using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

public class ReadWriter
{
    private static Dictionary<Tuple<char, char>, int> Alphabet
    {
        get
        {
            var temp = new Dictionary<Tuple<char, char>, int>();
            for (int i = (int)'A'; i <= (int)'Z'; i++)
            {
                temp.Add(new Tuple<char, char>((char)i, (char)(i + 32)), 0);
            }
            return temp;
        }
    }

    public static Tuple<char, char> GetMostAndLeastCommonLetters(string path)
    {
        if (File.Exists(path))
        {
            var collector = File.ReadAllText(path);
            var alphabet = Alphabet;

            foreach (char nig in collector)
            {
                var crutch = alphabet.Keys.ToList().Find(x => (x.Item1 == nig) || (x.Item2 == nig));
                if (crutch != null)
                    alphabet[crutch]++;
            }
            return new Tuple<char, char>(alphabet.Keys.ToList().Find(x => alphabet.Values.Max() == alphabet[x]).Item1, alphabet.Keys.Where(x => alphabet[x] != 0).ToList().Find(x => (alphabet.Values.Min() == alphabet[x])).Item1);
        }
        else throw new IOException("kys");
    }

    public static void ReplaceMostRareLetter(Tuple<char, char> leastAndMostCommon, string inputPath, string outputPath)
    {
        if (File.Exists(inputPath))
        {
            var collector = File.ReadAllText(inputPath);
            var modifier = new StringBuilder(collector);
            modifier.Replace(leastAndMostCommon.Item2, leastAndMostCommon.Item1);
            using (StreamWriter fs = new StreamWriter(new FileStream(outputPath, FileMode.Create, FileAccess.Write)))
            {
                fs.Write(modifier);
            }
        }
        else throw new IOException("kys");
    }
}