using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace Legends.Core.Cryptography
{
    public class CRC32 : HashAlgorithm
    {
        public const uint DefaultPolynomial = 0xedb88320u;
        public const uint DefaultSeed = 0xffffffffu;

        private static readonly uint[] defaultTable =
            {
                0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA,
                0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3,
                0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988,
                0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91,
                0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE,
                0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,
                0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC,
                0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5,
                0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172,
                0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B,
                0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940,
                0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,
                0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116,
                0x21B4F4B5, 0x56B3C423, 0xCFBA9599, 0xB8BDA50F,
                0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924,
                0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D,
                0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A,
                0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,
                0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818,
                0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01,
                0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E,
                0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457,
                0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C,
                0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
                0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2,
                0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB,
                0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0,
                0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9,
                0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086,
                0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
                0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4,
                0x59B33D17, 0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD,
                0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A,
                0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683,
                0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8,
                0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,
                0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE,
                0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7,
                0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC,
                0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5,
                0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252,
                0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,
                0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60,
                0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79,
                0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236,
                0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F,
                0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04,
                0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,
                0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A,
                0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713,
                0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38,
                0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21,
                0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E,
                0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
                0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C,
                0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45,
                0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2,
                0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB,
                0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0,
                0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
                0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6,
                0xBAD03605, 0xCDD70693, 0x54DE5729, 0x23D967BF,
                0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94,
                0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D
            };

        private readonly uint _seed;
        private readonly uint[] _table;
        private uint _hash;

        public CRC32()
            : this(DefaultPolynomial, DefaultSeed)
        {
        }

        public CRC32(uint polynomial, uint seed)
        {
            _table = InitializeTable(polynomial);
            _seed = _hash = seed;
        }

        public override void Initialize()
        {
            _hash = _seed;
        }

        protected override void HashCore(byte[] buffer, int start, int length)
        {
            _hash = CalculateHash(_table, _hash, buffer, start, length);
        }

        protected override byte[] HashFinal()
        {
            var hashBuffer = UintToBigEndianBytes(~_hash);
            HashValue = hashBuffer;
            return hashBuffer;
        }

        public override int HashSize { get { return 32; } }

        public static uint Compute(byte[] buffer)
        {
            return ~CalculateHash(defaultTable, DefaultSeed, buffer, 0, buffer.Length);
        }

        public static uint Compute(uint seed, byte[] buffer)
        {
            return ~CalculateHash(defaultTable, seed, buffer, 0, buffer.Length);
        }

        public static uint Compute(uint polynomial, uint seed, byte[] buffer)
        {
            return ~CalculateHash(InitializeTable(polynomial), seed, buffer, 0, buffer.Length);
        }

        private static uint[] InitializeTable(uint polynomial)
        {
            if (polynomial == DefaultPolynomial)
                return defaultTable;

            var createTable = new uint[256];
            for (uint i = 0; i < 256; i++)
            {
                var entry = i;
                for (var j = 0; j < 8; j++)
                    entry = ((entry & 1) == 1) ? (entry >> 1) ^ polynomial : (entry >> 1);
                createTable[i] = entry;
            }

            return createTable;
        }

        private static uint CalculateHash(uint[] table, uint seed, byte[] buffer, int start, int size)
        {
            var crc = seed;
            for (var i = start; i < size - start; i++)
                crc = (crc >> 8) ^ table[buffer[i] ^ crc & 0xff];
            return crc;
        }

        private static byte[] UintToBigEndianBytes(uint uint32)
        {
            var result = BitConverter.GetBytes(uint32);
            if (BitConverter.IsLittleEndian)
                Array.Reverse(result);
            return result;
        }
    }

}
