// 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.Threading;
using Microsoft.CodeAnalysis.CSharp.Extensions.ContextQuery;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Shared.Extensions;
 
namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders
{
    internal class TypeVarKeywordRecommender : AbstractSyntacticSingleKeywordRecommender
    {
        public TypeVarKeywordRecommender()
            : base(SyntaxKind.TypeVarKeyword)
        {
        }
 
        protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
        {
            var token = context.TargetToken;
 
            if (token.Kind() == SyntaxKind.OpenBracketToken &&
                token.Parent.IsKind(SyntaxKind.AttributeList))
            {
                var typeParameters = token.GetAncestor<TypeParameterListSyntax>();
                var type = typeParameters.GetAncestorOrThis<TypeDeclarationSyntax>();
 
                if (type != null && type.TypeParameterList == typeParameters)
                {
                    return true;
                }
 
                var @delegate = typeParameters.GetAncestorOrThis<DelegateDeclarationSyntax>();
                if (@delegate != null && @delegate.TypeParameterList == typeParameters)
                {
                    return true;
                }
 
                var method = typeParameters.GetAncestorOrThis<MethodDeclarationSyntax>();
                if (method != null && method.TypeParameterList == typeParameters)
                {
                    return true;
                }
            }
 
            return false;
        }
    }
}