// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of dart.io;

/**
 * The type of an entity on the file system, such as a file, directory, or link.
 *
 * These constants are used by the [FileSystemEntity] class
 * to indicate the object's type.
 *
 */

class FileSystemEntityType {
  static const FILE = const FileSystemEntityType._internal(0);
  static const DIRECTORY = const FileSystemEntityType._internal(1);
  static const LINK = const FileSystemEntityType._internal(2);
  static const NOT_FOUND = const FileSystemEntityType._internal(3);
  static const _typeList = const [FileSystemEntityType.FILE,
                                  FileSystemEntityType.DIRECTORY,
                                  FileSystemEntityType.LINK,
                                  FileSystemEntityType.NOT_FOUND];
  final int _type;

  const FileSystemEntityType._internal(this._type);

  static FileSystemEntityType _lookup(int type) => _typeList[type];
  String toString() => const ['FILE', 'DIRECTORY', 'LINK', 'NOT_FOUND'][_type];
}

/**
 * A FileStat object represents the result of calling the POSIX stat() function
 * on a file system object.  It is an immutable object, representing the
 * snapshotted values returned by the stat() call.
 */
class FileStat {
  // These must agree with enum FileStat in file.h.
  static const _TYPE = 0;
  static const _CHANGED_TIME = 1;
  static const _MODIFIED_TIME = 2;
  static const _ACCESSED_TIME = 3;
  static const _MODE = 4;
  static const _SIZE = 5;

  static const _notFound = const FileStat._internalNotFound();

  /**
   * The time of the last change to the data or metadata of the file system
   * object.  On Windows platforms, this is instead the file creation time.
   */
  final DateTime changed;
  /**
   * The time of the last change to the data of the file system
   * object.
   */
  final DateTime modified;
  /**
   * The time of the last access to the data of the file system
   * object.  On Windows platforms, this may have 1 day granularity, and be
   * out of date by an hour.
   */
  final DateTime accessed;
  /**
   * The type of the object (file, directory, or link).  If the call to
   * stat() fails, the type of the returned object is NOT_FOUND.
   */
  final FileSystemEntityType type;
  /**
   * The mode of the file system object.  Permissions are encoded in the lower
   * 16 bits of this number, and can be decoded using the [modeString] getter.
   */
  final int mode;
  /**
   * The size of the file system object.
   */
  final int size;

  FileStat._internal(this.changed,
                     this.modified,
                     this.accessed,
                     this.type,
                     this.mode,
                     this.size);

  const FileStat._internalNotFound() :
      changed = null,  modified = null, accessed = null,
      type = FileSystemEntityType.NOT_FOUND, mode = 0, size = -1;

  external static _statSync(String path);


  /**
   * Calls the operating system's stat() function on [path].
   * Returns a [FileStat] object containing the data returned by stat().
   * If the call fails, returns a [FileStat] object with .type set to
   * FileSystemEntityType.NOT_FOUND and the other fields invalid.
   */
  static FileStat statSync(String path) {
    // Trailing path is not supported on Windows.
    if (Platform.isWindows) {
      path = FileSystemEntity._trimTrailingPathSeparators(path);
    }
    var data = _statSync(path);
    if (data is OSError) return FileStat._notFound;
    return new FileStat._internal(
        new DateTime.fromMillisecondsSinceEpoch(data[_CHANGED_TIME]),
        new DateTime.fromMillisecondsSinceEpoch(data[_MODIFIED_TIME]),
        new DateTime.fromMillisecondsSinceEpoch(data[_ACCESSED_TIME]),
        FileSystemEntityType._lookup(data[_TYPE]),
        data[_MODE],
        data[_SIZE]);
  }

