// 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.

import '../ast.dart';
import '../type_algebra.dart';

/// Helper visitor that clones a type if a nested type is replaced, and
/// otherwise returns `null`.
class ReplacementVisitor implements DartTypeVisitor1<DartType?, Variance> {
  const new();

  Nullability? visitNullability(DartType node) => null;

  @override
  DartType? visitFunctionType(FunctionType node, Variance variance) {
    Nullability? newNullability = visitNullability(node);

    StructuralParameterList? newTypeParameters;
    for (int i = 0; i < node.typeParameters.length; i++) {
      StructuralParameter typeParameter = node.typeParameters[i];
      // TODO(johnniwinther): Bounds should not be null, even in case of
      // cyclic typedefs. Currently
      //   instantiate_to_bound/non_simple_class_parametrized_typedef_cycle
      // fails with this.
      DartType? newBound = typeParameter.bound.accept1(
        this,
        variance.combine(Variance.invariant),
      );
      DartType? newDefaultType = typeParameter.defaultType.accept1(
        this,
        variance.combine(Variance.invariant),
      );
      if (newBound != null || newDefaultType != null) {
        newTypeParameters ??= StructuralParameterList.from(node.typeParameters);
        newTypeParameters[i] = new StructuralParameter(
          typeParameter.name,
          newBound ?? typeParameter.bound,
          newDefaultType ?? typeParameter.defaultType,
        );
      }
    }

    FunctionTypeInstantiator? instantiator;
    if (newTypeParameters != null) {
      List<DartType> typeParameterTypes = [
        for (StructuralParameter parameter in newTypeParameters)
          new StructuralParameterType.withDefaultNullability(parameter),
      ];
      instantiator = FunctionTypeInstantiator.fromInstantiation(
        node,
        typeParameterTypes,
      );
      for (int i = 0; i < newTypeParameters.length; i++) {
        newTypeParameters[i].bound = instantiator.substitute(
          newTypeParameters[i].bound,
        );
      }
    }

    DartType? visitType(DartType? type, Variance variance) {
      if (type == null) return null;
      DartType? result = type.accept1(this, variance);
      if (instantiator != null) {
        result = instantiator.substitute(result ?? type);
      }
      return result;
    }

    DartType? newReturnType = visitType(node.returnType, variance);
    DartTypeList? newPositionalParameters = null;
    for (int i = 0; i < node.positionalParameters.length; i++) {
      DartType? newType = visitType(
        node.positionalParameters[i],
        variance.combine(Variance.contravariant),
      );
      if (newType != null) {
        newPositionalParameters ??= DartTypeList.from(
          node.positionalParameters,
        );
        newPositionalParameters[i] = newType;
      }
    }
    NamedDartTypeList? newNamedParameters = null;
    for (int i = 0; i < node.namedParameters.length; i++) {
      DartType? newType = visitType(
        node.namedParameters[i].type,
        variance.combine(Variance.contravariant),
      );
      NamedType? newNamedType = createNamedType(
        node.namedParameters[i],
        newType,
      );
      if (newNamedType != null) {
        newNamedParameters ??= NamedDartTypeList.from(node.namedParameters);
        newNamedParameters[i] = newNamedType;
      }
    }

    return createFunctionType(
      node,
      newNullability,
      newTypeParameters,
      newReturnType,
      newPositionalParameters,
      newNamedParameters,
    );
  }

  @override
  DartType? visitRecordType(RecordType node, Variance variance) {
    Nullability? newNullability = visitNullability(node);

    DartType? visitType(DartType? type, Variance variance) {
      return type?.accept1(this, variance);
    }

    DartTypeList? newPositional = null;
    for (int i = 0; i < node.positional.length; i++) {
      DartType? newType = visitType(node.positional[i], variance);
      if (newType != null) {
        newPositional ??= DartTypeList.from(node.positional);
        newPositional[i] = newType;
      }
    }
    NamedDartTypeList? newNamed = null;
    for (int i = 0; i < node.named.length; i++) {
      DartType? newType = visitType(node.named[i].type, variance);
      NamedType? newNamedType = createNamedType(node.named[i], newType);
      if (newNamedType != null) {
        newNamed ??= NamedDartTypeList.from(node.named);
        newNamed[i] = newNamedType;
      }
    }

    return createRecordType(node, newNullability, newPositional, newNamed);
  }

  NamedType? createNamedType(NamedType node, DartType? newType) {
    if (newType == null) {
      return null;
    } else {
      return new NamedType(node.name, newType, isRequired: node.isRequired);
    }
  }

