import type {
  PageWorkerResponse,
  ParseWorkerRequest,
  ParseWorkerResponse,
  WorkerRequest,
  WorkerFailure,
  WorkerResponse,
} from './worker-protocol.js';

export type SourceKind = 'one' | 'onepkg';

export interface WorkerPort {
  onmessage: ((event: MessageEvent<WorkerResponse>) => void) | null;
  onerror: ((event: ErrorEvent) => void) | null;
  postMessage(message: WorkerRequest, transfer?: Transferable[]): void;
  terminate(): void;
}

type PendingRequest = {
  resolve: (response: ParseWorkerResponse | PageWorkerResponse) => void;
  reject: (error: WorkerClientError) => void;
};

export class WorkerClientError extends Error {
  constructor(
    readonly code: WorkerFailure['code'],
    message: string
  ) {
    super(message);
    this.name = 'WorkerClientError';
  }
}

function createModuleWorker(): WorkerPort {
  return new Worker(new URL('./onenote.worker.ts', import.meta.url), {
    type: 'module',
  }) as WorkerPort;
}

export class OneNoteWorkerClient {
  private readonly worker: WorkerPort;
  private readonly pending = new Map<string, PendingRequest>();
  private requestSequence = 0;
  private terminated = false;

  constructor(workerFactory: () => WorkerPort = createModuleWorker) {
    this.worker = workerFactory();
    this.worker.onmessage = ({ data }) => {
      if (!('requestId' in data)) return;
      const pending = this.pending.get(data.requestId);
      if (!pending) return;
      this.pending.delete(data.requestId);
      pending.resolve(data);
    };
    this.worker.onerror = () => {
      const error = new WorkerClientError(
        'worker-failure',
        'The local parser worker stopped unexpectedly.'
      );
      for (const request of this.pending.values()) request.reject(error);
      this.pending.clear();
    };
  }

  parseSource(
    kind: SourceKind,
    fileName: string,
    bytes: ArrayBuffer
  ): Promise<ParseWorkerResponse> {
    if (this.terminated) {
      return Promise.reject(
        new WorkerClientError(
          'worker-failure',
          'The local parser worker has already been terminated.'
        )
      );
    }

    const requestId = `parse-${++this.requestSequence}`;
    const request: ParseWorkerRequest = {
      type: kind === 'one' ? 'parse-one' : 'parse-onepkg',
      requestId,
      fileName,
      bytes,
    };

    return new Promise((resolve, reject) => {
      this.pending.set(requestId, {
        resolve: (response) => resolve(response as ParseWorkerResponse),
        reject,
      });
      this.worker.postMessage(request, [bytes]);
    });
  }

  getPage(
    sessionId: string,
    pageId: string,
    sectionId?: string
  ): Promise<PageWorkerResponse> {
    if (this.terminated) {
      return Promise.reject(
        new WorkerClientError(
          'worker-failure',
          'The local parser worker has already been terminated.'
        )
      );
    }

    const requestId = `page-${++this.requestSequence}`;
    return new Promise((resolve, reject) => {
      this.pending.set(requestId, {
        resolve: (response) => resolve(response as PageWorkerResponse),
        reject,
      });
      this.worker.postMessage({
        type: 'get-page',
        requestId,
        sessionId,
        pageId,
        ...(sectionId === undefined ? {} : { sectionId }),
      });
    });
  }

  terminate(): void {
    if (this.terminated) return;
    this.terminated = true;
    this.worker.terminate();
    const error = new WorkerClientError(
      'worker-failure',
      'The local parser request was cancelled.'
    );
    for (const request of this.pending.values()) request.reject(error);
    this.pending.clear();
  }
}