// 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;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Simplification;
 
namespace Microsoft.CodeAnalysis.CSharp.Extensions
{
    internal static class StringExtensions
    {
        public static string EscapeIdentifier(
            this string identifier,
            bool isQueryContext = false)
        {
            var nullIndex = identifier.IndexOf('\0');
            if (nullIndex >= 0)
            {
                identifier = identifier[..nullIndex];
            }
 
            var needsEscaping = SyntaxFacts.GetKeywordKind(identifier) != SyntaxKind.None;
 
            // Check if we need to escape this contextual keyword
            needsEscaping = needsEscaping || (isQueryContext && SyntaxFacts.IsQueryContextualKeyword(SyntaxFacts.GetContextualKeywordKind(identifier)));
 
            return needsEscaping ? "@" + identifier : identifier;
        }
 
        public static SyntaxToken ToIdentifierToken(
            this string identifier,
            bool isQueryContext = false)
        {
            var escaped = identifier.EscapeIdentifier(isQueryContext);
 
            if (escaped.Length == 0 || escaped[0] != '@')
            {
                return SyntaxFactory.Identifier(escaped);
            }
 
            var unescaped = identifier.StartsWith("@", StringComparison.Ordinal)
                ? identifier[1..]
                : identifier;
 
            var token = SyntaxFactory.Identifier(
                default, SyntaxKind.None, "@" + unescaped, unescaped, default);
 
            if (!identifier.StartsWith("@", StringComparison.Ordinal))
            {
                token = token.WithAdditionalAnnotations(Simplifier.Annotation);
            }
 
            return token;
        }
 
        public static IdentifierNameSyntax ToIdentifierName(this string identifier)
            => SyntaxFactory.IdentifierName(identifier.ToIdentifierToken());
    }
}