use chrono::Utc;
use sea_orm::{ActiveModelTrait, ConnectionTrait, PaginatorTrait, Set};
use serde::{Deserialize, Serialize};
use tokio::sync::{broadcast, mpsc};
use tracing::{error, info};
use uuid::Uuid;

use crate::entity::dead_letter_event;
use crate::entity::domain_event;

/// 领域事件
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DomainEvent {
    pub id: Uuid,
    pub event_type: String,
    pub tenant_id: Uuid,
    pub payload: serde_json::Value,
    pub timestamp: chrono::DateTime<Utc>,
    pub correlation_id: Uuid,
}

impl DomainEvent {
    pub fn new(event_type: impl Into<String>, tenant_id: Uuid, payload: serde_json::Value) -> Self {
        Self {
            id: Uuid::now_v7(),
            event_type: event_type.into(),
            tenant_id,
            payload,
            timestamp: Utc::now(),
            correlation_id: Uuid::now_v7(),
        }
    }
}

/// 当前事件 payload schema 版本
pub const EVENT_SCHEMA_VERSION: &str = "v1";

/// 构造统一信封格式的事件 payload。
///
/// 自动注入 `schema_version` 和 `occurred_at`，业务数据通过 `data` 传入。
/// 用法：`build_event_payload(serde_json::json!({ "patient_id": ..., }))`
pub fn build_event_payload(data: serde_json::Value) -> serde_json::Value {
    let mut envelope = serde_json::json!({
        "schema_version": EVENT_SCHEMA_VERSION,
        "occurred_at": Utc::now().to_rfc3339(),
    });
    if let serde_json::Value::Object(ref mut map) = envelope
        && let serde_json::Value::Object(data_map) = data
    {
        for (k, v) in data_map {
            map.insert(k, v);
        }
    }
    envelope
}

/// 检查事件是否已被指定消费者处理。
///
/// 查询 `processed_events` 表判断 event_id + consumer_id 是否已存在。
pub async fn is_event_processed(
    db: &sea_orm::DatabaseConnection,
    event_id: Uuid,
    consumer_id: &str,
) -> Result<bool, sea_orm::DbErr> {
    use sea_orm::{ColumnTrait, EntityTrait, QueryFilter};

    let count = crate::entity::processed_event::Entity::find()
        .filter(crate::entity::processed_event::Column::EventId.eq(event_id))
        .filter(crate::entity::processed_event::Column::ConsumerId.eq(consumer_id))
        .count(db)
        .await?;
    Ok(count > 0)
}

/// 标记事件已被指定消费者处理。
///
/// 插入 `processed_events` 记录，重复插入会因主键冲突被安全忽略。
pub async fn mark_event_processed(
    db: &sea_orm::DatabaseConnection,
    event_id: Uuid,
    consumer_id: &str,
) -> Result<(), sea_orm::DbErr> {
    use sea_orm::ActiveModelTrait;
    use sea_orm::Set;

    let model = crate::entity::processed_event::ActiveModel {
        event_id: Set(event_id),
        consumer_id: Set(consumer_id.to_string()),
        processed_at: Set(Utc::now()),
    };
    // INSERT ... ON CONFLICT DO NOTHING（主键冲突时安全忽略）
    match model.insert(db).await {
        Ok(_) => Ok(()),
        Err(e) => {
            // 唯一约束冲突 = 已处理，不是错误
            if e.to_string().contains("duplicate") || e.to_string().contains("violates unique") {
                Ok(())
            } else {
                Err(e)
            }
        }
    }
}

