private _watch()

in packages/jest-haste-map/src/index.ts [817:1028]
177 lines of code
31 McCabe index (conditional complexity)

  private _watch(hasteMap: InternalHasteMap): Promise<void> {
    if (!this._options.watch) {
      return Promise.resolve();
    }

    // In watch mode, we'll only warn about module collisions and we'll retain
    // all files, even changes to node_modules.
    this._options.throwOnModuleCollision = false;
    this._options.retainAllFiles = true;

    // WatchmanWatcher > FSEventsWatcher > sane.NodeWatcher
    const Watcher =
      canUseWatchman && this._options.useWatchman
        ? WatchmanWatcher
        : FSEventsWatcher.isSupported()
        ? FSEventsWatcher
        : NodeWatcher;

    const extensions = this._options.extensions;
    const ignorePattern = this._options.ignorePattern;
    const rootDir = this._options.rootDir;

    let changeQueue: Promise<null | void> = Promise.resolve();
    let eventsQueue: EventsQueue = [];
    // We only need to copy the entire haste map once on every "frame".
    let mustCopy = true;

    const createWatcher = (root: string): Promise<Watcher> => {
      const watcher = new Watcher(root, {
        dot: true,
        glob: extensions.map(extension => `**/*.${extension}`),
        ignored: ignorePattern,
      });

      return new Promise((resolve, reject) => {
        const rejectTimeout = setTimeout(
          () => reject(new Error('Failed to start watch mode.')),
          MAX_WAIT_TIME,
        );

        watcher.once('ready', () => {
          clearTimeout(rejectTimeout);
          watcher.on('all', onChange);
          resolve(watcher);
        });
      });
    };

    const emitChange = () => {
      if (eventsQueue.length) {
        mustCopy = true;
        const changeEvent: ChangeEvent = {
          eventsQueue,
          hasteFS: new HasteFS({files: hasteMap.files, rootDir}),
          moduleMap: new HasteModuleMap({
            duplicates: hasteMap.duplicates,
            map: hasteMap.map,
            mocks: hasteMap.mocks,
            rootDir,
          }),
        };
        this.emit('change', changeEvent);
        eventsQueue = [];
      }
    };

    const onChange = (
      type: string,
      filePath: string,
      root: string,
      stat?: Stats,
    ) => {
      filePath = path.join(root, normalizePathSep(filePath));
      if (
        (stat && stat.isDirectory()) ||
        this._ignore(filePath) ||
        !extensions.some(extension => filePath.endsWith(extension))
      ) {
        return;
      }

      const relativeFilePath = fastPath.relative(rootDir, filePath);
      const fileMetadata = hasteMap.files.get(relativeFilePath);

      // The file has been accessed, not modified
      if (
        type === 'change' &&
        fileMetadata &&
        stat &&
        fileMetadata[H.MTIME] === stat.mtime.getTime()
      ) {
        return;
      }

      changeQueue = changeQueue
        .then(() => {
          // If we get duplicate events for the same file, ignore them.
          if (
            eventsQueue.find(
              event =>
                event.type === type &&
                event.filePath === filePath &&
                ((!event.stat && !stat) ||
                  (!!event.stat &&
                    !!stat &&
                    event.stat.mtime.getTime() === stat.mtime.getTime())),
            )
          ) {
            return null;
          }

          if (mustCopy) {
            mustCopy = false;
            hasteMap = {
              clocks: new Map(hasteMap.clocks),
              duplicates: new Map(hasteMap.duplicates),
              files: new Map(hasteMap.files),
              map: new Map(hasteMap.map),
              mocks: new Map(hasteMap.mocks),
            };
          }

          const add = () => {
            eventsQueue.push({filePath, stat, type});
            return null;
          };

          const fileMetadata = hasteMap.files.get(relativeFilePath);

          // If it's not an addition, delete the file and all its metadata
          if (fileMetadata != null) {
            const moduleName = fileMetadata[H.ID];
            const platform =
              getPlatformExtension(filePath, this._options.platforms) ||
              H.GENERIC_PLATFORM;
            hasteMap.files.delete(relativeFilePath);

            let moduleMap = hasteMap.map.get(moduleName);
            if (moduleMap != null) {
              // We are forced to copy the object because jest-haste-map exposes
              // the map as an immutable entity.
              moduleMap = copy(moduleMap);
              delete moduleMap[platform];
              if (Object.keys(moduleMap).length === 0) {
                hasteMap.map.delete(moduleName);
              } else {
                hasteMap.map.set(moduleName, moduleMap);
              }
            }

            if (
              this._options.mocksPattern &&
              this._options.mocksPattern.test(filePath)
            ) {
              const mockName = getMockName(filePath);
              hasteMap.mocks.delete(mockName);
            }

            this._recoverDuplicates(hasteMap, relativeFilePath, moduleName);
          }

          // If the file was added or changed,
          // parse it and update the haste map.
          if (type === 'add' || type === 'change') {
            invariant(
              stat,
              'since the file exists or changed, it should have stats',
            );
            const fileMetadata: FileMetaData = [
              '',
              stat.mtime.getTime(),
              stat.size,
              0,
              '',
              null,
            ];
            hasteMap.files.set(relativeFilePath, fileMetadata);
            const promise = this._processFile(
              hasteMap,
              hasteMap.map,
              hasteMap.mocks,
              filePath,
              {forceInBand: true},
            );
            // Cleanup
            this._cleanup();
            if (promise) {
              return promise.then(add);
            } else {
              // If a file in node_modules has changed,
              // emit an event regardless.
              add();
            }
          } else {
            add();
          }
          return null;
        })
        .catch((error: Error) => {
          this._console.error(
            `jest-haste-map: watch error:\n  ${error.stack}\n`,
          );
        });
    };

    this._changeInterval = setInterval(emitChange, CHANGE_INTERVAL);
    return Promise.all(this._options.roots.map(createWatcher)).then(
      watchers => {
        this._watchers = watchers;
      },
    );
  }