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


public class Program
{
	public static void Main()
	{
		AnyBaseConverter converter10 = new("0123456789");
		AnyBaseConverter converter62 = new("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz");
		
		string year = "9999";
		string month = "12";
		string day = "31";
		string hours = "23";
		string minutes = "59";
		string seconds = "59";
		string milliseconds = "999";

		string dt0 = $"{year}{month}{day}{hours}{minutes}{seconds}{milliseconds}"; // yyyyMMddHHmmssfff
		string sn = "99999999999999999"; // 17 digits of serial number
		string sum = "99999"; // 5 digits of transaction sum
		string s0 = dt0 + sn + sum;
		Console.WriteLine($"initial: {s0.Length} {s0}");

		string dayOfYear = "365"; // december 31
		string timeInSeconds = "86399"; // 23:59:59

		string dt1 = $"{year}{dayOfYear}{timeInSeconds}{milliseconds}";
		string s1 = dt1 + sn + sum;
		Console.WriteLine($"base10: {s1.Length} {s1}");

		byte[] sBytes = converter10.Decode(s1);
		string sBytesStr = new StringBuilder()
			.AppendJoin(", ", sBytes.Select(b => b.ToString()))
			.ToString();
		Console.WriteLine($"base256: {sBytes.Length} [{sBytesStr}]");

		string s2 = converter62.Encode(sBytes);
		Console.WriteLine($"base62: {s2.Length} {s2}");
	}
}


public class AnyBaseConverter
{
	// Adapted code of Base62 encoding from:
	// https://github .com/ghost1face/base62/blob/master/Base62/Base62Converter.cs

	public AnyBaseConverter(string characterSet)
	{
		if (characterSet == "")
			throw new ArgumentException("Character set cannot be empty", characterSet);
		if (characterSet.Length > 256)
			throw new ArgumentException("Character set length must not exceed 256 characters", characterSet);
		this.Base = characterSet.Length;
		this.CharacterSet = characterSet;
		this.CharacterIds = characterSet.Select((c, i) => (c, i)).ToDictionary(ci => ci.c, ci => ci.i);
		if (this.CharacterIds.Count != this.CharacterSet.Length)
			throw new ArgumentException("Characters in character set must not repeat", "characterSet");
	}

	public int Base { get; }
	public string CharacterSet { get; }
	private readonly Dictionary<char, int> CharacterIds;

	public string Encode(byte[] bytes)
	{
		byte[] converted = this.ConvertBase(bytes, 256, this.Base);
		StringBuilder builder = new StringBuilder(converted.Length);
		foreach (byte c in converted.AsSpan())
			builder.Append(this.CharacterSet[c]);
		return builder.ToString();
	}

	public byte[] Decode(string value)
	{
		byte[] arr = new byte[value.Length];
		for (int i = 0; i < arr.Length; i++)
		{
			int characterId = this.CharacterIds.GetValueOrDefault(value[i], -1);
			if (characterId == -1) throw new ArgumentException("Character must be in specified set, found: " + value);
			arr[i] = (byte)characterId;
		}
		byte[] converted = ConvertBase(arr, this.Base, 256);
		return converted;
	}

	private byte[] ConvertBase(byte[] source, int sourceBase, int targetBase)
	{
		int count;
		List<byte> result = new();
		List<byte> quotient = new();
		while ((count = source.Length) > 0)
		{
			quotient.Clear();
			int remainder = 0;

			for (var i = 0; i < count; i++)
			{
				int accumulator = source[i] + remainder * sourceBase;
				byte digit = (byte)((accumulator - (accumulator % targetBase)) / targetBase);
				remainder = accumulator % targetBase;
				if (quotient.Count > 0 || digit != 0)
					quotient.Add(digit);
			}

			result.Add((byte)remainder);
			source = quotient.ToArray();
		}

		byte[] output = new byte[result.Count];
		for (var (i, j) = (0, result.Count - 1); j >= 0; i++, j--)
			output[i] = result[j];

		return output;
	}
}