// 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.

pub(crate) mod close_downgraded_region;
pub(crate) mod downgrade_leader_region;
pub(crate) mod flush_leader_region;
pub(crate) mod manager;
pub(crate) mod migration_abort;
pub(crate) mod migration_end;
pub(crate) mod migration_start;
pub(crate) mod open_candidate_region;
#[cfg(test)]
pub mod test_util;
pub(crate) mod update_metadata;
pub(crate) mod upgrade_candidate_region;
pub(crate) mod utils;

use std::any::Any;
use std::collections::{HashMap, HashSet};
use std::fmt::{Debug, Display};
use std::time::Duration;

use common_error::ext::BoxedError;
use common_event_recorder::{Event, PersistentEventContext};
use common_meta::cache_invalidator::CacheInvalidatorRef;
use common_meta::ddl::RegionFailureDetectorControllerRef;
use common_meta::instruction::CacheIdent;
use common_meta::key::datanode_table::{DatanodeTableKey, DatanodeTableValue};
use common_meta::key::table_route::TableRouteValue;
use common_meta::key::topic_name::TopicNameKey;
use common_meta::key::topic_region::{ReplayCheckpoint, TopicRegionKey};
use common_meta::key::{DeserializedValueWithBytes, TableMetadataManagerRef};
use common_meta::kv_backend::{KvBackendRef, ResettableKvBackendRef};
use common_meta::lock_key::{CatalogLock, RegionLock, SchemaLock, TableLock};
use common_meta::peer::Peer;
use common_meta::region_keeper::{MemoryRegionKeeperRef, OperatingRegionGuard};
use common_meta::rpc::ddl::TriggerReason;
use common_procedure::error::{
    Error as ProcedureError, FromJsonSnafu, Result as ProcedureResult, ToJsonSnafu,
};
use common_procedure::{
    Context as ProcedureContext, EventContext, LockKey, Procedure, Status, StringKey,
};
use common_telemetry::{debug, error, info};
use manager::RegionMigrationProcedureGuard;
pub use manager::{
    RegionMigrationManagerRef, RegionMigrationProcedureTask, RegionMigrationProcedureTracker,
    RegionMigrationTriggerReason,
};
use serde::{Deserialize, Deserializer, Serialize};
use snafu::{OptionExt, ResultExt};
use store_api::storage::{RegionId, TableId};
use tokio::time::Instant;

use self::migration_start::RegionMigrationStart;
use crate::error::{self, Result};
use crate::event::region_migration::{REGION_MIGRATION_EVENT_TYPE, RegionMigrationEvent};
use crate::metrics::{
    METRIC_META_REGION_MIGRATION_ERROR, METRIC_META_REGION_MIGRATION_EXECUTE,
    METRIC_META_REGION_MIGRATION_STAGE_ELAPSED,
};
use crate::service::mailbox::MailboxRef;

/// The default timeout for region migration.
pub const DEFAULT_REGION_MIGRATION_TIMEOUT: Duration = Duration::from_secs(120);

#[derive(Debug, Deserialize)]
#[serde(untagged)]
enum SingleOrMultiple<T> {
    Single(T),
    Multiple(Vec<T>),
}

fn single_or_multiple_from<'de, D, T>(deserializer: D) -> std::result::Result<Vec<T>, D::Error>
where
    D: Deserializer<'de>,
    T: Deserialize<'de>,
{
    let helper = SingleOrMultiple::<T>::deserialize(deserializer)?;
    Ok(match helper {
        SingleOrMultiple::Single(x) => vec![x],
        SingleOrMultiple::Multiple(xs) => xs,
    })
}

/// It's shared in each step and available even after recovering.
///
/// It will only be updated/stored after the Red node has succeeded.
///
/// **Notes: Stores with too large data in the context might incur replication overhead.**
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub struct PersistentContext {
    /// The table catalog.
    #[deprecated(note = "use `catalog_and_schema` instead")]
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub(crate) catalog: Option<String>,
    /// The table schema.
    #[deprecated(note = "use `catalog_and_schema` instead")]
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub(crate) schema: Option<String>,
    /// The catalog and schema of the regions.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub(crate) catalog_and_schema: Vec<(String, String)>,
    /// The [Peer] of migration source.
    pub(crate) from_peer: Peer,
    /// The [Peer] of migration destination.
    pub(crate) to_peer: Peer,
    /// The [RegionId] of migration region.
    #[serde(deserialize_with = "single_or_multiple_from", alias = "region_id")]
    pub(crate) region_ids: Vec<RegionId>,
    /// The timeout for downgrading leader region and upgrading candidate region operations.
    #[serde(with = "humantime_serde", default = "default_timeout")]
    pub(crate) timeout: Duration,
    /// The trigger reason persisted for compatibility with versions without procedure context.
    #[serde(default)]
    trigger_reason: RegionMigrationTriggerReason,
}

impl PersistentContext {
    pub fn new(
        catalog_and_schema: Vec<(String, String)>,
        from_peer: Peer,
        to_peer: Peer,
        region_ids: Vec<RegionId>,
        timeout: Duration,
        trigger_reason: RegionMigrationTriggerReason,
    ) -> Self {
        #[allow(deprecated)]
        Self {
            catalog: None,
            schema: None,
            catalog_and_schema,
            from_peer,
            to_peer,
            region_ids,
            timeout,
            trigger_reason,
        }
    }
}

impl RegionMigrationTriggerReason {
    fn to_trigger_reason(self) -> TriggerReason {
        match self {
            Self::Manual => TriggerReason::Manual,
            Self::AutoRebalance => TriggerReason::AutoRebalance,
            Self::Failover => TriggerReason::RegionFailover,
            Self::Unknown => TriggerReason::Unknown,
        }
    }

    pub(crate) fn from_trigger_reason(reason: TriggerReason) -> Self {
        match reason {
            TriggerReason::Manual => Self::Manual,
            TriggerReason::AutoRebalance => Self::AutoRebalance,
            TriggerReason::RegionFailover => Self::Failover,
            _ => Self::Unknown,
        }
    }
}

fn default_timeout() -> Duration {
    Duration::from_secs(10)
}

impl PersistentContext {
    pub fn lock_key(&self) -> Vec<StringKey> {
        let mut lock_keys =
            Vec::with_capacity(self.region_ids.len() + 2 + self.catalog_and_schema.len() * 2);
        #[allow(deprecated)]
        if let (Some(catalog), Some(schema)) = (&self.catalog, &self.schema) {
            lock_keys.push(CatalogLock::Read(catalog).into());
            lock_keys.push(SchemaLock::read(catalog, schema).into());
        }
        for (catalog, schema) in self.catalog_and_schema.iter() {
            lock_keys.push(CatalogLock::Read(catalog).into());
            lock_keys.push(SchemaLock::read(catalog, schema).into());
        }

        // Sort the region ids to ensure the same order of region ids.
        let mut region_ids = self.region_ids.clone();
        region_ids.sort_unstable();
        for region_id in region_ids {
            lock_keys.push(RegionLock::Write(region_id).into());
        }
        lock_keys
    }

    /// Returns the table ids of the regions.
    ///
    /// The return value is a set of table ids.
    pub fn region_table_ids(&self) -> Vec<TableId> {
        self.region_ids
            .iter()
            .map(|region_id| region_id.table_id())
            .collect::<HashSet<_>>()
            .into_iter()
            .collect()
    }

    /// Returns the table regions map.
    ///
    /// The key is the table id, the value is the region ids of the table.
    pub fn table_regions(&self) -> HashMap<TableId, Vec<RegionId>> {
        let mut table_regions = HashMap::new();
        for region_id in &self.region_ids {
            table_regions
                .entry(region_id.table_id())
                .or_insert_with(Vec::new)
                .push(*region_id);
        }
        table_regions
    }
}

