_schedule_compaction_millis: AtomicI64,
    /// Provider to get current time.
    time_provider: TimeProviderRef,
    /// The topic's latest entry id since the region's last flushing.
    /// **Only used for remote WAL pruning.**
    ///
    /// The value will be updated to the latest offset of the topic
    /// if region receives a flush request or schedules a periodic flush task
    /// and the region's memtable is empty.
    ///
    /// There are no WAL entries in range [flushed_entry_id, topic_latest_entry_id] for current region,
    /// which means these WAL entries maybe able to be pruned up to `topic_latest_entry_id`.
    pub(crate) topic_latest_entry_id: AtomicU64,
    /// Region stats.
    pub(crate) region_stats: RegionStats,
    /// manifest stats
    stats: ManifestStats,
}

/// Runtime statistics of a region.
#[derive(Debug)]
pub(crate) struct RegionStats {
    /// The total bytes written to the region.
    pub(crate) written_bytes: Arc<AtomicU64>,
    /// The total query CPU time of the region in nanoseconds.
    pub(crate) query_cpu_time: Arc<AtomicU64>,
    /// The total scanned bytes of the region.
    pub(crate) query_scanned_bytes: Arc<AtomicU64>,
}

impl RegionStats {
    pub(crate) fn new() -> Self {
        Self {
            written_bytes: Arc::new(AtomicU64::new(0)),
            query_cpu_time: Arc::new(AtomicU64::new(0)),
            query_scanned_bytes: Arc::new(AtomicU64::new(0)),
        }
    }

    pub(crate) fn query_stat_counters(&self) -> RegionQueryStatCounters {
        RegionQueryStatCounters {
            query_cpu_time: self.query_cpu_time.clone(),
            query_scanned_bytes: self.query_scanned_bytes.clone(),
        }
    }
}

pub type MitoRegionRef = Arc<MitoRegion>;

#[derive(Debug, Clone)]
pub(crate) struct StagingPartitionInfo {
    pub(crate) partition_directive: StagingPartitionDirective,
    pub(crate) partition_rule_version: u64,
}

impl StagingPartitionInfo {
    /// Returns the partition expression carried by the staging directive, if any.
    pub(crate) fn partition_expr(&self) -> Option<&str> {
        self.partition_directive.partition_expr()
    }

    /// Builds staging partition info from a directive and derives its version marker.
    pub(crate) fn from_partition_directive(partition_directive: StagingPartitionDirective) -> Self {
        let partition_rule_version = match &partition_directive {
            StagingPartitionDirective::UpdatePartitionExpr(expr) => {
                partition_expr_version(Some(expr))
            }
            StagingPartitionDirective::RejectAllWrites => 0,
        };
        Self {
            partition_directive,
            partition_rule_version,
        }
    }
}

impl MitoRegion {
    fn remove_region_metrics(&self) {
        let region_id = self.region_id.as_u64().to_string();
        let labels = &[region_id.as_str()];
        let _ = REGION_QUERY_CPU_TIME.remove_label_values(labels);
        let _ = REGION_QUERY_SCANNED_BYTES.remove_label_values(labels);
    }

    /// Stop background managers for this region.
    pub(crate) async fn stop(&self) {
        self.manifest_ctx
            .manifest_manager
            .write()
            .await
            .stop()
            .await;

        info!(
            "Stopped region manifest manager, region_id: {}",
            self.region_id
        );
    }

    /// Returns current metadata of the region.
    pub fn metadata(&self) -> RegionMetadataRef {
        let version_data = self.version_control.current();
        version_data.version.metadata.clone()
    }

    /// Returns primary key encoding of the region.
    pub(crate) fn primary_key_encoding(&self) -> PrimaryKeyEncoding {
        let version_data = self.version_control.current();
        version_data.version.metadata.primary_key_encoding
    }

    /// Returns current version of the region.
    pub(crate) fn version(&self) -> VersionRef {
        let version_data = self.version_control.current();
        version_data.version
    }

    /// Returns whether writes to this region should skip WAL.
    pub(crate) fn skip_wal(&self) -> bool {
        self.provider == Provider::Noop || self.version().options.skip_wal
    }

    /// Returns last flush timestamp in millis.
    pub(crate) fn last_flush_millis(&self) -> i64 {
        self.last_flush_millis.load(Ordering::Relaxed)
    }

    /// Update flush time to current time.
    pub(crate) fn update_flush_millis(&self) {
        let now = self.time_provider.current_time_millis();
        self.last_flush_millis.store(now, Ordering::Relaxed);
    }

    /// Returns last schedule compaction timestamp in millis.
    pub(crate) fn last_schedule_compaction_millis(&self) -> i64 {
        self.last_schedule_compaction_millis.load(Ordering::Relaxed)
    }

    /// Update schedule compaction time to current time.
    pub(crate) fn update_schedule_compaction_millis(&self) {
        let now = self.time_provider.current_time_millis();
        self.last_schedule_compaction_millis
            .store(now, Ordering::Relaxed);
    }

    /// Returns the table dir.
    pub(crate) fn table_dir(&self) -> &str {
        self.access_layer.table_dir()
    }

    /// Returns the path type of the region.
    pub(crate) fn path_type(&self) -> PathType {
        self.access_layer.path_type()
    }

    /// Returns whether the region is writable.
    pub(crate) fn is_writable(&self) -> bool {
        matches!(
            self.manifest_ctx.state.load(),
            RegionRoleState::Leader(RegionLeaderState::Writable)
                | RegionRoleState::Leader(RegionLeaderState::Staging)
        )
    }

    /// Returns whether the region is flushable.
    pub(crate) fn is_flushable(&self) -> bool {
        matches!(
            self.manifest_ctx.state.load(),
            RegionRoleState::Leader(RegionLeaderState::Writable)
                | RegionRoleState::Leader(RegionLeaderState::Staging)
                | RegionRoleState::Leader(RegionLeaderState::Downgrading)
        )
    }

    /// Returns whether the region should abort index building.
    pub(crate) fn should_abort_index(&self) -> bool {
        matches!(
            self.manifest_ctx.state.load(),
            RegionRoleState::Follower
                | RegionRoleState::Leader(RegionLeaderState::Dropping)
                | RegionRoleState::Leader(RegionLeaderState::Truncating)
                | RegionRoleState::Leader(RegionLeaderState::Downgrading)
                | RegionRoleState::Leader(RegionLeaderState::Staging)
        )
    }

    /// Returns whether the region is downgrading.
    pub(crate) fn is_downgrading(&self) -> bool {
        matches!(
            self.manifest_ctx.state.load(),
            RegionRoleState::Leader(RegionLeaderState::Downgrading)
        )
    }

    /// Returns whether the region is in staging mode.
    pub(crate) fn is_staging(&self) -> bool {
        self.manifest_ctx.state.load() == RegionRoleState::Leader(RegionLeaderState::Staging)
    }

    /// Returns whether the region is entering staging mode.
    pub(crate) fn is_enter_staging(&self) -> bool {
        self.manifest_ctx.state.load()
            == RegionRoleState::Leader(RegionLeaderState::EnteringStaging)
    }

    pub fn region_id(&self) -> RegionId {
        self.region_id
    }

    pub fn find_committed_sequence(&self) -> SequenceNumber {
        self.version_control.committed_sequence()
    }

    /// Returns the latest sequence that has already been persisted into SSTs.
    ///
    /// Incremental memtable-only reads must use a cursor greater than or equal to
    /// this boundary; older cursors are stale because the corresponding updates may
    /// already have been flushed out of memtables.
    pub fn flushed_sequence(&self) -> SequenceNumber {
        self.version_control.current().version.flushed_sequence
    }

    /// Returns whether the region is readonly.
    pub fn is_follower(&self) -> bool {
        self.manifest_ctx.state.load() == RegionRoleState::Follower
    }

    /// Returns the state of the region.
    pub(crate) fn state(&self) -> RegionRoleState {
        self.manifest_ctx.state.load()
    }

    /// Sets the region role state.
    pub(crate) fn set_role(&self, next_role: RegionRole) {
        self.manifest_ctx.set_role(next_role, self.region_id);
    }

    pub(crate) fn region_role(&self) -> RegionRole {
        match self.state() {
            RegionRoleState::Follower => RegionRole::Follower,
            RegionRoleState::Leader(RegionLeaderState::Staging) => RegionRole::StagingLeader,
            RegionRoleState::Leader(RegionLeaderState::Downgrading) => {
                RegionRole::DowngradingLeader
            }
            RegionRoleState::Leader(_) => RegionRole::Leader,
        }
    }

    /// Sets the altering state.
    /// You should call this method in the worker loop.
    pub(crate) fn set_altering(&self) -> Result<()> {
        self.compare_exchange_state(
            RegionLeaderState::Writable,
            RegionRoleState::Leader(RegionLeaderState::Altering),
        )
    }

    /// Sets the dropping state.
    /// You should call this method in the worker loop.
    pub(crate) fn set_dropping(&self, expect: RegionLeaderState) -> Result<()> {
        self.compare_exchange_state(expect, RegionRoleState::Leader(RegionLeaderState::Dropping))
    }

    /// Sets the truncating state.
    /// You should call this method in the worker loop.
    pub(crate) fn set_truncating(&self) -> Result<()> {
        self.compare_exchange_state(
            RegionLeaderState::Writable,
            RegionRoleState::Leader(RegionLeaderState::Truncating),
        )
    }

    /// Sets the editing state.
    /// You should call this method in the worker loop.
    pub(crate) fn set_editing(&self, expect: RegionLeaderState) -> Result<()> {
        self.compare_exchange_state(expect, RegionRoleState::Leader(RegionLeaderState::Editing))
    }

    /// Sets the staging state.
    ///
    /// You should call this method in the worker loop.
    /// Transitions from Writable to Staging state.
    /// Cleans any existing staging manifests before entering staging mode.
    pub(crate) async fn set_staging(
        &self,
        manager: &mut RwLockWriteGuard<'_, RegionManifestManager>,
    ) -> Result<()> {
        manager.store().clear_staging_manifests().await?;

        self.compare_exchange_state(
            RegionLeaderState::Writable,
            RegionRoleState::Leader(RegionLeaderState::Staging),
        )
    }