  /**
   * Asynchronously calls the operating system's stat() function on [path].
   * Returns a Future which completes with a [FileStat] object containing
   * the data returned by stat().
   * If the call fails, completes the future with a [FileStat] object with
   * .type set to FileSystemEntityType.NOT_FOUND and the other fields invalid.
   */
  static Future<FileStat> stat(String path) {
    // Trailing path is not supported on Windows.
    if (Platform.isWindows) {
      path = FileSystemEntity._trimTrailingPathSeparators(path);
    }
    return _IOService.dispatch(_FILE_STAT, [path]).then((response) {
      if (_isErrorResponse(response)) {
        return FileStat._notFound;
      }
      // Unwrap the real list from the "I'm not an error" wrapper.
      List data = response[1];
      return new FileStat._internal(
          new DateTime.fromMillisecondsSinceEpoch(data[_CHANGED_TIME]),
          new DateTime.fromMillisecondsSinceEpoch(data[_MODIFIED_TIME]),
          new DateTime.fromMillisecondsSinceEpoch(data[_ACCESSED_TIME]),
          FileSystemEntityType._lookup(data[_TYPE]),
          data[_MODE],
          data[_SIZE]);
    });
  }

  String toString() => """
FileStat: type $type
          changed $changed
          modified $modified
          accessed $accessed
          mode ${modeString()}
          size $size""";

  /**
   * Returns the mode value as a human-readable string, in the format
   * "rwxrwxrwx", reflecting the user, group, and world permissions to
   * read, write, and execute the file system object, with "-" replacing the
   * letter for missing permissions.  Extra permission bits may be represented
   * by prepending "(suid)", "(guid)", and/or "(sticky)" to the mode string.
   */
  String modeString() {
    var permissions = mode & 0xFFF;
    var codes = const ['---', '--x', '-w-', '-wx', 'r--', 'r-x', 'rw-', 'rwx'];
    var result = [];
    if ((permissions & 0x800) != 0) result.add("(suid) ");
    if ((permissions & 0x400) != 0) result.add("(guid) ");
    if ((permissions & 0x200) != 0) result.add("(sticky) ");
    result
        ..add(codes[(permissions >> 6) & 0x7])
        ..add(codes[(permissions >> 3) & 0x7])
        ..add(codes[permissions & 0x7]);
    return result.join();
  }
}


/**
 * The common super class for [File], [Directory], and [Link] objects.
 *
 * [FileSystemEntity] objects are returned from directory listing
 * operations. To determine if a FileSystemEntity is a [File], a
 * [Directory], or a [Link] perform a type check:
 *
 *     if (entity is File) (entity as File).readAsStringSync();
 *
 * You can also use the [type] or [typeSync] methods to determine
 * the type of a file system object.
 *
 * Most methods in this class occur in synchronous and asynchronous pairs,
 * for example, [exists] and [existsSync].
 * Unless you have a specific reason for using the synchronous version
 * of a method, prefer the asynchronous version to avoid blocking your program.
 *
 * Here's the exists method in action:
 *
 *     entity.exists().then((isThere) {
 *       isThere ? print('exists') : print('non-existent');
 *     });
 *
 *
 * ## Other resources
 *
 * [Dart by Example](https://www.dartlang.org/dart-by-example/#files-directories-and-symlinks)
 * provides additional task-oriented code samples that show how to use 
 * various API from the [Directory] class and the [File] class,
 * both subclasses of FileSystemEntity.
 *
 * * [I/O for Command-Line Apps](https://www.dartlang.org/docs/dart-up-and-running/contents/ch03.html#ch03-dartio---file-and-socket-io-for-command-line-apps)
 * a section from _A Tour of the Dart Libraries_
 * covers files and directories.
 *
 * * [Write Command-Line Apps](https://www.dartlang.org/docs/tutorials/cmdline/),
 * a tutorial about writing command-line apps, includes information
 * about files and directories.

 */
abstract class FileSystemEntity {
  String get path;

  /**
   * Checks whether the file system entity with this path exists. Returns
   * a [:Future<bool>:] that completes with the result.
   *
   * Since FileSystemEntity is abstract, every FileSystemEntity object
   * is actually an instance of one of the subclasses [File],
   * [Directory], and [Link].  Calling [exists] on an instance of one
   * of these subclasses checks whether the object exists in the file
   * system object exists and is of the correct type (file, directory,
   * or link).  To check whether a path points to an object on the
   * file system, regardless of the object's type, use the [type]
   * static method.
   *
   */
  Future<bool> exists();

