react-native/local-cli/server/util/debugger-ui/DeltaPatcher.js

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @format
 */

/**
 * This file is a copy of the reference `DeltaPatcher`, located in
 * metro. The reason to not reuse that file is that in this context
 * we cannot have flow annotations or CJS syntax (since this file is directly)
 * injected into a static HTML page.
 *
 * TODO: Find a simple and lightweight way to compile `DeltaPatcher` to avoid
 * having this duplicated file.
 */
(function(global) {
  'use strict';

  /**
   * This is a reference client for the Delta Bundler: it maintains cached the
   * last patched bundle delta and it's capable of applying new Deltas received
   * from the Bundler.
   */
  class DeltaPatcher {
    constructor() {
      this._lastBundle = {
        pre: new Map(),
        post: new Map(),
        modules: new Map(),
      };
      this._initialized = false;
      this._lastNumModifiedFiles = 0;
      this._lastModifiedDate = new Date();
    }

    static get(id) {
      let deltaPatcher = this._deltaPatchers.get(id);

      if (!deltaPatcher) {
        deltaPatcher = new DeltaPatcher();
        this._deltaPatchers.set(id, deltaPatcher);
      }

      return deltaPatcher;
    }

    /**
     * Applies a Delta Bundle to the current bundle.
     */
    applyDelta(deltaBundle) {
      // Make sure that the first received delta is a fresh one.
      if (!this._initialized && !deltaBundle.reset) {
        throw new Error(
          'DeltaPatcher should receive a fresh Delta when being initialized',
        );
      }

      this._initialized = true;

      // Reset the current delta when we receive a fresh delta.
      if (deltaBundle.reset) {
        this._lastBundle = {
          pre: new Map(),
          post: new Map(),
          modules: new Map(),
        };
      }

      this._lastNumModifiedFiles =
        deltaBundle.pre.size + deltaBundle.post.size + deltaBundle.delta.size;

      if (this._lastNumModifiedFiles > 0) {
        this._lastModifiedDate = new Date();
      }

      this._patchMap(this._lastBundle.pre, deltaBundle.pre);
      this._patchMap(this._lastBundle.post, deltaBundle.post);
      this._patchMap(this._lastBundle.modules, deltaBundle.delta);

      return this;
    }

    /**
     * Returns the number of modified files in the last received Delta. This is
     * currently used to populate the `X-Metro-Files-Changed-Count` HTTP header
     * when metro serves the whole JS bundle, and can potentially be removed once
     * we only send the actual deltas to clients.
     */
    getLastNumModifiedFiles() {
      return this._lastNumModifiedFiles;
    }

    getLastModifiedDate() {
      return this._lastModifiedDate;
    }

    getAllModules() {
      return [].concat(
        Array.from(this._lastBundle.pre.values()),
        Array.from(this._lastBundle.modules.values()),
        Array.from(this._lastBundle.post.values()),
      );
    }

    _patchMap(original, patch) {
      for (const [key, value] of patch.entries()) {
        if (value == null) {
          original.delete(key);
        } else {
          original.set(key, value);
        }
      }
    }
  }

  DeltaPatcher._deltaPatchers = new Map();

  global.DeltaPatcher = DeltaPatcher;
})(window);