/// 消费事件 — 带幂等检查和 dead-letter 兜底。
///
/// 如果事件已被处理（幂等），返回 `ConsumeResult::AlreadyProcessed`。
/// 如果处理成功，标记为已处理并返回 `ConsumeResult::Success`。
/// 如果处理失败，将事件转入 dead_letter_events 表并返回 `ConsumeResult::DeadLettered`。
pub async fn consume_with_retry<F, Fut>(
    db: &sea_orm::DatabaseConnection,
    event: &DomainEvent,
    consumer_id: &str,
    handler: F,
) -> ConsumeResult
where
    F: FnOnce(&DomainEvent) -> Fut,
    Fut: std::future::Future<Output = Result<(), String>>,
{
    if is_event_processed(db, event.id, consumer_id)
        .await
        .unwrap_or(false)
    {
        return ConsumeResult::AlreadyProcessed;
    }

    match handler(event).await {
        Ok(()) => {
            if let Err(e) = mark_event_processed(db, event.id, consumer_id).await {
                tracing::warn!(
                    event_id = %event.id,
                    consumer_id = consumer_id,
                    error = %e,
                    "标记事件已处理失败（非致命）"
                );
            }
            ConsumeResult::Success
        }
        Err(err) => {
            tracing::error!(
                event_id = %event.id,
                event_type = %event.event_type,
                consumer_id = consumer_id,
                error = %err,
                "事件消费失败，转入 dead-letter"
            );
            if let Err(e) = insert_dead_letter(db, event, consumer_id, &err).await {
                tracing::error!(
                    event_id = %event.id,
                    error = %e,
                    "Dead-letter 写入失败"
                );
            }
            ConsumeResult::DeadLettered(err)
        }
    }
}

/// 消费结果
#[derive(Debug)]
pub enum ConsumeResult {
    Success,
    AlreadyProcessed,
    DeadLettered(String),
}

/// 将失败事件写入 dead_letter_events 表
pub async fn insert_dead_letter(
    db: &sea_orm::DatabaseConnection,
    event: &DomainEvent,
    consumer_id: &str,
    error_msg: &str,
) -> Result<(), sea_orm::DbErr> {
    let model = dead_letter_event::ActiveModel {
        id: Set(Uuid::now_v7()),
        tenant_id: Set(Some(event.tenant_id)),
        original_event_id: Set(event.id),
        event_type: Set(event.event_type.clone()),
        payload: Set(Some(event.payload.clone())),
        consumer_id: Set(consumer_id.to_string()),
        attempts: Set(1),
        last_error: Set(Some(error_msg.to_string())),
        created_at: Set(Utc::now()),
        resolved_at: Set(None),
    };
    model.insert(db).await?;
    Ok(())
}

/// 过滤事件接收器 — 只接收匹配 `event_type_prefix` 的事件
pub struct FilteredEventReceiver {
    receiver: mpsc::Receiver<DomainEvent>,
}

impl FilteredEventReceiver {
    /// 接收下一个匹配的事件
    pub async fn recv(&mut self) -> Option<DomainEvent> {
        self.receiver.recv().await
    }
}

/// 订阅句柄 — 用于取消过滤订阅
pub struct SubscriptionHandle {
    cancel_tx: mpsc::Sender<()>,
    join_handle: tokio::task::JoinHandle<()>,
}

impl SubscriptionHandle {
    /// 取消订阅并等待后台任务结束
    pub async fn cancel(self) {
        let _ = self.cancel_tx.send(()).await;
        let _ = self.join_handle.await;
    }
}

/// 进程内事件总线
#[derive(Clone)]
pub struct EventBus {
    sender: broadcast::Sender<DomainEvent>,
}

impl EventBus {
    pub fn new(capacity: usize) -> Self {
        let (sender, _) = broadcast::channel(capacity);
        Self { sender }
    }