  DartType? createFunctionType(
    FunctionType node,
    Nullability? newNullability,
    StructuralParameterList? newTypeParameters,
    DartType? newReturnType,
    DartTypeList? newPositionalParameters,
    NamedDartTypeList? newNamedParameters,
  ) {
    if (newNullability == null &&
        newReturnType == null &&
        newPositionalParameters == null &&
        newNamedParameters == null) {
      // No nullability or types had to be substituted.
      return null;
    } else {
      return new FunctionType(
        newPositionalParameters ?? node.positionalParameters,
        newReturnType ?? node.returnType,
        newNullability ?? node.nullability,
        namedParameters: newNamedParameters ?? node.namedParameters,
        typeParameters: newTypeParameters ?? node.typeParameters,
        requiredParameterCount: node.requiredParameterCount,
      );
    }
  }

  DartType? createRecordType(
    RecordType node,
    Nullability? newNullability,
    DartTypeList? newPositional,
    NamedDartTypeList? newNamed,
  ) {
    if (newNullability == null && newPositional == null && newNamed == null) {
      // No nullability or types had to be substituted.
      return null;
    } else {
      return new RecordType(
        newPositional ?? node.positional,
        newNamed ?? node.named,
        newNullability ?? node.nullability,
      );
    }
  }

  @override
  DartType? visitInterfaceType(InterfaceType node, Variance variance) {
    Nullability? newNullability = visitNullability(node);
    DartTypeList? newTypeArguments = null;
    for (int i = 0; i < node.typeArguments.length; i++) {
      DartType? substitution = node.typeArguments[i].accept1(this, variance);
      if (substitution != null) {
        newTypeArguments ??= DartTypeList.from(node.typeArguments);
        newTypeArguments[i] = substitution;
      }
    }
    return createInterfaceType(node, newNullability, newTypeArguments);
  }

  DartType? createInterfaceType(
    InterfaceType node,
    Nullability? newNullability,
    DartTypeList? newTypeArguments,
  ) {
    if (newNullability == null && newTypeArguments == null) {
      // No nullability or type arguments needed to be substituted.
      return null;
    } else {
      return new InterfaceType.byReference(
        node.classReference,
        newNullability ?? node.nullability,
        newTypeArguments ?? node.typeArguments,
      );
    }
  }

  @override
  DartType? visitFutureOrType(FutureOrType node, Variance variance) {
    Nullability? newNullability = visitNullability(node);
    DartType? newTypeArgument = node.typeArgument.accept1(this, variance);
    return createFutureOrType(node, newNullability, newTypeArgument);
  }

  DartType? createFutureOrType(
    FutureOrType node,
    Nullability? newNullability,
    DartType? newTypeArgument,
  ) {
    if (newNullability == null && newTypeArgument == null) {
      // No nullability or type arguments needed to be substituted.
      return null;
    } else {
      newTypeArgument ??= node.typeArgument;
      newNullability ??= node.declaredNullability;

      // The top-level nullability of a FutureOr should remain the same, with
      // the exception of the case of [Nullability.undetermined].  In that case
      // it remains undetermined if the nullability of [typeArgument] is
      // undetermined, and otherwise it should become
      // [Nullability.nonNullable].
      Nullability adjustedNullability;
      if (newNullability == Nullability.undetermined) {
        if (newTypeArgument.nullability == Nullability.undetermined) {
          adjustedNullability = Nullability.undetermined;
        } else {
          adjustedNullability = Nullability.nonNullable;
        }
      } else {
        adjustedNullability = newNullability;
      }

      return new FutureOrType(newTypeArgument, adjustedNullability);
    }
  }

  @override
  DartType? visitDynamicType(DynamicType node, Variance variance) => null;

  @override
  DartType? visitNeverType(NeverType node, Variance variance) {
    Nullability? newNullability = visitNullability(node);
    return createNeverType(node, newNullability);
  }

  DartType? createNeverType(NeverType node, Nullability? newNullability) {
    if (newNullability == null) {
      // No nullability needed to be substituted.
      return null;
    } else {
      return NeverType.fromNullability(newNullability);
    }
  }

  @override
  DartType? visitNullType(NullType node, Variance variance) => null;

  @override
  DartType? visitInvalidType(InvalidType node, Variance variance) => null;

  @override
  DartType? visitVoidType(VoidType node, Variance variance) => null;

  @override
  DartType? visitTypeParameterType(TypeParameterType node, Variance variance) {
    Nullability? newNullability = visitNullability(node);
    return createTypeParameterType(node, newNullability);
  }