/// Metrics of region migration.
#[derive(Debug, Clone, Default)]
pub struct Metrics {
    /// Elapsed time of downgrading region and upgrading region.
    operations_elapsed: Duration,
    /// Elapsed time of flushing leader region.
    flush_leader_region_elapsed: Duration,
    /// Elapsed time of downgrading leader region.
    downgrade_leader_region_elapsed: Duration,
    /// Elapsed time of open candidate region.
    open_candidate_region_elapsed: Duration,
    /// Elapsed time of upgrade candidate region.
    upgrade_candidate_region_elapsed: Duration,
}

impl Display for Metrics {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let total = self.flush_leader_region_elapsed
            + self.downgrade_leader_region_elapsed
            + self.open_candidate_region_elapsed
            + self.upgrade_candidate_region_elapsed;
        write!(
            f,
            "total: {:?}, flush_leader_region_elapsed: {:?}, downgrade_leader_region_elapsed: {:?}, open_candidate_region_elapsed: {:?}, upgrade_candidate_region_elapsed: {:?}",
            total,
            self.flush_leader_region_elapsed,
            self.downgrade_leader_region_elapsed,
            self.open_candidate_region_elapsed,
            self.upgrade_candidate_region_elapsed
        )
    }
}

impl Metrics {
    /// Updates the elapsed time of downgrading region and upgrading region.
    pub fn update_operations_elapsed(&mut self, elapsed: Duration) {
        self.operations_elapsed += elapsed;
    }

    /// Updates the elapsed time of flushing leader region.
    pub fn update_flush_leader_region_elapsed(&mut self, elapsed: Duration) {
        self.flush_leader_region_elapsed += elapsed;
    }

    /// Updates the elapsed time of downgrading leader region.
    pub fn update_downgrade_leader_region_elapsed(&mut self, elapsed: Duration) {
        self.downgrade_leader_region_elapsed += elapsed;
    }

    /// Updates the elapsed time of open candidate region.
    pub fn update_open_candidate_region_elapsed(&mut self, elapsed: Duration) {
        self.open_candidate_region_elapsed += elapsed;
    }

    /// Updates the elapsed time of upgrade candidate region.
    pub fn update_upgrade_candidate_region_elapsed(&mut self, elapsed: Duration) {
        self.upgrade_candidate_region_elapsed += elapsed;
    }
}

impl Drop for Metrics {
    fn drop(&mut self) {
        let total = self.flush_leader_region_elapsed
            + self.downgrade_leader_region_elapsed
            + self.open_candidate_region_elapsed
            + self.upgrade_candidate_region_elapsed;
        METRIC_META_REGION_MIGRATION_STAGE_ELAPSED
            .with_label_values(&["total"])
            .observe(total.as_secs_f64());

        if !self.flush_leader_region_elapsed.is_zero() {
            METRIC_META_REGION_MIGRATION_STAGE_ELAPSED
                .with_label_values(&["flush_leader_region"])
                .observe(self.flush_leader_region_elapsed.as_secs_f64());
        }

        if !self.downgrade_leader_region_elapsed.is_zero() {
            METRIC_META_REGION_MIGRATION_STAGE_ELAPSED
                .with_label_values(&["downgrade_leader_region"])
                .observe(self.downgrade_leader_region_elapsed.as_secs_f64());
        }

        if !self.open_candidate_region_elapsed.is_zero() {
            METRIC_META_REGION_MIGRATION_STAGE_ELAPSED
                .with_label_values(&["open_candidate_region"])
                .observe(self.open_candidate_region_elapsed.as_secs_f64());
        }

        if !self.upgrade_candidate_region_elapsed.is_zero() {
            METRIC_META_REGION_MIGRATION_STAGE_ELAPSED
                .with_label_values(&["upgrade_candidate_region"])
                .observe(self.upgrade_candidate_region_elapsed.as_secs_f64());
        }
    }
}

/// It's shared in each step and available in executing (including retrying).
///
/// It will be dropped if the procedure runner crashes.
///
/// The additional remote fetches are only required in the worst cases.
#[derive(Debug, Clone, Default)]
pub struct VolatileContext {
    /// `opening_region_guard` will be set after the
    /// [OpenCandidateRegion](crate::procedure::region_migration::open_candidate_region::OpenCandidateRegion) step.
    ///
    /// `opening_region_guards` should be consumed after
    /// the corresponding [RegionRoute](common_meta::rpc::router::RegionRoute) of the opening region
    /// was written into [TableRouteValue](common_meta::key::table_route::TableRouteValue).
    opening_region_guards: Vec<OperatingRegionGuard>,
    /// The deadline of leader region lease.
    leader_region_lease_deadline: Option<Instant>,
    /// The datanode table values.
    from_peer_datanode_table_values: Option<HashMap<TableId, DatanodeTableValue>>,
    /// The last_entry_ids of leader regions.
    leader_region_last_entry_ids: HashMap<RegionId, u64>,
    /// The last_entry_ids of leader metadata regions (Only used for metric engine).
    leader_region_metadata_last_entry_ids: HashMap<RegionId, u64>,
    /// Metrics of region migration.
    metrics: Metrics,
}

impl VolatileContext {
    /// Sets the `leader_region_lease_deadline` if it does not exist.
    pub fn set_leader_region_lease_deadline(&mut self, lease_timeout: Duration) {
        if self.leader_region_lease_deadline.is_none() {
            self.leader_region_lease_deadline = Some(Instant::now() + lease_timeout);
        }
    }

    /// Resets the `leader_region_lease_deadline`.
    pub fn reset_leader_region_lease_deadline(&mut self) {
        self.leader_region_lease_deadline = None;
    }

    /// Sets the `leader_region_last_entry_id`.
    pub fn set_last_entry_id(&mut self, region_id: RegionId, last_entry_id: u64) {
        self.leader_region_last_entry_ids
            .insert(region_id, last_entry_id);
    }

    /// Sets the `leader_region_metadata_last_entry_id`.
    pub fn set_metadata_last_entry_id(&mut self, region_id: RegionId, last_entry_id: u64) {
        self.leader_region_metadata_last_entry_ids
            .insert(region_id, last_entry_id);
    }
}

/// Used to generate new [Context].
pub trait ContextFactory {
    fn new_context(self, persistent_ctx: PersistentContext) -> Context;
}

/// Default implementation.
#[derive(Clone)]
pub struct DefaultContextFactory {
    volatile_ctx: VolatileContext,
    in_memory_key: ResettableKvBackendRef,
    table_metadata_manager: TableMetadataManagerRef,
    opening_region_keeper: MemoryRegionKeeperRef,
    region_failure_detector_controller: RegionFailureDetectorControllerRef,
    mailbox: MailboxRef,
    server_addr: String,
    cache_invalidator: CacheInvalidatorRef,
}

impl DefaultContextFactory {
    /// Returns an [`DefaultContextFactory`].
    pub fn new(
        in_memory_key: ResettableKvBackendRef,
        table_metadata_manager: TableMetadataManagerRef,
        opening_region_keeper: MemoryRegionKeeperRef,
        region_failure_detector_controller: RegionFailureDetectorControllerRef,
        mailbox: MailboxRef,
        server_addr: String,
        cache_invalidator: CacheInvalidatorRef,
    ) -> Self {
        Self {
            volatile_ctx: VolatileContext::default(),
            in_memory_key,
            table_metadata_manager,
            opening_region_keeper,
            region_failure_detector_controller,
            mailbox,
            server_addr,
            cache_invalidator,
        }
    }
}

impl ContextFactory for DefaultContextFactory {
    fn new_context(self, persistent_ctx: PersistentContext) -> Context {
        Context {
            persistent_ctx,
            volatile_ctx: self.volatile_ctx,
            in_memory: self.in_memory_key,
            table_metadata_manager: self.table_metadata_manager,
            opening_region_keeper: self.opening_region_keeper,
            region_failure_detector_controller: self.region_failure_detector_controller,
            mailbox: self.mailbox,
            server_addr: self.server_addr,
            cache_invalidator: self.cache_invalidator,
        }
    }
}

