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

namespace AesSingleFile
{
  class AesCoreSingle
  {
    /// <summary>
    /// 使用用戶口令，生成符合AES標準的key和iv。
    /// </summary>
    /// <param name="password">用戶輸入的口令</param>
    /// <returns>返回包含密鑰和向量的元組</returns>
    private (byte[] Key, byte[] IV) GenerateKeyAndIV(string password)
    {
      byte[] key = new byte[32];
      byte[] iv = new byte[16];
      byte[] hash = default;
      if (string.IsNullOrWhiteSpace(password))
        throw new ArgumentException("必須輸入口令！");
      using (SHA384 sha = SHA384.Create())
      {
        byte[] buffer = Encoding.UTF8.GetBytes(password);
        hash = sha.ComputeHash(buffer);
      }
      //用SHA384的原因：生成的384位哈希值正好被分成兩段使用。(32+16)*8=384。
      Array.Copy(hash, 0, key, 0, 32);//生成256位密鑰（32*8=256）
      Array.Copy(hash, 32, iv, 0, 16);//生成128位向量（16*8=128）
      return (Key: key, IV: iv);
    }

    public byte[] EncryptByte(byte[] buffer, string password)
    {
      byte[] encrypted;
      using (Aes aes = Aes.Create())
      {
        //設定密鑰和向量
        (aes.Key, aes.IV) = GenerateKeyAndIV(password);
        //設定運算模式和填充模式
        aes.Mode = CipherMode.CBC;//默認
        aes.Padding = PaddingMode.PKCS7;//默認
        //創建加密器對象（加解密方法不同處僅僅這一句話）
        var encryptor = aes.CreateEncryptor(aes.Key, aes.IV);
        using (MemoryStream msEncrypt = new MemoryStream())
        {
          using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))//選擇Write模式
          {
            csEncrypt.Write(buffer, 0, buffer.Length);//對原數組加密并寫入流中
            csEncrypt.FlushFinalBlock();//使用Write模式需要此句，但Read模式必須要有。
            encrypted = msEncrypt.ToArray();//從流中寫入數組（加密之后，數組變長，詳見方法AesCoreSingleTest內容）
          }
        }
      }
      return encrypted;
    }
    public byte[] DecryptByte(byte[] buffer, string password)
    {
      byte[] decrypted;
      using (Aes aes = Aes.Create())
      {
        //設定密鑰和向量
        (aes.Key, aes.IV) = GenerateKeyAndIV(password);
        //設定運算模式和填充模式
        aes.Mode = CipherMode.CBC;//默認
        aes.Padding = PaddingMode.PKCS7;//默認
        //創建解密器對象（加解密方法不同處僅僅這一句話）
        var decryptor = aes.CreateDecryptor(aes.Key, aes.IV);
        using (MemoryStream msDecrypt = new MemoryStream(buffer))
        {
          using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))//選擇Read模式
          {
            byte[] buffer_T = new byte[buffer.Length];/*--s1:創建臨時數組，用于包含可用字節+無用字節--*/

            int i = csDecrypt.Read(buffer_T, 0, buffer.Length);/*--s2:對加密數組進行解密，并通過i確定實際多少字節可用--*/

