// 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;

namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders;

internal sealed class DefaultKeywordRecommender() : AbstractSyntacticSingleKeywordRecommender(SyntaxKind.DefaultKeyword, isValidInPreprocessorContext: true)
{
    protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        return
            IsValidPreProcessorContext(context) ||
            context.IsStatementContext ||
            context.IsGlobalStatementContext ||
            context.IsAnyExpressionContext ||
            context.TargetToken.IsSwitchLabelContext() ||
            context.SyntaxTree.IsTypeParameterConstraintStartContext(position, context.LeftToken);
    }

    private static bool IsValidPreProcessorContext(CSharpSyntaxContext context)
    {
        // cases:
        //   #line |
        //   #line d|
        //   # line |
        //   # line d|

        var previousToken1 = context.TargetToken;
        var previousToken2 = previousToken1.GetPreviousToken(includeSkipped: true);

        return
            previousToken1.Kind() == SyntaxKind.LineKeyword &&
            previousToken2.Kind() == SyntaxKind.HashToken;
    }
}