// Copyright 2019 Dart Mockito authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import 'package:analyzer/dart/constant/value.dart';
import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/dart/element/type.dart' as analyzer;
import 'package:build/build.dart';
import 'package:code_builder/code_builder.dart';
import 'package:dart_style/dart_style.dart';

/// For a source Dart library, generate the mocks referenced therein.
///
/// Given an input library, 'foo.dart', this builder will search the top-level
/// elements for an annotation, `@GenerateMocks`, from the mockito package. For
/// example:
///
/// ```dart
/// @GenerateMocks([Foo])
/// void main() {}
/// ```
///
/// If this builder finds any classes to mock (for example, `Foo`, above), it
/// will produce a "'.mocks.dart' file with such mocks. In this example,
/// 'foo.mocks.dart' will be created.
class MockBuilder implements Builder {
  @override
  Future build(BuildStep buildStep) async {
    final entryLib = await buildStep.inputLibrary;
    final resolver = buildStep.resolver;

    final mockLibraryAsset = buildStep.inputId.changeExtension('.mocks.dart');

    final mockLibrary = Library((lBuilder) {
      for (final element in entryLib.topLevelElements) {
        final annotation = element.metadata.firstWhere(
            (annotation) =>
                annotation.element is ConstructorElement &&
                annotation.element.enclosingElement.name == 'GenerateMocks',
            orElse: () => null);
        if (annotation == null) continue;
        final generateMocksValue = annotation.computeConstantValue();
        // TODO(srawlins): handle `generateMocksValue == null`?
        final classesToMock = generateMocksValue.getField('classes');
        if (classesToMock.isNull) {
          throw InvalidMockitoAnnotationException(
              'The "classes" argument has unknown types');
        }

        _buildMockClasses(classesToMock.toListValue(), lBuilder);
      }
    });

    if (mockLibrary.body.isEmpty) {
      // Nothing to mock here!
      return;
    }

    final emitter = DartEmitter.scoped();
    final mockLibraryContent =
        DartFormatter().format(mockLibrary.accept(emitter).toString());

    await buildStep.writeAsString(mockLibraryAsset, mockLibraryContent);
  }

  /// Build mock classes for [classesToMock], a list of classes obtained from a
  /// `@GenerateMocks` annotation.
  void _buildMockClasses(
      List<DartObject> classesToMock, LibraryBuilder lBuilder) {
    for (final classToMock in classesToMock) {
      final dartTypeToMock = classToMock.toTypeValue();
      if (dartTypeToMock == null) {
        throw InvalidMockitoAnnotationException(
            'The "classes" argument includes a non-type: $classToMock');
      }

      final elementToMock = dartTypeToMock.element;
      if (elementToMock is ClassElement) {
        if (elementToMock.isEnum) {
          throw InvalidMockitoAnnotationException(
              'The "classes" argument includes an enum: '
              '${elementToMock.displayName}');
        }
        // TODO(srawlins): Catch when someone tries to generate mocks for an
        // un-subtypable class, like bool, String, FutureOr, etc.
        lBuilder.body.add(_buildCodeForClass(dartTypeToMock, elementToMock));
      } else if (elementToMock is GenericFunctionTypeElement &&
          elementToMock.enclosingElement is FunctionTypeAliasElement) {
        throw InvalidMockitoAnnotationException(
            'The "classes" argument includes a typedef: '
            '${elementToMock.enclosingElement.displayName}');
      } else {
        throw InvalidMockitoAnnotationException(
            'The "classes" argument includes a non-class: '
            '${elementToMock.displayName}');
      }
    }
  }

  Class _buildCodeForClass(
      analyzer.DartType dartType, ClassElement classToMock) {
    final className = dartType.displayName;

    return Class((cBuilder) {
      cBuilder
        ..name = 'Mock$className'
        ..extend = refer('Mock', 'package:mockito/mockito.dart')
        ..docs.add('/// A class which mocks [$className].')
        ..docs.add('///')
        ..docs.add('/// See the documentation for Mockito\'s code generation '
            'for more information.');
      // For each type parameter on [classToMock], the Mock class needs a type
      // parameter with same type variables, and a mirrored type argument for
      // the "implements" clause.
      var typeArguments = <Reference>[];
      if (classToMock.typeParameters != null) {
        for (var typeParameter in classToMock.typeParameters) {
          cBuilder.types.add(_typeParameterReference(typeParameter));
          typeArguments.add(refer(typeParameter.name));
        }
      }
      cBuilder.implements.add(TypeReference((b) {
        b
          ..symbol = dartType.name
          ..url = _typeImport(dartType)
          ..types.addAll(typeArguments);
      }));
      for (final field in classToMock.fields) {
        if (field.isPrivate || field.isStatic) {
          continue;
        }
        // Handle getters when we handle non-nullable return types.
        final setter = field.setter;
        if (setter != null) {
          cBuilder.methods.add(
              Method((mBuilder) => _buildOverridingSetter(mBuilder, setter)));
        }
      }
      for (final method in classToMock.methods) {
        if (method.isPrivate || method.isStatic) {
          continue;
        }
        if (_returnTypeIsNonNullable(method) ||
            _hasNonNullableParameter(method)) {
          cBuilder.methods.add(
              Method((mBuilder) => _buildOverridingMethod(mBuilder, method)));
        }
      }
    });
  }