/// The context of procedure execution.
pub struct Context {
    persistent_ctx: PersistentContext,
    volatile_ctx: VolatileContext,
    in_memory: KvBackendRef,
    table_metadata_manager: TableMetadataManagerRef,
    opening_region_keeper: MemoryRegionKeeperRef,
    region_failure_detector_controller: RegionFailureDetectorControllerRef,
    mailbox: MailboxRef,
    server_addr: String,
    cache_invalidator: CacheInvalidatorRef,
}

impl Context {
    pub(crate) fn trigger_reason(
        &self,
        event_context: Option<&PersistentEventContext>,
    ) -> RegionMigrationTriggerReason {
        event_context
            .map(|ctx| RegionMigrationTriggerReason::from_trigger_reason(ctx.reason))
            .unwrap_or(self.persistent_ctx.trigger_reason)
    }
    /// Returns the next operation's timeout.
    pub fn next_operation_timeout(&self) -> Option<Duration> {
        self.persistent_ctx
            .timeout
            .checked_sub(self.volatile_ctx.metrics.operations_elapsed)
    }

    /// Updates operations elapsed.
    pub fn update_operations_elapsed(&mut self, instant: Instant) {
        self.volatile_ctx
            .metrics
            .update_operations_elapsed(instant.elapsed());
    }

    /// Updates the elapsed time of flushing leader region.
    pub fn update_flush_leader_region_elapsed(&mut self, instant: Instant) {
        self.volatile_ctx
            .metrics
            .update_flush_leader_region_elapsed(instant.elapsed());
    }

    /// Updates the elapsed time of downgrading leader region.
    pub fn update_downgrade_leader_region_elapsed(&mut self, instant: Instant) {
        self.volatile_ctx
            .metrics
            .update_downgrade_leader_region_elapsed(instant.elapsed());
    }

    /// Updates the elapsed time of open candidate region.
    pub fn update_open_candidate_region_elapsed(&mut self, instant: Instant) {
        self.volatile_ctx
            .metrics
            .update_open_candidate_region_elapsed(instant.elapsed());
    }

    /// Updates the elapsed time of upgrade candidate region.
    pub fn update_upgrade_candidate_region_elapsed(&mut self, instant: Instant) {
        self.volatile_ctx
            .metrics
            .update_upgrade_candidate_region_elapsed(instant.elapsed());
    }

    /// Returns address of meta server.
    pub fn server_addr(&self) -> &str {
        &self.server_addr
    }

    /// Returns the table ids of the regions.
    pub fn region_table_ids(&self) -> Vec<TableId> {
        self.persistent_ctx
            .region_ids
            .iter()
            .map(|region_id| region_id.table_id())
            .collect::<HashSet<_>>()
            .into_iter()
            .collect()
    }

    /// Returns the `table_routes` of [VolatileContext] if any.
    /// Otherwise, returns the value retrieved from remote.
    ///
    /// Retry:
    /// - Failed to retrieve the metadata of table.
    pub async fn get_table_route_values(
        &self,
    ) -> Result<HashMap<TableId, DeserializedValueWithBytes<TableRouteValue>>> {
        let table_ids = self.persistent_ctx.region_table_ids();
        let table_routes = self
            .table_metadata_manager
            .table_route_manager()
            .table_route_storage()
            .batch_get_with_raw_bytes(&table_ids)
            .await
            .context(error::TableMetadataManagerSnafu)
            .map_err(BoxedError::new)
            .with_context(|_| error::RetryLaterWithSourceSnafu {
                reason: format!("Failed to get table routes: {table_ids:?}"),
            })?;
        let table_routes = table_ids
            .into_iter()
            .zip(table_routes)
            .filter_map(|(table_id, table_route)| {
                table_route.map(|table_route| (table_id, table_route))
            })
            .collect::<HashMap<_, _>>();
        Ok(table_routes)
    }

    /// Returns the `table_route` of [VolatileContext] if any.
    /// Otherwise, returns the value retrieved from remote.
    ///
    /// Retry:
    /// - Failed to retrieve the metadata of table.
    pub async fn get_table_route_value(
        &self,
        table_id: TableId,
    ) -> Result<DeserializedValueWithBytes<TableRouteValue>> {
        let table_route_value = self
            .table_metadata_manager
            .table_route_manager()
            .table_route_storage()
            .get_with_raw_bytes(table_id)
            .await
            .context(error::TableMetadataManagerSnafu)
            .map_err(BoxedError::new)
            .with_context(|_| error::RetryLaterWithSourceSnafu {
                reason: format!("Failed to get table routes: {table_id:}"),
            })?
            .context(error::TableRouteNotFoundSnafu { table_id })?;
        Ok(table_route_value)
    }

    /// Returns the `from_peer_datanode_table_values` of [VolatileContext] if any.
    /// Otherwise, returns the value retrieved from remote.
    ///
    /// Retry:
    /// - Failed to retrieve the metadata of datanode table.
    pub async fn get_from_peer_datanode_table_values(
        &mut self,
    ) -> Result<&HashMap<TableId, DatanodeTableValue>> {
        let from_peer_datanode_table_values =
            &mut self.volatile_ctx.from_peer_datanode_table_values;
        if from_peer_datanode_table_values.is_none() {
            let table_ids = self.persistent_ctx.region_table_ids();
            let datanode_table_keys = table_ids
                .iter()
                .map(|table_id| DatanodeTableKey {
                    datanode_id: self.persistent_ctx.from_peer.id,
                    table_id: *table_id,
                })
                .collect::<Vec<_>>();
            let datanode_table_values = self
                .table_metadata_manager
                .datanode_table_manager()
                .batch_get(&datanode_table_keys)
                .await
                .context(error::TableMetadataManagerSnafu)
                .map_err(BoxedError::new)
                .with_context(|_| error::RetryLaterWithSourceSnafu {
                    reason: format!("Failed to get DatanodeTable: {table_ids:?}"),
                })?
                .into_iter()
                .map(|(k, v)| (k.table_id, v))
                .collect();
            *from_peer_datanode_table_values = Some(datanode_table_values);
        }
        Ok(from_peer_datanode_table_values.as_ref().unwrap())
    }

    /// Returns the `from_peer_datanode_table_value` of [VolatileContext] if any.
    /// Otherwise, returns the value retrieved from remote.
    ///
    /// Retry:
    /// - Failed to retrieve the metadata of datanode table.
    pub async fn get_from_peer_datanode_table_value(
        &self,
        table_id: TableId,
    ) -> Result<DatanodeTableValue> {
        let datanode_table_value = self
            .table_metadata_manager
            .datanode_table_manager()
            .get(&DatanodeTableKey {
                datanode_id: self.persistent_ctx.from_peer.id,
                table_id,
            })
            .await
            .context(error::TableMetadataManagerSnafu)
            .map_err(BoxedError::new)
            .with_context(|_| error::RetryLaterWithSourceSnafu {
                reason: format!("Failed to get DatanodeTable: {table_id}"),
            })?
            .context(error::DatanodeTableNotFoundSnafu {
                table_id,
                datanode_id: self.persistent_ctx.from_peer.id,
            })?;
        Ok(datanode_table_value)
    }

