// 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());
}