  /**
   * Synchronously checks whether the file system entity with this path
   * exists.
   *
   * Since FileSystemEntity is abstract, every FileSystemEntity object
   * is actually an instance of one of the subclasses [File],
   * [Directory], and [Link].  Calling [existsSync] on an instance of
   * one of these subclasses checks whether the object exists in the
   * file system object exists and is of the correct type (file,
   * directory, or link).  To check whether a path points to an object
   * on the file system, regardless of the object's type, use the
   * [typeSync] static method.
   */
  bool existsSync();

  /**
   * Renames this file system entity. Returns a `Future<FileSystemEntity>`
   * that completes with a [FileSystemEntity] instance for the renamed
   * file system entity.
   *
   * If [newPath] identifies an existing entity of the same type, that entity
   * is replaced. If [newPath] identifies an existing entity of a different
   * type, the operation fails and the future completes with an exception.
   */
  Future<FileSystemEntity> rename(String newPath);

   /**
   * Synchronously renames this file system entity. Returns a [FileSystemEntity]
   * instance for the renamed entity.
   *
   * If [newPath] identifies an existing entity of the same type, that entity
   * is replaced. If [newPath] identifies an existing entity of a different
   * type, the operation fails and an exception is thrown.
   */
  FileSystemEntity renameSync(String newPath);

  /**
   * Resolves the path of a file system object relative to the
   * current working directory, resolving all symbolic links on
   * the path and resolving all '..' and '.' path segments.
   * [resolveSymbolicLinks] returns a [:Future<String>:]
   *
   * [resolveSymbolicLinks] uses the operating system's native filesystem api
   * to resolve the path, using the realpath function on linux and
   * Mac OS, and the GetFinalPathNameByHandle function on Windows.
   * If the path does not point to an existing file system object,
   * [resolveSymbolicLinks] completes the returned Future with an FileSystemException.
   *
   * On Windows, symbolic links are resolved to their target before applying
   * a '..' that follows, and on other platforms, the '..' is applied to the
   * symbolic link without resolving it.  The second behavior can be emulated
   * on Windows by processing any '..' segments before calling
   * [resolveSymbolicLinks].  One way of doing this is with the URI class:
   * [:new Uri.parse('.').resolveUri(new Uri.file(input)).toFilePath();],
   * since [resolve] removes '..' segments.
   */
  Future<String> resolveSymbolicLinks() {
    return _IOService.dispatch(_FILE_RESOLVE_SYMBOLIC_LINKS, [path])
        .then((response) {
          if (_isErrorResponse(response)) {
            throw _exceptionFromResponse(response,
                                         "Cannot resolve symbolic links",
                                         path);
          }
          return response;
        });
  }

  /**
   * Resolves the path of a file system object relative to the
   * current working directory, resolving all symbolic links on
   * the path and resolving all '..' and '.' path segments.
   *
   * [resolveSymbolicLinksSync] uses the operating system's native
   * filesystem api to resolve the path, using the realpath function
   * on linux and Mac OS, and the GetFinalPathNameByHandle function on Windows.
   * If the path does not point to an existing file system object,
   * [resolveSymbolicLinksSync] throws a FileSystemException.
   *
   * On Windows, symbolic links are resolved to their target before applying
   * a '..' that follows, and on other platforms, the '..' is applied to the
   * symbolic link without resolving it.  The second behavior can be emulated
   * on Windows by processing any '..' segments before calling
   * [resolveSymbolicLinks].  One way of doing this is with the URI class:
   * [:new Uri.parse('.').resolveUri(new Uri.file(input)).toFilePath();],
   * since [resolve] removes '..' segments.
   */
  String resolveSymbolicLinksSync() {
    var result = _resolveSymbolicLinks(path);
    _throwIfError(result, "Cannot resolve symbolic links", path);
    return result;
  }


  /**
   * Calls the operating system's stat() function on the [path] of this
   * [FileSystemEntity].  Identical to [:FileStat.stat(this.path):].
   *
   * Returns a [:Future<FileStat>:] object containing the data returned by
   * stat().
   *
   * If the call fails, completes the future with a [FileStat] object
   * with .type set to
   * FileSystemEntityType.NOT_FOUND and the other fields invalid.
   */
  Future<FileStat> stat();