    /// Notifies the RegionSupervisor to register failure detectors of failed region.
    ///
    /// The original failure detector was removed once the procedure was triggered.
    /// Now, we need to register the failure detector for the failed region again.
    pub async fn register_failure_detectors(&self) {
        let datanode_id = self.persistent_ctx.from_peer.id;
        let region_ids = &self.persistent_ctx.region_ids;
        let detecting_regions = region_ids
            .iter()
            .map(|region_id| (datanode_id, *region_id))
            .collect::<Vec<_>>();
        self.region_failure_detector_controller
            .register_failure_detectors(detecting_regions)
            .await;
        info!(
            "Registered failure detectors after migration failures for datanode {}, regions {:?}",
            datanode_id, region_ids
        );
    }

    /// Notifies the RegionSupervisor to reset failure detectors of candidate regions.
    pub async fn reset_failure_detectors_for_candidate_regions(&self) {
        let datanode_id = self.persistent_ctx.to_peer.id;
        let region_ids = &self.persistent_ctx.region_ids;
        let detecting_regions = region_ids
            .iter()
            .map(|region_id| (datanode_id, *region_id))
            .collect::<Vec<_>>();
        self.region_failure_detector_controller
            .reset_failure_detectors(detecting_regions)
            .await;
        info!(
            "Reset failure detectors after migration success for datanode {}, regions {:?}",
            datanode_id, region_ids
        );
    }

    /// Notifies the RegionSupervisor to deregister failure detectors.
    ///
    /// The original failure detectors won't be removed once the procedure was triggered.
    /// We need to deregister the failure detectors for the original region if the procedure is finished.
    pub async fn deregister_failure_detectors(&self) {
        let datanode_id = self.persistent_ctx.from_peer.id;
        let region_ids = &self.persistent_ctx.region_ids;
        let detecting_regions = region_ids
            .iter()
            .map(|region_id| (datanode_id, *region_id))
            .collect::<Vec<_>>();

        self.region_failure_detector_controller
            .deregister_failure_detectors(detecting_regions)
            .await;
    }

    /// Notifies the RegionSupervisor to deregister failure detectors for the candidate regions on the destination peer.
    ///
    /// The candidate regions may be created on the destination peer,
    /// so we need to deregister the failure detectors for the candidate regions if the procedure is aborted.
    pub async fn deregister_failure_detectors_for_candidate_regions(&self) {
        let to_peer_id = self.persistent_ctx.to_peer.id;
        let region_ids = &self.persistent_ctx.region_ids;
        let detecting_regions = region_ids
            .iter()
            .map(|region_id| (to_peer_id, *region_id))
            .collect::<Vec<_>>();

        self.region_failure_detector_controller
            .deregister_failure_detectors(detecting_regions)
            .await;
    }

    /// Fetches replay checkpoints and merges them with topic pruned entry ids.
    pub async fn get_replay_checkpoints_with_topic_pruned_entry_ids(
        &self,
        region_topics: &[(RegionId, String, bool)],
    ) -> Result<HashMap<RegionId, ReplayCheckpoint>> {
        let topic_region_keys = region_topics
            .iter()
            .map(|(region_id, topic, _)| TopicRegionKey::new(*region_id, topic))
            .collect::<Vec<_>>();
        let topic_region_values = self
            .table_metadata_manager
            .topic_region_manager()
            .batch_get(topic_region_keys)
            .await
            .context(error::TableMetadataManagerSnafu)?;

        let topic_name_keys = region_topics
            .iter()
            .map(|(_, topic, _)| topic.as_str())
            .collect::<HashSet<_>>()
            .into_iter()
            .map(TopicNameKey::new)
            .collect::<Vec<_>>();
        let topic_name_values = self
            .table_metadata_manager
            .topic_name_manager()
            .batch_get(topic_name_keys)
            .await
            .context(error::TableMetadataManagerSnafu)?;
        debug!(
            "Fetched topic region values: {:?}, topic name values: {:?}",
            topic_region_values, topic_name_values
        );

        let replay_checkpoints = region_topics
            .iter()
            .filter_map(|(region_id, topic, is_metric_engine)| {
                let checkpoint = topic_region_values
                    .get(region_id)
                    .and_then(|value| value.checkpoint);
                let pruned_entry_id = topic_name_values
                    .get(topic)
                    .map(|value| value.pruned_entry_id);

                ReplayCheckpoint::merge_with_topic_pruned_entry_id(
                    checkpoint,
                    pruned_entry_id,
                    *is_metric_engine,
                )
                .map(|checkpoint| (*region_id, checkpoint))
            })
            .collect::<HashMap<_, _>>();

        Ok(replay_checkpoints)
    }

    /// Broadcasts the invalidate table cache message.
    pub async fn invalidate_table_cache(&self) -> Result<()> {
        let table_ids = self.region_table_ids();
        let mut cache_idents = Vec::with_capacity(table_ids.len());
        for table_id in &table_ids {
            cache_idents.push(CacheIdent::TableId(*table_id));
        }
        // ignore the result
        let ctx = common_meta::cache_invalidator::Context::default();
        let _ = self.cache_invalidator.invalidate(&ctx, &cache_idents).await;
        Ok(())
    }

    /// Returns the [PersistentContext] of the procedure.
    pub fn persistent_ctx(&self) -> PersistentContext {
        self.persistent_ctx.clone()
    }
}

#[async_trait::async_trait]
#[typetag::serde(tag = "region_migration_state")]
pub(crate) trait State: Sync + Send + Debug {
    fn name(&self) -> &'static str {
        let type_name = std::any::type_name::<Self>();
        // short name
        type_name.split("::").last().unwrap_or(type_name)
    }

    /// Yields the next [State] and [Status].
    async fn next(
        &mut self,
        ctx: &mut Context,
        procedure_ctx: &ProcedureContext,
    ) -> Result<(Box<dyn State>, Status)>;

    /// Returns as [Any](std::any::Any).
    fn as_any(&self) -> &dyn Any;
}

/// Persistent data of [RegionMigrationProcedure].
#[derive(Debug, Serialize, Deserialize)]
pub struct RegionMigrationDataOwned {
    persistent_ctx: PersistentContext,
    state: Box<dyn State>,
}

/// Persistent data of [RegionMigrationProcedure].
#[derive(Debug, Serialize)]
pub struct RegionMigrationData<'a> {
    persistent_ctx: &'a PersistentContext,
    state: &'a dyn State,
}

pub(crate) struct RegionMigrationProcedure {
    state: Box<dyn State>,
    context: Context,
    _guards: Vec<RegionMigrationProcedureGuard>,
}

impl RegionMigrationProcedure {
    const TYPE_NAME: &'static str = "metasrv-procedure::RegionMigration";

    pub fn new(
        persistent_context: PersistentContext,
        context_factory: impl ContextFactory,
        guards: Vec<RegionMigrationProcedureGuard>,
    ) -> Self {
        let state = Box::new(RegionMigrationStart {});
        Self::new_inner(state, persistent_context, context_factory, guards)
    }

    fn new_inner(
        state: Box<dyn State>,
        persistent_context: PersistentContext,
        context_factory: impl ContextFactory,
        guards: Vec<RegionMigrationProcedureGuard>,
    ) -> Self {
        Self {
            state,
            context: context_factory.new_context(persistent_context),
            _guards: guards,
        }
    }

    fn from_json(
        json: &str,
        context_factory: impl ContextFactory,
        tracker: RegionMigrationProcedureTracker,
    ) -> ProcedureResult<Self> {
        let RegionMigrationDataOwned {
            persistent_ctx,
            state,
        } = serde_json::from_str(json).context(FromJsonSnafu)?;
        let guards = persistent_ctx
            .region_ids
            .iter()
            .flat_map(|region_id| {
                tracker.insert_running_procedure(&RegionMigrationProcedureTask {
                    region_id: *region_id,
                    from_peer: persistent_ctx.from_peer.clone(),
                    to_peer: persistent_ctx.to_peer.clone(),
                    timeout: persistent_ctx.timeout,
                    trigger_reason: persistent_ctx.trigger_reason,
                })
            })
            .collect::<Vec<_>>();

        let context = context_factory.new_context(persistent_ctx);

