// 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.

#nullable disable

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 OnKeywordRecommender : AbstractSyntacticSingleKeywordRecommender
    {
        public OnKeywordRecommender()
            : base(SyntaxKind.OnKeyword)
        {
        }

        protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
        {
            // cases:
            //   join a in expr |
            //   join a in expr o|
            //   join a.b c in expr |
            //   join a.b c in expr o|

            var token = context.TargetToken;

            var join = token.GetAncestor<JoinClauseSyntax>();
            if (join == null)
            {
                return false;
            }

            // join a in expr |
            // join a.b c in expr |

            var lastToken = join.InExpression.GetLastToken(includeSkipped: true);

            if (join.InExpression.Width() > 0 &&
                token == lastToken)
            {
                return true;
            }

            return false;
        }
    }
}