    /// Sets the entering staging state.
    pub(crate) fn set_entering_staging(&self) -> Result<()> {
        self.compare_exchange_state(
            RegionLeaderState::Writable,
            RegionRoleState::Leader(RegionLeaderState::EnteringStaging),
        )
    }

    /// Exits the staging state back to writable.
    ///
    /// You should call this method in the worker loop.
    /// Transitions from Staging to Writable state.
    pub fn exit_staging(&self) -> Result<()> {
        self.manifest_ctx.exit_staging(
            self.region_id,
            RegionRoleState::Leader(RegionLeaderState::Writable),
        )
    }

    /// Sets the region role state gracefully. This acquires the manifest write lock.
    pub(crate) async fn set_role_state_gracefully(
        &self,
        state: SettableRegionRoleState,
    ) -> Result<()> {
        let mut manager: RwLockWriteGuard<'_, RegionManifestManager> =
            self.manifest_ctx.manifest_manager.write().await;
        let current_state = self.state();
        let mut wait_for_checkpoint = false;

        let hook_payload: Option<PendingManifestHook> = match state {
            SettableRegionRoleState::Leader => {
                // Exit staging mode and return to normal writable leader
                // Only allowed from staging state
                match current_state {
                    RegionRoleState::Leader(RegionLeaderState::Staging) => {
                        info!("Exiting staging mode for region {}", self.region_id);
                        // Use the success exit path that merges all staged manifests
                        self.exit_staging_on_success(&mut manager).await?
                    }
                    RegionRoleState::Leader(RegionLeaderState::Writable) => {
                        // Already in desired state - no-op
                        info!("Region {} already in normal leader mode", self.region_id);
                        None
                    }
                    _ => {
                        // Only staging -> leader transition is allowed
                        return Err(RegionStateSnafu {
                            region_id: self.region_id,
                            state: current_state,
                            expect: RegionRoleState::Leader(RegionLeaderState::Staging),
                        }
                        .build());
                    }
                }
            }

            SettableRegionRoleState::StagingLeader => {
                // Enter staging mode from normal writable leader
                // Only allowed from writable leader state
                match current_state {
                    RegionRoleState::Leader(RegionLeaderState::Writable) => {
                        info!("Entering staging mode for region {}", self.region_id);
                        self.set_staging(&mut manager).await?;
                    }
                    RegionRoleState::Leader(RegionLeaderState::Staging) => {
                        // Already in desired state - no-op
                        info!("Region {} already in staging mode", self.region_id);
                    }
                    _ => {
                        return Err(RegionStateSnafu {
                            region_id: self.region_id,
                            state: current_state,
                            expect: RegionRoleState::Leader(RegionLeaderState::Writable),
                        }
                        .build());
                    }
                }
                None
            }

            SettableRegionRoleState::Follower => {
                // Make this region a follower
                match current_state {
                    RegionRoleState::Leader(RegionLeaderState::Staging) => {
                        info!(
                            "Exiting staging and demoting region {} to follower",
                            self.region_id
                        );
                        self.exit_staging()?;
                        self.set_role(RegionRole::Follower);
                        wait_for_checkpoint = true;
                    }
                    RegionRoleState::Leader(_) => {
                        info!("Demoting region {} from leader to follower", self.region_id);
                        self.set_role(RegionRole::Follower);
                        wait_for_checkpoint = true;
                    }
                    RegionRoleState::Follower => {
                        // Already in desired state - no-op
                        info!("Region {} already in follower mode", self.region_id);
                    }
                }
                None
            }

            SettableRegionRoleState::DowngradingLeader => {
                // downgrade this region to downgrading leader
                match current_state {
                    RegionRoleState::Leader(RegionLeaderState::Staging) => {
                        info!(
                            "Exiting staging and entering downgrade for region {}",
                            self.region_id
                        );
                        self.exit_staging()?;
                        self.set_role(RegionRole::DowngradingLeader);
                        wait_for_checkpoint = true;
                    }
                    RegionRoleState::Leader(RegionLeaderState::Writable) => {
                        info!("Starting downgrade for region {}", self.region_id);
                        self.set_role(RegionRole::DowngradingLeader);
                        wait_for_checkpoint = true;
                    }
                    RegionRoleState::Leader(RegionLeaderState::Downgrading) => {
                        // Already in desired state - no-op
                        info!("Region {} already in downgrading mode", self.region_id);
                        wait_for_checkpoint = true;
                    }
                    _ => {
                        warn!(
                            "Cannot start downgrade for region {} from state {:?}",
                            self.region_id, current_state
                        );
                    }
                }
                None
            }
        };

        // The state is changed before waiting, so no new writable-leader work
        // can race with the barrier. Keep the manager lock while joining to
        // serialize the barrier with checkpoint scheduling.
        if wait_for_checkpoint {
            manager.wait_for_pending_checkpoint().await;
        }

        // Hack(zhongzc): If we have just become leader (writable), persist any backfilled metadata.
        let mut backfill_hook_payload: Option<PendingManifestHook> = None;
        if self.state() == RegionRoleState::Leader(RegionLeaderState::Writable) {
            // Persist backfilled metadata if manifest is missing fields (e.g., partition_expr)
            let manifest_meta = &manager.manifest().metadata;
            let current_version = self.version();
            let current_meta = &current_version.metadata;
            if manifest_meta.partition_expr.is_none() && current_meta.partition_expr.is_some() {
                let action = RegionMetaAction::Change(RegionChange {
                    metadata: current_meta.clone(),
                    sst_format: current_version.options.sst_format.unwrap_or_default(),
                    append_mode: None,
                });
                let action_list = RegionMetaActionList::with_action(action);
                match self
                    .manifest_ctx
                    .update_locked(&mut manager, action_list, false)
                    .await
                {
                    Ok(pending) => {
                        info!(
                            "Successfully persisted backfilled metadata for region {}, version: {}",
                            self.region_id,
                            pending.version()
                        );
                        backfill_hook_payload = Some(pending);
                    }
                    Err(e) => {
                        warn!(e; "Failed to persist backfilled metadata for region {}", self.region_id);
                    }
                }
            }
        }

        drop(manager);

        // Merge both payloads so consumers see the complete set of actions in
        // one notification. The lock is released, so it's safe to fire.
        let merged = match (hook_payload, backfill_hook_payload) {
            (Some(staging), Some(backfill)) => Some(staging.merge(backfill)),
            (Some(payload), None) => Some(payload),
            (None, Some(payload)) => Some(payload),
            (None, None) => None,
        };

        if let Some(pending) = merged {
            pending.fire().await;
        }

        Ok(())
    }

    /// Switches the region state to `RegionRoleState::Leader(RegionLeaderState::Writable)` if the current state is `expect`.
    /// Otherwise, logs an error.
    pub(crate) fn switch_state_to_writable(&self, expect: RegionLeaderState) {
        if let Err(e) = self
            .compare_exchange_state(expect, RegionRoleState::Leader(RegionLeaderState::Writable))
        {
            error!(e; "failed to switch region state to writable, expect state is {:?}", expect);
        }
    }

    /// Switches the region state to `RegionRoleState::Leader(RegionLeaderState::Staging)` if the current state is `expect`.
    /// Otherwise, logs an error.
    pub(crate) fn switch_state_to_staging(&self, expect: RegionLeaderState) {
        if let Err(e) =
            self.compare_exchange_state(expect, RegionRoleState::Leader(RegionLeaderState::Staging))
        {
            error!(e; "failed to switch region state to staging, expect state is {:?}", expect);
        }
    }

    /// Returns the region statistic.
    pub(crate) fn region_statistic(&self) -> RegionStatistic {
        let version = self.version();
        let memtables = &version.memtables;
        let memtable_usage = (memtables.mutable_usage() + memtables.immutables_usage()) as u64;

        let sst_usage = version.ssts.owned_sst_usage(self.region_id);
        let index_usage = version.ssts.owned_index_usage(self.region_id);
        let flushed_entry_id = version.flushed_entry_id;

        let wal_usage = self.estimated_wal_usage(memtable_usage);
        let manifest_usage = self.stats.total_manifest_size();
        let num_rows = version.ssts.owned_num_rows(self.region_id) + version.memtables.num_rows();
        let num_files = version.ssts.owned_num_files(self.region_id);
        let manifest_version = self.stats.manifest_version();
        let file_removed_cnt = self.stats.file_removed_cnt();

        let topic_latest_entry_id = self.topic_latest_entry_id.load(Ordering::Relaxed);
        let written_bytes = self.region_stats.written_bytes.load(Ordering::Relaxed);
        let query_cpu_time = self.region_stats.query_cpu_time.load(Ordering::Relaxed);
        let query_scanned_bytes = self
            .region_stats
            .query_scanned_bytes
            .load(Ordering::Relaxed);

        RegionStatistic {
            num_rows,
            memtable_size: memtable_usage,
            wal_size: wal_usage,
            manifest_size: manifest_usage,
            sst_size: sst_usage,
            sst_num: num_files,
            index_size: index_usage,
            manifest: RegionManifestInfo::Mito {
                manifest_version,
                flushed_entry_id,
                file_removed_cnt,
            },
            data_topic_latest_entry_id: topic_latest_entry_id,
            metadata_topic_latest_entry_id: topic_latest_entry_id,
            written_bytes,
            query_cpu_time,
            query_scanned_bytes,
        }
    }

    /// Estimated WAL size in bytes.
    /// Use the memtables size to estimate the size of wal.
    fn estimated_wal_usage(&self, memtable_usage: u64) -> u64 {
        ((memtable_usage as f32) * ESTIMATED_WAL_FACTOR) as u64
    }

    /// Sets the state of the region to given state if the current state equals to
    /// the expected.
    fn compare_exchange_state(
        &self,
        expect: RegionLeaderState,
        state: RegionRoleState,
    ) -> Result<()> {
        self.manifest_ctx
            .state
            .compare_exchange(RegionRoleState::Leader(expect), state)
            .map_err(|actual| {
                RegionStateSnafu {
                    region_id: self.region_id,
                    state: actual,
                    expect: RegionRoleState::Leader(expect),
                }
                .build()
            })?;
        Ok(())
    }

    pub fn access_layer(&self) -> AccessLayerRef {
        self.access_layer.clone()
    }