        Ok(Self {
            state,
            context,
            _guards: guards,
        })
    }

    async fn rollback_inner(&mut self, procedure_ctx: &ProcedureContext) -> Result<()> {
        let _timer = METRIC_META_REGION_MIGRATION_EXECUTE
            .with_label_values(&["rollback"])
            .start_timer();
        let ctx = &self.context;
        let table_regions = ctx.persistent_ctx.table_regions();
        for (table_id, regions) in table_regions {
            let table_lock = TableLock::Write(table_id).into();
            let _guard = procedure_ctx.provider.acquire_lock(&table_lock).await;
            let table_route = ctx.get_table_route_value(table_id).await?;
            let region_routes = table_route.region_routes().unwrap();
            let downgraded = region_routes
                .iter()
                .filter(|route| regions.contains(&route.region.id))
                .any(|route| route.is_leader_downgrading());
            if downgraded {
                info!(
                    "Rollbacking downgraded region leader table route, table: {table_id}, regions: {regions:?}"
                );
                let table_metadata_manager = &ctx.table_metadata_manager;
                table_metadata_manager
                    .update_leader_region_status(table_id, &table_route, |route| {
                        if regions.contains(&route.region.id) {
                            Some(None)
                        } else {
                            None
                        }
                    })
                    .await
                    .context(error::TableMetadataManagerSnafu)
                    .map_err(BoxedError::new)
                    .with_context(|_| error::RetryLaterWithSourceSnafu {
                        reason: format!("Failed to update the table route during the rollback downgraded leader region: {regions:?}"),
                    })?;
            }
        }
        self.context
            .deregister_failure_detectors_for_candidate_regions()
            .await;
        self.context.register_failure_detectors().await;

        Ok(())
    }
}

#[async_trait::async_trait]
impl Procedure for RegionMigrationProcedure {
    fn type_name(&self) -> &str {
        Self::TYPE_NAME
    }

    async fn rollback(&mut self, ctx: &ProcedureContext) -> ProcedureResult<()> {
        self.rollback_inner(ctx)
            .await
            .map_err(ProcedureError::external)
    }

    fn rollback_supported(&self) -> bool {
        true
    }

    #[tracing::instrument(skip_all, fields(
        state = %self.state.name(),
        region_count = self.context.persistent_ctx.region_ids.len(),
        from_peer = self.context.persistent_ctx.from_peer.id,
        to_peer = self.context.persistent_ctx.to_peer.id,
    ))]
    async fn execute(&mut self, ctx: &ProcedureContext) -> ProcedureResult<Status> {
        let state = &mut self.state;

        let name = state.name();
        let _timer = METRIC_META_REGION_MIGRATION_EXECUTE
            .with_label_values(&[name])
            .start_timer();
        match state.next(&mut self.context, ctx).await {
            Ok((next, status)) => {
                *state = next;
                Ok(status)
            }
            Err(e) => {
                if e.is_retryable() {
                    METRIC_META_REGION_MIGRATION_ERROR
                        .with_label_values(&[name, "retryable"])
                        .inc();
                    Err(ProcedureError::retry_later(e))
                } else {
                    // Consumes the opening region guard before deregistering the failure detectors.
                    self.context.volatile_ctx.opening_region_guards.clear();
                    self.context
                        .deregister_failure_detectors_for_candidate_regions()
                        .await;
                    error!(
                        e;
                        "Region migration procedure failed, regions: {:?}, from_peer: {}, to_peer: {}, {}",
                        self.context.persistent_ctx.region_ids,
                        self.context.persistent_ctx.from_peer,
                        self.context.persistent_ctx.to_peer,
                        self.context.volatile_ctx.metrics,
                    );
                    METRIC_META_REGION_MIGRATION_ERROR
                        .with_label_values(&[name, "external"])
                        .inc();
                    Err(ProcedureError::external(e))
                }
            }
        }
    }

    fn dump(&self) -> ProcedureResult<String> {
        let data = RegionMigrationData {
            state: self.state.as_ref(),
            persistent_ctx: &self.context.persistent_ctx,
        };
        serde_json::to_string(&data).context(ToJsonSnafu)
    }

    fn lock_key(&self) -> LockKey {
        LockKey::new(self.context.persistent_ctx.lock_key())
    }

    fn event(&self, ctx: &EventContext<'_>) -> Option<Box<dyn Event>> {
        if !ctx.event_type_filter.allows(REGION_MIGRATION_EVENT_TYPE) {
            return None;
        }

        Some(Box::new(RegionMigrationEvent::from_persistent_ctx(
            &self.context.persistent_ctx,
            self.context
                .trigger_reason(ctx.event_context)
                .to_trigger_reason(),
        )))
    }
}

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

    use common_meta::distributed_time_constants::default_distributed_time_constants;
    use common_meta::instruction::Instruction;
    use common_meta::key::test_utils::new_test_table_info;
    use common_meta::rpc::router::{Region, RegionRoute};

    use super::*;
    use crate::handler::HeartbeatMailbox;
    use crate::procedure::region_migration::open_candidate_region::OpenCandidateRegion;
    use crate::procedure::region_migration::test_util::*;
    use crate::procedure::test_util::{
        new_downgrade_region_reply, new_flush_region_reply_for_region, new_open_region_reply,
        new_upgrade_region_reply,
    };
    use crate::service::mailbox::Channel;

    fn new_persistent_context() -> PersistentContext {
        test_util::new_persistent_context(1, 2, RegionId::new(1024, 1))
    }

    #[test]
    fn test_lock_key() {
        let persistent_context = new_persistent_context();
        let expected_keys = persistent_context.lock_key();

        let env = TestingEnv::new();
        let context = env.context_factory();

        let procedure = RegionMigrationProcedure::new(persistent_context, context, vec![]);

        let key = procedure.lock_key();
        let keys = key.keys_to_lock().cloned().collect::<Vec<_>>();

        for key in expected_keys {
            assert!(keys.contains(&key));
        }
    }

    #[test]
    fn test_data_serialization() {
        let persistent_context = new_persistent_context();

        let env = TestingEnv::new();
        let context = env.context_factory();

        let procedure = RegionMigrationProcedure::new(persistent_context, context, vec![]);

        let serialized = procedure.dump().unwrap();
        let expected = r#"{"persistent_ctx":{"catalog_and_schema":[["greptime","public"]],"from_peer":{"id":1,"addr":""},"to_peer":{"id":2,"addr":""},"region_ids":[4398046511105],"timeout":"10s","trigger_reason":"Unknown"},"state":{"region_migration_state":"RegionMigrationStart"}}"#;
        assert_eq!(expected, serialized);
    }

