import mqtt, { type MqttClient, type IClientOptions } from "mqtt";
import {
  AuthReason,
  Transport,
  TransportConfig,
  buildCleanConnectFlags,
} from "./types.js";

/** 基于 MQTT.js 5 的真实传输。 */
export class MqttTransport implements Transport {
  private client?: MqttClient;
  private cfg?: TransportConfig;
  private cred = "";
  private stopped = false;
  private upTopic = "";
  private downTopic = "";
  private attempt = 0;

  setCredential(passwordOrToken: string): void {
    this.cred = passwordOrToken;
  }

  async start(cfg: TransportConfig): Promise<void> {
    this.cfg = cfg;
    this.stopped = false;
    this.upTopic = `nix/c/${cfg.endpointId}/up`;
    this.downTopic = `nix/c/${cfg.endpointId}/down`;
    await this.connectLoop();
  }

  private async connectLoop(): Promise<void> {
    const cfg = this.cfg!;
    while (!this.stopped) {
      const wait = cfg.backoff.delay(this.attempt);
      if (wait > 0) await sleep(wait);
      if (this.stopped) return;
      try {
        await this.oneConnect();
        this.attempt = 0;
        return;
      } catch (e) {
        this.attempt++;
        cfg.backoff.markOffline();
        cfg.onOffline();
        if (this.stopped) return;
        // 认证失败等会设 stopped
      }
    }
  }

  private oneConnect(): Promise<void> {
    const cfg = this.cfg!;
    const { cleanStart, sessionExpiry } = buildCleanConnectFlags();
    cfg.onConnectPacket?.(cleanStart, sessionExpiry);

    const url = normalizeWSURL(cfg.url, cfg.allowTcp);
    const opts: IClientOptions = {
      clientId: cfg.endpointId,
      username: cfg.endpointId,
      password: this.cred,
      protocolVersion: 5,
      clean: cleanStart,
      connectTimeout: cfg.connectTimeoutMs,
      reconnectPeriod: 0, // 自行退避
      properties: {
        sessionExpiryInterval: sessionExpiry,
      },
      wsOptions: {},
    };

    return new Promise((resolve, reject) => {
      const client = mqtt.connect(url, opts);
      this.client = client;
      let settled = false;

      const fail = (err: Error) => {
        if (settled) return;
        settled = true;
        client.end(true);
        reject(err);
      };

      client.on("connect", async () => {
        try {
          cfg.backoff.markOnline();
          await client.subscribeAsync(this.downTopic, { qos: 1 });
          await cfg.mqttReady();
          if (!settled) {
            settled = true;
            resolve();
          }
          // 断线后自行重连
          client.on("close", () => {
            if (this.stopped) return;
            cfg.backoff.markOffline();
            cfg.onOffline();
            this.attempt++;
            void this.connectLoop();
          });
        } catch (e) {
          fail(e as Error);
        }
      });

      client.on("message", (_topic, payload) => {
        cfg.onDown(payload);
      });

      client.on("error", (err) => {
        // MQTT.js 用 error 报告部分失败
        const msg = String(err?.message ?? err);
        if (/Not authorized|Bad user|banned|0x86|0x87|0x8A/i.test(msg)) {
          const reason: AuthReason = this.cred.startsWith("nst_")
            ? "session_invalid"
            : "bad_credentials";
          this.stopped = true;
          cfg.onAuthFailed(reason);
        }
        fail(err);
      });

      client.on("disconnect", (packet) => {
        const code = packet?.reasonCode;
        if (code === 0x8e) {
          this.stopped = true;
          cfg.onKicked();
        }
      });

      setTimeout(() => {
        if (!settled) fail(new Error("connect timeout"));
      }, cfg.connectTimeoutMs);
    });
  }

  async publishUp(payload: Uint8Array | string): Promise<void> {
    const c = this.client;
    if (!c || !c.connected) throw new Error("not connected");
    const buf = typeof payload === "string" ? Buffer.from(payload) : Buffer.from(payload);
    await c.publishAsync(this.upTopic, buf, { qos: 1 });
  }

  async stop(): Promise<void> {
    this.stopped = true;
    const c = this.client;
    this.client = undefined;
    if (c) await new Promise<void>((r) => c.end(true, {}, () => r()));
  }
}

function normalizeWSURL(raw: string, allowTcp: boolean): string {
  const u = new URL(raw);
  if (u.protocol === "http:") u.protocol = "ws:";
  if (u.protocol === "https:") u.protocol = "wss:";
  if (u.protocol === "ws:" || u.protocol === "wss:") {
    if (!u.pathname || u.pathname === "/") u.pathname = "/mqtt";
    return u.toString();
  }
  if (u.protocol === "mqtt:" || u.protocol === "mqtts:") {
    if (!allowTcp) throw new Error("裸 TCP 需显式 allowTcp");
    return u.toString();
  }
  throw new Error(`unsupported scheme ${u.protocol}`);
}

function sleep(ms: number): Promise<void> {
  return new Promise((r) => setTimeout(r, ms));
}