// Copyright (c) 2017, 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.

library vm.constants_native_effects;

import '../ast.dart';
import '../transformations/constants.dart';
import '../core_types.dart';

class VmConstantsBackend extends ConstantsBackend {
  final Class immutableMapClass;

  VmConstantsBackend._(this.immutableMapClass);

  /// If [defines] is not `null` it will be used for handling
  /// `const {bool,...}.fromEnvironment()` otherwise the current VM's values
  /// will be used.
  factory VmConstantsBackend(CoreTypes coreTypes) {
    final Library coreLibrary = coreTypes.coreLibrary;
    final Class immutableMapClass = coreLibrary.classes
        .firstWhere((Class klass) => klass.name == '_ImmutableMap');
    assert(immutableMapClass != null);

    return new VmConstantsBackend._(immutableMapClass);
  }

  @override
  Constant lowerConstant(Constant constant) {
    if (constant is MapConstant) {
      // The _ImmutableMap class is implemented via one field pointing to a list
      // of key/value pairs -- see runtime/lib/immutable_map.dart!
      final List<Constant> kvListPairs =
          new List<Constant>(2 * constant.entries.length);
      for (int i = 0; i < constant.entries.length; i++) {
        final ConstantMapEntry entry = constant.entries[i];
        kvListPairs[2 * i] = entry.key;
        kvListPairs[2 * i + 1] = entry.value;
      }
      // This is a bit fishy, since we merge the key and the value type by
      // putting both into the same list.
      final kvListConstant = new ListConstant(const DynamicType(), kvListPairs);
      assert(immutableMapClass.fields.length == 1);
      final Field kvPairListField = immutableMapClass.fields[0];
      return new InstanceConstant(immutableMapClass.reference, <DartType>[
        constant.keyType,
        constant.valueType,
      ], <Reference, Constant>{
        kvPairListField.reference: kvListConstant,
      });
    }

    return constant;
  }
}