// 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 Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.CSharp.Utilities;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.CSharp.Extensions;
 
internal static class UsingDirectiveSyntaxExtensions
{
    public static void SortUsingDirectives(
        this List<UsingDirectiveSyntax> usingDirectives,
        SyntaxList<UsingDirectiveSyntax> existingDirectives,
        bool placeSystemNamespaceFirst)
    {
        var systemFirstInstance = UsingsAndExternAliasesDirectiveComparer.SystemFirstInstance;
        var normalInstance = UsingsAndExternAliasesDirectiveComparer.NormalInstance;
 
        var specialCaseSystem = placeSystemNamespaceFirst;
        var comparers = specialCaseSystem
            ? (systemFirstInstance, normalInstance)
            : (normalInstance, systemFirstInstance);
 
        // First, see if the usings were sorted according to the user's preference.  If so,
        // keep the same sorting after we add the using.  However, if the usings weren't sorted
        // according to their preference, then see if they're sorted in the other way.  If so
        // preserve that sorting as well.  That way if the user is working with a file that 
        // was written on a machine with a different default, the usings will stay in a 
        // reasonable order.
        if (existingDirectives.IsSorted(comparers.Item1))
        {
            usingDirectives.Sort(comparers.Item1);
        }
        else if (existingDirectives.IsSorted(comparers.Item2))
        {
            usingDirectives.Sort(comparers.Item2);
        }
    }
}