    /// Returns the region info entry of the region.
    pub(crate) fn region_info_entry(&self, node_id: Option<u64>) -> RegionInfoEntry {
        let region_id = self.region_id;
        let version = self.version();
        let state = self.state();
        let role = self.region_role();
        let region_options = serde_json::to_string(&version.options)
            .unwrap_or_else(|err| serde_json::json!({ "error": err.to_string() }).to_string());
        let sst_format = match version.options.sst_format.unwrap_or_default() {
            crate::sst::FormatType::PrimaryKey => "primary_key",
            crate::sst::FormatType::Flat => "flat",
        }
        .to_string();

        RegionInfoEntry {
            region_id,
            table_id: region_id.table_id(),
            region_number: region_id.region_number(),
            region_group: region_id.region_group(),
            region_sequence: region_id.region_sequence(),
            state: state.as_str().to_string(),
            role: role.to_string(),
            writable: self.is_writable(),
            committed_sequence: self.find_committed_sequence(),
            flushed_sequence: Some(self.flushed_sequence()).filter(|sequence| *sequence > 0),
            manifest_version: self.stats.manifest_version(),
            compaction_time_window: version
                .compaction_time_window
                .map(|duration| humantime::format_duration(duration).to_string()),
            region_options,
            sst_format,
            node_id,
        }
    }

    /// Returns the SST entries of the region.
    pub async fn manifest_sst_entries(&self) -> Vec<ManifestSstEntry> {
        let table_dir = self.table_dir();
        let path_type = self.access_layer.path_type();

        let visible_ssts = self
            .version()
            .ssts
            .levels()
            .iter()
            .flat_map(|level| level.files().map(|file| file.file_id().file_id()))
            .collect::<HashSet<_>>();

        let manifest_files = self.manifest_ctx.manifest().await.files.clone();
        let staging_files = self
            .manifest_ctx
            .staging_manifest()
            .await
            .map(|m| m.files.clone())
            .unwrap_or_default();
        let files = manifest_files
            .into_iter()
            .chain(staging_files)
            .collect::<HashMap<_, _>>();

        files
            .values()
            .map(|meta| {
                let region_id = self.region_id;
                let origin_region_id = meta.region_id;
                let (index_version, index_file_path, index_file_size) = if meta.index_file_size > 0
                {
                    let index_file_path = index_file_path(table_dir, meta.index_id(), path_type);
                    (
                        meta.index_version,
                        Some(index_file_path),
                        Some(meta.index_file_size),
                    )
                } else {
                    (0, None, None)
                };
                let visible = visible_ssts.contains(&meta.file_id);
                ManifestSstEntry {
                    table_dir: table_dir.to_string(),
                    region_id,
                    table_id: region_id.table_id(),
                    region_number: region_id.region_number(),
                    region_group: region_id.region_group(),
                    region_sequence: region_id.region_sequence(),
                    file_id: meta.file_id.to_string(),
                    index_version,
                    level: meta.level,
                    file_path: sst_file_path(table_dir, meta.file_id(), path_type),
                    file_size: meta.file_size,
                    max_row_group_uncompressed_size: meta.max_row_group_uncompressed_size,
                    index_file_path,
                    index_file_size,
                    num_rows: meta.num_rows,
                    num_row_groups: meta.num_row_groups,
                    num_series: Some(meta.num_series),
                    min_ts: meta.time_range.0,
                    max_ts: meta.time_range.1,
                    sequence: meta.sequence.map(|s| s.get()),
                    partition_expr: meta.partition_expr.as_ref().map(ToString::to_string),
                    origin_region_id,
                    node_id: None,
                    visible,
                    primary_key_min: meta.primary_key_min.clone(),
                    primary_key_max: meta.primary_key_max.clone(),
                }
            })
            .collect()
    }

    /// Returns the file metas of the region by file ids.
    pub async fn file_metas(&self, file_ids: &[FileId]) -> Vec<Option<FileMeta>> {
        let manifest_files = self.manifest_ctx.manifest().await.files.clone();

        file_ids
            .iter()
            .map(|file_id| manifest_files.get(file_id).cloned())
            .collect::<Vec<_>>()
    }

    /// Returns all live SST file metas and the current manifest version from
    /// the region manifest, merging both the normal and staging manifests.
    ///
    /// While the region is in staging mode (e.g. during region copy/migration),
    /// the authoritative live file set lives in the staging manifest, so this
    /// method merges both — matching the semantics of [`manifest_sst_entries`].
    ///
    /// The returned manifest version is the staging version when a staging
    /// manifest is present, otherwise the normal manifest version.
    pub async fn all_manifest_files(&self) -> (Vec<FileMeta>, ManifestVersion) {
        let manifest = self.manifest_ctx.manifest().await;
        let staging = self
            .manifest_ctx
            .staging_manifest()
            .await
            .map(|m| (m.files.clone(), m.manifest_version));

        let version = staging
            .as_ref()
            .map(|(_, v)| *v)
            .unwrap_or(manifest.manifest_version);

        let files = match staging {
            Some((staging_files, _)) => {
                let merged = manifest
                    .files
                    .clone()
                    .into_iter()
                    .chain(staging_files)
                    .collect::<std::collections::HashMap<_, _>>();
                merged.into_values().collect()
            }
            None => manifest.files.values().cloned().collect(),
        };

        (files, version)
    }

    /// Exit staging mode successfully by merging all staged manifests and making them visible.
    /// Merges staged manifest actions into the live manifest and exits staging mode.
    ///
    /// The caller must hold the manifest write lock and pass it via `manager`.
    /// Returns `Ok(Some(pending))` when staging manifests were merged, or
    /// `Ok(None)` when there were no staged manifests to merge.
    ///
    /// **Important:** [`fire`](PendingManifestHook::fire) the receipt only after
    /// dropping the lock — the hook may read the manifest and deadlock otherwise.
    pub(crate) async fn exit_staging_on_success(
        &self,
        manager: &mut RwLockWriteGuard<'_, RegionManifestManager>,
    ) -> Result<Option<PendingManifestHook>> {
        let current_state = self.manifest_ctx.current_state();
        ensure!(
            current_state == RegionRoleState::Leader(RegionLeaderState::Staging),
            RegionStateSnafu {
                region_id: self.region_id,
                state: current_state,
                expect: RegionRoleState::Leader(RegionLeaderState::Staging),
            }
        );

        // Merge all staged manifest actions
        let merged_actions = match manager.merge_staged_actions(current_state).await? {
            Some(actions) => actions,
            None => {
                info!(
                    "No staged manifests to merge for region {}, exiting staging mode without changes",
                    self.region_id
                );
                // Even if no manifests to merge, we still need to exit staging mode
                self.exit_staging()?;
                return Ok(None);
            }
        };
        let expect_change = merged_actions.actions.iter().any(|a| a.is_change());
        let expect_partition_expr_change = merged_actions
            .actions
            .iter()
            .any(|a| a.is_partition_expr_change());
        let expect_edit = merged_actions.actions.iter().any(|a| a.is_edit());
        ensure!(
            !(expect_change && expect_partition_expr_change),
            UnexpectedSnafu {
                reason: "unexpected both change and partition expr change actions in merged actions"
            }
        );
        ensure!(
            expect_change || expect_partition_expr_change,
            UnexpectedSnafu {
                reason: "expect a change or partition expr change action in merged actions"
            }
        );
        ensure!(
            expect_edit,
            UnexpectedSnafu {
                reason: "expect an edit action in merged actions"
            }
        );

        let (merged_partition_expr_change, merged_change, merged_edit) =
            merged_actions.clone().split_region_change_and_edit();
        if let Some(change) = &merged_change {
            // In staging exit we only allow metadata-only updates. A `Change`
            // action is accepted only when column definitions are unchanged;
            // otherwise it is treated as a schema change and rejected.
            let current_column_metadatas = &self.version().metadata.column_metadatas;
            ensure!(
                change.metadata.column_metadatas == *current_column_metadatas,
                UnexpectedSnafu {
                    reason: "change action alters column metadata in staging exit"
                }
            );
        }

        // Submit merged actions using the manifest manager's update method.
        // Pass `false` so it saves to normal directory, not staging.
        let pending = self
            .manifest_ctx
            .update_locked(manager, merged_actions, false)
            .await?;
        let new_version = pending.version();
        info!(
            "Successfully submitted merged staged manifests for region {}, new version: {}",
            self.region_id, new_version
        );

        // Apply the merged changes to in-memory version control
        if let Some(change) = merged_partition_expr_change {
            let mut new_metadata = self.version().metadata.as_ref().clone();
            new_metadata.set_partition_expr(change.partition_expr);
            self.version_control.alter_metadata(new_metadata.into());
        }
        if let Some(change) = merged_change {
            self.version_control.alter_metadata(change.metadata);
        }
        self.version_control
            .apply_edit(Some(merged_edit), &[], self.file_purger.clone());

        // Clear all staging manifests and transit state
        if let Err(e) = manager.clear_staging_manifest_and_dir().await {
            error!(e; "Failed to clear staging manifest dir for region {}", self.region_id);
        }
        self.exit_staging()?;

        // Return the hook payload; the caller invokes the hook after dropping the lock.
        Ok(Some(pending))
    }

    /// Returns the partition expression string for this region.
    ///
    /// If the region is currently in staging state, this returns the partition expression held in
    /// the staging partition field. Otherwise, it returns the partition expression from the primary
    /// region metadata (current committed version).
    pub fn maybe_staging_partition_expr_str(&self) -> Option<String> {
        let is_staging = self.is_staging();
        if is_staging {
            let staging_partition_info = self.manifest_ctx.staging_partition_info();
            if staging_partition_info.is_none() {
                warn!(
                    "Staging partition expr is none for region {} in staging state",
                    self.region_id
                );
            }
            staging_partition_info
                .as_ref()
                .and_then(|info| info.partition_expr().map(ToString::to_string))
        } else {
            let version = self.version();
            version.metadata.partition_expr.clone()
        }
    }

    pub fn expected_partition_expr_version(&self) -> u64 {
        if self.is_staging() {
            self.manifest_ctx
                .staging_partition_info()
                .as_ref()
                .map(|info| info.partition_rule_version)
                .unwrap_or_default()
        } else {
            self.version().metadata.partition_expr_version
        }
    }

