packages/flutter_tools/test/src/test_build_system.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';

import 'package:flutter_tools/src/build_system/build_system.dart';

class TestBuildSystem implements BuildSystem {
  /// Create a [BuildSystem] instance that returns the provided results in order.
  TestBuildSystem.list(this._results, [this._onRun])
    : _exception = null,
      _singleResult = null;

  /// Create a [BuildSystem] instance that returns the provided result for every build
  /// and buildIncremental request.
  TestBuildSystem.all(this._singleResult, [this._onRun])
    : _exception = null,
      _results = <BuildResult>[];

  /// Create a [BuildSystem] instance that always throws the provided error for every build
  /// and buildIncremental request.
  TestBuildSystem.error(this._exception)
    : _singleResult = null,
      _results = <BuildResult>[],
      _onRun = null;

  final List<BuildResult> _results;
  final BuildResult? _singleResult;
  final Exception? _exception;
  final void Function(Target target, Environment environment)? _onRun;
  int _nextResult = 0;

  @override
  Future<BuildResult> build(Target target, Environment environment, {BuildSystemConfig buildSystemConfig = const BuildSystemConfig()}) async {
    if (_onRun != null) {
      _onRun?.call(target, environment);
    }
    if (_exception != null) {
      throw _exception!;
    }
    if (_singleResult != null) {
      return _singleResult!;
    }
    if (_nextResult >= _results.length) {
      throw StateError('Unexpected build request of ${target.name}');
    }
    return _results[_nextResult++];
  }

  @override
  Future<BuildResult> buildIncremental(Target target, Environment environment, BuildResult? previousBuild) async {
    if (_onRun != null) {
      _onRun?.call(target, environment);
    }
    if (_exception != null) {
      throw _exception!;
    }
    if (_singleResult != null) {
      return _singleResult!;
    }
    if (_nextResult >= _results.length) {
      throw StateError('Unexpected buildIncremental request of ${target.name}');
    }
    return _results[_nextResult++];
  }
}