// 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.ContextQuery;
using Microsoft.CodeAnalysis.CSharp.Utilities;
 
namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders;
 
internal class ImplicitKeywordRecommender : AbstractSyntacticSingleKeywordRecommender
{
    private static readonly ISet<SyntaxKind> s_validNonInterfaceMemberModifiers = new HashSet<SyntaxKind>(SyntaxFacts.EqualityComparer)
        {
            SyntaxKind.StaticKeyword,
            SyntaxKind.PublicKeyword,
            SyntaxKind.ExternKeyword,
            SyntaxKind.UnsafeKeyword,
        };
 
    private static readonly ISet<SyntaxKind> s_validInterfaceMemberModifiers = new HashSet<SyntaxKind>(SyntaxFacts.EqualityComparer)
        {
            SyntaxKind.StaticKeyword,
            SyntaxKind.PublicKeyword,
            SyntaxKind.AbstractKeyword,
            SyntaxKind.UnsafeKeyword,
        };
 
    public ImplicitKeywordRecommender()
        : base(SyntaxKind.ImplicitKeyword)
    {
    }
 
    protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        if (context.IsMemberDeclarationContext(validModifiers: s_validNonInterfaceMemberModifiers, validTypeDeclarations: SyntaxKindSet.ClassStructRecordTypeDeclarations, canBePartial: false, cancellationToken: cancellationToken))
        {
            // operators must be both public and static
            var modifiers = context.PrecedingModifiers;
 
            return
                modifiers.Contains(SyntaxKind.PublicKeyword) &&
                modifiers.Contains(SyntaxKind.StaticKeyword);
        }
        else if (context.IsMemberDeclarationContext(validModifiers: s_validInterfaceMemberModifiers, validTypeDeclarations: SyntaxKindSet.InterfaceOnlyTypeDeclarations, canBePartial: false, cancellationToken: cancellationToken))
        {
            // operators must be both abstract and static
            var modifiers = context.PrecedingModifiers;
 
            return
                modifiers.Contains(SyntaxKind.AbstractKeyword) &&
                modifiers.Contains(SyntaxKind.StaticKeyword);
        }
 
        return false;
    }
}