    /// Returns whether writes should be rejected for this region in staging mode.
    pub(crate) fn reject_all_writes_in_staging(&self) -> bool {
        if !self.is_staging() {
            return false;
        }
        self.manifest_ctx
            .staging_partition_info()
            .as_ref()
            .map(|info| {
                matches!(
                    info.partition_directive,
                    StagingPartitionDirective::RejectAllWrites
                )
            })
            .unwrap_or(false)
    }
}

impl Drop for MitoRegion {
    fn drop(&mut self) {
        self.remove_region_metrics();
    }
}

/// Result of publishing rebuilt index metadata to the manifest.
#[derive(Debug)]
pub(crate) enum IndexPublication {
    /// The index metadata was committed.
    Committed {
        manifest_version: ManifestVersion,
        file_meta: FileMeta,
    },
    /// The build no longer matches the current manifest.
    Stale(IndexPublicationStale),
}

/// Why an index publication became stale.
#[derive(Debug, PartialEq, Eq)]
pub(crate) enum IndexPublicationStale {
    /// The source SST or region incarnation is no longer publishable.
    SourceChanged,
    /// The SST still matches, but the schema generation changed.
    SchemaChanged,
}

/// Manifest state an index build is based on.
///
/// Both fields must still match when the rebuilt index is published. The file
/// metadata identifies the exact SST generation, while the schema version
/// identifies the exact index definition used by the builder.
#[derive(Clone, Debug, PartialEq, Eq)]
pub(crate) struct IndexBuildSource {
    pub(crate) file_meta: FileMeta,
    pub(crate) schema_version: u64,
}

impl IndexBuildSource {
    pub(crate) fn new(file_meta: FileMeta, schema_version: u64) -> Self {
        Self {
            file_meta,
            schema_version,
        }
    }
}

/// Context to update the region manifest.
#[derive(Debug)]
pub(crate) struct ManifestContext {
    /// Manager to maintain manifest for this region. Logical writes go through
    /// [`update_locked`](Self::update_locked) (or an [`update_manifest`](Self::update_manifest)
    /// variant) so they produce a [`PendingManifestHook`].
    pub(crate) manifest_manager: tokio::sync::RwLock<RegionManifestManager>,
    /// The state of the region. The region checks the state before updating
    /// manifest.
    state: AtomicCell<RegionRoleState>,
    /// Partition info of the region in staging mode.
    ///
    /// During the staging mode, the region metadata in [`VersionControlRef`] is not updated,
    /// so we need to store the partition info separately.
    staging_partition_info: Mutex<Option<StagingPartitionInfo>>,
    /// Optional region hook for observing manifest mutations.
    hook: Option<RegionHookRef>,
}

impl ManifestContext {
    pub(crate) fn new(
        manager: RegionManifestManager,
        state: RegionRoleState,
        hook: Option<RegionHookRef>,
    ) -> Self {
        ManifestContext {
            manifest_manager: tokio::sync::RwLock::new(manager),
            state: AtomicCell::new(state),
            staging_partition_info: Mutex::new(None),
            hook,
        }
    }

    /// Returns the region hook if one is registered.
    pub(crate) fn hook(&self) -> Option<RegionHookRef> {
        self.hook.clone()
    }

    pub(crate) fn staging_partition_info(&self) -> Option<StagingPartitionInfo> {
        self.staging_partition_info.lock().unwrap().clone()
    }

    pub(crate) fn set_staging_partition_info(&self, staging_partition_info: StagingPartitionInfo) {
        let mut current = self.staging_partition_info.lock().unwrap();
        debug_assert!(current.is_none());
        *current = Some(staging_partition_info);
    }

    fn clear_staging_partition_info(&self) {
        *self.staging_partition_info.lock().unwrap() = None;
    }

    pub(crate) fn exit_staging(
        &self,
        region_id: RegionId,
        next_state: RegionRoleState,
    ) -> Result<()> {
        self.state
            .compare_exchange(
                RegionRoleState::Leader(RegionLeaderState::Staging),
                next_state,
            )
            .map_err(|actual| {
                RegionStateSnafu {
                    region_id,
                    state: actual,
                    expect: RegionRoleState::Leader(RegionLeaderState::Staging),
                }
                .build()
            })?;
        self.clear_staging_partition_info();
        Ok(())
    }

    pub(crate) async fn manifest_version(&self) -> ManifestVersion {
        self.manifest_manager
            .read()
            .await
            .manifest()
            .manifest_version
    }

    pub(crate) async fn has_update(&self) -> Result<bool> {
        self.manifest_manager.read().await.has_update().await
    }

    /// Returns the current region role state.
    pub(crate) fn current_state(&self) -> RegionRoleState {
        self.state.load()
    }

    /// Installs the manifest changes from the current version to the target version (inclusive).
    ///
    /// Returns installed [RegionManifest].
    /// **Note**: This function is not guaranteed to install the target version strictly.
    /// The installed version may be greater than the target version.
    pub(crate) async fn install_manifest_to(
        &self,
        version: ManifestVersion,
    ) -> Result<Arc<RegionManifest>> {
        let mut manager = self.manifest_manager.write().await;
        manager.install_manifest_to(version).await?;

        Ok(manager.manifest())
    }

    /// Updates the manifest if current state is `expect_state`.
    pub(crate) async fn update_manifest(
        &self,
        expect_state: RegionLeaderState,
        action_list: RegionMetaActionList,
        is_staging: bool,
    ) -> Result<ManifestVersion> {
        self.update_manifest_with_state_check(action_list, is_staging, |current_state, region_id| {
            // If expect_state is not downgrading, the current state must be either `expect_state` or downgrading.
            //
            // A downgrading leader rejects user writes but still allows
            // flushing the memtable and updating the manifest.
            if expect_state != RegionLeaderState::Downgrading {
                if current_state == RegionRoleState::Leader(RegionLeaderState::Downgrading) {
                    info!(
                        "Region {} is in downgrading leader state, updating manifest. Expect state is {:?}",
                        region_id, expect_state
                    );
                }
                ensure!(
                    current_state == RegionRoleState::Leader(expect_state)
                        || current_state == RegionRoleState::Leader(RegionLeaderState::Downgrading),
                    UpdateManifestSnafu {
                        region_id,
                        state: current_state,
                    }
                );
            } else {
                ensure!(
                    current_state == RegionRoleState::Leader(expect_state),
                    RegionStateSnafu {
                        region_id,
                        state: current_state,
                        expect: RegionRoleState::Leader(expect_state),
                    }
                );
            }

            Ok(())
        })
        .await
    }

    /// Updates the manifest for compaction.
    ///
    /// Compaction may finish while a direct external region edit is in the transient
    /// `Editing` state. Direct external edits can remove files both when followers
    /// apply sync-region metadata and when a writable leader performs a direct edit
    /// such as `edit_region()`. Allowing compaction to publish in `Editing` is still
    /// safe because publication happens under the manifest write lock and compaction
    /// rechecks that its input files are still valid before committing.
    ///
    /// This intentionally writes to the normal manifest path (`is_staging = false`).
    /// Entering staging cancels or waits for active compactions before switching the
    /// region to `Staging`, so a compaction that started before staging still finishes
    /// against the normal manifest. Even if a manual compaction is requested while the
    /// region is already staging, compaction only sees SSTs in the normal visible
    /// region version; SSTs from staging manifests are not applied to region version
    /// control until staging exits successfully.
    pub(crate) async fn update_manifest_for_compaction(
        &self,
        action_list: RegionMetaActionList,
    ) -> Result<ManifestVersion> {
        self.update_manifest_with_state_check(action_list, false, |current_state, region_id| {
            ensure!(
                matches!(
                    current_state,
                    RegionRoleState::Leader(RegionLeaderState::Writable)
                        | RegionRoleState::Leader(RegionLeaderState::Editing)
                        | RegionRoleState::Leader(RegionLeaderState::Downgrading)
                ),
                UpdateManifestSnafu {
                    region_id,
                    state: current_state,
                }
            );

            Ok(())
        })
        .await
    }

    /// Conditionally publishes rebuilt index metadata for `source`.
    ///
    /// The source SST and schema-generation checks share the manifest write lock
    /// with the update, so a concurrent compaction, schema change, or another
    /// index build cannot commit between them.
    pub(crate) async fn update_manifest_for_index(
        &self,
        source: &IndexBuildSource,
        updated: FileMeta,
    ) -> Result<IndexPublication> {
        let manager = self.manifest_manager.write().await;
        let manifest = manager.manifest();
        let current_state = self.state.load();
        if !matches!(
            current_state,
            RegionRoleState::Leader(RegionLeaderState::Writable)
                | RegionRoleState::Leader(RegionLeaderState::Downgrading)
        ) || manager.is_stopped()
        {
            return Ok(IndexPublication::Stale(
                IndexPublicationStale::SourceChanged,
            ));
        }

        if manifest.files.get(&source.file_meta.file_id) != Some(&source.file_meta) {
            return Ok(IndexPublication::Stale(
                IndexPublicationStale::SourceChanged,
            ));
        }

        if manifest.metadata.schema_version != source.schema_version {
            return Ok(IndexPublication::Stale(
                IndexPublicationStale::SchemaChanged,
            ));
        }

        // Only index metadata is allowed to change in this publication.
        let mut committed = source.file_meta.clone();
        committed.available_indexes = updated.available_indexes;
        committed.indexes = updated.indexes;
        committed.index_file_size = updated.index_file_size;
        committed.index_version = updated.index_version;

        let edit = crate::manifest::action::RegionEdit {
            files_to_add: vec![committed.clone()],
            files_to_remove: Vec::new(),
            timestamp_ms: Some(chrono::Utc::now().timestamp_millis()),
            flushed_sequence: None,
            flushed_entry_id: None,
            committed_sequence: None,
            compaction_time_window: None,
        };
        let action_list = RegionMetaActionList::with_action(RegionMetaAction::Edit(edit));
        let manifest_version = self.update_and_fire(manager, action_list, false).await?;

