content: // 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;
  
  /**
   * [Link] objects are references to filesystem links.
   *
   */
  abstract class Link implements FileSystemEntity {
    /**
     * Creates a Link object.
     */
    factory Link(String path) => new _Link(path);
  
    /**
     * Creates a symbolic link. Returns a [:Future<Link>:] that completes with
     * the link when it has been created. If the link exists,
     * the future will complete with an error.
     *
     * If [recursive] is false, the default, the link is created
     * only if all directories in its path exist.
     * If [recursive] is true, all non-existing path
     * components are created. The directories in the path of [target] are
     * not affected, unless they are also in [path].
     *
     * On the Windows platform, this will only work with directories, and the
     * target directory must exist. The link will be created as a Junction.
     * Only absolute links will be created, and relative paths to the target
     * will be converted to absolute paths by joining them with the path of the
     * directory the link is contained in.
     *
     * On other platforms, the posix symlink() call is used to make a symbolic
     * link containing the string [target].  If [target] is a relative path,
     * it will be interpreted relative to the directory containing the link.
     */
    Future<Link> create(String target, {bool recursive: false});
  
    /**
     * Synchronously create the link. Calling [createSync] on an existing link
     * will throw an exception.
     *
     * If [recursive] is false, the default, the link is created only if all
     * directories in its path exist. If [recursive] is true, all
     * non-existing path components are created. The directories in
     * the path of [target] are not affected, unless they are also in [path].
     *
     * On the Windows platform, this will only work with directories, and the
     * target directory must exist. The link will be created as a Junction.
     * Only absolute links will be created, and relative paths to the target
     * will be converted to absolute paths.
     *
     * On other platforms, the posix symlink() call is used to make a symbolic
     * link containing the string [target].  If [target] is a relative path,
     * it will be interpreted relative to the directory containing the link.
     */
    void createSync(String target, {bool recursive: false});
  
    /**
     * Synchronously updates the link. Calling [updateSync] on a non-existing link
     * will throw an exception.
     *
     * On the Windows platform, this will only work with directories, and the
     * target directory must exist.
     */
    void updateSync(String target);
  
    /**
     * Updates the link. Returns a [:Future<Link>:] that completes with the
     * link when it has been updated.  Calling [update] on a non-existing link
     * will complete its returned future with an exception.
     *
     * On the Windows platform, this will only work with directories, and the
     * target directory must exist.
     */
    Future<Link> update(String target);
  
    Future<String> resolveSymbolicLinks();
  
    String resolveSymbolicLinksSync();
  
    /**
     * Renames this link. Returns a `Future<Link>` that completes
     * with a [Link] instance for the renamed link.
     *
     * If [newPath] identifies an existing link, that link is
     * replaced. If [newPath] identifies an existing file or directory,
     * the operation fails and the future completes with an exception.
     */
    Future<Link> rename(String newPath);
  
     /**
     * Synchronously renames this link. Returns a [Link]
     * instance for the renamed link.
     *
     * If [newPath] identifies an existing link, that link is
     * replaced. If [newPath] identifies an existing file or directory
     * the operation fails and an exception is thrown.
     */
    Link renameSync(String newPath);
  
    /**
     * Returns a [Link] instance whose path is the absolute path to [this].
     *
     * The absolute path is computed by prefixing
     * a relative path with the current working directory, and returning
     * an absolute path unchanged.
     */
    Link get absolute;
  
    /**
     * Gets the target of the link. Returns a future that completes with
     * the path to the target.
     *
     * If the returned target is a relative path, it is relative to the
     * directory containing the link.
     *
     * If the link does not exist, or is not a link, the future completes with
     * a FileSystemException.
     */
    Future<String> target();
  
    /**
     * Synchronously gets the target of the link. Returns the path to the target.
     *
     * If the returned target is a relative path, it is relative to the
     * directory containing the link.
     *
     * If the link does not exist, or is not a link, throws a FileSystemException.
     */
    String targetSync();
  }
  
  
  class _Link extends FileSystemEntity implements Link {
    final String path;
  
    _Link(String this.path) {
      if (path is! String) {
        throw new ArgumentError('${Error.safeToString(path)} '
                                'is not a String');
      }
    }
  
  
    String toString() => "Link: '$path'";
  
    Future<bool> exists() => FileSystemEntity.isLink(path);
  
    bool existsSync() => FileSystemEntity.isLinkSync(path);
  
    Link get absolute => new Link(_absolutePath);
  
    Future<FileStat> stat() => FileStat.stat(path);
  
    FileStat statSync() => FileStat.statSync(path);
  
