// 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.Collections.Generic;
using System.Threading;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Extensions.ContextQuery;
using Microsoft.CodeAnalysis.CSharp.Utilities;
 
namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders
{
    internal class AsyncKeywordRecommender : AbstractSyntacticSingleKeywordRecommender
    {
        public AsyncKeywordRecommender()
            : base(SyntaxKind.AsyncKeyword, isValidInPreprocessorContext: false)
        {
        }
 
        private static readonly ISet<SyntaxKind> s_validLocalFunctionModifiers = new HashSet<SyntaxKind>(SyntaxFacts.EqualityComparer)
        {
            SyntaxKind.StaticKeyword,
            SyntaxKind.UnsafeKeyword
        };
 
        protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
        {
            if (context.TargetToken.IsKindOrHasMatchingText(SyntaxKind.PartialKeyword) ||
                context.PrecedingModifiers.Contains(SyntaxKind.AsyncKeyword))
            {
                return false;
            }
 
            return InMemberDeclarationContext(position, context, cancellationToken)
                || context.SyntaxTree.IsLambdaDeclarationContext(position, otherModifier: SyntaxKind.StaticKeyword, cancellationToken)
                || context.SyntaxTree.IsLocalFunctionDeclarationContext(position, s_validLocalFunctionModifiers, cancellationToken);
        }
 
        private static bool InMemberDeclarationContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
        {
            return context.IsGlobalStatementContext
                || context.SyntaxTree.IsGlobalMemberDeclarationContext(position, SyntaxKindSet.AllGlobalMemberModifiers, cancellationToken)
                || context.IsMemberDeclarationContext(
                    validModifiers: SyntaxKindSet.AllMemberModifiers,
                    validTypeDeclarations: SyntaxKindSet.ClassInterfaceStructRecordTypeDeclarations,
                    canBePartial: true,
                    cancellationToken: cancellationToken);
        }
    }
}