            //csDecrypt.FlushFinalBlock();//使用Read模式不能有此句，但write模式必須要有。

            decrypted = new byte[i];/*--s3:創建只容納可用字節的數組--*/

            Array.Copy(buffer_T, 0, decrypted, 0, i);/*--s4:從bufferT拷貝出可用字節到decrypted--*/
          }
        }
        return decrypted;
      }
    }
    public byte[] EnOrDecryptByte(byte[] buffer, string password, ActionDirection direction)
    {
      if (buffer == null)
        throw new ArgumentNullException("buffer為空");
      if (password == null || password == "")
        throw new ArgumentNullException("password為空");
      if (direction == ActionDirection.EnCrypt)
        return EncryptByte(buffer, password);
      else
        return DecryptByte(buffer, password);
    }
    public enum ActionDirection//該枚舉說明是加密還是解密
    {
      EnCrypt,//加密
      DeCrypt//解密
    }
    public static void AesCoreSingleTest(string s_in, string password)//驗證加密解密模塊正確性方法
    {
      byte[] buffer = Encoding.UTF8.GetBytes(s_in);
      AesCoreSingle aesCore = new AesCoreSingle();
      byte[] buffer_ed = aesCore.EncryptByte(buffer, password);
      byte[] buffer_ed2 = aesCore.DecryptByte(buffer_ed, password);
      string s = Encoding.UTF8.GetString(buffer_ed2);
      string s2 = "下列字符串\n" + s + '\n' + $"原buffer長度 → {buffer.Length}, 加密后buffer_ed長度 → {buffer_ed.Length}, 解密后buffer_ed2長度 → {buffer_ed2.Length}";
      MessageBox.Show(s2);
      /* 字符串在加密前后的變化(默認CipherMode.CBC運算模式, PaddingMode.PKCS7填充模式)
       * 1、如果數組長度為16的倍數，則加密后的數組長度=原長度+16
        如對于下列字符串
        D:\User\Documents\Administrator - DOpus Config - 2020-06-301.ocb
        使用UTF8編碼轉化為字節數組后，
        原buffer → 64, 加密后buffer_ed → 80, 解密后buffer_ed2 → 64
       * 2、如果數組長度不為16的倍數，則加密后的數組長度=16倍數向上取整
        如對于下列字符串
        D:\User\Documents\cc_20200630_113921.reg
        使用UTF8編碼轉化為字節數組后
        原buffer → 40, 加密后buffer_ed → 48, 解密后buffer_ed2 → 40
        參考文獻：
        1-《AES補位填充PaddingMode.Zeros模式》http://blog.chinaunix.net/uid-29641438-id-5786927.html
        2-《關于PKCS5Padding與PKCS7Padding的區別》https://www.cnblogs.com/midea0978/articles/1437257.html
        3-《AES-128 ECB 加密有感》http://blog.sina.com.cn/s/blog_60cf051301015orf.html
       */
    }

    /***---聲明CancellationTokenSource對象--***/
    private CancellationTokenSource cts;//using System.Threading;引用
    public Task EnOrDecryptFileAsync(Stream inStream, long inStream_Seek, Stream outStream, long outStream_Seek, string password, ActionDirection direction, IProgress<int> progress)
    {
      /***---實例化CancellationTokenSource對象--***/
      cts&#63;.Dispose();//cts為空，不動作，cts不為空，執行Dispose。
      cts = new CancellationTokenSource();

      Task mytask = new Task(
        () =>
        {
          EnOrDecryptFile(inStream, inStream_Seek, outStream, outStream_Seek, password, direction, progress);
        }, cts.Token, TaskCreationOptions.LongRunning);
      mytask.Start();
      return mytask;
    }
    public void EnOrDecryptFile(Stream inStream, long inStream_Seek, Stream outStream, long outStream_Seek, string password, ActionDirection direction, IProgress<int> progress)
    {
      if (inStream == null || outStream == null)
        throw new ArgumentException("輸入流與輸出流是必須的");
      //--調整流的位置(通常是為了避開文件頭部分)
      inStream.Seek(inStream_Seek, SeekOrigin.Begin);
      outStream.Seek(outStream_Seek, SeekOrigin.Begin);
      //用于記錄處理進度
      long total_Length = inStream.Length - inStream_Seek;
      long totalread_Length = 0;
      //初始化報告進度
      progress.Report(0);

      using (Aes aes = Aes.Create())
      {
        //設定密鑰和向量
        (aes.Key, aes.IV) = GenerateKeyAndIV(password);
        //創建加密器解密器對象（加解密方法不同處僅僅這一句話）
        ICryptoTransform cryptor;
        if (direction == ActionDirection.EnCrypt)
          cryptor = aes.CreateEncryptor(aes.Key, aes.IV);
        else
          cryptor = aes.CreateDecryptor(aes.Key, aes.IV);
        using (CryptoStream cstream = new CryptoStream(outStream, cryptor, CryptoStreamMode.Write))
        {
          byte[] buffer = new byte[512 * 1024];//每次讀取512kb的數據
          int readLen = 0;
          while ((readLen = inStream.Read(buffer, 0, buffer.Length)) != 0)
          {
            // 向加密流寫入數據
            cstream.Write(buffer, 0, readLen);
            totalread_Length += readLen;
            //匯報處理進度
            if (progress != null)
            {
              long per = 100 * totalread_Length / total_Length;
              progress.Report(Convert.ToInt32(per));
            }
          }
        }
      }
    }
  }
}