use chrono::Utc;
use sea_orm::{
    ActiveModelTrait, ColumnTrait, EntityTrait, QueryFilter, QueryOrder, QuerySelect, Set,
};
use sqlx::postgres::PgListener;
use std::time::Duration;

use erp_core::entity::domain_event;
use erp_core::events::{DomainEvent, EventBus};

const MAX_RETRY: i32 = 5;
const FALLBACK_POLL_INTERVAL_SECS: u64 = 30;
const NOTIFY_CHANNEL: &str = "outbox_channel";
const RECONNECT_DELAY_SECS: u64 = 5;

/// 启动 outbox relay 后台任务。
///
/// 先执行一次性扫描（处理服务重启前遗留的 pending 事件），
/// 然后通过 PostgreSQL LISTEN/NOTIFY 监听新事件，配合 30s 兜底轮询。
pub fn start_outbox_relay(
    db: sea_orm::DatabaseConnection,
    event_bus: EventBus,
    database_url: String,
) {
    let db_clone = db.clone();
    let event_bus_clone = event_bus.clone();
    let url = database_url.clone();

    tokio::spawn(async move {
        // 启动时立即处理一次（恢复重启前未广播的事件）
        match process_pending_events(&db_clone, &event_bus_clone).await {
            Ok(count) if count > 0 => tracing::info!(count = count, "启动时 outbox relay 恢复完成"),
            Ok(_) => tracing::info!("启动时 outbox relay 无待处理事件"),
            Err(e) => tracing::warn!(error = %e, "启动时 outbox relay 处理失败"),
        }

        // 进入 LISTEN/NOTIFY 主循环（带自动重连）
        loop {
            if let Err(e) = run_listener(&db_clone, &event_bus_clone, &url).await {
                tracing::warn!(error = %e, "PgListener 断开连接，{}s 后重连", RECONNECT_DELAY_SECS);
            }
            tokio::time::sleep(Duration::from_secs(RECONNECT_DELAY_SECS)).await;

            // 重连后执行一次兜底扫描
            if let Err(e) = process_pending_events(&db_clone, &event_bus_clone).await {
                tracing::warn!(error = %e, "重连后 outbox relay 处理失败");
            }
        }
    });
}

/// 运行 PgListener 监听循环。
///
/// 使用 `tokio::select!` 在 LISTEN 通知和 30s 定时器之间竞争，
/// 确保即使 NOTIFY 丢失也能兜底处理。
async fn run_listener(
    db: &sea_orm::DatabaseConnection,
    event_bus: &EventBus,
    database_url: &str,
) -> Result<(), sqlx::Error> {
    let mut listener = PgListener::connect(database_url).await?;
    listener.listen(NOTIFY_CHANNEL).await?;
    tracing::info!("Outbox relay LISTEN/NOTIFY 已连接，监听 {}", NOTIFY_CHANNEL);

    let mut fallback = tokio::time::interval(Duration::from_secs(FALLBACK_POLL_INTERVAL_SECS));

    loop {
        tokio::select! {
            // LISTEN/NOTIFY 通知触发
            notification = listener.recv() => {
                match notification {
                    Ok(notif) => {
                        tracing::debug!(
                            channel = %notif.channel(),
                            payload = %notif.payload(),
                            "收到 outbox NOTIFY"
                        );
                        if let Err(e) = process_pending_events(db, event_bus).await {
                            tracing::warn!(error = %e, "NOTIFY 触发的 outbox 处理失败");
                        }
                    }
                    Err(e) => return Err(e),
                }
            }
            // 30s 兜底轮询
            _ = fallback.tick() => {
                tracing::debug!("outbox relay 兜底轮询触发");
                if let Err(e) = process_pending_events(db, event_bus).await {
                    tracing::warn!(error = %e, "兜底轮询 outbox 处理失败");
                }
            }
        }
    }
}

async fn process_pending_events(
    db: &sea_orm::DatabaseConnection,
    event_bus: &EventBus,
) -> Result<usize, sea_orm::DbErr> {
    let pending = domain_event::Entity::find()
        .filter(domain_event::Column::Status.eq("pending"))
        .filter(domain_event::Column::Attempts.lt(MAX_RETRY))
        .order_by_asc(domain_event::Column::CreatedAt)
        .limit(100)
        .all(db)
        .await?;

    if pending.is_empty() {
        return Ok(0);
    }

    let count = pending.len();
    tracing::info!(count = count, "处理待发领域事件");

    for event_model in pending {
        // 重建 DomainEvent 并广播（保留原始 ID 和时间戳）
        let domain_event = DomainEvent {
            id: event_model.id,
            event_type: event_model.event_type.clone(),
            tenant_id: event_model.tenant_id,
            payload: event_model.payload.clone().unwrap_or(serde_json::json!({})),
            timestamp: event_model.created_at,
            correlation_id: event_model.correlation_id.unwrap_or(event_model.id),
        };

        event_bus.broadcast(domain_event);

        // 标记为 published，增加 attempts 计数
        let mut active: domain_event::ActiveModel = event_model.into();
        active.status = Set("published".to_string());
        active.published_at = Set(Some(Utc::now()));
        active.attempts = Set(erp_core::sea_orm_ext::bump_version(&active.attempts));
        active.update(db).await?;
    }

    Ok(count)
}