//! df-relay 中继服务核心实现
//!
//! 设计依据:设计文档「Layer2」—— axum WS Server + 广播中继。
//! 接受两类连接:小程序(device_id 鉴权)+ 桌面端(token 配对),按 device_id
//! 配对转发(非全局广播),纯转发无业务逻辑。
//!
//! 协议(简单握手):
//! 1. 客户端建立 WS 后,首条消息发 JSON `Hello { kind, device_id, token }` 宣告身份。
//! 2. relay 校验 token(MVP:env `DF_RELAY_TOKEN` 或硬编码常量;生产级鉴权留 Phase3)。
//! 3. 校验通过 → 注册连接、进入收发循环;失败 → 发 Error 帧 + Close。
//! 4. 后续消息按 kind 路由:Event(device→miniapp)/ Command(miniapp→device)/ Control。
//!
//! ## 鉴权模型(MC-4 现状与风险)
//! MVP 单共享 token(`DF_RELAY_TOKEN`),无 per-device 绑定:**任何持 token 客户端可声明任意
//! `device_id` 并冒充该设备收发指令**。生产级 per-device token(配对时按 device 颁发独立 token
//! 并存储)涉及配对流程改造(需 df-miniapp/df-tunnel 配合),当前批次不实施,仅做最小加固:
//! - 连接建立时校验 `device_id` 格式(非空 + 长度上限,见 `validate_device_id`)。
//! - token 比较用常量时间比较(RLY-4),防时序侧信道。
//! 完整 per-device 鉴权留设计文档 Phase3。
//!
//! AiChatEvent JSON 透传:relay 不解析 payload,只按 device_id + 方向转发。

use std::net::SocketAddr;

use async_trait::async_trait;
use axum::{
    extract::{
        ws::{Message, WebSocket, WebSocketUpgrade},
        State,
    },
    response::IntoResponse,
    routing::get,
    Router,
};
use futures_util::{SinkExt, StreamExt};
use serde::{Deserialize, Serialize};
use tokio::sync::mpsc;

use crate::broadcast::{BroadcastMessage, ClientKind, MessageKind};
use crate::conn::{next_conn_id, ConnHandle, ConnId, RelayState};
use crate::error::{RelayError, Result};

/// 读取期望 token(必需:env `DF_RELAY_TOKEN` 必须设置)。
/// RLY-5:不再 panic,改为返回 Option——缺失时由连接层显式拒绝握手(main 启动时也已校验)。
/// 生产级鉴权(每 device 独立 token + 过期刷新)留 Phase3。
fn expected_token() -> Option<String> {
    std::env::var("DF_RELAY_TOKEN").ok()
}

/// RLY-3:入站文本帧大小上限(1 MiB)。
/// 防恶意/异常客户端发超大帧耗尽内存与转发带宽;超限直接断开连接。
const MAX_FRAME_BYTES: usize = 1 * 1024 * 1024;

/// 常量时间字符串比较(RLY-4,防时序侧信道)。
///
/// 没有引入 subtle 依赖;用等长逐字节异或累加 + 尾随等量循环掩蔽长度差,
/// 比较时长不随首字节差异提前返回。长度本身不保密(可被包长度观测),故长度不等直接返回。
fn constant_time_eq(a: &str, b: &str) -> bool {
    let a = a.as_bytes();
    let b = b.as_bytes();
    // 用最大长度循环,短者补 0 参与异或,时长恒等于较长者,不泄露首字节命中点
    let len = a.len().max(b.len());
    let mut diff: u8 = 0;
    for i in 0..len {
        let av = a.get(i).copied().unwrap_or(0);
        let bv = b.get(i).copied().unwrap_or(0);
        diff |= av ^ bv;
    }
    diff == 0
}

/// MC-4 最小加固:校验 device_id 格式。
/// 拒绝空串与超长(防内存/日志注入),仅做基础防御;per-device token 绑定留 Phase3。
fn validate_device_id(id: &str) -> bool {
    !id.is_empty() && id.len() <= 128 && id.chars().all(|c| !c.is_control())
}

/// 客户端首消息:身份宣告(简单协议)
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Hello {
    /// 客户端类型("device" / "miniapp")
    pub kind: ClientKindWire,
    /// 配对绑定的设备 ID
    pub device_id: String,
    /// 配对 token
    pub token: String,
}

