?using System;
using System.Collections.Generic;
using System.Text;
using System.IO;

namespace LSB_Algorithm
{
    class LSBEncrypt
    {
        //原始圖片路徑
        private string _originalPicPath = null;
        //隱藏信息路徑
        private string _hidingInfoPath = null;
        //原始圖片的文件流
        private FileStream _picStream = null;
        //隱藏信息的文件流
        private FileStream _infoStream = null;

        /// <summary>
        /// LSBEncrypt類的構造函數
        /// </summary>
        /// <param name="path1">原始圖片路徑</param>
        /// <param name="path2">隱藏信息的路徑</param>
        public LSBEncrypt(string path1, string path2)
        {
            _originalPicPath = path1;
            _hidingInfoPath = path2;
        }

        /// <summary>
        /// 將長整型數轉換為24位二進制表示的字節數組
        /// </summary>
        /// <param name="x">要轉換的長整型數，這個數的大小不會超過2的24次方</param>
        /// <returns>二進制表示的字節數組</returns>
        private byte[] ConvertToBinaryArray(long x)
        {
            byte[] binaryArray = new byte[24];
            for (int i = 0; i != 23; i++)
            {
                binaryArray[23 - i] = (byte)(x & 1);
                x = x >> 1;
            }
            return binaryArray;
        }

        /// <summary>
        /// 將3個字節的字節數組轉換為24位(8bit * 3)二進制表示的字節數組
        /// </summary>
        /// <param name="array">長度為3的字節數組</param>
        /// <returns>二進制表示的字節數組</returns>
        private byte[] ConvertToBinaryArray(byte[] array)
        {
            byte[] binaryArray = new byte[24];
            int a = array[0];
            int b = array[1];
            int c = array[2];
            for (int i = 0; i != 8; i++)
            {
                binaryArray[7 - i] = (byte)(a & 1);
                a = a >> 1;
            }
            for (int i = 0; i != 8; i++)
            {
                binaryArray[15 - i] = (byte)(b & 1);
                b = b >> 1;
            }
            for (int i = 0; i != 8; i++)
            {
                binaryArray[23 - i] = (byte)(c & 1);
                c = c >> 1;
            }
            return binaryArray;
        }

        /// <summary>
        /// 將圖像的第55至第66字節的LSB替換為隱藏信息文件的長度
        /// </summary>
        private void HideInfoLength()
        {
            byte[] picBlock = new byte[12];
            //讀取原始圖像的第55至第66字節的內容塊
            _picStream.Position = 54;
            _picStream.Read(picBlock, 0, picBlock.Length);
            byte[] lenArray = ConvertToBinaryArray(_infoStream.Length);
            //置入隱藏文件的長度信息
            int index = 0;
            for (int i = 0; i < 4; i++)
            {
                //置a7，a6位
                picBlock[i * 3] = (byte)((lenArray[index++] == 0) ? (picBlock[i * 3] & 253) : (picBlock[i * 3] | 2));
                picBlock[i * 3] = (byte)((lenArray[index++] == 0) ? (picBlock[i * 3] & 254) : (picBlock[i * 3] | 1));
                //置a5位
                picBlock[i * 3 + 1] = (byte)((lenArray[index++] == 0) ? (picBlock[i * 3 + 1] & 254) : (picBlock[i * 3 + 1] | 1));
                //置a4,a3,a2位
                picBlock[i * 3 + 2] = (byte)((lenArray[index++] == 0) ? (picBlock[i * 3 + 2] & 251) : (picBlock[i * 3 + 2] | 4));
                picBlock[i * 3 + 2] = (byte)((lenArray[index++] == 0) ? (picBlock[i * 3 + 2] & 253) : (picBlock[i * 3 + 2] | 2));
                picBlock[i * 3 + 2] = (byte)((lenArray[index++] == 0) ? (picBlock[i * 3 + 2] & 254) : (picBlock[i * 3 + 2] | 1));
            }
            //將原始文件流重定位到第55字節處并將已嵌入長度信息的12字節塊寫回
            _picStream.Position = 54;
            _picStream.Write(picBlock, 0, picBlock.Length);
            _picStream.Flush();
        }

        /// <summary>
        /// 將隱藏信息以每3個字節寫入原始圖像從第67字節開始的每12字節塊的LSB中
        /// </summary>
        private void HideInfoContent()
        {
            int readCnt = 0;
            //計算循環處理的次數
            long infoLen = _infoStream.Length;
            int cnt = (int)(infoLen % 3 == 0 ? infoLen / 3 : infoLen / 3 + 1);
            _picStream.Position = 66;
            for (int i = 0; i < cnt; i++)
            {
                //每次循環讀取BMP圖像的下一個12字節的內容
                byte[] picBlock = new byte[12];
                readCnt = _picStream.Read(picBlock, 0, picBlock.Length);
                //讀取待隱藏信息的下一個3字節內容
                byte[] readBuffer = new byte[3];
                _infoStream.Read(readBuffer, 0, readBuffer.Length);
                byte[] infoBlock = ConvertToBinaryArray(readBuffer);
                //置位操作
                int index = 0;
                for (int ii = 0; ii < 4; ii++)
                {
                    //置a7，a6位
                    picBlock[ii * 3] = (byte)((infoBlock[index++] == 0) ? (picBlock[ii * 3] & 253) : (picBlock[ii * 3] | 2));
                    picBlock[ii * 3] = (byte)((infoBlock[index++] == 0) ? (picBlock[ii * 3] & 254) : (picBlock[ii * 3] | 1));
                    //置a5位
                    picBlock[ii * 3 + 1] = (byte)((infoBlock[index++] == 0) ? (picBlock[ii * 3 + 1] & 254) : (picBlock[ii * 3 + 1] | 1));
                    //置a4,a3,a2位
                    picBlock[ii * 3 + 2] = (byte)((infoBlock[index++] == 0) ? (picBlock[ii * 3 + 2] & 251) : (picBlock[ii * 3 + 2] | 4));
                    picBlock[ii * 3 + 2] = (byte)((infoBlock[index++] == 0) ? (picBlock[ii * 3 + 2] & 253) : (picBlock[ii * 3 + 2] | 2));
                    picBlock[ii * 3 + 2] = (byte)((infoBlock[index++] == 0) ? (picBlock[ii * 3 + 2] & 254) : (picBlock[ii * 3 + 2] | 1));
                }
                _picStream.Position -= readCnt;
                _picStream.Write(picBlock, 0, picBlock.Length);
            }
            _picStream.Flush();
        }

        /// <summary>
        /// 執行信息隱藏操作
        /// </summary>
        public void ExecuteEncrypt()
        {
            _picStream = new FileStream(_originalPicPath, FileMode.Open, FileAccess.ReadWrite);
            _infoStream = new FileStream(_hidingInfoPath, FileMode.Open, FileAccess.Read);
            HideInfoLength();
            HideInfoContent();
            _picStream.Close();
            _infoStream.Close();
        }
    }
}