    #[test]
    fn test_event_hook_uses_current_persistent_context() {
        let env = TestingEnv::new();
        let procedure =
            RegionMigrationProcedure::new(new_persistent_context(), env.context_factory(), vec![]);
        let state = common_procedure::ProcedureState::Running;
        let triggers = [
            common_procedure::EventTrigger::Recovered,
            common_procedure::EventTrigger::Retrying {
                phase: common_procedure::RetryPhase::Execute,
                attempt: 1,
            },
            common_procedure::EventTrigger::RollingBack,
            common_procedure::EventTrigger::Succeeded,
            common_procedure::EventTrigger::Failed,
            common_procedure::EventTrigger::Poisoned,
        ];

        for trigger in triggers {
            let event = procedure
                .event(&EventContext {
                    procedure_id: common_procedure::ProcedureId::random(),
                    lifecycle_state: &state,
                    trigger,
                    event_type_filter: Arc::new(common_event_recorder::EventTypeFilter::All),
                    event_context: None,
                })
                .unwrap();
            assert_eq!(event.event_type(), "region_migration");
            assert_eq!(event.extra_rows().unwrap().len(), 1);
        }
    }

    #[test]
    fn test_backward_compatibility() {
        let persistent_ctx = PersistentContext {
            #[allow(deprecated)]
            catalog: Some("greptime".into()),
            #[allow(deprecated)]
            schema: Some("public".into()),
            catalog_and_schema: vec![],
            from_peer: Peer::empty(1),
            to_peer: Peer::empty(2),
            region_ids: vec![RegionId::new(1024, 1)],
            timeout: Duration::from_secs(10),
            trigger_reason: RegionMigrationTriggerReason::Unknown,
        };
        // NOTES: Changes it will break backward compatibility.
        let serialized = r#"{"catalog":"greptime","schema":"public","from_peer":{"id":1,"addr":""},"to_peer":{"id":2,"addr":""},"region_id":4398046511105}"#;
        let deserialized: PersistentContext = serde_json::from_str(serialized).unwrap();

        assert_eq!(persistent_ctx, deserialized);
    }

    #[test]
    fn test_legacy_trigger_reason_survives_recovery_and_repersistence() {
        let serialized = r#"{"persistent_ctx":{"catalog":"greptime","schema":"public","from_peer":{"id":1,"addr":""},"to_peer":{"id":2,"addr":""},"region_id":4398046511105,"trigger_reason":"Failover"},"state":{"region_migration_state":"RegionMigrationStart"}}"#;
        let env = TestingEnv::new();
        let procedure = RegionMigrationProcedure::from_json(
            serialized,
            env.context_factory(),
            RegionMigrationProcedureTracker::default(),
        )
        .unwrap();
        assert_eq!(
            procedure.context.persistent_ctx.trigger_reason,
            RegionMigrationTriggerReason::Failover
        );
        let repersisted = procedure.dump().unwrap();
        assert_eq!(
            serde_json::from_str::<serde_json::Value>(&repersisted).unwrap()["persistent_ctx"]["trigger_reason"],
            "Failover"
        );

        let recovered = RegionMigrationProcedure::from_json(
            &repersisted,
            env.context_factory(),
            RegionMigrationProcedureTracker::default(),
        )
        .unwrap();
        assert_eq!(
            recovered.context.trigger_reason(None),
            RegionMigrationTriggerReason::Failover
        );
        let event_context = PersistentEventContext::new(TriggerReason::AutoRebalance);
        assert_eq!(
            recovered.context.trigger_reason(Some(&event_context)),
            RegionMigrationTriggerReason::AutoRebalance
        );

        let state = common_procedure::ProcedureState::Running;
        let event = recovered
            .event(&EventContext {
                procedure_id: common_procedure::ProcedureId::random(),
                lifecycle_state: &state,
                trigger: common_procedure::EventTrigger::Recovered,
                event_type_filter: Arc::new(common_event_recorder::EventTypeFilter::All),
                event_context: None,
            })
            .unwrap();
        assert_eq!(
            event.extra_rows().unwrap()[0].values[3].value_data,
            Some(api::v1::value::ValueData::StringValue(
                "Failover".to_string()
            ))
        );
    }

    #[test]
    fn test_migration_reason_uses_event_context() {
        let env = TestingEnv::new();
        let context = env.context_factory().new_context(new_persistent_context());
        let event_context = PersistentEventContext::new(TriggerReason::RegionFailover);

        assert_eq!(
            context.trigger_reason(Some(&event_context)),
            RegionMigrationTriggerReason::Failover
        );

        let procedure =
            RegionMigrationProcedure::new(new_persistent_context(), env.context_factory(), vec![]);
        let state = common_procedure::ProcedureState::Running;
        let event = procedure
            .event(&EventContext {
                procedure_id: common_procedure::ProcedureId::random(),
                lifecycle_state: &state,
                trigger: common_procedure::EventTrigger::Submitted,
                event_type_filter: Arc::new(common_event_recorder::EventTypeFilter::All),
                event_context: Some(&event_context),
            })
            .unwrap();
        assert_eq!(
            event.extra_rows().unwrap()[0].values[3].value_data,
            Some(api::v1::value::ValueData::StringValue(
                "Failover".to_string()
            ))
        );
    }

    #[derive(Debug, Serialize, Deserialize, Default)]
    pub struct MockState;

    #[async_trait::async_trait]
    #[typetag::serde]
    impl State for MockState {
        async fn next(
            &mut self,
            _ctx: &mut Context,
            _procedure_ctx: &ProcedureContext,
        ) -> Result<(Box<dyn State>, Status)> {
            Ok((Box::new(MockState), Status::done()))
        }

        fn as_any(&self) -> &dyn Any {
            self
        }
    }

    #[tokio::test]
    async fn test_execution_after_deserialized() {
        let env = TestingEnv::new();

        fn new_mock_procedure(env: &TestingEnv) -> RegionMigrationProcedure {
            let persistent_context = new_persistent_context();
            let context_factory = env.context_factory();
            let state = Box::<MockState>::default();
            RegionMigrationProcedure::new_inner(state, persistent_context, context_factory, vec![])
        }

        let ctx = TestingEnv::procedure_context();
        let mut procedure = new_mock_procedure(&env);
        let mut status = None;
        for _ in 0..3 {
            status = Some(procedure.execute(&ctx).await.unwrap());
        }
        assert!(status.unwrap().is_done());

        let ctx = TestingEnv::procedure_context();
        let mut procedure = new_mock_procedure(&env);

        status = Some(procedure.execute(&ctx).await.unwrap());

        let serialized = procedure.dump().unwrap();

        let context_factory = env.context_factory();
        let tracker = env.tracker();
        let mut procedure =
            RegionMigrationProcedure::from_json(&serialized, context_factory, tracker.clone())
                .unwrap();
        for region_id in &procedure.context.persistent_ctx.region_ids {
            assert!(tracker.contains(*region_id));
        }

        for _ in 1..3 {
            status = Some(procedure.execute(&ctx).await.unwrap());
        }
        assert!(status.unwrap().is_done());
    }

    #[tokio::test]
    async fn test_broadcast_invalidate_table_cache() {
        let mut env = TestingEnv::new();
        let persistent_context = test_util::new_persistent_context(1, 2, RegionId::new(1024, 1));
        let ctx = env.context_factory().new_context(persistent_context);
        let mailbox_ctx = env.mailbox_context();

