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

namespace MAX.Core.Cryptography;

public sealed class DESHelper
{

	//默认密钥向量
	private static readonly byte[] IVKey = { 36, 109, 97, 120, 111, 110, 120, 36 };
	/// <summary>
	/// DES加密字符串
	/// </summary>
	/// <param name="encryptString">待加密的字符串</param>
	/// <param name="encryptKey">加密密钥,要求为8位</param>
	/// <returns>加密成功返回加密后的字符串,失败返回源串</returns>
	public static string Encrypt(string encryptString, string encryptKey)
	{
		try
		{
			encryptKey = GetSubString(encryptKey, 8, "");
			encryptKey = encryptKey.PadRight(8, ' ');
			byte[] rgbKey = Encoding.UTF8.GetBytes(encryptKey.Substring(0, 8));
			byte[] rgbIV = IVKey;
			byte[] inputByteArray = Encoding.UTF8.GetBytes(encryptString);
			DES dCSP = DES.Create();
			MemoryStream mStream = new();
			CryptoStream cStream = new(mStream, dCSP.CreateEncryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
			cStream.Write(inputByteArray, 0, inputByteArray.Length);
			cStream.FlushFinalBlock();
			return Convert.ToBase64String(mStream.ToArray());
		}
		catch
		{
			return encryptString;
		}
	}

	/// <summary>
	/// DES解密字符串
	/// </summary>
	/// <param name="decryptString">待解密的字符串</param>
	/// <param name="decryptKey">解密密钥,要求为8位,和加密密钥相同</param>
	/// <returns>解密成功返回解密后的字符串,失败返源串</returns>
	public static string Decrypt(string decryptString, string decryptKey)
	{
		try
		{
			decryptKey = GetSubString(decryptKey, 0, 8, "");
			decryptKey = decryptKey.PadRight(8, ' ');
			byte[] rgbKey = Encoding.UTF8.GetBytes(decryptKey);
			byte[] rgbIV = IVKey;
			byte[] inputByteArray = Convert.FromBase64String(decryptString);
			DES DCSP = DES.Create();

			MemoryStream mStream = new();
			CryptoStream cStream = new(mStream, DCSP.CreateDecryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
			cStream.Write(inputByteArray, 0, inputByteArray.Length);
			cStream.FlushFinalBlock();
			return Encoding.UTF8.GetString(mStream.ToArray());
		}
		catch
		{
			return string.Empty;
		}

	}

	#region 截取字符串函数

	/// <summary>
	/// 截取字符串函数
	/// </summary>
	/// <param name="Str">所要截取的字符串</param>
	/// <param name="Num">截取字符串的长度</param>
	/// <returns></returns>
	public static string GetSubString(string Str, int Num)
	{
		if (Str is null or "")
		{
			return "";
		}
		string outstr = string.Empty;
		int n = 0;
		foreach (char ch in Str)
		{
			n += Encoding.Default.GetByteCount(ch.ToString());

			if (n > Num)
			{
				break;
			}
			else
			{
				outstr += ch;
			}
		}

		return outstr;
	}
	/// <summary>
	/// 截取字符串函数,如果超过指定长度则将超出的部分用指定字符串代替
	/// </summary>
	/// <param name="Str">所要截取的字符串</param>
	/// <param name="Num">截取字符串的长度</param>
	/// <param name="LastStr">截取字符串后省略部分的字符串</param>
	/// <returns></returns>
	public static string GetSubString(string Str, int Num, string LastStr)
	{
		return GetSubString(Str, 0, Num, LastStr);
	}

	#endregion

	#region 截取字符串，超过部分用指定字符串替换

	/* 宗波于 2010-6-12 日添加， 来源于DiscuzNt */
	/// <summary>
	/// 取指定长度的字符串
	/// </summary>
	/// <param name="p_SrcString">要检查的字符串</param>
	/// <param name="p_StartIndex">起始位置</param>
	/// <param name="p_Length">指定长度</param>
	/// <param name="p_TailString">用于替换的字符串</param>
	/// <returns>截取后的字符串</returns>
	public static string GetSubString(string p_SrcString, int p_StartIndex, int p_Length, string p_TailString)
	{
		string myResult = p_SrcString;

		byte[] bComments = Encoding.UTF8.GetBytes(p_SrcString);
		foreach (char c in Encoding.UTF8.GetChars(bComments))
		{    //当是日文或韩文时(注:中文的范围:\u4e00 - \u9fa5, 日文在\u0800 - \u4e00, 韩文为\xAC00-\xD7A3)
			if (c is (> '\u0800' and < '\u4e00') or (> '\xAC00' and < '\xD7A3'))
			{
				//if (System.Text.RegularExpressions.Regex.IsMatch(p_SrcString, "[\u0800-\u4e00]+") || System.Text.RegularExpressions.Regex.IsMatch(p_SrcString, "[\xAC00-\xD7A3]+"))
				//当截取的起始位置超出字段串长度时
				if (p_StartIndex >= p_SrcString.Length)
				{
					return "";
				}
				else
				{
					return p_SrcString.Substring(p_StartIndex,
												   p_Length + p_StartIndex > p_SrcString.Length ? p_SrcString.Length - p_StartIndex : p_Length);
				}
			}
		}

		if (p_Length >= 0)
		{
			byte[] bsSrcString = Encoding.Default.GetBytes(p_SrcString);

			//当字符串长度大于起始位置
			if (bsSrcString.Length > p_StartIndex)
			{
				int p_EndIndex = bsSrcString.Length;

				//当要截取的长度在字符串的有效长度范围内
				if (bsSrcString.Length > p_StartIndex + p_Length)
				{
					p_EndIndex = p_Length + p_StartIndex;
				}
				else
				{   //当不在有效范围内时,只取到字符串的结尾

					p_Length = bsSrcString.Length - p_StartIndex;
					p_TailString = "";
				}

				int nRealLength = p_Length;
				int[] anResultFlag = new int[p_Length];
				byte[] bsResult = null;

				int nFlag = 0;
				for (int i = p_StartIndex; i < p_EndIndex; i++)
				{
					if (bsSrcString[i] > 127)
					{
						nFlag++;
						if (nFlag == 3)
						{
							nFlag = 1;
						}
					}
					else
					{
						nFlag = 0;
					}

					anResultFlag[i] = nFlag;
				}

				if (bsSrcString[p_EndIndex - 1] > 127 && anResultFlag[p_Length - 1] == 1)
				{
					nRealLength = p_Length + 1;
				}

				bsResult = new byte[nRealLength];

				Array.Copy(bsSrcString, p_StartIndex, bsResult, 0, nRealLength);

				myResult = Encoding.Default.GetString(bsResult);
				myResult += p_TailString;
			}
		}

		return myResult;
	}


	#endregion

}