// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
#nullable disable
 
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using System.Threading;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CodeGeneration;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.GenerateMember.GenerateParameterizedMember;
 
internal partial class AbstractGenerateParameterizedMemberService<TService, TSimpleNameSyntax, TExpressionSyntax, TInvocationExpressionSyntax>
{
    internal abstract class AbstractInvocationInfo : SignatureInfo
    {
        protected abstract bool IsIdentifierName();
 
        protected abstract ImmutableArray<ITypeParameterSymbol> GetCapturedTypeParameters(CancellationToken cancellationToken);
        protected abstract ImmutableArray<ITypeParameterSymbol> GenerateTypeParameters(CancellationToken cancellationToken);
 
        protected AbstractInvocationInfo(SemanticDocument document, State state)
            : base(document, state)
        {
        }
 
        protected override ImmutableArray<ITypeParameterSymbol> DetermineTypeParametersWorker(
            CancellationToken cancellationToken)
        {
            var typeParameters = ComputeTypeParameters(cancellationToken);
            return typeParameters.SelectAsArray(MassageTypeParameter);
        }
 
        private ImmutableArray<ITypeParameterSymbol> ComputeTypeParameters(
            CancellationToken cancellationToken)
        {
            if (IsIdentifierName())
            {
                // If the user wrote something like Goo(x) then we still might want to generate
                // a generic method if the expression 'x' captured any method type variables.
                var capturedTypeParameters = GetCapturedTypeParameters(cancellationToken);
                var availableTypeParameters = State.TypeToGenerateIn.GetAllTypeParameters();
                var result = capturedTypeParameters.Except<ITypeParameterSymbol>(availableTypeParameters, SymbolEqualityComparer.Default).ToImmutableArray();
                return result;
            }
            else
            {
                return GenerateTypeParameters(cancellationToken);
            }
        }
 
        private ITypeParameterSymbol MassageTypeParameter(
            ITypeParameterSymbol typeParameter)
        {
            var constraints = typeParameter.ConstraintTypes.Where(ts => !ts.IsUnexpressibleTypeParameterConstraint()).ToList();
            var classTypes = constraints.Where(ts => ts.TypeKind == TypeKind.Class).ToList();
            var nonClassTypes = constraints.Where(ts => ts.TypeKind != TypeKind.Class).ToList();
 
            classTypes = MergeClassTypes(classTypes);
            constraints = [.. classTypes, .. nonClassTypes];
            if (constraints.SequenceEqual(typeParameter.ConstraintTypes))
            {
                return typeParameter;
            }
 
            return CodeGenerationSymbolFactory.CreateTypeParameter(
                attributes: default,
                varianceKind: typeParameter.Variance,
                name: typeParameter.Name,
                constraintTypes: constraints.AsImmutable(),
                hasConstructorConstraint: typeParameter.HasConstructorConstraint,
                hasReferenceConstraint: typeParameter.HasReferenceTypeConstraint,
                hasValueConstraint: typeParameter.HasValueTypeConstraint,
                hasUnmanagedConstraint: typeParameter.HasUnmanagedTypeConstraint,
                hasNotNullConstraint: typeParameter.HasNotNullConstraint);
        }
 
        private List<ITypeSymbol> MergeClassTypes(List<ITypeSymbol> classTypes)
        {
            var compilation = Document.SemanticModel.Compilation;
            for (var i = classTypes.Count - 1; i >= 0; i--)
            {
                // For example, 'Attribute'.
                var type1 = classTypes[i];
 
                for (var j = 0; j < classTypes.Count; j++)
                {
                    if (j != i)
                    {
                        // For example 'GooAttribute'.
                        var type2 = classTypes[j];
 
                        if (IsImplicitReferenceConversion(compilation, type2, type1))
                        {
                            // If there's an implicit reference conversion (i.e. from
                            // GooAttribute to Attribute), then we don't need Attribute as it's
                            // implied by the second attribute;
                            classTypes.RemoveAt(i);
                            break;
                        }
                    }
                }
            }
 
            return classTypes;
        }
 
        protected abstract bool IsImplicitReferenceConversion(Compilation compilation, ITypeSymbol sourceType, ITypeSymbol targetType);
    }
}