        Ok(IndexPublication::Committed {
            manifest_version,
            file_meta: committed,
        })
    }

    /// Performs a manifest write under a caller-held write lock and returns a
    /// [`PendingManifestHook`] to [`fire`](PendingManifestHook::fire) after
    /// dropping the lock. This is the sole caller of
    /// [`RegionManifestManager::update`], so it is the funnel through which all
    /// logical manifest writes notify the hook.
    ///
    /// Does not validate state or edit applicability — the caller must do so
    /// while still holding the lock (see `update_manifest_with_state_check`
    /// and `MitoRegion::exit_staging_on_success`).
    pub(crate) async fn update_locked(
        &self,
        manager: &mut RegionManifestManager,
        action_list: RegionMetaActionList,
        is_staging: bool,
    ) -> Result<PendingManifestHook> {
        let region_id = manager.manifest().metadata.region_id;
        // Clone before `action_list` is moved into `update` so the hook still
        // sees what was written.
        let action_list_for_hook = self.hook.as_ref().map(|_| action_list.clone());
        let version = if !is_staging
            && self.state.load() == RegionRoleState::Leader(RegionLeaderState::Downgrading)
        {
            manager.update_normal_without_checkpoint(action_list).await
        } else {
            manager.update(action_list, is_staging).await
        }
        .inspect_err(|e| error!(e; "Failed to update manifest, region_id: {}", region_id))?;

        Ok(PendingManifestHook::new(
            region_id,
            action_list_for_hook,
            version,
            self.hook.clone(),
            is_staging,
        ))
    }

    /// Updates the manifest using a caller-held write lock, releases the lock,
    /// and then fires the manifest hook.
    ///
    /// Callers must perform state and applicability checks before calling this
    /// method so the checks and update remain in the same lock critical section.
    async fn update_and_fire(
        &self,
        mut manager: RwLockWriteGuard<'_, RegionManifestManager>,
        action_list: RegionMetaActionList,
        is_staging: bool,
    ) -> Result<ManifestVersion> {
        let region_id = manager.manifest().metadata.region_id;
        let pending = self
            .update_locked(&mut manager, action_list, is_staging)
            .await?;
        let version = pending.version();

        // Hook implementations may read the manifest or send region requests
        // that acquire this lock.
        drop(manager);

        if self.state.load() == RegionRoleState::Follower {
            warn!(
                "Region {} becomes follower while updating manifest which may cause inconsistency, manifest version: {version}",
                region_id
            );
        }

        pending.fire().await;
        Ok(version)
    }

    async fn update_manifest_with_state_check(
        &self,
        action_list: RegionMetaActionList,
        is_staging: bool,
        check_state: impl FnOnce(RegionRoleState, RegionId) -> Result<()>,
    ) -> Result<ManifestVersion> {
        // Acquires the write lock of the manifest manager.
        let manager = self.manifest_manager.write().await;
        // Gets current manifest.
        let manifest = manager.manifest();
        // Checks state inside the lock. This is to ensure that we won't update the manifest
        // after `set_readonly_gracefully()` is called.
        let current_state = self.state.load();
        check_state(current_state, manifest.metadata.region_id)?;

        for action in &action_list.actions {
            // Checks whether the edit is still applicable.
            let RegionMetaAction::Edit(edit) = &action else {
                continue;
            };

            // Checks whether the region is truncated.
            let Some(truncated_entry_id) = manifest.truncated_entry_id else {
                continue;
            };

            // This is an edit from flush.
            if let Some(flushed_entry_id) = edit.flushed_entry_id {
                // A flush edit is valid after truncate in two cases:
                // 1. `flushed_entry_id` moves past `truncated_entry_id`, meaning it definitely
                //    flushed data newer than the truncate point.
                // 2. `flushed_entry_id` equals `truncated_entry_id`, but `flushed_sequence`
                //    increases. This happens in skip-WAL tables where entry id can stay at 0,
                //    while sequence still advances for post-truncate writes.
                //
                // We still reject stale flushes from before truncate:
                // if entry id is equal and sequence does not advance, the flush is outdated.
                let is_newer_entry = truncated_entry_id < flushed_entry_id;
                let is_same_entry_with_newer_sequence = truncated_entry_id == flushed_entry_id
                    && edit.flushed_sequence.is_some_and(|flushed_sequence| {
                        manifest.flushed_sequence < flushed_sequence
                    });

                ensure!(
                    is_newer_entry || is_same_entry_with_newer_sequence,
                    RegionTruncatedSnafu {
                        region_id: manifest.metadata.region_id,
                    }
                );
            }

            // This is an edit from compaction.
            if !edit.files_to_remove.is_empty() {
                // Input files of the compaction task has been truncated.
                for file in &edit.files_to_remove {
                    ensure!(
                        manifest.files.contains_key(&file.file_id),
                        RegionTruncatedSnafu {
                            region_id: manifest.metadata.region_id,
                        }
                    );
                }
            }
        }

        self.update_and_fire(manager, action_list, is_staging).await
    }

    /// Sets the [`RegionRole`].
    ///
    /// ```text
    ///                  +---------------------+
    ///                  |   Staging Leader    |
    ///                  +----------+----------+
    ///                             |
    ///                             v
    ///     +----------+     +------+-------+     +-------------+
    ///     | Follower | <-> |    Leader    | <-> | Downgrading |
    ///     +-----+----+     +------+-------+     +------+------+
    ///           ^                 ^                    |
    ///           +-----------------+--------------------+
    ///
    /// ```
    ///
    /// # State Transitions
    ///
    /// From `Follower`:
    /// - `Follower -> Leader`
    ///
    /// From `Leader`:
    /// - `Leader -> Follower`
    /// - `Leader -> Downgrading Leader`
    ///
    /// From `Staging Leader`:
    /// - `Staging Leader -> Leader`
    /// - `Staging Leader -> Follower`
    /// - `Staging Leader -> Downgrading Leader`
    ///
    /// From `Downgrading Leader`:
    /// - `Downgrading Leader -> Leader`
    /// - `Downgrading Leader -> Follower`
    pub(crate) fn set_role(&self, next_role: RegionRole, region_id: RegionId) {
        match next_role {
            RegionRole::Follower => {
                if self
                    .exit_staging(region_id, RegionRoleState::Follower)
                    .is_ok()
                {
                    info!(
                        "Convert region {} to follower, previous role state: {:?}",
                        region_id,
                        RegionRoleState::Leader(RegionLeaderState::Staging)
                    );
                    return;
                }
                match self.state.fetch_update(|state| {
                    if !matches!(state, RegionRoleState::Follower) {
                        Some(RegionRoleState::Follower)
                    } else {
                        None
                    }
                }) {
                    Ok(state) => info!(
                        "Convert region {} to follower, previous role state: {:?}",
                        region_id, state
                    ),
                    Err(state) => {
                        if state != RegionRoleState::Follower {
                            warn!(
                                "Failed to convert region {} to follower, current role state: {:?}",
                                region_id, state
                            )
                        }
                    }
                }
            }
            RegionRole::Leader => {
                if self
                    .exit_staging(
                        region_id,
                        RegionRoleState::Leader(RegionLeaderState::Writable),
                    )
                    .is_ok()
                {
                    info!(
                        "Convert region {} to leader, previous role state: {:?}",
                        region_id,
                        RegionRoleState::Leader(RegionLeaderState::Staging)
                    );
                    return;
                }
                match self.state.fetch_update(|state| {
                    if matches!(
                        state,
                        RegionRoleState::Follower
                            | RegionRoleState::Leader(RegionLeaderState::Downgrading)
                    ) {
                        Some(RegionRoleState::Leader(RegionLeaderState::Writable))
                    } else {
                        None
                    }
                }) {
                    Ok(state) => info!(
                        "Convert region {} to leader, previous role state: {:?}",
                        region_id, state
                    ),
                    Err(state) => {
                        if state != RegionRoleState::Leader(RegionLeaderState::Writable) {
                            warn!(
                                "Failed to convert region {} to leader, current role state: {:?}",
                                region_id, state
                            )
                        }
                    }
                }
            }
            RegionRole::StagingLeader => {
                info!(
                    "Ignore direct conversion of region {} to staging leader; staging requires the dedicated workflow",
                    region_id
                );
            }
            RegionRole::DowngradingLeader => {
                if self
                    .exit_staging(
                        region_id,
                        RegionRoleState::Leader(RegionLeaderState::Downgrading),
                    )
                    .is_ok()
                {
                    info!(
                        "Convert region {} to downgrading region, previous role state: {:?}",
                        region_id,
                        RegionRoleState::Leader(RegionLeaderState::Staging)
                    );
                    return;
                }
                match self.state.compare_exchange(
                    RegionRoleState::Leader(RegionLeaderState::Writable),
                    RegionRoleState::Leader(RegionLeaderState::Downgrading),
                ) {
                    Ok(state) => info!(
                        "Convert region {} to downgrading region, previous role state: {:?}",
                        region_id, state
                    ),
                    Err(state) => {
                        if state != RegionRoleState::Leader(RegionLeaderState::Downgrading) {
                            warn!(
                                "Failed to convert region {} to downgrading leader, current role state: {:?}",
                                region_id, state
                            )
                        }
                    }
                }
            }
        }
    }

    /// Returns the normal manifest of the region.
    pub(crate) async fn manifest(&self) -> Arc<crate::manifest::action::RegionManifest> {
        self.manifest_manager.read().await.manifest()
    }

    /// Returns the staging manifest of the region.
    pub(crate) async fn staging_manifest(
        &self,
    ) -> Option<Arc<crate::manifest::action::RegionManifest>> {
        self.manifest_manager.read().await.staging_manifest()
    }
}

pub(crate) type ManifestContextRef = Arc<ManifestContext>;

