using System;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace BaseNcoding
{
	public abstract class Base
	{
		public uint CharsCount { get; }

		public double BitsPerChars => (double)BlockBitsCount / BlockCharsCount;

		public int BlockBitsCount { get; protected set; }

		public int BlockCharsCount { get; protected set; }

		public string Alphabet { get; }

		public char Special { get; }

		public abstract bool HasSpecial { get; }

		public Encoding Encoding { get; set; }

		public bool Parallel { get; set; }

		protected readonly int[] InvAlphabet;

		public Base(uint charsCount, string alphabet, char special, Encoding encoding = null, bool parallel = false)
		{
			if (alphabet.Length != charsCount)
				throw new ArgumentException($"Base string should contain {charsCount} chars");

			for (int i = 0; i < charsCount; i++)
				for (int j = i + 1; j < charsCount; j++)
					if (alphabet[i] == alphabet[j])
						throw new ArgumentException("Base string should contain distinct chars");

			if (alphabet.Contains(special))
				throw new ArgumentException("Base string should not contain special char");

			CharsCount = charsCount;
			Alphabet = alphabet;
			Special = special;
			int bitsPerChar = LogBase2(charsCount);
			BlockBitsCount = Lcm(bitsPerChar, 8);
			BlockCharsCount = BlockBitsCount / bitsPerChar;

			InvAlphabet = new int[Alphabet.Max() + 1];

			for (int i = 0; i < InvAlphabet.Length; i++)
				InvAlphabet[i] = -1;

			for (int i = 0; i < charsCount; i++)
				InvAlphabet[Alphabet[i]] = i;

			Encoding = encoding ?? Encoding.UTF8;
			Parallel = parallel;
		}

		public virtual string EncodeString(string data)
		{
			return Encode(Encoding.GetBytes(data));
		}

		public abstract string Encode(byte[] data);

		public string DecodeToString(string data)
		{
			return Encoding.GetString(Decode(Regex.Replace(data, @"\r\n?|\n", "")));
		}

		public abstract byte[] Decode(string data);

		/// <summary>
		/// From: http://stackoverflow.com/a/600306/1046374
		/// </summary>
		/// <param name="x"></param>
		/// <returns></returns>
		public static bool IsPowerOf2(uint x)
		{
			uint xint = x;
			if (x - xint != 0)
				return false;

			return (xint & (xint - 1)) == 0;
		}

		/// <summary>
		/// From: http://stackoverflow.com/a/13569863/1046374
		/// </summary>
		public static int Lcm(int a, int b)
		{
			int num1, num2;
			if (a > b)
			{
				num1 = a;
				num2 = b;
			}
			else
			{
				num1 = b;
				num2 = a;
			}

			for (int i = 1; i <= num2; i++)
			{
				int mult = num1 * i;
				if (mult % num2 == 0)
					return mult;
			}

			return num2;
		}

		private static int LogBase2(uint x)
		{
			int r = 0;
			while ((x >>= 1) != 0)
				r++;
			return r;
		}

		private static int LogBaseN(uint x, uint n)
		{
			int r = 0;
			while ((x /= n) != 0)
				r++;
			return r;
		}

		public static int GetOptimalBitsCount2(uint charsCount, out uint charsCountInBits,
			uint maxBitsCount = 64, bool base2BitsCount = false)
		{
			int result = 0;
			charsCountInBits = 0;
			int n1 = LogBase2(charsCount);
			double charsCountLog = Math.Log(2, charsCount);
			double maxRatio = 0;

			for (int n = n1; n <= maxBitsCount; n++)
			{
				if (base2BitsCount && n % 8 != 0)
					continue;

				uint l1 = (uint)Math.Ceiling(n * charsCountLog);
				double ratio = (double)n / l1;
				if (ratio > maxRatio)
				{
					maxRatio = ratio;
					result = n;
					charsCountInBits = l1;
				}
			}

			return result;
		}

		protected static int GetOptimalBitsCount(uint charsCount, out uint charsCountInBits,
			uint maxBitsCount = 64, uint radix = 2)
		{
			int result = 0;
			charsCountInBits = 0;
			int n0 = LogBaseN(charsCount, radix);
			double charsCountLog = Math.Log(radix, charsCount);
			double maxRatio = 0;

			for (int n = n0; n <= maxBitsCount; n++)
			{
				uint k = (uint)Math.Ceiling(n * charsCountLog);
				double ratio = (double)n / k;
				if (ratio > maxRatio)
				{
					maxRatio = ratio;
					result = n;
					charsCountInBits = k;
				}
			}

			return result;
		}
	}
}