/*
  Copyright 2018 Google LLC

  Use of this source code is governed by an MIT-style
  license that can be found in the LICENSE file or at
  https://opensource.org/licenses/MIT.
*/

import {logger} from 'workbox-core/_private/logger.mjs';

import {createHeaders} from './utils/createHeaders.mjs';
import {concatenateToResponse} from './concatenateToResponse.mjs';
import {isSupported} from './isSupported.mjs';

import './_version.mjs';

/**
 * A shortcut to create a strategy that could be dropped-in to Workbox's router.
 *
 * On browsers that do not support constructing new `ReadableStream`s, this
 * strategy will automatically wait for all the `sourceFunctions` to complete,
 * and create a final response that concatenates their values together.
 *
 * @param {
 *   Array<function(workbox.routing.Route~handlerCallback)>} sourceFunctions
 * Each function should return a {@link workbox.streams.StreamSource} (or a
 * Promise which resolves to one).
 * @param {HeadersInit} [headersInit] If there's no `Content-Type` specified,
 * `'text/html'` will be used by default.
 * @return {workbox.routing.Route~handlerCallback}
 *
 * @memberof workbox.streams
 */
export function strategy(sourceFunctions, headersInit) {
  return async ({event, url, params}) => {
    if (isSupported()) {
      const {done, response} = concatenateToResponse(sourceFunctions.map(
          (fn) => fn({event, url, params})), headersInit);
      event.waitUntil(done);
      return response;
    }

    if (process.env.NODE_ENV !== 'production') {
      logger.log(`The current browser doesn't support creating response ` +
        `streams. Falling back to non-streaming response instead.`);
    }

    // Fallback to waiting for everything to finish, and concatenating the
    // responses.
    const parts = await Promise.all(
        sourceFunctions.map(
            (sourceFunction) => sourceFunction({event, url, params})
        ).map(async (responsePromise) => {
          const response = await responsePromise;
          if (response instanceof Response) {
            return response.blob();
          }

          // Otherwise, assume it's something like a string which can be used
          // as-is when constructing the final composite blob.
          return response;
        })
    );

    const headers = createHeaders(headersInit);
    // Constructing a new Response from a Blob source is well-supported.
    // So is constructing a new Blob from multiple source Blobs or strings.
    return new Response(new Blob(parts), {headers});
  };
}