/// Regions indexed by ids.
#[derive(Debug, Default)]
pub(crate) struct RegionMap {
    regions: RwLock<HashMap<RegionId, MitoRegionRef>>,
}

impl RegionMap {
    /// Returns true if the region exists.
    pub(crate) fn is_region_exists(&self, region_id: RegionId) -> bool {
        let regions = self.regions.read().unwrap();
        regions.contains_key(&region_id)
    }

    /// Inserts a new region into the map.
    pub(crate) fn insert_region(&self, region: MitoRegionRef) {
        let mut regions = self.regions.write().unwrap();
        regions.insert(region.region_id, region);
    }

    /// Gets region by region id.
    pub(crate) fn get_region(&self, region_id: RegionId) -> Option<MitoRegionRef> {
        let regions = self.regions.read().unwrap();
        regions.get(&region_id).cloned()
    }

    /// Gets writable region by region id.
    ///
    /// Returns error if the region does not exist or is readonly.
    pub(crate) fn writable_region(&self, region_id: RegionId) -> Result<MitoRegionRef> {
        let region = self
            .get_region(region_id)
            .context(RegionNotFoundSnafu { region_id })?;
        ensure!(
            region.is_writable(),
            RegionStateSnafu {
                region_id,
                state: region.state(),
                expect: RegionRoleState::Leader(RegionLeaderState::Writable),
            }
        );
        Ok(region)
    }

    /// Gets readonly region by region id.
    ///
    /// Returns error if the region does not exist or is writable.
    pub(crate) fn follower_region(&self, region_id: RegionId) -> Result<MitoRegionRef> {
        let region = self
            .get_region(region_id)
            .context(RegionNotFoundSnafu { region_id })?;
        ensure!(
            region.is_follower(),
            RegionStateSnafu {
                region_id,
                state: region.state(),
                expect: RegionRoleState::Follower,
            }
        );

        Ok(region)
    }

    /// Gets region by region id.
    ///
    /// Calls the callback if the region does not exist.
    pub(crate) fn get_region_or<F: OnFailure>(
        &self,
        region_id: RegionId,
        cb: &mut F,
    ) -> Option<MitoRegionRef> {
        match self
            .get_region(region_id)
            .context(RegionNotFoundSnafu { region_id })
        {
            Ok(region) => Some(region),
            Err(e) => {
                cb.on_failure(e);
                None
            }
        }
    }

    /// Gets writable region by region id.
    ///
    /// Calls the callback if the region does not exist or is readonly.
    pub(crate) fn writable_region_or<F: OnFailure>(
        &self,
        region_id: RegionId,
        cb: &mut F,
    ) -> Option<MitoRegionRef> {
        match self.writable_region(region_id) {
            Ok(region) => Some(region),
            Err(e) => {
                cb.on_failure(e);
                None
            }
        }
    }

    /// Gets writable non-staging region by region id.
    ///
    /// Returns error if the region does not exist, is readonly, or is in staging mode.
    pub(crate) fn writable_non_staging_region(&self, region_id: RegionId) -> Result<MitoRegionRef> {
        let region = self.writable_region(region_id)?;
        if region.is_staging() {
            return Err(crate::error::RegionStateSnafu {
                region_id,
                state: region.state(),
                expect: RegionRoleState::Leader(RegionLeaderState::Writable),
            }
            .build());
        }
        Ok(region)
    }

    /// Gets staging region by region id.
    ///
    /// Returns error if the region does not exist or is not in staging state.
    pub(crate) fn staging_region(&self, region_id: RegionId) -> Result<MitoRegionRef> {
        let region = self
            .get_region(region_id)
            .context(RegionNotFoundSnafu { region_id })?;
        ensure!(
            region.is_staging(),
            RegionStateSnafu {
                region_id,
                state: region.state(),
                expect: RegionRoleState::Leader(RegionLeaderState::Staging),
            }
        );
        Ok(region)
    }

    /// Gets flushable region by region id.
    ///
    /// Returns error if the region does not exist or not flushable.
    pub(crate) fn flushable_region(&self, region_id: RegionId) -> Result<MitoRegionRef> {
        let region = self
            .get_region(region_id)
            .context(RegionNotFoundSnafu { region_id })?;
        ensure!(
            region.is_flushable(),
            FlushableRegionStateSnafu {
                region_id,
                state: region.state(),
            }
        );
        Ok(region)
    }

    /// Remove region by id.
    pub(crate) fn remove_region(&self, region_id: RegionId) -> Option<MitoRegionRef> {
        let mut regions = self.regions.write().unwrap();
        regions.remove(&region_id)
    }

    /// List all regions.
    pub(crate) fn list_regions(&self) -> Vec<MitoRegionRef> {
        let regions = self.regions.read().unwrap();
        regions.values().cloned().collect()
    }

    /// Clear the map.
    pub(crate) fn clear(&self) {
        self.regions.write().unwrap().clear();
    }
}

pub(crate) type RegionMapRef = Arc<RegionMap>;

/// Opening regions
#[derive(Debug, Default)]
pub(crate) struct OpeningRegions {
    regions: RwLock<HashMap<RegionId, Vec<OptionOutputTx>>>,
}

impl OpeningRegions {
    /// Registers `sender` for an opening region; Otherwise, it returns `None`.
    pub(crate) fn wait_for_opening_region(
        &self,
        region_id: RegionId,
        sender: OptionOutputTx,
    ) -> Option<OptionOutputTx> {
        let mut regions = self.regions.write().unwrap();
        match regions.entry(region_id) {
            Entry::Occupied(mut senders) => {
                senders.get_mut().push(sender);
                None
            }
            Entry::Vacant(_) => Some(sender),
        }
    }

    /// Returns true if the region exists.
    pub(crate) fn is_region_exists(&self, region_id: RegionId) -> bool {
        let regions = self.regions.read().unwrap();
        regions.contains_key(&region_id)
    }

    /// Inserts a new region into the map.
    pub(crate) fn insert_sender(&self, region: RegionId, sender: OptionOutputTx) {
        let mut regions = self.regions.write().unwrap();
        regions.insert(region, vec![sender]);
    }

    /// Remove region by id.
    pub(crate) fn remove_sender(&self, region_id: RegionId) -> Vec<OptionOutputTx> {
        let mut regions = self.regions.write().unwrap();
        regions.remove(&region_id).unwrap_or_default()
    }

    #[cfg(test)]
    pub(crate) fn sender_len(&self, region_id: RegionId) -> usize {
        let regions = self.regions.read().unwrap();
        if let Some(senders) = regions.get(&region_id) {
            senders.len()
        } else {
            0
        }
    }
}

pub(crate) type OpeningRegionsRef = Arc<OpeningRegions>;

/// The regions that are catching up.
#[derive(Debug, Default)]
pub(crate) struct CatchupRegions {
    regions: RwLock<HashSet<RegionId>>,
}

impl CatchupRegions {
    /// Returns true if the region exists.
    pub(crate) fn is_region_exists(&self, region_id: RegionId) -> bool {
        let regions = self.regions.read().unwrap();
        regions.contains(&region_id)
    }

    /// Inserts a new region into the set.
    pub(crate) fn insert_region(&self, region_id: RegionId) {
        let mut regions = self.regions.write().unwrap();
        regions.insert(region_id);
    }

    /// Remove region by id.
    pub(crate) fn remove_region(&self, region_id: RegionId) {
        let mut regions = self.regions.write().unwrap();
        regions.remove(&region_id);
    }
}

pub(crate) type CatchupRegionsRef = Arc<CatchupRegions>;

/// Manifest stats.
#[derive(Default, Debug, Clone)]
pub struct ManifestStats {
    pub(crate) total_manifest_size: Arc<AtomicU64>,
    pub(crate) manifest_version: Arc<AtomicU64>,
    pub(crate) file_removed_cnt: Arc<AtomicU64>,
}

impl ManifestStats {
    fn total_manifest_size(&self) -> u64 {
        self.total_manifest_size.load(Ordering::Relaxed)
    }

    fn manifest_version(&self) -> u64 {
        self.manifest_version.load(Ordering::Relaxed)
    }

    fn file_removed_cnt(&self) -> u64 {
        self.file_removed_cnt.load(Ordering::Relaxed)
    }
}

/// Parses the partition expression from a JSON string.
pub fn parse_partition_expr(partition_expr_str: Option<&str>) -> Result<Option<PartitionExpr>> {
    match partition_expr_str {
        None => Ok(None),
        Some("") => Ok(None),
        Some(json_str) => {
            let expr = partition::expr::PartitionExpr::from_json_str(json_str)
                .with_context(|_| InvalidPartitionExprSnafu { expr: json_str })?;
            Ok(expr)
        }
    }
}

#[cfg(test)]
mod tests {
    use std::sync::Arc;

    use common_datasource::compression::CompressionType;
    use common_test_util::temp_dir::create_temp_dir;
    use crossbeam_utils::atomic::AtomicCell;
    use object_store::ObjectStore;
    use object_store::services::Fs;
    use store_api::logstore::provider::Provider;
    use store_api::region_engine::RegionRole;
    use store_api::region_request::PathType;
    use store_api::storage::{FileId, RegionId};

    use crate::access_layer::AccessLayer;
    use crate::error::Error;
    use crate::manifest::action::{
        RegionChange, RegionEdit, RegionMetaAction, RegionMetaActionList, RegionPartitionExprChange,
    };
    use crate::manifest::manager::{RegionManifestManager, RegionManifestOptions};
    use crate::region::{
        IndexBuildSource, IndexPublication, IndexPublicationStale, ManifestContext, ManifestStats,
        MitoRegion, RegionLeaderState, RegionRoleState, RegionStats,
    };
    use crate::sst::FormatType;
    use crate::sst::index::intermediate::IntermediateManager;
    use crate::sst::index::puffin_manager::PuffinManagerFactory;
    use crate::test_util::scheduler_util::SchedulerEnv;
    use crate::test_util::version_util::VersionControlBuilder;
    use crate::time_provider::StdTimeProvider;

    #[test]
    fn test_region_state_lock_free() {
        assert!(AtomicCell::<RegionRoleState>::is_lock_free());
    }

