use std::str::FromStr;

/// Request/response types for the storage controller
/// API (`/control/v1` prefix).  Implemented by the server
/// in [`storage_controller::http`]
use serde::{Deserialize, Serialize};
use utils::id::{NodeId, TenantId};

use crate::{
    models::{ShardParameters, TenantConfig},
    shard::{ShardStripeSize, TenantShardId},
};

#[derive(Serialize, Deserialize)]
pub struct TenantCreateResponseShard {
    pub shard_id: TenantShardId,
    pub node_id: NodeId,
    pub generation: u32,
}

#[derive(Serialize, Deserialize)]
pub struct TenantCreateResponse {
    pub shards: Vec<TenantCreateResponseShard>,
}

#[derive(Serialize, Deserialize)]
pub struct NodeRegisterRequest {
    pub node_id: NodeId,

    pub listen_pg_addr: String,
    pub listen_pg_port: u16,

    pub listen_http_addr: String,
    pub listen_http_port: u16,
}

#[derive(Serialize, Deserialize)]
pub struct NodeConfigureRequest {
    pub node_id: NodeId,

    pub availability: Option<NodeAvailabilityWrapper>,
    pub scheduling: Option<NodeSchedulingPolicy>,
}

#[derive(Serialize, Deserialize)]
pub struct TenantPolicyRequest {
    pub placement: Option<PlacementPolicy>,
    pub scheduling: Option<ShardSchedulingPolicy>,
}

#[derive(Serialize, Deserialize, Debug)]
pub struct TenantLocateResponseShard {
    pub shard_id: TenantShardId,
    pub node_id: NodeId,

    pub listen_pg_addr: String,
    pub listen_pg_port: u16,

    pub listen_http_addr: String,
    pub listen_http_port: u16,
}

#[derive(Serialize, Deserialize)]
pub struct TenantLocateResponse {
    pub shards: Vec<TenantLocateResponseShard>,
    pub shard_params: ShardParameters,
}

#[derive(Serialize, Deserialize)]
pub struct TenantDescribeResponse {
    pub tenant_id: TenantId,
    pub shards: Vec<TenantDescribeResponseShard>,
    pub stripe_size: ShardStripeSize,
    pub policy: PlacementPolicy,
    pub config: TenantConfig,
}

#[derive(Serialize, Deserialize)]
pub struct NodeDescribeResponse {
    pub id: NodeId,

    pub availability: NodeAvailabilityWrapper,
    pub scheduling: NodeSchedulingPolicy,

    pub listen_http_addr: String,
    pub listen_http_port: u16,

    pub listen_pg_addr: String,
    pub listen_pg_port: u16,
}

#[derive(Serialize, Deserialize)]
pub struct TenantDescribeResponseShard {
    pub tenant_shard_id: TenantShardId,

    pub node_attached: Option<NodeId>,
    pub node_secondary: Vec<NodeId>,

    pub last_error: String,

    /// A task is currently running to reconcile this tenant's intent state with the state on pageservers
    pub is_reconciling: bool,
    /// This shard failed in sending a compute notification to the cloud control plane, and a retry is pending.
    pub is_pending_compute_notification: bool,
    /// A shard split is currently underway
    pub is_splitting: bool,

    pub scheduling_policy: ShardSchedulingPolicy,
}

/// Explicitly migrating a particular shard is a low level operation
/// TODO: higher level "Reschedule tenant" operation where the request
/// specifies some constraints, e.g. asking it to get off particular node(s)
#[derive(Serialize, Deserialize, Debug)]
pub struct TenantShardMigrateRequest {
    pub tenant_shard_id: TenantShardId,
    pub node_id: NodeId,
}

/// Utilisation score indicating how good a candidate a pageserver
/// is for scheduling the next tenant. See [`crate::models::PageserverUtilization`].
/// Lower values are better.
#[derive(Serialize, Deserialize, Clone, Copy, Eq, PartialEq, PartialOrd, Ord, Debug)]
pub struct UtilizationScore(pub u64);

impl UtilizationScore {
    pub fn worst() -> Self {
        UtilizationScore(u64::MAX)
    }
}

