// 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 ThisKeywordRecommender : AbstractSyntacticSingleKeywordRecommender
{
    public ThisKeywordRecommender()
        : base(SyntaxKind.ThisKeyword)
    {
    }
 
    protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        return
            IsInstanceExpressionOrStatement(context) ||
            IsThisParameterModifierContext(context) ||
            IsConstructorInitializerContext(context);
    }
 
    private static bool IsInstanceExpressionOrStatement(CSharpSyntaxContext context)
    {
        if (context.IsInstanceContext)
        {
            return context.IsNonAttributeExpressionContext || context.IsStatementContext;
        }
 
        return false;
    }
 
    private static bool IsConstructorInitializerContext(CSharpSyntaxContext context)
    {
        // cases:
        //   Goo() : |
 
        var token = context.TargetToken;
 
        if (token.Kind() == SyntaxKind.ColonToken &&
            token.Parent is ConstructorInitializerSyntax &&
            token.Parent.IsParentKind(SyntaxKind.ConstructorDeclaration))
        {
            var constructor = token.GetRequiredAncestor<ConstructorDeclarationSyntax>();
            if (constructor.Modifiers.Any(SyntaxKind.StaticKeyword))
            {
                return false;
            }
 
            return true;
        }
 
        return false;
    }
 
    private static bool IsThisParameterModifierContext(CSharpSyntaxContext context)
    {
        if (context.SyntaxTree.IsParameterModifierContext(
                context.Position, context.LeftToken, includeOperators: false, out var parameterIndex, out var previousModifier))
        {
            if (previousModifier is SyntaxKind.None or
                SyntaxKind.RefKeyword or
                SyntaxKind.InKeyword or
                SyntaxKind.ReadOnlyKeyword)
            {
                if (parameterIndex == 0 &&
                    context.SyntaxTree.IsPossibleExtensionMethodContext(context.LeftToken))
                {
                    return true;
                }
            }
        }
 
        return false;
    }
 
    protected override bool ShouldPreselect(CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        var outerType = context.SemanticModel.GetEnclosingNamedType(context.Position, cancellationToken);
        return context.InferredTypes.Any(static (t, outerType) => Equals(t, outerType), outerType);
    }
}