using System;

using System.Collections.Generic;

using System.Linq;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string str1 = "Straße";

        string str2 = "Strasse";

        // BFF thinks they are different

        // XeroWeb SQL thinks they are the same

​

        bool isEqualInvariant = string.Equals(str1, str2, StringComparison.InvariantCultureIgnoreCase); 

        bool isEqualOrdinal = string.Equals(str1, str2, StringComparison.OrdinalIgnoreCase);

        bool toLowerInvariantCheck = str1.ToLowerInvariant() ==  str2.ToLowerInvariant();

        bool isEqualCaseAndAccentInvariantCheck = NormaliseCaseAndAccents(str1) ==  NormaliseCaseAndAccents(str2);

        Console.WriteLine("InvariantCultureIgnoreCase: " + isEqualInvariant);

        Console.WriteLine("OrdinalIgnoreCase: " + isEqualOrdinal);

        Console.WriteLine("ToLowerInvariant: " + toLowerInvariantCheck);

        Console.WriteLine("ToLowerInvariant: " + isEqualCaseAndAccentInvariantCheck);

        Console.WriteLine();

        string normalisedStr2 = NormaliseCaseAndAccents(str2);

​

        Console.WriteLine("Collection check: " + NormaliseCaseAndAccents(new[] { "code 1", "code 2", str1 }).Any(existing => existing == normalisedStr2));

    }

    private static string NormaliseCaseAndAccents(string value)

    {

        return NormaliseCaseAndAccents(new[] {value}).First();

    }

​

    private static IEnumerable<string> NormaliseCaseAndAccents(IEnumerable<string> values)

    {

        var accentMap = new(string Anglo, string Accents)[]

        {

            ("a", "ªáàâäãå"),

            ("c", "ç"),

            ("d", "ð"),

            ("e", "éèêë"),

            ("f", "ƒ"),

            ("i", "íìîï"),

            ("n", "ñ"),

            ("o", "ºóòôöõø"),

            ("s", "š"),

            ("t", "þ"),

            ("u", "úùûü"),

            ("y", "ýÿ"),

            ("z", "ž"),

            ("ae", "æ"),

            ("oe", "œ"),

            ("ss", "ß"),

            ("tm", "™")

        }.Where(a => values.Any(v => Regex.Match(v, $"[{a.Accents}]").Success));

​

        return values.Select(v =>

        {

            foreach (var m in accentMap)

            {

                v = Regex.Replace(v, $"[{m.Accents}]", m.Anglo);

            }

​

            return v.ToLowerInvariant();

        });

    }

​

}