// 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 IntoKeywordRecommender() : AbstractSyntacticSingleKeywordRecommender(SyntaxKind.IntoKeyword)
{
    protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        return
            IsValidContextForJoin(context) ||
            IsValidContextForSelect(context) ||
            IsValidContextForGroup(context);
    }

    private static bool IsValidContextForSelect(CSharpSyntaxContext context)
    {
        var token = context.TargetToken;

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

        if (select.Expression.Width() == 0)
        {
            return false;
        }

        // cases:
        //   select x.|
        //   select x.i|
        var lastCompleteToken = token.GetPreviousTokenIfTouchingWord(context.Position);
        if (lastCompleteToken.Kind() == SyntaxKind.DotToken)
        {
            return false;
        }

        var lastToken = select.Expression.GetLastToken(includeSkipped: true);
        if (lastToken == token)
        {
            return true;
        }

        return false;
    }

    private static bool IsValidContextForGroup(CSharpSyntaxContext context)
    {
        var token = context.TargetToken;

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

        if (group.ByExpression.Width() == 0 ||
            group.GroupExpression.Width() == 0)
        {
            return false;
        }

        var lastToken = group.ByExpression.GetLastToken(includeSkipped: true);

        if (lastToken == token)
        {
            return true;
        }

        return false;
    }

    private static bool IsValidContextForJoin(CSharpSyntaxContext context)
    {
        // cases:
        //   join a in expr o1 equals o2 |
        //   join a in expr o1 equals o2 i|

        var token = context.TargetToken;
        var join = token.GetAncestor<JoinClauseSyntax>();

        if (join == null)
        {
            // happens for:
            //   join a in expr on o1 equals o2 e|
            if (!token.IntersectsWith(context.Position))
            {
                return false;
            }

            token = token.GetPreviousToken(includeSkipped: true);
            join = token.GetAncestor<JoinClauseSyntax>();

            if (join == null)
            {
                return false;
            }
        }

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

        // join a in expr on o1 equals o2 |
        if (token == lastToken &&
            !lastToken.IntersectsWith(context.Position))
        {
            return true;
        }

        return false;
    }
}