  /**
   * Synchronously calls the operating system's stat() function on the
   * [path] of this [FileSystemEntity].
   * Identical to [:FileStat.statSync(this.path):].
   *
   * Returns a [FileStat] object containing the data returned by stat().
   *
   * If the call fails, returns a [FileStat] object with .type set to
   * FileSystemEntityType.NOT_FOUND and the other fields invalid.
   */
  FileStat statSync();

  /**
   * Deletes this [FileSystemEntity].
   *
   * If the [FileSystemEntity] is a directory, and if [recursive] is false,
   * the directory must be empty. Otherwise, if [recursive] is true, the
   * directory and all sub-directories and files in the directories are
   * deleted. Links are not followed when deleting recursively. Only the link
   * is deleted, not its target.
   *
   * If [recursive] is true, the [FileSystemEntity] is deleted even if the type
   * of the [FileSystemEntity] doesn't match the content of the file system.
   * This behavior allows [delete] to be used to unconditionally delete any file
   * system object.
   *
   * Returns a [:Future<FileSystemEntity>:] that completes with this
   * [FileSystemEntity] when the deletion is done. If the [FileSystemEntity]
   * cannot be deleted, the future completes with an exception.
   */
  Future<FileSystemEntity> delete({bool recursive: false})
      => _delete(recursive: recursive);

  /**
   * Synchronously deletes this [FileSystemEntity].
   *
   * If the [FileSystemEntity] is a directory, and if [recursive] is false,
   * the directory must be empty. Otherwise, if [recursive] is true, the
   * directory and all sub-directories and files in the directories are
   * deleted. Links are not followed when deleting recursively. Only the link
   * is deleted, not its target.
   *
   * If [recursive] is true, the [FileSystemEntity] is deleted even if the type
   * of the [FileSystemEntity] doesn't match the content of the file system.
   * This behavior allows [deleteSync] to be used to unconditionally delete any
   * file system object.
   *
   * Throws an exception if the [FileSystemEntity] cannot be deleted.
   */
  void deleteSync({bool recursive: false})
      => _deleteSync(recursive: recursive);


  /**
   * Start watching the [FileSystemEntity] for changes.
   *
   * The implementation uses platform-dependent event-based APIs for receiving
   * file-system notifications, thus behavior depends on the platform.
   *
   *   * `Windows`: Uses `ReadDirectoryChangesW`. The implementation only
   *     supports watching directories. Recursive watching is supported.
   *   * `Linux`: Uses `inotify`. The implementation supports watching both
   *     files and directories. Recursive watching is not supported.
   *     Note: When watching files directly, delete events might not happen
   *     as expected.
   *   * `Mac OS`: Uses `FSEvents`. The implementation supports watching both
   *     files and directories. Recursive watching is supported.
   *
   * The system will start listening for events once the returned [Stream] is
   * being listened to, not when the call to [watch] is issued.
   *
   * The returned value is an endless broadcast [Stream], that only stops when
   * one of the following happends:
   *
   *   * The [Stream] is canceled, e.g. by calling `cancel` on the
   *      [StreamSubscription].
   *   * The [FileSystemEntity] being watches, is deleted.
   *
   * Use `events` to specify what events to listen for. The constants in
   * [FileSystemEvent] can be or'ed together to mix events. Default is
   * [FileSystemEvent.ALL].
   */
  Stream<FileSystemEvent> watch({int events: FileSystemEvent.ALL,
                                 bool recursive: false})
     => _FileSystemWatcher.watch(_trimTrailingPathSeparators(path),
                                 events,
                                 recursive);

  Future<FileSystemEntity> _delete({bool recursive: false});
  void _deleteSync({bool recursive: false});