        // No receivers.
        ctx.invalidate_table_cache().await.unwrap();

        let (tx, mut rx) = tokio::sync::mpsc::channel(1);

        mailbox_ctx
            .insert_heartbeat_response_receiver(Channel::Frontend(1), tx)
            .await;

        ctx.invalidate_table_cache().await.unwrap();

        let resp = rx.recv().await.unwrap().unwrap();
        let msg = resp.mailbox_message.unwrap();

        let instruction = HeartbeatMailbox::json_instruction(&msg).unwrap();
        assert_eq!(
            instruction,
            Instruction::InvalidateCaches(vec![CacheIdent::TableId(1024)])
        );
    }

    fn procedure_flow_steps(from_peer_id: u64, to_peer_id: u64) -> Vec<Step> {
        vec![
            // MigrationStart
            Step::next(
                "Should be the open candidate region",
                None,
                Assertion::simple(assert_open_candidate_region, assert_need_persist),
            ),
            // OpenCandidateRegion
            Step::next(
                "Should be the flush leader region",
                Some(mock_datanode_reply(
                    to_peer_id,
                    Arc::new(|id| Ok(new_open_region_reply(id, true, None))),
                )),
                Assertion::simple(assert_flush_leader_region, assert_no_persist),
            ),
            // Flush Leader Region
            Step::next(
                "Should be the flush leader region",
                Some(mock_datanode_reply(
                    from_peer_id,
                    Arc::new(move |id| {
                        Ok(new_flush_region_reply_for_region(
                            id,
                            RegionId::new(1024, 1),
                            true,
                            None,
                        ))
                    }),
                )),
                Assertion::simple(assert_update_metadata_downgrade, assert_no_persist),
            ),
            // UpdateMetadata::Downgrade
            Step::next(
                "Should be the downgrade leader region",
                None,
                Assertion::simple(assert_downgrade_leader_region, assert_no_persist),
            ),
            // Downgrade Candidate
            Step::next(
                "Should be the upgrade candidate region",
                Some(mock_datanode_reply(
                    from_peer_id,
                    Arc::new(|id| Ok(new_downgrade_region_reply(id, None, true, None))),
                )),
                Assertion::simple(assert_upgrade_candidate_region, assert_no_persist),
            ),
            // Upgrade Candidate
            Step::next(
                "Should be the update metadata for upgrading",
                Some(mock_datanode_reply(
                    to_peer_id,
                    Arc::new(|id| Ok(new_upgrade_region_reply(id, true, true, None))),
                )),
                Assertion::simple(assert_update_metadata_upgrade, assert_no_persist),
            ),
            // UpdateMetadata::Upgrade
            Step::next(
                "Should be the close downgraded region",
                None,
                Assertion::simple(assert_close_downgraded_region, assert_no_persist),
            ),
            // CloseDowngradedRegion
            Step::next(
                "Should be the region migration end",
                None,
                Assertion::simple(assert_region_migration_end, assert_done),
            ),
            // RegionMigrationEnd
            Step::next(
                "Should be the region migration end again",
                None,
                Assertion::simple(assert_region_migration_end, assert_done),
            ),
        ]
    }

    #[tokio::test]
    async fn test_procedure_flow() {
        common_telemetry::init_default_ut_logging();

        let persistent_context = test_util::new_persistent_context(1, 2, RegionId::new(1024, 1));
        let state = Box::new(RegionMigrationStart);

        // The table metadata.
        let from_peer_id = persistent_context.from_peer.id;
        let to_peer_id = persistent_context.to_peer.id;
        let from_peer = persistent_context.from_peer.clone();
        let to_peer = persistent_context.to_peer.clone();
        let region_id = persistent_context.region_ids[0];
        let table_info = new_test_table_info(1024);
        let region_routes = vec![RegionRoute {
            region: Region::new_test(region_id),
            leader_peer: Some(from_peer),
            follower_peers: vec![to_peer],
            ..Default::default()
        }];

        let suite = ProcedureMigrationTestSuite::new(persistent_context, state);
        suite.init_table_metadata(table_info, region_routes).await;

        let steps = procedure_flow_steps(from_peer_id, to_peer_id);
        let timer = Instant::now();

        // Run the table tests.
        let runner = ProcedureMigrationSuiteRunner::new(suite)
            .steps(steps)
            .run_once()
            .await;

        let region_lease = default_distributed_time_constants().region_lease.as_secs();

        // Ensure it didn't run into the slow path.
        assert!(timer.elapsed().as_secs() < region_lease / 2);

        runner.suite.verify_table_metadata().await;
    }

    #[tokio::test]
    async fn test_procedure_flow_open_candidate_region_retryable_error() {
        common_telemetry::init_default_ut_logging();

        let persistent_context = test_util::new_persistent_context(1, 2, RegionId::new(1024, 1));
        let state = Box::new(RegionMigrationStart);

        // The table metadata.
        let to_peer_id = persistent_context.to_peer.id;
        let from_peer = persistent_context.from_peer.clone();
        let region_id = persistent_context.region_ids[0];
        let table_info = new_test_table_info(1024);
        let region_routes = vec![RegionRoute {
            region: Region::new_test(region_id),
            leader_peer: Some(from_peer),
            follower_peers: vec![],
            ..Default::default()
        }];

        let suite = ProcedureMigrationTestSuite::new(persistent_context, state);
        suite.init_table_metadata(table_info, region_routes).await;

        let steps = vec![
            // Migration Start
            Step::next(
                "Should be the open candidate region",
                None,
                Assertion::simple(assert_open_candidate_region, assert_need_persist),
            ),
            // OpenCandidateRegion
            Step::next(
                "Should be throwing a non-retry error",
                Some(mock_datanode_reply(
                    to_peer_id,
                    Arc::new(|id| error::MailboxTimeoutSnafu { id }.fail()),
                )),
                Assertion::error(|error| assert!(error.is_retryable())),
            ),
            // OpenCandidateRegion
            Step::next(
                "Should be throwing a non-retry error again",
                Some(mock_datanode_reply(
                    to_peer_id,
                    Arc::new(|id| error::MailboxTimeoutSnafu { id }.fail()),
                )),
                Assertion::error(|error| assert!(error.is_retryable())),
            ),
        ];

        let setup_to_latest_persisted_state = Step::setup(
            "Sets state to UpdateMetadata::Downgrade",
            merge_before_test_fn(vec![
                setup_state(Arc::new(|| Box::new(OpenCandidateRegion))),
                Arc::new(reset_volatile_ctx),
            ]),
        );

        let steps = [
            steps.clone(),
            // Mocks the volatile ctx lost(i.g., Meta leader restarts).
            vec![setup_to_latest_persisted_state.clone()],
            steps.clone()[1..].to_vec(),
            vec![setup_to_latest_persisted_state],
            steps.clone()[1..].to_vec(),
        ]
        .concat();

        // Run the table tests.
        let runner = ProcedureMigrationSuiteRunner::new(suite)
            .steps(steps.clone())
            .run_once()
            .await;

        let table_routes_version = runner
            .env()
            .table_metadata_manager()
            .table_route_manager()
            .table_route_storage()
            .get(region_id.table_id())
            .await
            .unwrap()
            .unwrap()
            .version();
        // Should be unchanged.
        assert_eq!(table_routes_version.unwrap(), 0);
    }

    #[tokio::test]
    async fn test_procedure_flow_upgrade_candidate_with_retry_and_failed() {
        common_telemetry::init_default_ut_logging();

        let persistent_context = test_util::new_persistent_context(1, 2, RegionId::new(1024, 1));
        let state = Box::new(RegionMigrationStart);