/// Hello.kind 的传输表示(serde 字符串,与 ClientKind 解耦避免 rename 歧义)
#[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq)]
#[serde(rename_all = "snake_case")]
pub enum ClientKindWire {
    Device,
    Miniapp,
}

impl From<ClientKindWire> for ClientKind {
    fn from(w: ClientKindWire) -> Self {
        match w {
            ClientKindWire::Device => ClientKind::Device,
            ClientKindWire::Miniapp => ClientKind::Miniapp,
        }
    }
}

/// 中继服务抽象
///
/// 设计为 trait 便于测试 mock + 未来替换实现(如换 tonic gRPC 网关)。
#[async_trait]
pub trait RelayServer: Send + Sync {
    /// 启动 HTTP/WS 服务监听指定地址
    async fn start(&self, addr: &str) -> Result<()>;

    /// 广播消息给指定 device_id 绑定的对端
    async fn broadcast(&self, msg: BroadcastMessage) -> Result<()>;

    /// 查询 device 是否有在线连接(离线降级判断用)
    fn is_device_online(&self, device_id: &str) -> bool;
}

/// 默认中继服务(持有共享 RelayState)
pub struct DefaultRelayServer {
    state: RelayState,
}

impl DefaultRelayServer {
    pub fn new() -> Self {
        Self {
            state: RelayState::new(),
        }
    }

    /// 从既有 RelayState 构造(测试 / 外部复用)
    pub fn with_state(state: RelayState) -> Self {
        Self { state }
    }

    /// 暴露共享状态(外部可读连接数等)
    pub fn state(&self) -> RelayState {
        self.state.clone()
    }
}

impl Default for DefaultRelayServer {
    fn default() -> Self {
        Self::new()
    }
}

#[async_trait]
impl RelayServer for DefaultRelayServer {
    async fn start(&self, addr: &str) -> Result<()> {
        let socket_addr: SocketAddr = addr
            .parse()
            .map_err(|e| RelayError::Start(format!("地址解析失败 {addr}: {e}")))?;
        let app = build_router(self.state.clone());
        let listener = tokio::net::TcpListener::bind(&socket_addr)
            .await
            .map_err(|e| RelayError::Start(format!("监听绑定失败 {addr}: {e}")))?;
        tracing::info!(%addr, "df-relay WS 服务已启动");
        axum::serve(listener, app)
            .await
            .map_err(|e| RelayError::Start(format!("axum::serve 失败: {e}")))?;
        Ok(())
    }

    async fn broadcast(&self, msg: BroadcastMessage) -> Result<()> {
        let delivered = self.state.route(&msg).await;
        if delivered == 0 {
            // 对端离线不算硬错误(MVP 返回 Ok,离线降级由调用方据 is_device_online 判断)
            tracing::debug!(
                device_id = %msg.device_id,
                kind = ?msg.kind,
                "广播无对端在线(消息丢弃)"
            );
        }
        Ok(())
    }

    fn is_device_online(&self, device_id: &str) -> bool {
        // trait 同步签名:tokio Mutex 用 try_lock 快照,失败保守返回 false
        match self.state.inner().try_lock() {
            Ok(g) => g.is_device_online(device_id),
            Err(_) => false,
        }
    }
}

/// axum WS 路由构造
///
/// 暴露 `/ws/device`(桌面端连入)与 `/ws/miniapp`(小程序连入)两个端点,
/// 共享 RelayState。端点仅决定「期望的客户端类型」,真正的身份宣告在首消息
/// Hello 中再次校验(防误连/误用)。
pub fn build_router(state: RelayState) -> Router {
    Router::new()
        .route("/ws/device", get(device_ws_handler))
        .route("/ws/miniapp", get(miniapp_ws_handler))
        .with_state(state)
}

/// 桌面端 WS upgrade handler
async fn device_ws_handler(
    ws: WebSocketUpgrade,
    State(state): State<RelayState>,
) -> impl IntoResponse {
    tracing::debug!("桌面端 WS 连接接入");
    ws.on_upgrade(move |socket| handle_connection(socket, state, ClientKindWire::Device))
}

/// 小程序 WS upgrade handler
async fn miniapp_ws_handler(
    ws: WebSocketUpgrade,
    State(state): State<RelayState>,
) -> impl IntoResponse {
    tracing::debug!("小程序 WS 连接接入");
    ws.on_upgrade(move |socket| handle_connection(socket, state, ClientKindWire::Miniapp))
}