  /**
   * Checks whether two paths refer to the same object in the
   * file system. Returns a [:Future<bool>:] that completes with the result.
   *
   * Comparing a link to its target returns false, as does comparing two links
   * that point to the same target.  To check the target of a link, use
   * Link.target explicitly to fetch it.  Directory links appearing
   * inside a path are followed, though, to find the file system object.
   *
   * Completes the returned Future with an error if one of the paths points
   * to an object that does not exist.
   */
  static Future<bool> identical(String path1, String path2) {
    return _IOService.dispatch(_FILE_IDENTICAL, [path1, path2]).then((response) {
      if (_isErrorResponse(response)) {
        throw _exceptionFromResponse(response,
            "Error in FileSystemEntity.identical($path1, $path2)", "");
      }
      return response;
    });
  }

  static final RegExp _absoluteWindowsPathPattern =
      new RegExp(r'^(\\\\|[a-zA-Z]:[/\\])');

  /**
   * Returns a [bool] indicating whether this object's path is absolute.
   *
   * On Windows, a path is absolute if it starts with \\ or a drive letter
   * between a and z (upper or lower case) followed by :\ or :/.
   * On non-Windows, a path is absolute if it starts with /.
   */
  bool get isAbsolute {
    if (Platform.isWindows) {
      return path.startsWith(_absoluteWindowsPathPattern);
    } else {
      return path.startsWith('/');
    }
  }

  /**
   * Returns a [FileSystemEntity] whose path is the absolute path to [this].
   * The type of the returned instance is the type of [this].
   *
   * The absolute path is computed by prefixing
   * a relative path with the current working directory, and returning
   * an absolute path unchanged.
   */
  FileSystemEntity get absolute;

  String get _absolutePath {
    if (isAbsolute) return path;
    String current = Directory.current.path;
    if (current.endsWith('/') ||
        (Platform.isWindows && current.endsWith('\\'))) {
      return '$current$path';
    } else {
      return '$current${Platform.pathSeparator}$path';
    }
  }


  /**
   * Synchronously checks whether two paths refer to the same object in the
   * file system.
   *
   * Comparing a link to its target returns false, as does comparing two links
   * that point to the same target.  To check the target of a link, use
   * Link.target explicitly to fetch it.  Directory links appearing
   * inside a path are followed, though, to find the file system object.
   *
   * Throws an error if one of the paths points to an object that does not
   * exist.
   */
  static bool identicalSync(String path1, String path2) {
    var result = _identical(path1, path2);
    _throwIfError(result, 'Error in FileSystemEntity.identicalSync');
    return result;
  }

  /**
   * Test if [watch] is supported on the current system.
   *
   * Mac OS 10.6 and below is not supported.
   */
  static bool get isWatchSupported => _FileSystemWatcher.isSupported;

  /**
   * Finds the type of file system object that a path points to. Returns
   * a [:Future<FileSystemEntityType>:] that completes with the result.
   *
   * [FileSystemEntityType] has the constant instances FILE, DIRECTORY,
   * LINK, and NOT_FOUND.  [type] will return LINK only if the optional
   * named argument [followLinks] is false, and [path] points to a link.
   * If the path does not point to a file system object, or any other error
   * occurs in looking up the path, NOT_FOUND is returned.  The only
   * error or exception that may be put on the returned future is ArgumentError,
   * caused by passing the wrong type of arguments to the function.
   */
  static Future<FileSystemEntityType> type(String path,
                                           {bool followLinks: true})
      => _getTypeAsync(path, followLinks).then(FileSystemEntityType._lookup);

  /**
   * Synchronously finds the type of file system object that a path points to.
   * Returns a [FileSystemEntityType].
   *
   * [FileSystemEntityType] has the constant instances FILE, DIRECTORY,
   * LINK, and NOT_FOUND.  [type] will return LINK only if the optional
   * named argument [followLinks] is false, and [path] points to a link.
   * If the path does not point to a file system object, or any other error
   * occurs in looking up the path, NOT_FOUND is returned.  The only
   * error or exception that may be thrown is ArgumentError,
   * caused by passing the wrong type of arguments to the function.
   */
  static FileSystemEntityType typeSync(String path, {bool followLinks: true})
      => FileSystemEntityType._lookup(_getTypeSync(path, followLinks));

  /**
   * Checks if type(path, followLinks: false) returns
   * FileSystemEntityType.LINK.
   */
  static Future<bool> isLink(String path) => _getTypeAsync(path, false)
      .then((type) => (type == FileSystemEntityType.LINK._type));

