import { EventType } from "@umt/contracts";
import { useEffect, useRef, useState } from "react";
import { buildUrl } from "./api.ts";

// SSE 封装:整个页面共用一条 EventSource(按订阅引用计数开关)。
// - 服务端按事件类型发命名事件(event: <type>),所以按 type 订阅;"*" 订阅全部已知类型。
// - 记住最后一个 seq;断线后按指数退避重连 `/events?after=<seq>` 补读,不漏不重。
// - 收到 system.resync(起点已被裁剪)时,订阅者应整页重取(useSseInvalidate 自动处理)。
// 鉴权走 cookie 会话(EventSource 不能带 Authorization 头)。

export type SseEvent<P = unknown> = { seq: number; type: string; at: string; payload: P };
export type SseHandler = (event: SseEvent) => void;
export type SseStatus = "idle" | "connecting" | "open" | "reconnecting";

const KNOWN_TYPES: string[] = Object.values(EventType);
const WILDCARD = "*";

type Sub = { types: Set<string>; handler: SseHandler };

class SseClient {
  private es: EventSource | null = null;
  private subs = new Set<Sub>();
  private listened = new Set<string>();
  private lastSeq: number | null = null;
  private retry = 0;
  private timer: ReturnType<typeof setTimeout> | null = null;
  private statusListeners = new Set<(s: SseStatus) => void>();
  status: SseStatus = "idle";

  subscribe(types: string[], handler: SseHandler): () => void {
    const sub: Sub = { types: new Set(types), handler };
    this.subs.add(sub);
    if (!this.es && !this.timer) this.connect();
    else for (const t of this.expand(sub.types)) this.listen(t);
    return () => {
      this.subs.delete(sub);
      if (this.subs.size === 0) this.close();
    };
  }

  onStatus(fn: (s: SseStatus) => void): () => void {
    this.statusListeners.add(fn);
    return () => this.statusListeners.delete(fn);
  }

  private setStatus(s: SseStatus) {
    this.status = s;
    for (const fn of this.statusListeners) fn(s);
  }

  private expand(types: Set<string>): string[] {
    return types.has(WILDCARD) ? [...KNOWN_TYPES, ...[...types].filter((t) => t !== WILDCARD)] : [...types];
  }

  private connect() {
    if (typeof EventSource === "undefined") return;
    this.timer = null;
    this.setStatus(this.retry ? "reconnecting" : "connecting");
    const url = buildUrl("/events", { params: { after: this.lastSeq ?? undefined } });
    const es = new EventSource(url, { withCredentials: true });
    this.es = es;
    this.listened.clear();
    // resync 永远监听
    this.listen(EventType.resync);
    for (const sub of this.subs) for (const t of this.expand(sub.types)) this.listen(t);
    es.onopen = () => {
      this.retry = 0;
      this.setStatus("open");
    };
    es.onerror = () => {
      // 自己掌控重连(带 after=seq),不用浏览器默认重连
      es.close();
      if (this.es !== es) return;
      this.es = null;
      if (this.subs.size === 0) return;
      const delay = Math.min(30_000, 1000 * 2 ** this.retry);
      this.retry += 1;
      this.setStatus("reconnecting");
      this.timer = setTimeout(() => this.connect(), delay);
    };
  }

  private listen(type: string) {
    if (!this.es || this.listened.has(type)) return;
    this.listened.add(type);
    this.es.addEventListener(type, (e) => this.dispatch(type, e as MessageEvent<string>));
  }

  private dispatch(type: string, e: MessageEvent<string>) {
    let event: SseEvent;
    try {
      const parsed = JSON.parse(e.data) as Partial<SseEvent>;
      event =
        typeof parsed.seq === "number"
          ? (parsed as SseEvent)
          : { seq: this.lastSeq ?? 0, type, at: new Date().toISOString(), payload: parsed };
    } catch {
      return;
    }
    if (typeof event.seq === "number" && type !== EventType.resync) {
      if (this.lastSeq !== null && event.seq <= this.lastSeq) return; // 补读重叠去重
      this.lastSeq = event.seq;
    }
    for (const sub of this.subs) {
      if (type === EventType.resync || sub.types.has(type) || sub.types.has(WILDCARD)) sub.handler(event);
    }
  }

  private close() {
    if (this.timer) clearTimeout(this.timer);
    this.timer = null;
    this.es?.close();
    this.es = null;
    this.retry = 0;
    this.setStatus("idle");
  }
}

export const sse = new SseClient();

/**
 * 订阅 SSE 事件。types 为事件类型数组(见 contracts EventType),"*" 表示全部已知类型。
 * handler 可以每次渲染都变,不会重复订阅。system.resync 总会送达。
 */
export function useSse(types: string[], handler: SseHandler, enabled = true) {
  const ref = useRef(handler);
  ref.current = handler;
  const key = types.join("|");
  useEffect(() => {
    if (!enabled) return;
    return sse.subscribe(key.split("|"), (e) => ref.current(e));
  }, [key, enabled]);
}

/** 连接状态(给页面角落的"实时"指示用) */
export function useSseStatus(): SseStatus {
  const [s, setS] = useState<SseStatus>(sse.status);
  useEffect(() => sse.onStatus(setS), []);
  return s;
}