// 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.Linq;
using System.Threading;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Extensions.ContextQuery;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.CSharp.Utilities;
using Microsoft.CodeAnalysis.Shared.Extensions;
 
namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders;
 
internal class PartialKeywordRecommender : AbstractSyntacticSingleKeywordRecommender
{
    private static readonly ISet<SyntaxKind> s_validMemberModifiers = new HashSet<SyntaxKind>(SyntaxFacts.EqualityComparer)
    {
        SyntaxKind.AsyncKeyword,
        SyntaxKind.StaticKeyword
    };
 
    public PartialKeywordRecommender()
        : base(SyntaxKind.PartialKeyword)
    {
    }
 
    protected override bool IsValidContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        return
            context.IsGlobalStatementContext ||
            IsMemberDeclarationContext(context, cancellationToken) ||
            IsTypeDeclarationContext(context, cancellationToken);
    }
 
    private static bool IsMemberDeclarationContext(CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        if (context.IsMemberDeclarationContext(validModifiers: s_validMemberModifiers, validTypeDeclarations: SyntaxKindSet.ClassInterfaceStructRecordTypeDeclarations, canBePartial: false, cancellationToken: cancellationToken))
        {
            var token = context.LeftToken;
            var decl = token.GetRequiredAncestor<TypeDeclarationSyntax>();
 
            // partial methods must be in partial types
            if (!decl.Modifiers.Any(t => t.IsKindOrHasMatchingText(SyntaxKind.PartialKeyword)))
            {
                return false;
            }
 
            return true;
        }
 
        return false;
    }
 
    private static bool IsTypeDeclarationContext(CSharpSyntaxContext context, CancellationToken cancellationToken)
    {
        return context.IsTypeDeclarationContext(
            validModifiers: SyntaxKindSet.AllTypeModifiers,
            validTypeDeclarations: SyntaxKindSet.ClassInterfaceStructRecordTypeDeclarations,
            canBePartial: false,
            cancellationToken: cancellationToken);
    }
}