using System;

using System.Text;

using System.Globalization;

using System.Collections.Generic;

public class Program

{

    public static void Main() {

        string[] diaWords = new string[]

        {

            "café", "crème", "naïve",

            "Über", "schön", "Grüße", "Müller", "Hölle",

            "İstanbul", "Türkiye", "şeker",

            "piñata", "jalapeño", "señor"

        };

        foreach(string diaWord in diaWords){

            Console.WriteLine($"{diaWord} becomes {Normalise(diaWord)}");

        }

    }

    static readonly Dictionary<char, string> preEdgeCases = new() {

        {'Ä', "Ae"},

        {'ä', "ae"},

        {'Ö', "Oe"},

        {'ö', "oe"},

        {'Ü', "Ue"},

        {'ü', "ue"}

    };

    static readonly Dictionary<char, string> postEdgeCases = new() {

        {'ß', "ss"} 

    };

    static string Normalise(string input){

        // Pass 1: Pre-edge cases

        StringBuilder builder = new StringBuilder();

        foreach (char c in input) {

            if (preEdgeCases.TryGetValue(c, out string s)) {

                builder.Append(s);  

            } else {

                builder.Append(c);

            }

        }

        input = builder.ToString();

        builder.Clear();

        string normalized = input.Normalize(NormalizationForm.FormD);

​

        // Pass 2: Post-edge cases

        foreach (char c in normalized)

        {

            if (postEdgeCases.TryGetValue(c, out string s)) {

                builder.Append(s);  

            } else if (CharUnicodeInfo.GetUnicodeCategory(c) != UnicodeCategory.NonSpacingMark) {

                builder.Append(c);

            }

        }

​

        return builder.ToString().Normalize(NormalizationForm.FormC);   

    }

}