// 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.Globalization;
using Microsoft.CodeAnalysis.CSharp.Extensions;
 
namespace Microsoft.CodeAnalysis.CSharp.Utilities;
 
internal class TokenComparer : IComparer<SyntaxToken>
{
    public static readonly IComparer<SyntaxToken> NormalInstance = new TokenComparer(specialCaseSystem: false);
    public static readonly IComparer<SyntaxToken> SystemFirstInstance = new TokenComparer(specialCaseSystem: true);
 
    private readonly bool _specialCaseSystem;
 
    private TokenComparer(bool specialCaseSystem)
        => _specialCaseSystem = specialCaseSystem;
 
    public int Compare(SyntaxToken x, SyntaxToken y)
    {
        if (_specialCaseSystem &&
            x.GetPreviousToken(includeSkipped: true).Kind() is SyntaxKind.UsingKeyword or SyntaxKind.StaticKeyword &&
            y.GetPreviousToken(includeSkipped: true).Kind() is SyntaxKind.UsingKeyword or SyntaxKind.StaticKeyword)
        {
            var token1IsSystem = x.ValueText == nameof(System);
            var token2IsSystem = y.ValueText == nameof(System);
 
            if (token1IsSystem && !token2IsSystem)
            {
                return -1;
            }
            else if (!token1IsSystem && token2IsSystem)
            {
                return 1;
            }
        }
 
        return CompareWorker(x, y);
    }
 
    private static int CompareWorker(SyntaxToken x, SyntaxToken y)
    {
        if (x == y)
        {
            return 0;
        }
 
        // By using 'ValueText' we get the value that is normalized.  i.e.
        // @class will be 'class', and Unicode escapes will be converted
        // to actual Unicode.  This allows sorting to work properly across
        // tokens that have different source representations, but which
        // mean the same thing.
        var string1 = x.ValueText;
        var string2 = y.ValueText;
 
        // First check in a case insensitive manner.  This will put 
        // everything that starts with an 'a' or 'A' above everything
        // that starts with a 'b' or 'B'.
        var compare = CultureInfo.InvariantCulture.CompareInfo.Compare(string1, string2,
            CompareOptions.IgnoreCase | CompareOptions.IgnoreNonSpace | CompareOptions.IgnoreWidth);
        if (compare != 0)
        {
            return compare;
        }
 
        // Now, once we've grouped such that 'a' words and 'A' words are
        // together, sort such that 'a' words come before 'A' words.
        return CultureInfo.InvariantCulture.CompareInfo.Compare(string1, string2,
            CompareOptions.IgnoreNonSpace | CompareOptions.IgnoreWidth);
    }
}