packages/firebase_database/lib/src/database_reference.dart

// Copyright 2017, the Flutter 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 firebase_database;

/// DatabaseReference represents a particular location in your Firebase
/// Database and can be used for reading or writing data to that location.
///
/// This class is the starting point for all Firebase Database operations.
/// After you’ve obtained your first DatabaseReference via
/// `FirebaseDatabase.reference()`, you can use it to read data
/// (ie. `onChildAdded`), write data (ie. `setValue`), and to create new
/// `DatabaseReference`s (ie. `child`).
class DatabaseReference extends Query {
  DatabaseReference._(FirebaseDatabase database, List<String> pathComponents)
    : super._(database, pathComponents);

  /// Gets a DatabaseReference for the location at the specified relative
  /// path. The relative path can either be a simple child key (e.g. ‘fred’) or
  /// a deeper slash-separated path (e.g. ‘fred/name/first’).
  DatabaseReference child(String path) {
    return new DatabaseReference._(
      _database,
      (new List<String>.from(_pathComponents)..addAll(path.split('/')))
    );
  }

  /// Gets a DatabaseReference for the parent location. If this instance
  /// refers to the root of your Firebase Database, it has no parent, and
  /// therefore parent() will return null.
  DatabaseReference parent() {
    if (_pathComponents.isEmpty)
      return null;
    return new DatabaseReference._(
      _database,
      (new List<String>.from(_pathComponents)..removeLast())
    );
  }

  /// Gets a FIRDatabaseReference for the root location.
  DatabaseReference root() {
    return new DatabaseReference._(_database, <String>[]);
  }

  /// Gets the last token in a Firebase Database location (e.g. ‘fred’ in
  /// https://SampleChat.firebaseIO-demo.com/users/fred)
  String get key => _pathComponents.last;

  /// Generates a new child location using a unique key and returns a
  /// DatabaseReference to it. This is useful when the children of a Firebase
  /// Database location represent a list of items.
  ///
  /// The unique key generated by childByAutoId: is prefixed with a
  /// client-generated timestamp so that the resulting list will be
  /// chronologically-sorted.
  DatabaseReference push() {
    String key = PushIdGenerator.generatePushChildName();
    List<String> childPath = new List<String>.from(_pathComponents)..add(key);
    return new DatabaseReference._(_database, childPath);
  }

  /// Write data to this Firebase Database location.
  ///
  /// This will overwrite any data at this location and all child locations.
  ///
  /// Data types that are allowed are String, boolean, int, double, Map, List.
  ///
  /// The effect of the write will be visible immediately and the corresponding
  /// events will be triggered. Synchronization of the data to the Firebase
  /// Database servers will also be started.
  ///
  /// Passing null for the new value means all data at this location or any
  /// child location will be deleted.
  Future<Null> set(dynamic value) async {
    await _database._channel.invokeMethod(
      'DatabaseReference#set',
      { 'path': path, 'value': value },
    );
  }
}
class ServerValue {
  static const timestamp = const {'.sv' : 'timestamp'};
}