64 lines
2.0 KiB
Dart
Executable File
64 lines
2.0 KiB
Dart
Executable File
// Copyright 2017, the Chromium project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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import 'dart:math';
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/// Utility class for generating Firebase child node keys.
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///
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/// Since the Flutter plugin API is asynchronous, there's no way for us
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/// to use the native SDK to generate the node key synchronously and we
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/// have to do it ourselves if we want to be able to reference the
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/// newly-created node synchronously.
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///
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/// This code is based on a Firebase blog post and ported to Dart.
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/// https://firebase.googleblog.com/2015/02/the-2120-ways-to-ensure-unique_68.html
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class PushIdGenerator {
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static const String PUSH_CHARS =
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'-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz';
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static final Random _random = Random();
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static int? _lastPushTime;
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static final List<int?> _lastRandChars = List<int?>.filled(12, null, growable: false);
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static String generatePushChildName() {
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int now = DateTime.now().millisecondsSinceEpoch;
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final bool duplicateTime = (now == _lastPushTime);
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_lastPushTime = now;
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final List<String?> timeStampChars = List<String?>.filled(8, null, growable: false);
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for (int i = 7; i >= 0; i--) {
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timeStampChars[i] = PUSH_CHARS[now % 64];
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now = (now / 64).floor();
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}
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assert(now == 0);
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final StringBuffer result = StringBuffer(timeStampChars.join());
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if (!duplicateTime) {
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for (int i = 0; i < 12; i++) {
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_lastRandChars[i] = _random.nextInt(64);
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}
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} else {
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_incrementArray();
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}
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for (int i = 0; i < 12; i++) {
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result.write(PUSH_CHARS[_lastRandChars[i]!]);
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}
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assert(result.length == 20);
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return result.toString();
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}
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static void _incrementArray() {
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for (int i = 11; i >= 0; i--) {
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if (_lastRandChars[i] != 63) {
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_lastRandChars[i] = _lastRandChars[i]! + 1;
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return;
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}
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_lastRandChars[i] = 0;
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}
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}
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}
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