  // TODO(srawlins): Update this logic to correctly handle non-nullable return
  // types. Right now this logic does not seem to be available on DartType.
  bool _returnTypeIsNonNullable(MethodElement method) {
    var type = method.returnType;
    if (type.isDynamic || type.isVoid) return false;
    if (method.isAsynchronous && type.isDartAsyncFuture ||
        type.isDartAsyncFutureOr) {
      var typeArgument = (type as analyzer.InterfaceType).typeArguments.first;
      if (typeArgument.isDynamic || typeArgument.isVoid) {
        // An asynchronous method which returns `Future<void>`, for example,
        // does not need a dummy return value.
        return false;
      }
    }
    return true;
  }

  // TODO(srawlins): Update this logic to correctly handle non-nullable return
  // types. Right now this logic does not seem to be available on DartType.
  bool _hasNonNullableParameter(MethodElement method) =>
      method.parameters.isNotEmpty;

  /// Build a method which overrides [method], with all non-nullable
  /// parameter types widened to be nullable.
  ///
  /// This new method just calls `super.noSuchMethod`, optionally passing a
  /// return value for methods with a non-nullable return type.
  // TODO(srawlins): This method does no widening yet. Widen parameters. Include
  // tests for typedefs, old-style function parameters, and function types.
  // TODO(srawlins): This method declares no specific non-null return values
  // yet.
  void _buildOverridingMethod(MethodBuilder builder, MethodElement method) {
    // TODO(srawlins): generator methods like async*, sync*.
    // TODO(srawlins): abstract methods?
    builder
      ..name = method.displayName
      ..returns = _typeReference(method.returnType);

    if (method.typeParameters != null) {
      builder.types.addAll(method.typeParameters.map(_typeParameterReference));
    }

    if (method.isAsynchronous) {
      builder.modifier =
          method.isGenerator ? MethodModifier.asyncStar : MethodModifier.async;
    } else if (method.isGenerator) {
      builder.modifier = MethodModifier.syncStar;
    }

    // These two variables store the arguments that will be passed to the
    // [Invocation] built for `noSuchMethod`.
    final invocationPositionalArgs = <Expression>[];
    final invocationNamedArgs = <Expression, Expression>{};

    for (final parameter in method.parameters) {
      if (parameter.isRequiredPositional) {
        builder.requiredParameters.add(_matchingParameter(parameter));
        invocationPositionalArgs.add(refer(parameter.displayName));
      } else if (parameter.isOptionalPositional) {
        builder.optionalParameters.add(_matchingParameter(parameter));
        invocationPositionalArgs.add(refer(parameter.displayName));
      } else if (parameter.isNamed) {
        builder.optionalParameters.add(_matchingParameter(parameter));
        invocationNamedArgs[refer('#${parameter.displayName}')] =
            refer(parameter.displayName);
      }
    }
    // TODO(srawlins): Optionally pass a non-null return value to `noSuchMethod`
    // which `Mock.noSuchMethod` will simply return, in order to satisfy runtime
    // type checks.
    // TODO(srawlins): Handle getter invocations with `Invocation.getter`,
    // and operators???
    final invocation = refer('Invocation').property('method').call([
      refer('#${method.displayName}'),
      literalList(invocationPositionalArgs),
      if (invocationNamedArgs.isNotEmpty) literalMap(invocationNamedArgs),
    ]);
    final noSuchMethodArgs = <Expression>[invocation];
    if (_returnTypeIsNonNullable(method)) {
      final dummyReturnValue = _dummyValue(method.returnType);
      noSuchMethodArgs.add(dummyReturnValue);
    }
    final returnNoSuchMethod =
        refer('super').property('noSuchMethod').call(noSuchMethodArgs);

    builder.body = returnNoSuchMethod.code;
  }

  Expression _dummyValue(analyzer.DartType type) {
    if (type.isDartCoreBool) {
      return literalFalse;
    } else if (type.isDartCoreDouble) {
      return literalNum(0.0);
    } else if (type.isDartAsyncFuture || type.isDartAsyncFutureOr) {
      var typeArgument = (type as analyzer.InterfaceType).typeArguments.first;
      return refer('Future')
          .property('value')
          .call([_dummyValue(typeArgument)]);
    } else if (type.isDartCoreInt) {
      return literalNum(0);
    } else if (type.isDartCoreList) {
      return literalList([]);
    } else if (type.isDartCoreMap) {
      return literalMap({});
    } else if (type.isDartCoreNum) {
      return literalNum(0);
    } else if (type.isDartCoreSet) {
      // This is perhaps a dangerous hack. The code, `{}`, is parsed as a Set
      // literal if it is used in a context which explicitly expects a Set.
      return literalMap({});
    } else if (type.isDartCoreString) {
      return literalString('');
    } else {
      // TODO(srawlins): Returning null for now, but really this should only
      // ever get to a state where we have to make a Fake class which implements
      // the type, and return a no-op constructor call to that Fake class here.
      return literalNull;
    }
  }