/// WS 连接生命周期(握手 → 收发循环 → 注销)
///
/// 步骤:
/// 1. 等待首条 Hello 文本帧,校验 kind 与 token。
/// 2. 校验通过:分配 conn_id + mpsc,注册 ConnHandle,派发广播读取任务。
/// 3. 主循环:从 socket recv 文本帧 → 构造 BroadcastMessage → route 投递。
/// 4. 同时读取 mpsc 广播队列 → 写回 socket(双任务用 split sink/stream)。
/// 5. 任一端断开 → 注销连接、关闭 mpsc。
async fn handle_connection(socket: WebSocket, state: RelayState, expected: ClientKindWire) {
    // 握手阶段:等待首条 Hello
    let (mut socket_tx, mut socket_rx) = socket.split();

    let hello = match recv_hello(&mut socket_rx).await {
        Ok(h) => h,
        Err(e) => {
            tracing::warn!(error = %e, "握手失败:未收到合法 Hello");
            let _ = send_text(
                &mut socket_tx,
                r#"{"kind":"control","error":"handshake_failed"}"#,
            )
            .await;
            let _ = socket_tx.close().await;
            return;
        }
    };

    // 身份 + token 双因子校验
    if hello.kind != expected {
        tracing::warn!(
            ?hello.kind,
            ?expected,
            "握手失败:客户端类型与端点不匹配"
        );
        let _ = send_text(
            &mut socket_tx,
            r#"{"kind":"control","error":"kind_mismatch"}"#,
        )
        .await;
        let _ = socket_tx.close().await;
        return;
    }
    // MC-4 最小加固:device_id 格式校验(空/超长/含控制字符一律拒)。
    // 单共享 token 下 device_id 无强绑定,但格式校验可挡最基础的注入/异常输入。
    if !validate_device_id(&hello.device_id) {
        tracing::warn!(
            device_id = %hello.device_id,
            "握手失败:device_id 格式非法"
        );
        let _ = send_text(
            &mut socket_tx,
            r#"{"kind":"control","error":"invalid_device_id"}"#,
        )
        .await;
        let _ = socket_tx.close().await;
        return;
    }
    // RLY-5:token 未配置(服务启动时应已由 main 校验)→ 拒绝握手而非 panic
    let Some(expected) = expected_token() else {
        tracing::error!("DF_RELAY_TOKEN 未设置,拒绝握手");
        let _ = send_text(
            &mut socket_tx,
            r#"{"kind":"control","error":"server_misconfigured"}"#,
        )
        .await;
        let _ = socket_tx.close().await;
        return;
    };
    // RLY-4:常量时间比较防时序侧信道
    if !constant_time_eq(&hello.token, &expected) {
        tracing::warn!(
            device_id = %hello.device_id,
            "握手失败:token 校验不通过"
        );
        let _ = send_text(
            &mut socket_tx,
            r#"{"kind":"control","error":"auth_failed"}"#,
        )
        .await;
        let _ = socket_tx.close().await;
        return;
    }

    let conn_id = next_conn_id();
    let kind: ClientKind = hello.kind.into();
    let device_id = hello.device_id.clone();
    tracing::info!(
        conn_id = conn_id.0,
        ?kind,
        device_id = %device_id,
        "连接握手通过,进入收发循环"
    );

    // 握手通过:立即发 ack 控制帧给客户端。
    // 客户端据此判定握手成功(首条非 error 消息即 handshaked),不依赖等待对端首条业务消息 ——
    // 否则单端连入时(device 离线)relay 静默,客户端永卡 handshaking,send 被 handshaked 守卫拦截。
    let _ = send_text(
        &mut socket_tx,
        r#"{"kind":"control","payload":{"control_kind":"hello_ack"}}"#,
    )
    .await;

    // 建立广播投递 mpsc(连接读取任务消费 → 写回 socket)
    let (bc_tx, bc_rx) = mpsc::unbounded_channel::<BroadcastMessage>();
    let handle = ConnHandle::new(conn_id, kind, device_id.clone(), bc_tx);
    state.add_conn(handle).await;