    #[test]
    fn test_region_role_state_as_str() {
        assert_eq!("Follower", RegionRoleState::Follower.as_str());
        assert_eq!(
            "Leader(Writable)",
            RegionRoleState::Leader(RegionLeaderState::Writable).as_str()
        );
        assert_eq!(
            "Leader(Staging)",
            RegionRoleState::Leader(RegionLeaderState::Staging).as_str()
        );
        assert_eq!(
            "Leader(Downgrading)",
            RegionRoleState::Leader(RegionLeaderState::Downgrading).as_str()
        );
    }

    async fn build_test_region(env: &SchedulerEnv) -> MitoRegion {
        let builder = VersionControlBuilder::new();
        let version_control = Arc::new(builder.build());
        let metadata = version_control.current().version.metadata.clone();

        let manager = RegionManifestManager::new(
            metadata.clone(),
            0,
            RegionManifestOptions {
                manifest_dir: "".to_string(),
                object_store: env.access_layer.object_store().clone(),
                compress_type: CompressionType::Uncompressed,
                checkpoint_distance: 10,
                remove_file_options: Default::default(),
                manifest_cache: None,
            },
            FormatType::PrimaryKey,
            &Default::default(),
        )
        .await
        .unwrap();

        let manifest_ctx = Arc::new(ManifestContext::new(
            manager,
            RegionRoleState::Leader(RegionLeaderState::Writable),
            None,
        ));

        MitoRegion {
            region_id: metadata.region_id,
            version_control,
            access_layer: env.access_layer.clone(),
            manifest_ctx,
            file_purger: crate::test_util::new_noop_file_purger(),
            provider: Provider::noop_provider(),
            last_flush_millis: Default::default(),
            last_schedule_compaction_millis: Default::default(),
            time_provider: Arc::new(StdTimeProvider),
            topic_latest_entry_id: Default::default(),
            region_stats: RegionStats::new(),
            stats: ManifestStats::default(),
        }
    }

    fn empty_edit() -> RegionEdit {
        RegionEdit {
            files_to_add: Vec::new(),
            files_to_remove: Vec::new(),
            timestamp_ms: None,
            compaction_time_window: None,
            flushed_entry_id: None,
            flushed_sequence: None,
            committed_sequence: None,
        }
    }

    #[tokio::test]
    async fn test_compaction_update_manifest_allows_editing_state() {
        let env = SchedulerEnv::new().await;
        let region = build_test_region(&env).await;
        region.set_editing(RegionLeaderState::Writable).unwrap();

        let file_id = FileId::random();
        let action_list = RegionMetaActionList::with_action(RegionMetaAction::Edit(RegionEdit {
            files_to_add: vec![crate::sst::file::FileMeta {
                region_id: region.region_id,
                file_id,
                level: 1,
                ..Default::default()
            }],
            files_to_remove: Vec::new(),
            timestamp_ms: None,
            compaction_time_window: None,
            flushed_entry_id: None,
            flushed_sequence: None,
            committed_sequence: None,
        }));

        region
            .manifest_ctx
            .update_manifest_for_compaction(action_list)
            .await
            .unwrap();

        assert!(
            region
                .manifest_ctx
                .manifest()
                .await
                .files
                .contains_key(&file_id)
        );
    }

    #[tokio::test]
    async fn test_index_publication_rejects_older_source_generation() {
        let env = SchedulerEnv::new().await;
        let region = build_test_region(&env).await;
        let source = crate::sst::file::FileMeta {
            region_id: region.region_id,
            file_id: FileId::random(),
            level: 1,
            file_size: 1024,
            ..Default::default()
        };
        region
            .manifest_ctx
            .update_manifest(
                RegionLeaderState::Writable,
                RegionMetaActionList::with_action(RegionMetaAction::Edit(RegionEdit {
                    files_to_add: vec![source.clone()],
                    ..empty_edit()
                })),
                false,
            )
            .await
            .unwrap();

        let mut first_update = source.clone();
        first_update.index_version = 1;
        first_update.index_file_size = 128;
        let schema_version = region.version().metadata.schema_version;
        let initial_source = IndexBuildSource::new(source.clone(), schema_version);
        let first_committed = match region
            .manifest_ctx
            .update_manifest_for_index(&initial_source, first_update)
            .await
            .unwrap()
        {
            IndexPublication::Committed { file_meta, .. } => file_meta,
            IndexPublication::Stale(_) => panic!("first index publication should commit"),
        };

        let (ready_tx, ready_rx) = tokio::sync::oneshot::channel();
        let (release_tx, release_rx) = tokio::sync::oneshot::channel();
        let delayed_manifest_ctx = region.manifest_ctx.clone();
        let delayed_source = IndexBuildSource::new(first_committed.clone(), schema_version);
        let delayed_publication = tokio::spawn(async move {
            let mut delayed_update = delayed_source.file_meta.clone();
            delayed_update.index_version = 2;
            delayed_update.index_file_size = 128;
            ready_tx.send(()).unwrap();
            release_rx.await.unwrap();
            delayed_manifest_ctx
                .update_manifest_for_index(&delayed_source, delayed_update)
                .await
        });
        ready_rx.await.unwrap();

        let mut newer_update = first_committed.clone();
        newer_update.index_version = 3;
        newer_update.index_file_size = 256;
        let newer_source = IndexBuildSource::new(first_committed, schema_version);
        let newer_committed = match region
            .manifest_ctx
            .update_manifest_for_index(&newer_source, newer_update)
            .await
            .unwrap()
        {
            IndexPublication::Committed { file_meta, .. } => file_meta,
            IndexPublication::Stale(_) => panic!("newer index publication should commit"),
        };

        release_tx.send(()).unwrap();
        assert!(matches!(
            delayed_publication.await.unwrap().unwrap(),
            IndexPublication::Stale(IndexPublicationStale::SourceChanged)
        ));
        assert_eq!(
            region
                .manifest_ctx
                .manifest()
                .await
                .files
                .get(&source.file_id),
            Some(&newer_committed)
        );
    }

    #[tokio::test]
    async fn test_index_publication_rejects_older_schema_generation() {
        let env = SchedulerEnv::new().await;
        let region = build_test_region(&env).await;
        let source_meta = crate::sst::file::FileMeta {
            region_id: region.region_id,
            file_id: FileId::random(),
            level: 1,
            file_size: 1024,
            ..Default::default()
        };
        region
            .manifest_ctx
            .update_manifest(
                RegionLeaderState::Writable,
                RegionMetaActionList::with_action(RegionMetaAction::Edit(RegionEdit {
                    files_to_add: vec![source_meta.clone()],
                    ..empty_edit()
                })),
                false,
            )
            .await
            .unwrap();

        let old_schema_version = region.version().metadata.schema_version;
        let source = IndexBuildSource::new(source_meta.clone(), old_schema_version);
        let mut new_metadata = region.version().metadata.as_ref().clone();
        new_metadata.schema_version += 1;
        region
            .manifest_ctx
            .update_manifest(
                RegionLeaderState::Writable,
                RegionMetaActionList::with_action(RegionMetaAction::Change(RegionChange {
                    metadata: Arc::new(new_metadata),
                    sst_format: FormatType::PrimaryKey,
                    append_mode: None,
                })),
                false,
            )
            .await
            .unwrap();

        let mut updated = source_meta.clone();
        updated.index_version = 1;
        updated.index_file_size = 128;
        assert!(matches!(
            region
                .manifest_ctx
                .update_manifest_for_index(&source, updated)
                .await
                .unwrap(),
            IndexPublication::Stale(IndexPublicationStale::SchemaChanged)
        ));

        let manifest = region.manifest_ctx.manifest().await;
        assert_eq!(manifest.metadata.schema_version, old_schema_version + 1);
        assert_eq!(manifest.files.get(&source_meta.file_id), Some(&source_meta));
    }

    #[tokio::test]
    async fn test_exit_staging_partition_expr_change_and_edit_success() {
        let env = SchedulerEnv::new().await;
        let region = build_test_region(&env).await;

        let mut manager = region.manifest_ctx.manifest_manager.write().await;
        region.set_staging(&mut manager).await.unwrap();
        manager
            .update(
                RegionMetaActionList::new(vec![
                    RegionMetaAction::PartitionExprChange(RegionPartitionExprChange {
                        partition_expr: Some("expr_a".to_string()),
                    }),
                    RegionMetaAction::Edit(empty_edit()),
                ]),
                true,
            )
            .await
            .unwrap();

        let _hook_payload = region.exit_staging_on_success(&mut manager).await.unwrap();
        drop(manager);

        assert_eq!(
            region.version().metadata.partition_expr.as_deref(),
            Some("expr_a")
        );
        assert_eq!(
            region.state(),
            RegionRoleState::Leader(RegionLeaderState::Writable)
        );
    }

    #[tokio::test]
    async fn test_exit_staging_change_with_same_columns_success() {
        let env = SchedulerEnv::new().await;
        let region = build_test_region(&env).await;

        let mut manager = region.manifest_ctx.manifest_manager.write().await;
        region.set_staging(&mut manager).await.unwrap();

        let mut changed_metadata = region.version().metadata.as_ref().clone();
        changed_metadata.set_partition_expr(Some("expr_b".to_string()));

        manager
            .update(
                RegionMetaActionList::new(vec![
                    RegionMetaAction::Change(RegionChange {
                        metadata: Arc::new(changed_metadata),
                        sst_format: FormatType::PrimaryKey,
                        append_mode: None,
                    }),
                    RegionMetaAction::Edit(empty_edit()),
                ]),
                true,
            )
            .await
            .unwrap();

        let _hook_payload = region.exit_staging_on_success(&mut manager).await.unwrap();
        drop(manager);

        assert_eq!(
            region.version().metadata.partition_expr.as_deref(),
            Some("expr_b")
        );
        assert_eq!(
            region.state(),
            RegionRoleState::Leader(RegionLeaderState::Writable)
        );
    }