    /// 发布事件：先持久化到 domain_events 表（pending 状态），再内存广播，
    /// 最后更新为 published 并 NOTIFY outbox relay。
    ///
    /// 两阶段提交保证：即使广播后服务崩溃，事件仍为 pending 状态，
    /// 重启后 outbox relay 会重新广播。
    pub async fn publish(&self, event: DomainEvent, db: &sea_orm::DatabaseConnection) {
        // 1. 持久化为 pending 状态
        let event_id = event.id;
        let model = domain_event::ActiveModel {
            id: Set(event.id),
            tenant_id: Set(event.tenant_id),
            event_type: Set(event.event_type.clone()),
            payload: Set(Some(event.payload.clone())),
            correlation_id: Set(Some(event.correlation_id)),
            status: Set("pending".to_string()),
            attempts: Set(0),
            last_error: Set(None),
            created_at: Set(event.timestamp),
            published_at: Set(None),
        };

        let saved = match model.insert(db).await {
            Ok(m) => m,
            Err(e) => {
                tracing::warn!(event_id = %event_id, error = %e, "领域事件持久化失败");
                // 持久化失败仍然广播（best-effort）
                self.broadcast(event);
                return;
            }
        };

        // 2. 内存广播
        self.broadcast(event);

        // 3. 更新为 published
        let mut active: domain_event::ActiveModel = saved.into();
        active.status = Set("published".to_string());
        active.published_at = Set(Some(Utc::now()));
        if let Err(e) = active.update(db).await {
            tracing::warn!(event_id = %event_id, error = %e, "领域事件状态更新为 published 失败");
        }

        // 4. NOTIFY outbox relay（通知 outbox relay 有新事件到达）
        let notify_sql = sea_orm::Statement::from_string(
            sea_orm::DatabaseBackend::Postgres,
            format!("NOTIFY outbox_channel, '{}'", event_id),
        );
        if let Err(e) = db.execute(notify_sql).await {
            tracing::debug!(event_id = %event_id, error = %e, "NOTIFY outbox_channel 失败（非致命）");
        }
    }

    /// 仅内存广播（不持久化，用于内部测试等场景）。
    pub fn broadcast(&self, event: DomainEvent) {
        info!(event_type = %event.event_type, event_id = %event.id, "Event broadcast");
        if let Err(e) = self.sender.send(event) {
            error!("Failed to broadcast event: {}", e);
        }
    }

    /// 订阅所有事件，返回接收端
    pub fn subscribe(&self) -> broadcast::Receiver<DomainEvent> {
        self.sender.subscribe()
    }

    /// 按事件类型前缀过滤订阅。
    ///
    /// 为每次调用 spawn 一个 Tokio task 从 broadcast channel 读取，
    /// 只转发匹配 `event_type_prefix` 的事件到 mpsc channel（capacity 256）。
    pub fn subscribe_filtered(
        &self,
        event_type_prefix: String,
    ) -> (FilteredEventReceiver, SubscriptionHandle) {
        let mut broadcast_rx = self.sender.subscribe();
        let (mpsc_tx, mpsc_rx) = mpsc::channel(256);
        let (cancel_tx, mut cancel_rx) = mpsc::channel::<()>(1);

        let prefix = event_type_prefix.clone();
        let join_handle = tokio::spawn(async move {
            loop {
                tokio::select! {
                    biased;
                    _ = cancel_rx.recv() => {
                        tracing::info!(prefix = %prefix, "Filtered subscription cancelled");
                        break;
                    }
                    event = broadcast_rx.recv() => {
                        match event {
                            Ok(event) => {
                                if event.event_type.starts_with(&prefix)
                                    && mpsc_tx.send(event).await.is_err()
                                {
                                    break;
                                }
                            }
                            Err(broadcast::error::RecvError::Lagged(n)) => {
                                tracing::warn!(prefix = %prefix, lagged = n, "Filtered subscriber lagged");
                            }
                            Err(broadcast::error::RecvError::Closed) => {
                                break;
                            }
                        }
                    }
                }
            }
        });

        tracing::info!(prefix = %event_type_prefix, "Filtered subscription created");

        (
            FilteredEventReceiver { receiver: mpsc_rx },
            SubscriptionHandle {
                cancel_tx,
                join_handle,
            },
        )
    }
}