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

namespace BF
{
    /// <summary>
    /// 资源加密
    /// 考虑到效率效果
    /// MAX_ENCRYPT_LEN之前的数据使用aes加密
    /// MAX_ENCRYPT_LEN之后的数据使用混淆
    /// </summary>
    public class ResourcesProtect
    {
        const int MAX_ENCRYPT_LEN = 512; //最大Aes加密长度,超过部分按规则混合
        const int CONFUSE_OFFSET = 16; //混淆间隔
        const int BLOCK_SIZE = 16; //校准对齐基数

        /// <summary>
        /// 加密资源文件
        /// </summary>
        static public void DoEncrypt(string resPath, string key, string desPath, Func<string, bool> filter = null)
        {
            if (null != filter && !filter(resPath))
                return;

            byte[] buffer = Read(resPath);
            byte[] encryptBuffer = ExecuteEncrypt(buffer, key);
            Write(encryptBuffer, desPath);
        }

        /// <summary>
        /// 解密资源文件
        /// </summary>
        static public void DoDecrypt(string resPath, string key, string desPath, Func<string, bool> filter = null)
        {
            if (null != filter && !filter(resPath))
                return;

            byte[] buffer = Read(resPath);
            byte[] decryptBuffer = ExecuteDecrypt(buffer, key);
            Write(decryptBuffer, desPath);
        }

        static public byte[] Read(string resPath)
        {
            byte[] buffer = null;
            try
            {
                FileStream stream = new FileStream(resPath, FileMode.Open);
                if (null != stream)
                {
                    BinaryReader reader = new BinaryReader(stream, Encoding.UTF8);
                    buffer = reader.ReadBytes((int)stream.Length);
                    stream.Close();
                    stream.Dispose();
                    reader.Close();
                }
            }
            catch (Exception)
            {
                throw;
            }

            return buffer;
        }

        static public void Write(byte[] buffer, string resPath)
        {
            try
            {
                FileStream stream = new FileStream(resPath, FileMode.Create);
                if (null != stream)
                {
                    BinaryWriter writer = new BinaryWriter(stream);
                    writer.Write(buffer, 0, buffer.Length);
                    stream.Close();
                    stream.Dispose();
                    writer.Close();
                }
            }
            catch (Exception)
            {
                throw;
            }
        }

        /// <summary>
        /// aes加混淆加密接口
        /// </summary>
        static public byte[] ExecuteEncrypt(byte[] buffer, string key)
        {
            //这里后续附加混淆规则
            int bufferLen = buffer.Length;
            if (bufferLen > MAX_ENCRYPT_LEN)
            {
                //规定 ECBMode:(明文长度/16 + 1) * 16 = 密文长度
                int retLen = bufferLen - MAX_ENCRYPT_LEN + (MAX_ENCRYPT_LEN / BLOCK_SIZE + 1) * BLOCK_SIZE;
                byte[] encryBuffer = new byte[MAX_ENCRYPT_LEN];
                byte[] retBuffer = new byte[retLen];
                Array.Copy(buffer, encryBuffer, MAX_ENCRYPT_LEN);
                byte[] beEncryBuffer = AesEncrypt.Encrypt(encryBuffer, key);
                beEncryBuffer.CopyTo(retBuffer, 0);
                Array.Copy(buffer, MAX_ENCRYPT_LEN, retBuffer, beEncryBuffer.Length, bufferLen - MAX_ENCRYPT_LEN);

                for (int i = beEncryBuffer.Length, j = 0; i < retBuffer.Length; i += CONFUSE_OFFSET)
                {
                    retBuffer[i] += buffer[j];
                    j += 2;
                    if (j >= MAX_ENCRYPT_LEN)
                        j = 0;
                }

                return retBuffer;
            }
            else
            {
                return AesEncrypt.Encrypt(buffer, key);
            }
        }

        /// <summary>
        /// aes加混淆解密接口
        /// </summary>
        static public byte[] ExecuteDecrypt(byte[] buffer, string key)
        {
            //这里后续附加混淆规则
            int bufferLen = buffer.Length;
            if (bufferLen > MAX_ENCRYPT_LEN)
            {
                //规定 ECBMode:(明文长度/16 + 1) * 16 = 密文长度
                int decryLen = (MAX_ENCRYPT_LEN / BLOCK_SIZE + 1) * BLOCK_SIZE;
                byte[] decryBuffer = new byte[decryLen];
                Array.Copy(buffer, decryBuffer, decryLen);
                byte[] beDecryBuffer = AesEncrypt.Decrypt(decryBuffer, key);
                int retLen = bufferLen - decryLen + beDecryBuffer.Length;
                byte[] retBuffer = new byte[retLen];
                beDecryBuffer.CopyTo(retBuffer, 0);
                Array.Copy(buffer, decryLen, retBuffer, beDecryBuffer.Length, retBuffer.Length - beDecryBuffer.Length);

                for (int i = beDecryBuffer.Length, j = 0; i < retLen; i += CONFUSE_OFFSET)
                {
                    retBuffer[i] -= beDecryBuffer[j];
                    j += 2;
                    if (j >= beDecryBuffer.Length)
                        j = 0;
                }

                return retBuffer;
            }
            else
            {
                return AesEncrypt.Decrypt(buffer, key);
            }
        }

    }
}