    // 派发广播读取任务:从 bc_rx 取消息 → 序列化 → 写 socket
    let mut bc_task = tokio::spawn(broadcast_pump(bc_rx, socket_tx));

    // 主循环:从 socket recv → 构造 BroadcastMessage → route
    loop {
        tokio::select! {
            // socket 入帧
            maybe_msg = socket_rx.next() => {
                match maybe_msg {
                    Some(Ok(Message::Text(text))) => {
                        // RLY-3:入站帧超限(>1MiB)直接断开,防大帧耗尽内存/带宽
                        if text.len() > MAX_FRAME_BYTES {
                            tracing::warn!(
                                conn_id = conn_id.0,
                                len = text.len(),
                                "入站帧超限,断开连接"
                            );
                            break;
                        }
                        if let Err(e) = handle_inbound_text(&state, conn_id, kind, &device_id, &text).await {
                            tracing::warn!(conn_id = conn_id.0, error = %e, "入站消息处理失败,忽略");
                        }
                    }
                    Some(Ok(Message::Binary(_))) => {
                        // MVP 仅支持文本帧;二进制帧忽略(协议层可后续扩展)
                        tracing::debug!(conn_id = conn_id.0, "收到二进制帧,忽略");
                    }
                    Some(Ok(Message::Ping(_))) | Some(Ok(Message::Pong(_))) => {
                        // axum/tungstenite 协议层 Ping/Pong 自动处理,这里仅记录
                        tracing::trace!(conn_id = conn_id.0, "协议层 Ping/Pong");
                    }
                    Some(Ok(Message::Close(_))) | None => {
                        tracing::info!(conn_id = conn_id.0, "客户端主动关闭连接");
                        break;
                    }
                    Some(Err(e)) => {
                        tracing::warn!(conn_id = conn_id.0, error = %e, "socket 接收错误,断开");
                        break;
                    }
                }
            }
            // 广播 pump 任务结束(socket_tx 关闭或 mpsc 关闭)
            res = &mut bc_task => {
                match res {
                    Ok(()) => {
                        tracing::debug!(conn_id = conn_id.0, "广播 pump 任务正常结束");
                    }
                    Err(e) => {
                        tracing::warn!(conn_id = conn_id.0, error = %e, "广播 pump 任务 panic");
                    }
                }
                break;
            }
        }
    }

    // 注销连接
    if let Some(d) = state.remove_conn(conn_id).await {
        tracing::info!(conn_id = conn_id.0, device_id = %d, "连接已注销");
    }
    // 结束 pump 任务(若仍在运行)
    bc_task.abort();
}

/// 接收并解析首条 Hello 文本帧
async fn recv_hello(rx: &mut futures_util::stream::SplitStream<WebSocket>) -> Result<Hello> {
    let deadline = tokio::time::Duration::from_secs(10);
    let next = tokio::time::timeout(deadline, rx.next())
        .await
        .map_err(|_| RelayError::Client("握手超时(10s 未收到 Hello)".into()))?;
    let msg = next
        .ok_or_else(|| RelayError::Client("握手阶段连接关闭".into()))?
        .map_err(|e| RelayError::WebSocket(format!("握手 recv 失败: {e}")))?;
    let text = match msg {
        Message::Text(t) => t,
        Message::Binary(_) => {
            return Err(RelayError::Client("握手首帧必须为文本".into()));
        }
        _ => return Err(RelayError::Client("握手首帧类型非法".into())),
    };
    // RLY-3:Hello 帧同样限长(Hello 结构很小,超限视为异常/恶意)
    if text.len() > MAX_FRAME_BYTES {
        return Err(RelayError::Client(format!(
            "Hello 帧超限({} B > {MAX_FRAME_BYTES} B)",
            text.len()
        )));
    }
    let hello: Hello =
        serde_json::from_str(&text).map_err(|e| RelayError::Client(format!("Hello 解析失败: {e}")))?;
    Ok(hello)
}

/// 处理入站文本帧(构造 BroadcastMessage → route)
async fn handle_inbound_text(
    state: &RelayState,
    conn_id: ConnId,
    kind: ClientKind,
    device_id: &str,
    raw: &str,
) -> Result<()> {
    // 入站文本即业务 payload(relay 不解析),包成 BroadcastMessage
    // payload 直接用原始 JSON 值;若客户端发非 JSON 文本,则包成字符串值
    let payload: serde_json::Value =
        serde_json::from_str(raw).unwrap_or(serde_json::Value::String(raw.to_string()));