        // The table metadata.
        let from_peer_id = persistent_context.from_peer.id;
        let to_peer_id = persistent_context.to_peer.id;
        let from_peer = persistent_context.from_peer.clone();
        let region_id = persistent_context.region_ids[0];
        let table_info = new_test_table_info(1024);
        let region_routes = vec![RegionRoute {
            region: Region::new_test(region_id),
            leader_peer: Some(from_peer),
            follower_peers: vec![],
            ..Default::default()
        }];

        let suite = ProcedureMigrationTestSuite::new(persistent_context, state);
        suite.init_table_metadata(table_info, region_routes).await;

        let steps = vec![
            // MigrationStart
            Step::next(
                "Should be the open candidate region",
                None,
                Assertion::simple(assert_open_candidate_region, assert_need_persist),
            ),
            // OpenCandidateRegion
            Step::next(
                "Should be the flush leader region",
                Some(mock_datanode_reply(
                    to_peer_id,
                    Arc::new(|id| Ok(new_open_region_reply(id, true, None))),
                )),
                Assertion::simple(assert_flush_leader_region, assert_no_persist),
            ),
            // Flush Leader Region
            Step::next(
                "Should be the flush leader region",
                Some(mock_datanode_reply(
                    from_peer_id,
                    Arc::new(move |id| {
                        Ok(new_flush_region_reply_for_region(
                            id,
                            RegionId::new(1024, 1),
                            true,
                            None,
                        ))
                    }),
                )),
                Assertion::simple(assert_update_metadata_downgrade, assert_no_persist),
            ),
            // UpdateMetadata::Downgrade
            Step::next(
                "Should be the downgrade leader region",
                None,
                Assertion::simple(assert_downgrade_leader_region, assert_no_persist),
            ),
            // Downgrade Candidate
            Step::next(
                "Should be the upgrade candidate region",
                Some(mock_datanode_reply(
                    from_peer_id,
                    Arc::new(|id| Ok(new_downgrade_region_reply(id, None, true, None))),
                )),
                Assertion::simple(assert_upgrade_candidate_region, assert_no_persist),
            ),
            // Upgrade Candidate
            Step::next(
                "Should be the rollback metadata",
                Some(mock_datanode_reply(
                    to_peer_id,
                    Arc::new(|id| error::MailboxTimeoutSnafu { id }.fail()),
                )),
                Assertion::simple(assert_update_metadata_rollback, assert_no_persist),
            ),
            // UpdateMetadata::Rollback
            Step::next(
                "Should be the region migration abort",
                None,
                Assertion::simple(assert_region_migration_abort, assert_no_persist),
            ),
            // RegionMigrationAbort
            Step::next(
                "Should throw an error",
                None,
                Assertion::error(|error| {
                    assert!(!error.is_retryable());
                    assert_matches!(error, error::Error::MigrationAbort { .. });
                }),
            ),
        ];

        let setup_to_latest_persisted_state = Step::setup(
            "Sets state to OpenCandidateRegion",
            merge_before_test_fn(vec![
                setup_state(Arc::new(|| Box::new(OpenCandidateRegion))),
                Arc::new(reset_volatile_ctx),
            ]),
        );

        let steps = [
            steps.clone(),
            vec![setup_to_latest_persisted_state.clone()],
            steps.clone()[1..].to_vec(),
            vec![setup_to_latest_persisted_state],
            steps.clone()[1..].to_vec(),
        ]
        .concat();

        // Run the table tests.
        ProcedureMigrationSuiteRunner::new(suite)
            .steps(steps.clone())
            .run_once()
            .await;
    }

    #[tokio::test]
    async fn test_procedure_flow_upgrade_candidate_with_retry() {
        common_telemetry::init_default_ut_logging();

        let persistent_context = test_util::new_persistent_context(1, 2, RegionId::new(1024, 1));
        let state = Box::new(RegionMigrationStart);

        // The table metadata.
        let to_peer_id = persistent_context.to_peer.id;
        let from_peer_id = persistent_context.from_peer.id;
        let from_peer = persistent_context.from_peer.clone();
        let region_id = persistent_context.region_ids[0];
        let table_info = new_test_table_info(1024);
        let region_routes = vec![RegionRoute {
            region: Region::new_test(region_id),
            leader_peer: Some(from_peer),
            follower_peers: vec![],
            ..Default::default()
        }];

        let suite = ProcedureMigrationTestSuite::new(persistent_context, state);
        suite.init_table_metadata(table_info, region_routes).await;

        let steps = vec![
            // Migration Start
            Step::next(
                "Should be the open candidate region",
                None,
                Assertion::simple(assert_open_candidate_region, assert_need_persist),
            ),
            // OpenCandidateRegion
            Step::next(
                "Should be throwing a retryable error",
                Some(mock_datanode_reply(
                    to_peer_id,
                    Arc::new(|id| {
                        Ok(new_open_region_reply(
                            id,
                            false,
                            Some("mock retryable open region error".to_string()),
                        ))
                    }),
                )),
                Assertion::error(|error| assert!(error.is_retryable(), "err: {error:?}")),
            ),
            // OpenCandidateRegion
            Step::next(
                "Should be the update metadata for downgrading",
                Some(mock_datanode_reply(
                    to_peer_id,
                    Arc::new(|id| Ok(new_open_region_reply(id, true, None))),
                )),
                Assertion::simple(assert_flush_leader_region, assert_no_persist),
            ),
            // Flush Leader Region
            Step::next(
                "Should be the flush leader region",
                Some(mock_datanode_reply(
                    from_peer_id,
                    Arc::new(move |id| {
                        Ok(new_flush_region_reply_for_region(id, region_id, true, None))
                    }),
                )),
                Assertion::simple(assert_update_metadata_downgrade, assert_no_persist),
            ),
            // UpdateMetadata::Downgrade
            Step::next(
                "Should be the downgrade leader region",
                None,
                Assertion::simple(assert_downgrade_leader_region, assert_no_persist),
            ),
            // Downgrade Leader
            Step::next(
                "Should be the upgrade candidate region",
                Some(mock_datanode_reply(
                    from_peer_id,
                    merge_mailbox_messages(vec![
                        Arc::new(|id| error::MailboxTimeoutSnafu { id }.fail()),
                        Arc::new(|id| Ok(new_downgrade_region_reply(id, None, true, None))),
                    ]),
                )),
                Assertion::simple(assert_upgrade_candidate_region, assert_no_persist),
            ),
            // Upgrade Candidate
            Step::next(
                "Should be the update metadata for upgrading",
                Some(mock_datanode_reply(
                    to_peer_id,
                    merge_mailbox_messages(vec![
                        Arc::new(|id| error::MailboxTimeoutSnafu { id }.fail()),
                        Arc::new(|id| Ok(new_upgrade_region_reply(id, true, true, None))),
                    ]),
                )),
                Assertion::simple(assert_update_metadata_upgrade, assert_no_persist),
            ),
            // UpdateMetadata::Upgrade
            Step::next(
                "Should be the close downgraded region",
                None,
                Assertion::simple(assert_close_downgraded_region, assert_no_persist),
            ),
            // CloseDowngradedRegion
            Step::next(
                "Should be the region migration end",
                None,
                Assertion::simple(assert_region_migration_end, assert_done),
            ),
            // RegionMigrationEnd
            Step::next(
                "Should be the region migration end again",
                None,
                Assertion::simple(assert_region_migration_end, assert_done),
            ),
            // RegionMigrationStart
            Step::setup(
                "Sets state to RegionMigrationStart",
                merge_before_test_fn(vec![
                    setup_state(Arc::new(|| Box::new(RegionMigrationStart))),
                    Arc::new(reset_volatile_ctx),
                ]),
            ),
            // RegionMigrationEnd
            // Note: We can't run this test multiple times;
            // the `peer_id`'s `DatanodeTable` will be removed after first-time migration success.
            Step::next(
                "Should be the region migration end(has been migrated)",
                None,
                Assertion::simple(assert_region_migration_end, assert_done),
            ),
        ];

        let steps = [steps.clone()].concat();
        let timer = Instant::now();

        // Run the table tests.
        let runner = ProcedureMigrationSuiteRunner::new(suite)
            .steps(steps.clone())
            .run_once()
            .await;

        let region_lease = default_distributed_time_constants().region_lease.as_secs();
        // Ensure it didn't run into the slow path.
        assert!(timer.elapsed().as_secs() < region_lease);
        runner.suite.verify_table_metadata().await;
    }
}