  /**
   * Checks if type(path) returns FileSystemEntityType.FILE.
   */
  static Future<bool> isFile(String path) => _getTypeAsync(path, true)
      .then((type) => (type == FileSystemEntityType.FILE._type));

  /**
   * Checks if type(path) returns FileSystemEntityType.DIRECTORY.
   */
  static Future<bool> isDirectory(String path) => _getTypeAsync(path, true)
      .then((type) => (type == FileSystemEntityType.DIRECTORY._type));

  /**
   * Synchronously checks if typeSync(path, followLinks: false) returns
   * FileSystemEntityType.LINK.
   */
  static bool isLinkSync(String path) =>
      (_getTypeSync(path, false) == FileSystemEntityType.LINK._type);

  /**
   * Synchronously checks if typeSync(path) returns
   * FileSystemEntityType.FILE.
   */
  static bool isFileSync(String path) =>
      (_getTypeSync(path, true) == FileSystemEntityType.FILE._type);

  /**
   * Synchronously checks if typeSync(path) returns
   * FileSystemEntityType.DIRECTORY.
   */
  static bool isDirectorySync(String path) =>
      (_getTypeSync(path, true) == FileSystemEntityType.DIRECTORY._type);

  external static _getType(String path, bool followLinks);
  external static _identical(String path1, String path2);
  external static _resolveSymbolicLinks(String path);

  // Finds the next-to-last component when dividing at path separators.
  static final RegExp _parentRegExp = Platform.isWindows ?
     new RegExp(r'[^/\\][/\\]+[^/\\]') :
     new RegExp(r'[^/]/+[^/]');

  /**
   * Removes the final path component of a path, using the platform's
   * path separator to split the path.  Will not remove the root component
   * of a Windows path, like "C:\" or "\\server_name\".
   * Ignores trailing path separators, and leaves no trailing path separators.
   */
  static String parentOf(String path) {
    int rootEnd = -1;
    if (Platform.isWindows) {
      if (path.startsWith(_absoluteWindowsPathPattern)) {
        // Root ends at first / or \ after the first two characters.
        rootEnd = path.indexOf(new RegExp(r'[/\\]'), 2);
        if (rootEnd == -1) return path;
      } else if (path.startsWith('\\') || path.startsWith('/')) {
        rootEnd = 0;
      }
    } else if (path.startsWith('/')) {
      rootEnd = 0;
    }
    // Ignore trailing slashes.
    // All non-trivial cases have separators between two non-separators.
    int pos = path.lastIndexOf(_parentRegExp);
    if (pos > rootEnd) {
      return path.substring(0, pos + 1);
    } else if (rootEnd > -1) {
      return path.substring(0, rootEnd + 1);
    } else {
      return '.';
    }
  }

  /**
   * The directory containing [this].  If [this] is a root
   * directory, returns [this].
   */
  Directory get parent => new Directory(parentOf(path));

  static int _getTypeSync(String path, bool followLinks) {
    var result = _getType(path, followLinks);
    _throwIfError(result, 'Error getting type of FileSystemEntity');
    return result;
  }

  static Future<int> _getTypeAsync(String path, bool followLinks) {
    return _IOService.dispatch(_FILE_TYPE, [path, followLinks])
      .then((response) {
        if (_isErrorResponse(response)) {
          throw _exceptionFromResponse(response, "Error getting type", path);
        }
        return response;
      });
  }

  static _throwIfError(Object result, String msg, [String path]) {
    if (result is OSError) {
      throw new FileSystemException(msg, path, result);
    } else if (result is ArgumentError) {
      throw result;
    }
  }

  static String _trimTrailingPathSeparators(String path) {
    // Don't handle argument errors here.
    if (path is! String) return path;
    if (Platform.isWindows) {
      while (path.length > 1 &&
             (path.endsWith(Platform.pathSeparator) ||
              path.endsWith('/'))) {
        path = path.substring(0, path.length - 1);
      }
    } else {
      while (path.length > 1 && path.endsWith(Platform.pathSeparator)) {
        path = path.substring(0, path.length - 1);
      }
    }
    return path;
  }

