import { afterEach, describe, expect, it } from 'vitest';

import {
  GatewayConnection,
  GatewayOp,
  parseGatewaySnapshot,
  type GatewayDispatch,
  type GatewayStatus,
} from '@/api/gateway';
import { makeReadySnapshot } from './helpers';

/** Подставной WebSocket: рукопожатие и heartbeat полностью под контролем теста. */
class FakeSocket {
  static instances: FakeSocket[] = [];

  readonly url: string;
  readyState = 0;
  sent: string[] = [];
  onopen: ((event: Event) => void) | null = null;
  onmessage: ((event: MessageEvent) => void) | null = null;
  onerror: ((event: Event) => void) | null = null;
  onclose: ((event: CloseEvent) => void) | null = null;

  constructor(url: string) {
    this.url = url;
    FakeSocket.instances.push(this);
  }

  open(): void {
    this.readyState = 1;
    this.onopen?.(new Event('open'));
  }

  send(data: string): void {
    this.sent.push(data);
  }

  close(): void {
    this.readyState = 3;
  }

  /** Присылает кадр от сервера. */
  emit(packet: unknown): void {
    this.onmessage?.({ data: JSON.stringify(packet) } as MessageEvent);
  }

  /** Последний отправленный пакет в виде объекта. */
  lastSent(): { op: number; d: unknown } {
    const raw = this.sent.at(-1);
    if (raw === undefined) {
      throw new Error('socket has not sent anything');
    }
    return JSON.parse(raw) as { op: number; d: unknown };
  }

  closeFromServer(code = 1006): void {
    this.readyState = 3;
    this.onclose?.({ code } as CloseEvent);
  }
}

function makeConnection(handlers: {
  onDispatch?: (event: GatewayDispatch) => void;
  onStatus?: (status: GatewayStatus) => void;
  onInvalidSession?: () => void;
  onResumeIncomplete?: () => void;
}) {
  FakeSocket.instances = [];
  const connection = new GatewayConnection({
    url: 'ws://localhost/gateway',
    socketFactory: (url) => new FakeSocket(url) as unknown as WebSocket,
    handlers,
    // Быстрый backoff, чтобы тест переподключения не ждал секунду.
    baseBackoffMs: 5,
    helloTimeoutMs: 60_000,
  });
  connection.connect();
  connections.push(connection);
  return connection;
}

const connections: GatewayConnection[] = [];

afterEach(() => {
  // Закрываем соединения, иначе таймеры heartbeat продолжают жить между тестами.
  for (const connection of connections.splice(0)) {
    connection.close();
  }
  FakeSocket.instances = [];
});

describe('gateway client', () => {
  it('answers HELLO with IDENTIFY and an empty token', () => {
    const connection = makeConnection({});
    const socket = FakeSocket.instances[0];
    expect(socket).toBeDefined();
    socket?.open();

    socket?.emit({
      op: GatewayOp.HELLO,
      d: { heartbeat_interval_ms: 1000, session_id: 'sess-1' },
    });

    expect(socket?.lastSent()).toEqual({ op: GatewayOp.IDENTIFY, d: { token: '', resume_seq: 0 } });
    expect(connection.getStatus()).toBe('connecting');
    connection.close();
  });

  it('delivers READY to the dispatch handler', () => {
    const events: GatewayDispatch[] = [];
    const connection = makeConnection({ onDispatch: (event) => events.push(event) });
    const socket = FakeSocket.instances[0];
    socket?.open();
    socket?.emit({ op: GatewayOp.HELLO, d: { heartbeat_interval_ms: 1000, session_id: 's' } });
    socket?.emit({ op: GatewayOp.DISPATCH, t: 'READY', s: 1, d: makeReadySnapshot([
      { id: 'g-1', name: 'Main', channels: [{ id: 'c-1', name: 'general' }] },
    ]) });

    expect(events).toHaveLength(1);
    expect(events[0]?.t).toBe('READY');
    expect(connection.getStatus()).toBe('connected');
    expect(connection.getLastSeq()).toBe(1);

    const snapshot = parseGatewaySnapshot(events[0]?.d);
    expect(snapshot?.guilds[0]?.channels[0]?.name).toBe('general');
    connection.close();
  });

  it('ignores unknown events and unparsable frames', () => {
    const events: GatewayDispatch[] = [];
    const connection = makeConnection({ onDispatch: (event) => events.push(event) });
    const socket = FakeSocket.instances[0];
    socket?.open();
    socket?.emit({ op: GatewayOp.HELLO, d: { heartbeat_interval_ms: 1000, session_id: 's' } });
    socket?.emit({ op: GatewayOp.DISPATCH, t: 'GUILD_CREATE', s: 2, d: { id: 'g-9' } });
    socket?.emit({ op: 99, d: null });
    socket?.onmessage?.({ data: 'not json' } as MessageEvent);

    expect(events.map((event) => event.t)).toEqual(['GUILD_CREATE']);
    connection.close();
  });

  it('sends HEARTBEAT with the interval from HELLO and tracks the ack', async () => {
    const connection = makeConnection({});
    const socket = FakeSocket.instances[0];
    socket?.open();
    socket?.emit({ op: GatewayOp.HELLO, d: { heartbeat_interval_ms: 20, session_id: 's' } });

    await new Promise((resolve) => setTimeout(resolve, 45));
    const heartbeat = socket?.lastSent();
    expect(heartbeat).toEqual({ op: GatewayOp.HEARTBEAT, d: null });

    socket?.emit({ op: GatewayOp.HEARTBEAT_ACK, d: null });
    connection.close();
  });

  it('reconnects with RESUME and the last sequence number', async () => {
    const statuses: GatewayStatus[] = [];
    const connection = makeConnection({ onStatus: (status) => statuses.push(status) });
    const first = FakeSocket.instances[0];
    first?.open();
    first?.emit({ op: GatewayOp.HELLO, d: { heartbeat_interval_ms: 1000, session_id: 'sess-7' } });
    first?.emit({ op: GatewayOp.DISPATCH, t: 'READY', s: 42, d: makeReadySnapshot([]) });

    first?.closeFromServer();
    expect(connection.getStatus()).toBe('reconnecting');

    await new Promise((resolve) => setTimeout(resolve, 200));
    const second = FakeSocket.instances[1];
    expect(second).toBeDefined();
    second?.open();
    second?.emit({ op: GatewayOp.HELLO, d: { heartbeat_interval_ms: 1000, session_id: 'sess-7' } });

    expect(second?.lastSent()).toEqual({ op: GatewayOp.RESUME, d: { token: '', resume_seq: 42 } });
    expect(statuses).toContain('reconnecting');
    connection.close();
  });

  it('reports INVALID_SESSION to the handler', () => {
    let invalidated = 0;
    const connection = makeConnection({ onInvalidSession: () => (invalidated += 1) });
    const socket = FakeSocket.instances[0];
    socket?.open();
    socket?.emit({ op: GatewayOp.HELLO, d: { heartbeat_interval_ms: 1000, session_id: 's' } });
    socket?.emit({ op: GatewayOp.INVALID_SESSION, d: false });

    expect(invalidated).toBe(1);
    expect(connection.getStatus()).toBe('disconnected');
    connection.close();
  });
});