using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using System.Text;
using System.IO;

namespace libx
{

    public static class Utilitys
    {
        private static readonly MD5 md5 = MD5.Create();
        private static readonly CRC32 crc32 = new CRC32();

        public static string GetMD5Hash(string input)
        {
            byte[] data = md5.ComputeHash(Encoding.UTF8.GetBytes(input));
            return ToHash(data);
        }

        public static string GetMD5Hash(Stream input)
        {
            byte[] data = md5.ComputeHash(input);
            return ToHash(data);
        }

        public static bool VerifyMd5Hash(string input, string hash)
        {
            StringComparer comparer = StringComparer.OrdinalIgnoreCase;
            return 0 == comparer.Compare(input, hash);
        }

        public static string GetCRC32Hash(Stream input)
        {
            byte[] data = crc32.ComputeHash(input);
            return ToHash(data);
        }

        public static uint GetCrc(byte[] bytes)
        {
            return CRC32.Compute(bytes);
        }

        public static string GetCRC32Hash(byte[] bytes)
        {
            byte[] data = crc32.ComputeHash(bytes);
            return ToHash(data);
        }

        static string ToHash(byte[] data)
        {
            StringBuilder sb = new StringBuilder();
            foreach (byte t in data)
                sb.Append(t.ToString("x2"));
            return sb.ToString();
        }

        public static string GetCRC32Hash(string input)
        {
            byte[] data = crc32.ComputeHash(Encoding.UTF8.GetBytes(input));
            return ToHash(data);
        }

        public static bool VerifyCrc32Hash(string input, string hash)
        {
            StringComparer comparer = StringComparer.OrdinalIgnoreCase;
            return 0 == comparer.Compare(input, hash);
        }
    }

    sealed class CRC32 : HashAlgorithm
    {
        private const UInt32 DefaultPolynomial = 0xedb88320u;
        private const UInt32 DefaultSeed = 0xffffffffu;

        static UInt32[] _defaultTable;

        readonly UInt32 _seed;
        readonly UInt32[] _table;
        UInt32 _hash;

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

        public CRC32(UInt32 polynomial, UInt32 seed)
        {
            if (!BitConverter.IsLittleEndian)
                throw new PlatformNotSupportedException("Not supported on Big Endian processors");

            _table = InitializeTable(polynomial);
            this._seed = _hash = seed;
        }

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

        protected override void HashCore(byte[] array, int ibStart, int cbSize)
        {
            _hash = CalculateHash(_table, _hash, array, ibStart, cbSize);
        }

        protected override byte[] HashFinal()
        {
            byte[] hashBuffer = UInt32ToBigEndianBytes(~_hash);
            HashValue = hashBuffer;
            return hashBuffer;
        }

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

        public static UInt32 Compute(byte[] buffer)
        {
            return Compute(DefaultSeed, buffer);
        }

        public static UInt32 Compute(UInt32 seed, byte[] buffer)
        {
            return Compute(DefaultPolynomial, seed, buffer);
        }

        public static UInt32 Compute(UInt32 polynomial, UInt32 seed, byte[] buffer)
        {
            return ~CalculateHash(InitializeTable(polynomial), seed, buffer, 0, buffer.Length);
        }

        static UInt32[] InitializeTable(UInt32 polynomial)
        {
            if (polynomial == DefaultPolynomial && _defaultTable != null)
                return _defaultTable;

            uint[] createTable = new UInt32[256];
            for (int i = 0; i < 256; i++)
            {
                uint entry = (UInt32) i;
                for (int j = 0; j < 8; j++)
                    if ((entry & 1) == 1)
                        entry = (entry >> 1) ^ polynomial;
                    else
                        entry >>= 1;
                createTable[i] = entry;
            }

            if (polynomial == DefaultPolynomial)
                _defaultTable = createTable;

            return createTable;
        }

        static UInt32 CalculateHash(UInt32[] table, UInt32 seed, IList<byte> buffer, int start, int size)
        {
            uint hash = seed;
            for (int i = start; i < start + size; i++)
                hash = (hash >> 8) ^ table[buffer[i] ^ hash & 0xff];
            return hash;
        }

        static byte[] UInt32ToBigEndianBytes(UInt32 uint32)
        {
            byte[] result = BitConverter.GetBytes(uint32);

            if (BitConverter.IsLittleEndian)
                Array.Reverse(result);

            return result;
        }
    }
}