    // 心跳协议:miniapp 发 {control_kind: "ping"} → relay 直接回 pong(不经 device 透传)。
    // miniapp 用 pong 更新 lastPongTime 看门狗(防移动网络 TCP 半连接挂死)。
    // device 端收到 control 消息也仅 console.log,不影响业务。
    if let Some(control_kind) = payload
        .get("control_kind")
        .and_then(|v| v.as_str())
    {
        if control_kind == "ping" && kind == ClientKind::Miniapp {
            let pong_payload = serde_json::json!({"control_kind": "pong"});
            let pong_msg = BroadcastMessage {
                device_id: device_id.to_string(),
                kind: crate::broadcast::MessageKind::Control,
                source: conn_id,
                from: ClientKind::Device, // pong 来自 relay(代理 device),让 miniapp 识别为合法响应
                payload: pong_payload,
                ts: now_ms(),
            };
            let _ = state.route(&pong_msg).await;
            tracing::trace!(
                conn_id = conn_id.0,
                device_id = %device_id,
                "miniapp ping → relay pong(本地响应)"
            );
            return Ok(());
        }
    }

    let now = now_ms();
    let (msg_kind, from) = match kind {
        ClientKind::Device => (MessageKind::Event, ClientKind::Device),
        ClientKind::Miniapp => (MessageKind::Command, ClientKind::Miniapp),
    };
    let msg = BroadcastMessage {
        device_id: device_id.to_string(),
        kind: msg_kind,
        source: conn_id,
        from,
        payload,
        ts: now,
    };
    let delivered = state.route(&msg).await;
    tracing::debug!(
        conn_id = conn_id.0,
        ?msg_kind,
        device_id = %device_id,
        delivered,
        "入站消息已路由"
    );
    Ok(())
}

/// 广播 pump:从 mpsc 取消息,序列化后写回 socket sink
///
/// 任务退出条件:bc_rx 关闭(对端 handle 全部 drop)/ socket_tx 关闭出错。
async fn broadcast_pump(
    mut bc_rx: mpsc::UnboundedReceiver<BroadcastMessage>,
    mut socket_tx: futures_util::stream::SplitSink<WebSocket, Message>,
) {
    while let Some(msg) = bc_rx.recv().await {
        let text = match serde_json::to_string(&msg) {
            Ok(t) => t,
            Err(e) => {
                tracing::warn!(error = %e, "广播消息序列化失败,跳过");
                continue;
            }
        };
        if let Err(e) = socket_tx.send(Message::Text(text)).await {
            tracing::warn!(error = %e, "广播写回 socket 失败,pump 退出");
            break;
        }
    }
}

/// 便捷发送文本帧
async fn send_text(
    tx: &mut futures_util::stream::SplitSink<WebSocket, Message>,
    text: &str,
) -> Result<()> {
    tx.send(Message::Text(text.to_string()))
        .await
        .map_err(|e| RelayError::WebSocket(format!("发送失败: {e}")))
}

/// 当前毫秒时间戳(避开 chrono workspace 依赖,直接用 std + SystemTime)
fn now_ms() -> i64 {
    use std::time::{SystemTime, UNIX_EPOCH};
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|d| d.as_millis() as i64)
        .unwrap_or(0)
}

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

    #[test]
    fn constant_time_eq_equality_and_inequality() {
        assert!(constant_time_eq("abc", "abc"));
        assert!(!constant_time_eq("abc", "abd"));
        assert!(!constant_time_eq("abc", "ab"));
        assert!(!constant_time_eq("", "a"));
        assert!(constant_time_eq("", ""));
    }

    #[test]
    fn validate_device_id_basic() {
        assert!(validate_device_id("dev-1"));
        assert!(validate_device_id("a".repeat(128).as_str()), "上限 128 应放行");
        assert!(!validate_device_id(""), "空串拒绝");
        assert!(!validate_device_id("a".repeat(129).as_str()), "超长拒绝");
        assert!(!validate_device_id("dev\u{0001}"), "控制字符拒绝");
    }

    #[test]
    fn max_frame_is_one_mib() {
        assert_eq!(MAX_FRAME_BYTES, 1024 * 1024);
    }
}