  /// Returns a [Parameter] which matches [parameter].
  Parameter _matchingParameter(ParameterElement parameter) =>
      Parameter((pBuilder) {
        pBuilder
          ..name = parameter.displayName
          ..type = _typeReference(parameter.type);
        if (parameter.isNamed) pBuilder.named = true;
        if (parameter.defaultValueCode != null) {
          pBuilder.defaultTo = Code(parameter.defaultValueCode);
        }
      });

  /// Build a setter which overrides [setter], widening the single parameter
  /// type to be nullable if it is non-nullable.
  ///
  /// This new setter just calls `super.noSuchMethod`.
  // TODO(srawlins): This method does no widening yet.
  void _buildOverridingSetter(
      MethodBuilder builder, PropertyAccessorElement setter) {
    builder
      ..name = setter.displayName
      ..type = MethodType.setter;

    final invocationPositionalArgs = <Expression>[];
    // There should only be one required positional parameter. Should we assert
    // on that? Leave it alone?
    for (final parameter in setter.parameters) {
      if (parameter.isRequiredPositional) {
        builder.requiredParameters.add(Parameter((pBuilder) => pBuilder
          ..name = parameter.displayName
          ..type = _typeReference(parameter.type)));
        invocationPositionalArgs.add(refer(parameter.displayName));
      }
    }

    final invocation = refer('Invocation').property('setter').call([
      refer('#${setter.displayName}'),
      literalList(invocationPositionalArgs),
    ]);
    final returnNoSuchMethod =
        refer('super').property('noSuchMethod').call([invocation]);

    builder.body = returnNoSuchMethod.code;
  }

  /// Create a reference for [typeParameter], properly referencing all types
  /// in bounds.
  TypeReference _typeParameterReference(TypeParameterElement typeParameter) {
    return TypeReference((b) {
      b.symbol = typeParameter.name;
      if (typeParameter.bound != null) {
        b.bound = _typeReference(typeParameter.bound);
      }
    });
  }

  /// Create a reference for [type], properly referencing all attached types.
  ///
  /// This creates proper references for:
  /// * [InterfaceType]s (classes, generic classes),
  /// * FunctionType parameters (like `void callback(int i)`),
  /// * type aliases (typedefs), both new- and old-style.
  // TODO(srawlins): Contribute this back to a common location, like
  // package:source_gen?
  Reference _typeReference(analyzer.DartType type) {
    if (type is analyzer.InterfaceType) {
      return TypeReference((TypeReferenceBuilder trBuilder) {
        trBuilder
          ..symbol = type.name
          ..url = _typeImport(type);
        for (var typeArgument in type.typeArguments) {
          trBuilder.types.add(_typeReference(typeArgument));
        }
      });
    } else if (type is analyzer.FunctionType) {
      GenericFunctionTypeElement element = type.element;
      if (element == null) {
        // [type] represents a FunctionTypedFormalParameter.
        return FunctionType((b) {
          b
            ..returnType = _typeReference(type.returnType)
            ..requiredParameters
                .addAll(type.normalParameterTypes.map(_typeReference))
            ..optionalParameters
                .addAll(type.optionalParameterTypes.map(_typeReference));
          for (var parameter in type.namedParameterTypes.entries) {
            b.namedParameters[parameter.key] = _typeReference(parameter.value);
          }
        });
      }
      return TypeReference((TypeReferenceBuilder trBuilder) {
        var typedef = element.enclosingElement;
        trBuilder
          ..symbol = typedef.name
          ..url = _typeImport(type);
        for (var typeArgument in type.typeArguments)
          trBuilder.types.add(_typeReference(typeArgument));
      });
    } else {
      return refer(type.displayName, _typeImport(type));
    }
  }

  /// Returns the import URL for [type].
  ///
  /// For some types, like `dynamic`, this may return null.
  String _typeImport(analyzer.DartType type) {
    var library = type.element?.library;

    // For types like `dynamic`, return null; no import needed.
    if (library == null) return null;
    // TODO(srawlins): See what other code generators do here to guarantee sane
    // URIs.
    return library.source.uri.toString();
  }

  @override
  final buildExtensions = const {
    '.dart': ['.mocks.dart']
  };
}

/// An exception which is thrown when Mockito encounters an invalid annotation.
class InvalidMockitoAnnotationException implements Exception {
  final String message;

  InvalidMockitoAnnotationException(this.message);

  @override
  String toString() => 'Invalid @GenerateMocks annotation: $message';
}