import {
  APIError,
  AuthReason,
  Transport,
  TransportConfig,
  buildCleanConnectFlags,
  marshalJSON,
} from "./types.js";

export interface FakeConnect {
  cleanStart: boolean;
  sessionExpiry: number;
  password: string;
}

/** 单测用假 MQTT。 */
export class FakeTransport implements Transport {
  private cfg?: TransportConfig;
  private cred = "";
  private up: string[] = [];
  private connects: FakeConnect[] = [];
  autoHello = true;
  helloToken = "nst_test_token";
  helloServerTimeMs = 1_750_000_000_000;
  maxBodyBytes = 262144;
  maxMetaBytes = 4096;
  maxFrameBytes = 786432;

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

  async start(cfg: TransportConfig): Promise<void> {
    this.cfg = cfg;
    await this.simulateConnectOK();
  }

  async publishUp(payload: Uint8Array | string): Promise<void> {
    const s = typeof payload === "string" ? payload : new TextDecoder().decode(payload);
    this.up.push(s);
    if (this.autoHello) {
      try {
        const head = JSON.parse(s) as { type?: string; rid?: string };
        if (head.type === "hello" && head.rid) this.replyHello(head.rid);
      } catch {
        /* ignore */
      }
    }
  }

  async stop(): Promise<void> {
    this.cfg?.onOffline();
  }

  private replyHello(rid: string): void {
    const resp = marshalJSON({
      v: 1,
      type: "resp",
      rid,
      ok: true,
      data: {
        server_time_ms: this.helloServerTimeMs,
        server_version: "0.1.0",
        max_body_bytes: this.maxBodyBytes,
        max_meta_bytes: this.maxMetaBytes,
        max_frame_bytes: this.maxFrameBytes,
        max_ttl_seconds: 2592000,
        max_schedule_seconds: 31536000,
        ack_timeout_seconds: 300,
        session_token: this.helloToken,
      },
    });
    this.injectDown(resp);
  }

  async simulateConnectOK(): Promise<void> {
    const { cleanStart, sessionExpiry } = buildCleanConnectFlags();
    this.connects.push({ cleanStart, sessionExpiry, password: this.cred });
    this.cfg?.onConnectPacket?.(cleanStart, sessionExpiry);
    this.cfg?.backoff.markOnline();
    await this.cfg?.mqttReady();
  }

  async simulateReconnect(): Promise<void> {
    this.cfg?.backoff.markOffline();
    this.cfg?.onOffline();
    await this.simulateConnectOK();
  }

  simulateAuthFail(reason: AuthReason): void {
    this.cfg?.onAuthFailed(reason);
  }

  simulateKick(): void {
    this.cfg?.onKicked();
  }

  injectDown(payload: string | Uint8Array): void {
    const bytes = typeof payload === "string" ? new TextEncoder().encode(payload) : payload;
    this.cfg?.onDown(bytes);
  }

  replyOK(rid: string, data: unknown = {}): void {
    this.injectDown(marshalJSON({ v: 1, type: "resp", rid, ok: true, data }));
  }

  replyErr(rid: string, code: string, message: string): void {
    this.injectDown(
      marshalJSON({ v: 1, type: "resp", rid, ok: false, error: { code, message } }),
    );
  }

  upFrames(): string[] {
    return [...this.up];
  }

  getConnects(): FakeConnect[] {
    return [...this.connects];
  }

  findUp(type: string): Array<Record<string, unknown>> {
    const out: Array<Record<string, unknown>> = [];
    for (const s of this.up) {
      try {
        const m = JSON.parse(s) as Record<string, unknown>;
        if (m.type === type) out.push(m);
      } catch {
        /* ignore */
      }
    }
    return out;
  }
}

export function assertNever(_x: never): void {
  throw new APIError("bad_request", "unreachable");
}