// 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;
using Microsoft.CodeAnalysis.CSharp.Extensions.ContextQuery;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Shared.Extensions;
 
namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders;
 
internal class CheckedKeywordRecommender : AbstractSyntacticSingleKeywordRecommender
{
    public CheckedKeywordRecommender()
        : base(SyntaxKind.CheckedKeyword)
    {
    }
 
    protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        if (context.IsStatementContext ||
            context.IsGlobalStatementContext ||
            context.IsNonAttributeExpressionContext)
        {
            return true;
        }
 
        var targetToken = context.TargetToken;
 
        if (targetToken.Kind() == SyntaxKind.OperatorKeyword)
        {
            var previousPossiblySkippedToken = targetToken.GetPreviousToken(includeSkipped: true);
 
            if (previousPossiblySkippedToken.IsLastTokenOfNode<TypeSyntax>())
            {
                return true;
            }
 
            SyntaxToken previousToken;
 
            if (previousPossiblySkippedToken.IsLastTokenOfNode<ExplicitInterfaceSpecifierSyntax>())
            {
                var firstSpecifierToken = previousPossiblySkippedToken.GetRequiredAncestor<ExplicitInterfaceSpecifierSyntax>().GetFirstToken(includeSkipped: true);
 
                if (firstSpecifierToken.GetPreviousToken(includeSkipped: true).IsLastTokenOfNode<TypeSyntax>())
                {
                    return true;
                }
 
                previousToken = firstSpecifierToken.GetPreviousToken(includeSkipped: false);
            }
            else
            {
                previousToken = targetToken.GetPreviousToken(includeSkipped: false);
            }
 
            if (previousToken.Kind() == SyntaxKind.ExplicitKeyword)
            {
                return true;
            }
        }
 
        return false;
    }
}