#[derive(Serialize, Deserialize, Clone, Copy, Debug)]
#[serde(into = "NodeAvailabilityWrapper")]
pub enum NodeAvailability {
    // Normal, happy state
    Active(UtilizationScore),
    // Offline: Tenants shouldn't try to attach here, but they may assume that their
    // secondary locations on this node still exist.  Newly added nodes are in this
    // state until we successfully contact them.
    Offline,
}

impl PartialEq for NodeAvailability {
    fn eq(&self, other: &Self) -> bool {
        use NodeAvailability::*;
        matches!((self, other), (Active(_), Active(_)) | (Offline, Offline))
    }
}

impl Eq for NodeAvailability {}

// This wrapper provides serde functionality and it should only be used to
// communicate with external callers which don't know or care about the
// utilisation score of the pageserver it is targeting.
#[derive(Serialize, Deserialize, Clone, Copy, Debug)]
pub enum NodeAvailabilityWrapper {
    Active,
    Offline,
}

impl From<NodeAvailabilityWrapper> for NodeAvailability {
    fn from(val: NodeAvailabilityWrapper) -> Self {
        match val {
            // Assume the worst utilisation score to begin with. It will later be updated by
            // the heartbeats.
            NodeAvailabilityWrapper::Active => NodeAvailability::Active(UtilizationScore::worst()),
            NodeAvailabilityWrapper::Offline => NodeAvailability::Offline,
        }
    }
}

impl From<NodeAvailability> for NodeAvailabilityWrapper {
    fn from(val: NodeAvailability) -> Self {
        match val {
            NodeAvailability::Active(_) => NodeAvailabilityWrapper::Active,
            NodeAvailability::Offline => NodeAvailabilityWrapper::Offline,
        }
    }
}

#[derive(Serialize, Deserialize, Clone, Copy, Eq, PartialEq, Debug)]
pub enum ShardSchedulingPolicy {
    // Normal mode: the tenant's scheduled locations may be updated at will, including
    // for non-essential optimization.
    Active,

    // Disable optimizations, but permit scheduling when necessary to fulfil the PlacementPolicy.
    // For example, this still permits a node's attachment location to change to a secondary in
    // response to a node failure, or to assign a new secondary if a node was removed.
    Essential,

    // No scheduling: leave the shard running wherever it currently is.  Even if the shard is
    // unavailable, it will not be rescheduled to another node.
    Pause,

    // No reconciling: we will make no location_conf API calls to pageservers at all.  If the
    // shard is unavailable, it stays that way.  If a node fails, this shard doesn't get failed over.
    Stop,
}

impl Default for ShardSchedulingPolicy {
    fn default() -> Self {
        Self::Active
    }
}

#[derive(Serialize, Deserialize, Clone, Copy, Eq, PartialEq, Debug)]
pub enum NodeSchedulingPolicy {
    Active,
    Filling,
    Pause,
    Draining,
}

impl FromStr for NodeSchedulingPolicy {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s {
            "active" => Ok(Self::Active),
            "filling" => Ok(Self::Filling),
            "pause" => Ok(Self::Pause),
            "draining" => Ok(Self::Draining),
            _ => Err(anyhow::anyhow!("Unknown scheduling state '{s}'")),
        }
    }
}

impl From<NodeSchedulingPolicy> for String {
    fn from(value: NodeSchedulingPolicy) -> String {
        use NodeSchedulingPolicy::*;
        match value {
            Active => "active",
            Filling => "filling",
            Pause => "pause",
            Draining => "draining",
        }
        .to_string()
    }
}

/// Controls how tenant shards are mapped to locations on pageservers, e.g. whether
/// to create secondary locations.
#[derive(Clone, Serialize, Deserialize, Debug, PartialEq, Eq)]
pub enum PlacementPolicy {
    /// Normal live state: one attached pageserver and zero or more secondaries.
    Attached(usize),
    /// Create one secondary mode locations. This is useful when onboarding
    /// a tenant, or for an idle tenant that we might want to bring online quickly.
    Secondary,

    /// Do not attach to any pageservers.  This is appropriate for tenants that
    /// have been idle for a long time, where we do not mind some delay in making
    /// them available in future.
    Detached,
}

#[derive(Serialize, Deserialize, Debug)]
pub struct TenantShardMigrateResponse {}

#[cfg(test)]
mod test {
    use super::*;
    use serde_json;

    /// Check stability of PlacementPolicy's serialization
    #[test]
    fn placement_policy_encoding() -> anyhow::Result<()> {
        let v = PlacementPolicy::Attached(1);
        let encoded = serde_json::to_string(&v)?;
        assert_eq!(encoded, "{\"Attached\":1}");
        assert_eq!(serde_json::from_str::<PlacementPolicy>(&encoded)?, v);

        let v = PlacementPolicy::Detached;
        let encoded = serde_json::to_string(&v)?;
        assert_eq!(encoded, "\"Detached\"");
        assert_eq!(serde_json::from_str::<PlacementPolicy>(&encoded)?, v);
        Ok(())
    }
}