    Future<Link> create(String target, {bool recursive: false}) {
      if (Platform.operatingSystem == 'windows') {
        target = _makeWindowsLinkTarget(target);
      }
      return (recursive ? parent.create(recursive: true)
                        : new Future.value(null))
        .then((_) => _IOService.dispatch(_FILE_CREATE_LINK, [path, target]))
        .then((response) {
          if (_isErrorResponse(response)) {
            throw _exceptionFromResponse(
                response, "Cannot create link to target '$target'", path);
          }
          return this;
        });
    }
  
    void createSync(String target, {bool recursive: false}) {
      if (recursive) {
        parent.createSync(recursive: true);
      }
      if (Platform.operatingSystem == 'windows') {
        target = _makeWindowsLinkTarget(target);
      }
      var result = _File._createLink(path, target);
      throwIfError(result, "Cannot create link", path);
    }
  
    // Put target into the form "\??\C:\my\target\dir".
    String _makeWindowsLinkTarget(String target) {
      Uri base = new Uri.file('${Directory.current.path}\\');
      Uri link = new Uri.file(path);
      Uri destination = new Uri.file(target);
      String result = base.resolveUri(link).resolveUri(destination).toFilePath();
      if (result.length > 3 && result[1] == ':' && result[2] == '\\') {
        return '\\??\\$result';
      } else {
        throw new FileSystemException(
            'Target $result of Link.create on Windows cannot be converted' +
            ' to start with a drive letter.  Unexpected error.');
      }
    }
  
    void updateSync(String target) {
      // TODO(12414): Replace with atomic update, where supported by platform.
      // Atomically changing a link can be done by creating the new link, with
      // a different name, and using the rename() posix call to move it to
      // the old name atomically.
      deleteSync();
      createSync(target);
    }
  
    Future<Link> update(String target) {
      // TODO(12414): Replace with atomic update, where supported by platform.
      // Atomically changing a link can be done by creating the new link, with
      // a different name, and using the rename() posix call to move it to
      // the old name atomically.
      return delete().then((_) => create(target));
    }
  
    Future<Link> _delete({bool recursive: false}) {
      if (recursive) {
        return new Directory(path).delete(recursive: true).then((_) => this);
      }
      return _IOService.dispatch(_FILE_DELETE_LINK, [path]).then((response) {
        if (_isErrorResponse(response)) {
          throw _exceptionFromResponse(response, "Cannot delete link", path);
        }
        return this;
      });
    }
  
    void _deleteSync({bool recursive: false}) {
      if (recursive) {
        return new Directory(path).deleteSync(recursive: true);
      }
      var result = _File._deleteLinkNative(path);
      throwIfError(result, "Cannot delete link", path);
    }
  
    Future<Link> rename(String newPath) {
      return _IOService.dispatch(_FILE_RENAME_LINK, [path, newPath])
          .then((response) {
            if (_isErrorResponse(response)) {
              throw _exceptionFromResponse(
                  response, "Cannot rename link to '$newPath'", path);
            }
            return new Link(newPath);
          });
    }
  
    Link renameSync(String newPath) {
      var result = _File._renameLink(path, newPath);
      throwIfError(result, "Cannot rename link '$path' to '$newPath'");
      return new Link(newPath);
    }
  
    Future<String> target() {
      return _IOService.dispatch(_FILE_LINK_TARGET, [path]).then((response) {
        if (_isErrorResponse(response)) {
          throw _exceptionFromResponse(
              response, "Cannot get target of link", path);
        }
        return response;
      });
    }
  
    String targetSync() {
      var result = _File._linkTarget(path);
      throwIfError(result, "Cannot read link", path);
      return result;
    }
  
    static throwIfError(Object result, String msg, [String path = ""]) {
      if (result is OSError) {
        throw new FileSystemException(msg, path, result);
      }
    }
  
    bool _isErrorResponse(response) {
      return response is List && response[0] != _SUCCESS_RESPONSE;
    }
  
    _exceptionFromResponse(response, String message, String path) {
      assert(_isErrorResponse(response));
      switch (response[_ERROR_RESPONSE_ERROR_TYPE]) {
        case _ILLEGAL_ARGUMENT_RESPONSE:
          return new ArgumentError();
        case _OSERROR_RESPONSE:
          var err = new OSError(response[_OSERROR_RESPONSE_MESSAGE],
                                response[_OSERROR_RESPONSE_ERROR_CODE]);
          return new FileSystemException(message, path, err);
        default:
          return new Exception("Unknown error");
      }
    }
  }
  