// 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.
 
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Syntax;
 
namespace Microsoft.CodeAnalysis.CSharp.Extensions
{
    internal static class ITypeParameterSymbolExtensions
    {
        public static SyntaxList<TypeParameterConstraintClauseSyntax> GenerateConstraintClauses(
            this ImmutableArray<ITypeParameterSymbol> typeParameters)
        {
            return typeParameters.AsEnumerable().GenerateConstraintClauses();
        }
 
        public static SyntaxList<TypeParameterConstraintClauseSyntax> GenerateConstraintClauses(
            this IEnumerable<ITypeParameterSymbol> typeParameters)
        {
            var clauses = new List<TypeParameterConstraintClauseSyntax>();
 
            foreach (var typeParameter in typeParameters)
            {
                AddConstraintClauses(clauses, typeParameter);
            }
 
            return clauses.Count == 0 ? default : clauses.ToSyntaxList();
        }
 
        private static void AddConstraintClauses(
            List<TypeParameterConstraintClauseSyntax> clauses,
            ITypeParameterSymbol typeParameter)
        {
            var constraints = new List<TypeParameterConstraintSyntax>();
 
            if (typeParameter.HasReferenceTypeConstraint)
            {
                constraints.Add(SyntaxFactory.ClassOrStructConstraint(SyntaxKind.ClassConstraint));
            }
            else if (typeParameter.HasUnmanagedTypeConstraint)
            {
                constraints.Add(SyntaxFactory.TypeConstraint(SyntaxFactory.IdentifierName("unmanaged")));
            }
            else if (typeParameter.HasValueTypeConstraint)
            {
                constraints.Add(SyntaxFactory.ClassOrStructConstraint(SyntaxKind.StructConstraint));
            }
            else if (typeParameter.HasNotNullConstraint)
            {
                constraints.Add(SyntaxFactory.TypeConstraint(SyntaxFactory.IdentifierName("notnull")));
            }
 
            var constraintTypes =
                typeParameter.ConstraintTypes.Where(t => t.TypeKind == TypeKind.Class).Concat(
                typeParameter.ConstraintTypes.Where(t => t.TypeKind == TypeKind.Interface).Concat(
                typeParameter.ConstraintTypes.Where(t => t.TypeKind is not TypeKind.Class and not TypeKind.Interface)));
 
            foreach (var type in constraintTypes)
            {
                if (type.SpecialType != SpecialType.System_Object)
                {
                    constraints.Add(SyntaxFactory.TypeConstraint(type.GenerateTypeSyntax()));
                }
            }
 
            if (typeParameter.HasConstructorConstraint)
            {
                constraints.Add(SyntaxFactory.ConstructorConstraint());
            }
 
            if (constraints.Count == 0)
            {
                return;
            }
 
            clauses.Add(SyntaxFactory.TypeParameterConstraintClause(
                typeParameter.Name.ToIdentifierName(),
                SyntaxFactory.SeparatedList(constraints)));
        }
    }
}