const shortid = require('shortid');

class Request {
  constructor(type, id = shortid.generate()) {
    this.id = id;
    this.type = type;
  }
}

class AlbumRequest extends Request {
  constructor(album, type) {
    super(type);
  }
}

class SaveAlbumRequest extends AlbumRequest {
  constructor(album) {
    super(album, 'save');
  }
}

class loadAlbumRequest extends AlbumRequest {
  constructor(album) {
    super(album, 'load');
  }
}

class UpdateAlbumRequest extends AlbumRequest {
  constructor(album) {
    super(album, 'update'); 
  }
}

class RequestHandler {
  handleRequest(request) {
    
  }
}

class SaveAlbumRequestHandler extends RequestHandler {
  handle(request) {
    console.log('Saving Album');
    return {saved: true};
  }
}


class LoadAlbumRequestHandler extends RequestHandler {
  handle(request) {
    console.log('Loading Album');
    return {loaded: true};
  }
}

class UpdateAlbumRequestHandler extends RequestHandler {
  handle(request) {
    console.log('Updating Album');
    return {updated: true};
  }
}

class UnknownRequestHandler extends RequestHandler {
  handle(request) {
    console.error(`Unknown request ${request}`);
  }
}
class AlbumService {
  constructor() {
    this._requestHandlers = new Map();
    this._requestHandlers.set('save', new SaveAlbumRequestHandler());
    this._requestHandlers.set('load', new LoadAlbumRequestHandler());
    this._requestHandlers.set('update', new UpdateAlbumRequestHandler());
  }
  
  handleRequest(request) {
    const response = {requestId: request.id};
    const requestHandler = this._requestHandlers.get(request.type);
    if (requestHandler) {
      response.result = requestHandler.handle(request);
    }
    return new Promise.resolve(response);
  }
}

// Usage like this
const album = new Album({artist: 'Me', title: 'In the shower', year: 2018});
const service = new AlbumService();

(async () => {
  const response1 = await service.handleRequest(new SaveAlbumRequest(album));
  const response2 = await service.handleRequest(new LoadAlbumRequest(album));
  const response3 = await service.handleRequest(new UpdateAlbumRequest(album));
})();