  static String _ensureTrailingPathSeparators(String path) {
    // Don't handle argument errors here.
    if (path is! String) return path;
    if (path.isEmpty) path = '.';
    if (Platform.isWindows) {
      while (!path.endsWith(Platform.pathSeparator) && !path.endsWith('/')) {
        path = "$path${Platform.pathSeparator}";
      }
    } else {
      while (!path.endsWith(Platform.pathSeparator)) {
        path = "$path${Platform.pathSeparator}";
      }
    }
    return path;
  }
}


/**
 * Base event class emitted by [FileSystemEntity.watch].
 */
class FileSystemEvent {
  /**
   * Bitfield for [FileSystemEntity.watch], to enable [FileSystemCreateEvent]s.
   */
  static const int CREATE = 1 << 0;

  /**
   * Bitfield for [FileSystemEntity.watch], to enable [FileSystemModifyEvent]s.
   */
  static const int MODIFY = 1 << 1;

  /**
   * Bitfield for [FileSystemEntity.watch], to enable [FileSystemDeleteEvent]s.
   */
  static const int DELETE = 1 << 2;

  /**
   * Bitfield for [FileSystemEntity.watch], to enable [FileSystemMoveEvent]s.
   */
  static const int MOVE = 1 << 3;

  /**
   * Bitfield for [FileSystemEntity.watch], for enabling all of [CREATE],
   * [MODIFY], [DELETE] and [MOVE].
   */
  static const int ALL = CREATE | MODIFY | DELETE | MOVE;

  static const int _MODIFY_ATTRIBUTES = 1 << 4;
  static const int _DELETE_SELF = 1 << 5;
  static const int _IS_DIR = 1 << 6;

  /**
   * The type of event. See [FileSystemEvent] for a list of events.
   */
  final int type;

  /**
   * The path that triggered the event. Depending on the platform and the
   * FileSystemEntity, the path may be relative.
   */
  final String path;

  /**
   * Is `true` if the event target was a directory.
   */
  final bool isDirectory;

  FileSystemEvent._(this.type, this.path, this.isDirectory);
}


/**
 * File system event for newly created file system objects.
 */
class FileSystemCreateEvent extends FileSystemEvent {
  FileSystemCreateEvent._(path, isDirectory)
      : super._(FileSystemEvent.CREATE, path, isDirectory);

  String toString() => "FileSystemCreateEvent('$path')";
}


/**
 * File system event for modifications of file system objects.
 */
class FileSystemModifyEvent extends FileSystemEvent {
  /**
   * If the content was changed and not only the attributes, [contentChanged]
   * is `true`.
   */
  final bool contentChanged;

  FileSystemModifyEvent._(path, isDirectory, this.contentChanged)
      : super._(FileSystemEvent.MODIFY, path, isDirectory);

  String toString() =>
      "FileSystemModifyEvent('$path', contentChanged=$contentChanged)";
}


/**
 * File system event for deletion of file system objects.
 */
class FileSystemDeleteEvent extends FileSystemEvent {
  FileSystemDeleteEvent._(path, isDirectory)
      : super._(FileSystemEvent.DELETE, path, isDirectory);

  String toString() => "FileSystemDeleteEvent('$path')";
}


/**
 * File system event for moving of file system objects.
 */
class FileSystemMoveEvent extends FileSystemEvent {
  /**
   * If the underlaying implementation is able to identify the destination of
   * the moved file, [destination] will be set. Otherwise, it will be `null`.
   */
  final String destination;

  FileSystemMoveEvent._(path, isDirectory, this.destination)
      : super._(FileSystemEvent.MOVE, path, isDirectory);

  String toString() {
    var buffer = new StringBuffer();
    buffer.write("FileSystemMoveEvent('$path'");
    if (destination != null) buffer.write(", '$destination'");
    buffer.write(')');
    return buffer.toString();
  }
}


class _FileSystemWatcher {
  external static Stream<FileSystemEvent> watch(
      String path, int events, bool recursive);
  external static bool get isSupported;
}