/*
  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 type { SerwistPlugin } from "../../types.js";
import { createPartialResponse } from "./createPartialResponse.js";

/**
 * Makes it easy for a request with a `Range` header to be fulfilled by a cached response.
 *
 * It does this by intercepting the `cachedResponseWillBeUsed` plugin callback
 * and returning the appropriate subset of the cached response body.
 */
export class RangeRequestsPlugin implements SerwistPlugin {
  /**
   * @param options
   * @returns If request contains a `Range` header, then a
   * partial response whose body is a subset of `cachedResponse` is
   * returned. Otherwise, `cachedResponse` is returned as-is.
   * @private
   */
  cachedResponseWillBeUsed: SerwistPlugin["cachedResponseWillBeUsed"] = async ({ request, cachedResponse }) => {
    // Only return a sliced response if there's something valid in the cache,
    // and there's a Range: header in the request.
    if (cachedResponse && request.headers.has("range")) {
      return await createPartialResponse(request, cachedResponse);
    }

    // If there was no Range: header, or if cachedResponse wasn't valid, just
    // pass it through as-is.
    return cachedResponse;
  };
}