package com.ttstd.signaling.handler;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.ttstd.signaling.entity.RtcSignalMessage;
import org.springframework.stereotype.Component;
import org.springframework.web.socket.CloseStatus;
import org.springframework.web.socket.TextMessage;
import org.springframework.web.socket.WebSocketSession;
import org.springframework.web.socket.handler.TextWebSocketHandler;

import java.io.IOException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * WebRTC核心信令处理器
 * 继承TextWebSocketHandler：处理文本类型的WebSocket消息（WebRTC信令都是JSON文本）
 */
@Component
public class WebRtcSignalHandler extends TextWebSocketHandler {

    /**
     * 核心：维护在线用户的WebSocket会话映射
     * key: 用户ID（userId）
     * value: 该用户的WebSocket连接会话
     * ConcurrentHashMap：线程安全，解决多用户并发连接的线程安全问题
     */
    public static final Map<String, WebSocketSession> ONLINE_USER_SESSIONS = new ConcurrentHashMap<>();

    // JSON序列化工具，用于将消息实体与JSON字符串互转
    private final ObjectMapper objectMapper = new ObjectMapper();

    /**
     * 客户端成功建立WebSocket连接后触发
     * 约定：客户端连接时，通过请求参数传递userId，例如：ws://localhost:8080/ws/rtc?userId=user1001
     */
    @Override
    public void afterConnectionEstablished(WebSocketSession session) {
        // 获取连接的用户ID
        String userId = getUserIdFromSession(session);
        if (userId != null && !userId.isEmpty()) {
            // 将用户会话存入在线列表
            ONLINE_USER_SESSIONS.put(userId, session);
            System.out.println("用户[" + userId + "] 上线，当前在线人数：" + ONLINE_USER_SESSIONS.size());
        }
    }

    /**
     * 核心方法：接收客户端发送的信令消息，并完成【精准中转】
     */
    @Override
    protected void handleTextMessage(WebSocketSession session, TextMessage textMessage) throws Exception {
        // 1. 获取发送方用户ID
        String fromUserId = getUserIdFromSession(session);
        if (fromUserId == null || !ONLINE_USER_SESSIONS.containsKey(fromUserId)) {
            sendErrorMessage(session, "当前用户未登录或连接已失效");
            return;
        }

        // 2. 解析前端发送的信令消息JSON -> 转为实体类
        RtcSignalMessage signalMessage = objectMapper.readValue(textMessage.getPayload(), RtcSignalMessage.class);
        String toUserId = signalMessage.getToUserId(); // 目标用户ID
        String signalType = signalMessage.getSignalType(); // 信令类型：offer/answer/ice-candidate

        // 3. 核心逻辑：查询目标用户的连接会话，存在则中转消息，不存在则返回错误
        WebSocketSession targetSession = ONLINE_USER_SESSIONS.get(toUserId);
        if (targetSession != null && targetSession.isOpen()) {
            // 将信令消息原样转发给目标用户
            targetSession.sendMessage(new TextMessage(objectMapper.writeValueAsString(signalMessage)));
            System.out.println("信令中转成功：[" + fromUserId + "] -> [" + toUserId + "] 类型：" + signalType);
        } else {
            // 目标用户不在线/连接已关闭
            sendErrorMessage(session, "目标用户[" + toUserId + "] 不在线或连接已断开");
        }
    }

    /**
     * 客户端断开WebSocket连接后触发
     */
    @Override
    public void afterConnectionClosed(WebSocketSession session, CloseStatus status) {
        String userId = getUserIdFromSession(session);
        if (userId != null) {
            ONLINE_USER_SESSIONS.remove(userId);
            System.out.println("用户[" + userId + "] 下线，当前在线人数：" + ONLINE_USER_SESSIONS.size());
        }
    }

    /**
     * 处理WebSocket连接异常
     */
    @Override
    public void handleTransportError(WebSocketSession session, Throwable exception) {
        String userId = getUserIdFromSession(session);
        if (userId != null) {
            ONLINE_USER_SESSIONS.remove(userId);
            System.out.println("用户[" + userId + "] 连接异常，已移除会话，异常信息：" + exception.getMessage());
        }
    }

    // ========== 私有工具方法 ==========
    /**
     * 从WebSocket会话中获取请求参数里的userId
     */
    private String getUserIdFromSession(WebSocketSession session) {
        try {
            return session.getUri().getQuery().split("=")[1];
        } catch (Exception e) {
            return null;
        }
    }

    /**
     * 向客户端发送错误提示消息
     */
    private void sendErrorMessage(WebSocketSession session, String errorMsg) throws IOException {
        RtcSignalMessage errorMessage = new RtcSignalMessage(null, null, "error", errorMsg);
        session.sendMessage(new TextMessage(objectMapper.writeValueAsString(errorMessage)));
    }
}