  @override
  DartType? visitStructuralParameterType(
    StructuralParameterType node,
    Variance variance,
  ) {
    Nullability? newNullability = visitNullability(node);
    return createStructuralParameterType(node, newNullability);
  }

  @override
  DartType? visitIntersectionType(IntersectionType node, Variance variance) {
    DartType? newLeft = node.left.accept1(this, variance);
    DartType? newRight = node.right.accept1(this, variance);
    return createIntersectionType(
      node,
      newLeft as TypeParameterType?,
      newRight,
    );
  }

  DartType? createTypeParameterType(
    TypeParameterType node,
    Nullability? newNullability,
  ) {
    if (newNullability == null) {
      // No nullability needed to be substituted.
      return null;
    } else {
      return new TypeParameterType(node.parameter, newNullability);
    }
  }

  DartType? createStructuralParameterType(
    StructuralParameterType node,
    Nullability? newNullability,
  ) {
    if (newNullability == null) {
      // No nullability needed to be substituted.
      return null;
    } else {
      return new StructuralParameterType(node.parameter, newNullability);
    }
  }

  DartType? createIntersectionType(
    IntersectionType node,
    TypeParameterType? left,
    DartType? right,
  ) {
    if (left == null && right == null) {
      return null;
    } else {
      return new IntersectionType(left ?? node.left, right ?? node.right);
    }
  }

  @override
  DartType? visitTypedefType(TypedefType node, Variance variance) {
    Nullability? newNullability = visitNullability(node);
    DartTypeList? newTypeArguments = null;
    for (int i = 0; i < node.typeArguments.length; i++) {
      DartType? substitution = node.typeArguments[i].accept1(
        this,
        variance.combine(node.typedefNode.typeParameters[i].variance),
      );
      if (substitution != null) {
        newTypeArguments ??= DartTypeList.from(node.typeArguments);
        newTypeArguments[i] = substitution;
      }
    }
    return createTypedef(node, newNullability, newTypeArguments);
  }

  DartType? createTypedef(
    TypedefType node,
    Nullability? newNullability,
    DartTypeList? newTypeArguments,
  ) {
    if (newNullability == null && newTypeArguments == null) {
      // No nullability or type arguments needed to be substituted.
      return null;
    } else {
      return new TypedefType(
        node.typedefNode,
        newNullability ?? node.nullability,
        newTypeArguments ?? node.typeArguments,
      );
    }
  }

  @override
  DartType? visitExtensionType(ExtensionType node, Variance variance) {
    Nullability? newNullability = visitNullability(node);
    DartTypeList? newTypeArguments = null;
    for (int i = 0; i < node.typeArguments.length; i++) {
      DartType? substitution = node.typeArguments[i].accept1(
        this,
        variance.combine(
          node.extensionTypeDeclaration.typeParameters[i].variance,
        ),
      );
      if (substitution != null) {
        newTypeArguments ??= DartTypeList.from(node.typeArguments);
        newTypeArguments[i] = substitution;
      }
    }
    return createExtensionType(node, newNullability, newTypeArguments);
  }

  DartType? createExtensionType(
    ExtensionType node,
    Nullability? newNullability,
    DartTypeList? newTypeArguments,
  ) {
    if (newNullability == null && newTypeArguments == null) {
      // No nullability or type arguments needed to be substituted.
      return null;
    } else {
      return new ExtensionType(
        node.extensionTypeDeclaration,
        newNullability ?? node.declaredNullability,
        newTypeArguments ?? node.typeArguments,
      );
    }
  }

  @override
  DartType? visitAuxiliaryType(AuxiliaryType node, Variance variance) {
    // TODO(johnniwinther): Use [DartTypeVisitor1AuxiliaryFunction] to handle
    // [AuxiliaryType]s.
    return null;
  }

  @override
  DartType? visitFunctionTypeParameterType(
    FunctionTypeParameterType node,
    Variance arg,
  ) {
    // TODO(cstefantsova): Implement visitFunctionTypeParameterType.
    throw UnimplementedError(
      "Unimplemented support for $node (${node.runtimeType}).",
    );
  }

  @override
  DartType? visitClassTypeParameterType(
    ClassTypeParameterType node,
    Variance arg,
  ) {
    // TODO(cstefantsova): Implement visitClassTypeParameterType.
    throw UnimplementedError(
      "Unimplemented support for $node (${node.runtimeType}).",
    );
  }
}