// 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 sealed class CheckedKeywordRecommender() : AbstractSyntacticSingleKeywordRecommender(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;
    }
}