// 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.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Threading;
using Microsoft.CodeAnalysis.CSharp.Symbols;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Shared.Extensions;
 
namespace Microsoft.CodeAnalysis.CSharp.Extensions;
 
internal static partial class TypeSyntaxExtensions
{
    public static bool IsPotentialTypeName([NotNullWhen(true)] this TypeSyntax? typeSyntax, SemanticModel? semanticModelOpt, CancellationToken cancellationToken)
    {
        if (typeSyntax == null)
        {
            return false;
        }
 
        if (typeSyntax is PredefinedTypeSyntax or
            ArrayTypeSyntax or
            GenericNameSyntax or
            PointerTypeSyntax or
            NullableTypeSyntax)
        {
            return true;
        }
 
        if (semanticModelOpt == null)
        {
            return false;
        }
 
        if (typeSyntax is not NameSyntax nameSyntax)
        {
            return false;
        }
 
        var nameToken = nameSyntax.GetNameToken();
 
        var symbols = semanticModelOpt.LookupName(nameToken, cancellationToken);
        var firstSymbol = symbols.FirstOrDefault();
 
        var typeSymbol = firstSymbol is IAliasSymbol aliasSymbol
            ? aliasSymbol.Target
            : firstSymbol as ITypeSymbol;
 
        return typeSymbol != null
            && !typeSymbol.IsErrorType();
    }
 
    public static TypeSyntax GenerateReturnTypeSyntax(this IMethodSymbol method)
    {
        var returnType = method.ReturnType;
 
        if (method.ReturnsByRef)
        {
            return returnType.GenerateRefTypeSyntax(allowVar: false);
        }
        else if (method.ReturnsByRefReadonly)
        {
            return returnType.GenerateRefReadOnlyTypeSyntax(allowVar: false);
        }
        else
        {
            return returnType.GenerateTypeSyntax(allowVar: false);
        }
    }
}