﻿/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

namespace Kafka.Client.Utils
{
    using System;
    using System.Security.Cryptography;

    /// <summary>
    /// From http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net
    /// </summary>
    internal class Crc32Hasher : HashAlgorithm
    {
        public const UInt32 DefaultPolynomial = 0xedb88320;
        public const UInt32 DefaultSeed = 0xffffffff;

        private UInt32 hash;
        private UInt32 seed;
        private UInt32[] table;
        private static UInt32[] defaultTable;

        public Crc32Hasher()
        {
            table = InitializeTable(DefaultPolynomial);
            seed = DefaultSeed;
            Initialize();
        }

        public Crc32Hasher(UInt32 polynomial, UInt32 seed)
        {
            table = InitializeTable(polynomial);
            this.seed = seed;
            Initialize();
        }

        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()
        {
            byte[] hashBuffer = UInt32ToBigEndianBytes(~hash);
            this.HashValue = hashBuffer;
            return hashBuffer;
        }

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

        public static byte[] Compute(byte[] bytes)
        {
            var hasher = new Crc32Hasher();
            byte[] hash = hasher.ComputeHash(bytes);
            return hash;
        }

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

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

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

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

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

            if (polynomial == DefaultPolynomial)
                defaultTable = createTable;

            return createTable;
        }

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

        private byte[] UInt32ToBigEndianBytes(UInt32 x)
        {
            return new byte[] {
			    (byte)((x >> 24) & 0xff),
			    (byte)((x >> 16) & 0xff),
			    (byte)((x >> 8) & 0xff),
			    (byte)(x & 0xff)
		    };
        }
    }
}