    #[tokio::test]
    async fn test_exit_staging_change_with_different_columns_fails() {
        let env = SchedulerEnv::new().await;
        let region = build_test_region(&env).await;

        let mut manager = region.manifest_ctx.manifest_manager.write().await;
        region.set_staging(&mut manager).await.unwrap();

        let mut changed_metadata = region.version().metadata.as_ref().clone();
        changed_metadata.column_metadatas.rotate_left(1);

        manager
            .update(
                RegionMetaActionList::new(vec![
                    RegionMetaAction::Change(RegionChange {
                        metadata: Arc::new(changed_metadata),
                        sst_format: FormatType::PrimaryKey,
                        append_mode: None,
                    }),
                    RegionMetaAction::Edit(empty_edit()),
                ]),
                true,
            )
            .await
            .unwrap();

        let result = region.exit_staging_on_success(&mut manager).await;
        assert!(matches!(result, Err(Error::Unexpected { .. })));
    }

    #[tokio::test]
    async fn test_exit_staging_partition_expr_change_and_change_conflict_fails() {
        let env = SchedulerEnv::new().await;
        let region = build_test_region(&env).await;

        let mut manager = region.manifest_ctx.manifest_manager.write().await;
        region.set_staging(&mut manager).await.unwrap();

        let mut changed_metadata = region.version().metadata.as_ref().clone();
        changed_metadata.set_partition_expr(Some("expr_c".to_string()));

        manager
            .update(
                RegionMetaActionList::new(vec![
                    RegionMetaAction::PartitionExprChange(RegionPartitionExprChange {
                        partition_expr: Some("expr_c".to_string()),
                    }),
                    RegionMetaAction::Change(RegionChange {
                        metadata: Arc::new(changed_metadata),
                        sst_format: FormatType::PrimaryKey,
                        append_mode: None,
                    }),
                    RegionMetaAction::Edit(empty_edit()),
                ]),
                true,
            )
            .await
            .unwrap();

        let result = region.exit_staging_on_success(&mut manager).await;
        assert!(matches!(result, Err(Error::Unexpected { .. })));
    }

    #[tokio::test]
    async fn test_set_region_state() {
        let env = SchedulerEnv::new().await;
        let builder = VersionControlBuilder::new();
        let version_control = Arc::new(builder.build());
        let manifest_ctx = env
            .mock_manifest_context(version_control.current().version.metadata.clone())
            .await;

        let region_id = RegionId::new(1024, 0);
        // Leader -> Follower
        manifest_ctx.set_role(RegionRole::Follower, region_id);
        assert_eq!(manifest_ctx.state.load(), RegionRoleState::Follower);

        // Follower -> Leader
        manifest_ctx.set_role(RegionRole::Leader, region_id);
        assert_eq!(
            manifest_ctx.state.load(),
            RegionRoleState::Leader(RegionLeaderState::Writable)
        );

        // Direct Leader -> StagingLeader should be ignored.
        manifest_ctx.set_role(RegionRole::StagingLeader, region_id);
        assert_eq!(
            manifest_ctx.state.load(),
            RegionRoleState::Leader(RegionLeaderState::Writable)
        );

        // Leader -> Downgrading Leader
        manifest_ctx.set_role(RegionRole::DowngradingLeader, region_id);
        assert_eq!(
            manifest_ctx.state.load(),
            RegionRoleState::Leader(RegionLeaderState::Downgrading)
        );

        // Downgrading Leader -> Follower
        manifest_ctx.set_role(RegionRole::Follower, region_id);
        assert_eq!(manifest_ctx.state.load(), RegionRoleState::Follower);

        // Can't downgrade from follower (Follower -> Downgrading Leader)
        manifest_ctx.set_role(RegionRole::DowngradingLeader, region_id);
        assert_eq!(manifest_ctx.state.load(), RegionRoleState::Follower);

        // Set region role too Downgrading Leader
        manifest_ctx.set_role(RegionRole::Leader, region_id);
        manifest_ctx.set_role(RegionRole::DowngradingLeader, region_id);
        assert_eq!(
            manifest_ctx.state.load(),
            RegionRoleState::Leader(RegionLeaderState::Downgrading)
        );

        // Downgrading Leader -> Leader
        manifest_ctx.set_role(RegionRole::Leader, region_id);
        assert_eq!(
            manifest_ctx.state.load(),
            RegionRoleState::Leader(RegionLeaderState::Writable)
        );
    }

    #[tokio::test]
    async fn test_staging_state_validation() {
        let env = SchedulerEnv::new().await;
        let builder = VersionControlBuilder::new();
        let version_control = Arc::new(builder.build());

        // Create context with staging state using the correct pattern from SchedulerEnv
        let staging_ctx = {
            let manager = RegionManifestManager::new(
                version_control.current().version.metadata.clone(),
                0,
                RegionManifestOptions {
                    manifest_dir: "".to_string(),
                    object_store: env.access_layer.object_store().clone(),
                    compress_type: CompressionType::Uncompressed,
                    checkpoint_distance: 10,
                    remove_file_options: Default::default(),
                    manifest_cache: None,
                },
                FormatType::PrimaryKey,
                &Default::default(),
            )
            .await
            .unwrap();
            Arc::new(ManifestContext::new(
                manager,
                RegionRoleState::Leader(RegionLeaderState::Staging),
                None,
            ))
        };

        // Test staging state behavior
        assert_eq!(
            staging_ctx.current_state(),
            RegionRoleState::Leader(RegionLeaderState::Staging)
        );

        // Test writable context for comparison
        let writable_ctx = env
            .mock_manifest_context(version_control.current().version.metadata.clone())
            .await;

        assert_eq!(
            writable_ctx.current_state(),
            RegionRoleState::Leader(RegionLeaderState::Writable)
        );
    }

    #[tokio::test]
    async fn test_staging_state_transitions() {
        let builder = VersionControlBuilder::new();
        let version_control = Arc::new(builder.build());
        let metadata = version_control.current().version.metadata.clone();

        // Create MitoRegion for testing state transitions
        let temp_dir = create_temp_dir("");
        let path_str = temp_dir.path().display().to_string();
        let fs_builder = Fs::default().root(&path_str);
        let object_store = ObjectStore::new(fs_builder).unwrap().finish();

        let index_aux_path = temp_dir.path().join("index_aux");
        let puffin_mgr = PuffinManagerFactory::new(&index_aux_path, 4096, None, None)
            .await
            .unwrap();
        let intm_mgr = IntermediateManager::init_fs(index_aux_path.to_str().unwrap())
            .await
            .unwrap();

        let access_layer = Arc::new(AccessLayer::new(
            "",
            PathType::Bare,
            object_store,
            puffin_mgr,
            intm_mgr,
        ));

        let manager = RegionManifestManager::new(
            metadata.clone(),
            0,
            RegionManifestOptions {
                manifest_dir: "".to_string(),
                object_store: access_layer.object_store().clone(),
                compress_type: CompressionType::Uncompressed,
                checkpoint_distance: 10,
                remove_file_options: Default::default(),
                manifest_cache: None,
            },
            FormatType::PrimaryKey,
            &Default::default(),
        )
        .await
        .unwrap();

        let manifest_ctx = Arc::new(ManifestContext::new(
            manager,
            RegionRoleState::Leader(RegionLeaderState::Writable),
            None,
        ));

        let region = MitoRegion {
            region_id: metadata.region_id,
            version_control,
            access_layer,
            manifest_ctx: manifest_ctx.clone(),
            file_purger: crate::test_util::new_noop_file_purger(),
            provider: Provider::noop_provider(),
            last_flush_millis: Default::default(),
            last_schedule_compaction_millis: Default::default(),
            time_provider: Arc::new(StdTimeProvider),
            topic_latest_entry_id: Default::default(),
            region_stats: RegionStats::new(),
            stats: ManifestStats::default(),
        };

        // Test initial state
        assert_eq!(
            region.state(),
            RegionRoleState::Leader(RegionLeaderState::Writable)
        );
        assert!(!region.is_staging());

        // Test transition to staging
        let mut manager = manifest_ctx.manifest_manager.write().await;
        region.set_staging(&mut manager).await.unwrap();
        drop(manager);
        assert_eq!(
            region.state(),
            RegionRoleState::Leader(RegionLeaderState::Staging)
        );
        assert!(region.is_staging());

        // Test transition back to writable
        region.exit_staging().unwrap();
        assert_eq!(
            region.state(),
            RegionRoleState::Leader(RegionLeaderState::Writable)
        );
        assert!(!region.is_staging());

        // Test staging directory cleanup: Create dirty staging files before entering staging mode
        {
            // Create some dummy staging manifest files to simulate interrupted session
            let manager = manifest_ctx.manifest_manager.write().await;
            let dummy_actions = RegionMetaActionList::new(vec![]);
            let dummy_bytes = dummy_actions.encode().unwrap();

            // Create dirty staging files with versions 100 and 101
            manager.store().save(100, &dummy_bytes, true).await.unwrap();
            manager.store().save(101, &dummy_bytes, true).await.unwrap();
            drop(manager);

            // Verify dirty files exist before entering staging
            let manager = manifest_ctx.manifest_manager.read().await;
            let dirty_manifests = manager.store().fetch_staging_manifests().await.unwrap();
            assert_eq!(
                dirty_manifests.len(),
                2,
                "Should have 2 dirty staging files"
            );
            drop(manager);

            // Enter staging mode - this should clean up the dirty files
            let mut manager = manifest_ctx.manifest_manager.write().await;
            region.set_staging(&mut manager).await.unwrap();
            drop(manager);

            // Verify dirty files are cleaned up after entering staging
            let manager = manifest_ctx.manifest_manager.read().await;
            let cleaned_manifests = manager.store().fetch_staging_manifests().await.unwrap();
            assert_eq!(
                cleaned_manifests.len(),
                0,
                "Dirty staging files should be cleaned up"
            );
            drop(manager);

            // Exit staging to restore normal state for remaining tests
            region.exit_staging().unwrap();
        }

        // Test invalid transitions
        let mut manager = manifest_ctx.manifest_manager.write().await;
        assert!(region.set_staging(&mut manager).await.is_ok()); // Writable -> Staging should work
        drop(manager);
        let mut manager = manifest_ctx.manifest_manager.write().await;
        assert!(region.set_staging(&mut manager).await.is_err()); // Staging -> Staging should fail
        drop(manager);
        assert!(region.exit_staging().is_ok()); // Staging -> Writable should work
        assert!(region.exit_staging().is_err()); // Writable -> Writable should fail
    }
}
