﻿// 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.Linq;
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)
                {
                    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);
        }
    }
}
