// Copyright (c) 2018, 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 dart2js.js_emitter.instantiation_stub_generator;

import '../elements/entities.dart';
import '../io/source_information.dart';
import '../js/js.dart' as jsAst;
import '../js/js.dart' show js;
import '../js_backend/namer.dart' show Namer;
import '../universe/call_structure.dart' show CallStructure;
import '../universe/selector.dart' show Selector;
import '../universe/world_builder.dart'
    show CodegenWorldBuilder, SelectorConstraints;
import '../world.dart' show ClosedWorld;

import 'model.dart';

import 'code_emitter_task.dart' show CodeEmitterTask;

// Generator of stubs required for Instantiation classes.
class InstantiationStubGenerator {
  // ignore: UNUSED_FIELD
  final CodeEmitterTask _emitterTask;
  final Namer _namer;
  final CodegenWorldBuilder _codegenWorldBuilder;
  final ClosedWorld _closedWorld;
  // ignore: UNUSED_FIELD
  final SourceInformationStrategy _sourceInformationStrategy;

  InstantiationStubGenerator(
      this._emitterTask,
      this._namer,
      this._codegenWorldBuilder,
      this._closedWorld,
      this._sourceInformationStrategy);

  /// Generates a stub to forward a call selector with no type arguments to a
  /// call selector with stored types.
  ///
  /// [instantiationClass] is the class containing the captured type arguments.
  /// [callSelector] is the selector with no type arguments. [targetSelector] is
  /// the selector accepting the type arguments.
  ParameterStubMethod _generateStub(
      ClassEntity instantiationClass,
      FieldEntity functionField,
      Selector callSelector,
      Selector targetSelector) {
    // TODO(sra): Generate source information for stub that has no member.
    //
    //SourceInformationBuilder sourceInformationBuilder =
    //    _sourceInformationStrategy.createBuilderForContext(member);
    //SourceInformation sourceInformation =
    //    sourceInformationBuilder.buildStub(member, callStructure);

    assert(callSelector.typeArgumentCount == 0);
    int typeArgumentCount = targetSelector.typeArgumentCount;
    assert(typeArgumentCount > 0);

    // The forwarding stub for three arguments of an instantiation with two type
    // arguments looks like this:
    //
    // ```
    // call$3: function(a0, a1, a2) {
    //   return this._f.call$2$3(a0, a1, a2, this.$ti[0], this.$ti[1]);
    // }
    // ```

    List<jsAst.Parameter> parameters = <jsAst.Parameter>[];
    List<jsAst.Expression> arguments = <jsAst.Expression>[];

    for (int i = 0; i < callSelector.argumentCount; i++) {
      String jsName = 'a$i';
      arguments.add(js('#', jsName));
      parameters.add(new jsAst.Parameter(jsName));
    }

    for (int i = 0; i < targetSelector.typeArgumentCount; i++) {
      arguments.add(js('this.#[#]', [_namer.rtiFieldJsName, js.number(i)]));
    }

    jsAst.Fun function = js('function(#) { return this.#.#(#); }', [
      parameters,
      _namer.fieldPropertyName(functionField),
      _namer.invocationName(targetSelector),
      arguments,
    ]);
    // TODO(sra): .withSourceInformation(sourceInformation);

    jsAst.Name name = _namer.invocationName(callSelector);
    return new ParameterStubMethod(name, null, function);
  }

  // Returns all stubs for an instantiation class.
  //
  List<StubMethod> generateStubs(
      ClassEntity instantiationClass, FunctionEntity member) {
    // 1. Find the number of type parameters in [instantiationClass].
    int typeArgumentCount = _closedWorld.dartTypes
        .getThisType(instantiationClass)
        .typeArguments
        .length;
    assert(typeArgumentCount > 0);

    // 2. Find the function field access path.
    FieldEntity functionField;
    _codegenWorldBuilder.forEachInstanceField(instantiationClass,
        (ClassEntity enclosing, FieldEntity field) {
      if (field.name == '_genericClosure') functionField = field;
    });
    assert(functionField != null,
        "Can't find Closure field of $instantiationClass");

    String call = _namer.closureInvocationSelectorName;
    Map<Selector, SelectorConstraints> callSelectors =
        _codegenWorldBuilder.invocationsByName(call);

    List<StubMethod> stubs = <StubMethod>[];

    // For every call-selector generate a stub to the corresponding selector
    // with filled-in type arguments.

    for (Selector selector in callSelectors.keys) {
      CallStructure callStructure = selector.callStructure;
      if (callStructure.typeArgumentCount != 0) continue;
      CallStructure genericCallStructrure =
          callStructure.withTypeArgumentCount(typeArgumentCount);
      Selector genericSelector =
          new Selector.call(selector.memberName, genericCallStructrure);
      stubs.add(_generateStub(
          instantiationClass, functionField, selector, genericSelector));
    }

    // TODO(sra): Generate $signature() stub that forwards to
    // $instantiatedSignature() method of _f.

    return stubs;
  }
}