showHTML.ts

import { middlewareCreator } from '../../utils';
import type { HTMLGenerator, SendFile } from '../../services';
import type { AsyncExpressMiddleware, Response, NextFunction } from '../../types';
/**
 * The options to customize the behavior of the middleware.
 *
 * @group Middlewares/ShowHTML
 */
export type ShowHTMLOptions = {
  /**
   * The name of the file the middleware will serve. If the {@link HTMLGenerator} service
   * is available, it will be overriden by the service.
   *
   * @default 'index.html'
   */
  file: string;
};
/**
 * The options to construct a {@link ShowHTML}.
 *
 * @group Middlewares/ShowHTML
 */
export type ShowHTMLConstructorOptions = Partial<ShowHTMLOptions> & {
  /**
   * A dictionary with the dependencies to inject.
   */
  inject: {
    sendFile: SendFile;
    /**
     * A function to get a possible {@link HTMLGenerator}. This is injected as a "getter"
     * to not interrupt the DIC "lifecycle": middlewares are initialized right when the
     * app starts, and injecting a reference would force the service to be initialized
     * too, even if a request is not being made.
     */
    getHTMLGenerator?: () => HTMLGenerator | undefined;
  };
};
/**
 * The options for the middleware creator that will mount an instance of {@link ShowHTML}.
 *
 * @group Middlewares/ShowHTML
 */
export type ShowHTMLMiddlewareOptions = Partial<ShowHTMLOptions> & {
  /**
   * The name of an {@link HTMLGenerator} service already available in the application.
   *
   * @default 'htmlGenerator'
   */
  htmlGeneratorServiceName?: string;
};

/**
 * A very simple middleware service to send an HTML on a server response. The special
 * _'feature'_ of this service is that it can be hooked up to an {@link HTMLGenerator}
 * service and it will automatically server the file generated by it.
 *
 * @group Middleware Classes
 * @group Middlewares/ShowHTML
 * @prettierignore
 */
export class ShowHTML {
  /**
   * The service that serves a file.
   */
  protected readonly _sendFile: SendFile;
  /**
   * A function to get a possible {@link HTMLGenerator}. This is injected as a "getter"
   * to not interrupt the DIC "lifecycle": middlewares are initialized right when the
   * app starts, and injecting a reference would force the service to be initialized
   * too, even if a request is not being made.
   */
  protected readonly _getHTMLGenerator: () => HTMLGenerator | undefined;
  /**
   * The customization options for the middleware.
   */
  protected _options: ShowHTMLOptions;
  /**
   * Whether or not the file is ready to be served. In case the middleware uses an
   * {@link HTMLGenerator} service, the file needs to be generated before being available,
   * and that's why this flag exists.
   */
  protected _fileReady: boolean = false;
  /**
   * @param options  The options to construct the class.
   */
  constructor({ inject, ...options }: ShowHTMLConstructorOptions) {
    this._sendFile = inject.sendFile;
    this._getHTMLGenerator = inject.getHTMLGenerator || (() => undefined);
    this._options = {
      file: 'index.html',
      ...options,
    };
  }
  /**
   * Generates the middleware that serves the HTML file.
   */
  getMiddleware(): AsyncExpressMiddleware {
    return async (_, res, next) => {
      // If the file is ready to be served, serve it.
      if (this._fileReady) {
        this._sendResponse(res, next);
        return;
      }

      const htmlGenerator = this._getHTMLGenerator();
      // If there's no generator, switch the flag and just serve the file.
      if (!htmlGenerator) {
        this._fileReady = true;
        this._sendResponse(res, next);
        return;
      }

      try {
        // Wait for the HTML to be generated.
        await htmlGenerator.whenReady();
        // Update the local option.
        this._options.file = htmlGenerator.options.file;
        // Switch the flag and serve the file.
        this._fileReady = true;
        this._sendResponse(res, next);
      } catch (error) {
        next(error);
      }
    };
  }
  /**
   * The customization options.
   */
  get options(): Readonly<ShowHTMLOptions> {
    return { ...this._options };
  }
  /**
   * Serves the HTML file to the response.
   *
   * @param res   The response object generated by the application.
   * @param next  The function to call the next middleware.
   */
  protected _sendResponse(res: Response, next: NextFunction): void {
    res.setHeader('Content-Type', 'text/html');
    this._sendFile({
      res,
      next,
      filepath: this._options.file,
    });
  }
}
/**
 * Creates the middleware that serves an HTML file in the response.
 *
 * @group Middlewares
 * @group Middlewares/ShowHTML
 */
export const showHTMLMiddleware = middlewareCreator(
  (options: ShowHTMLMiddlewareOptions = {}) =>
    (app) => {
      const { htmlGeneratorServiceName = 'htmlGenerator', ...rest } = options;
      return new ShowHTML({
        inject: {
          sendFile: app.get('sendFile'),
          getHTMLGenerator: () => app.try(htmlGeneratorServiceName),
        },
        ...rest,
      }).getMiddleware();
    },
);