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

namespace Ant.Service.Utility
{
    /// <summary>
    /// 
    /// </summary>
    public class PasswordUtils
    {
        #region field & constructor

        //private static readonly Log _log = new Log(typeof(PasswordUtil));

        private const int saltLength = 4;

        public PasswordUtils() { }

        #endregion

        /// <summary>
        /// 对比用户明文密码是否和加密后密码一致
        /// </summary>
        /// <param name="dbPassword">数据库中单向加密后的密码</param>
        /// <param name="userPassword">用户明文密码</param>
        /// <returns></returns>
		public static bool ComparePasswords(string dbPassword, string userPassword)
        {
            byte[] dbPwd = Convert.FromBase64String(dbPassword);

            byte[] hashedPwd = HashString(userPassword);

            if (dbPwd.Length == 0 || hashedPwd.Length == 0 || dbPwd.Length != hashedPwd.Length + saltLength)
            {
                return false;
            }

            byte[] saltValue = new byte[saltLength];
            //	int saltOffset = dbPwd.Length - hashedPwd.Length;
            int saltOffset = hashedPwd.Length;
            for (int i = 0; i < saltLength; i++)
                saltValue[i] = dbPwd[saltOffset + i];

            byte[] saltedPassword = CreateSaltedPassword(saltValue, hashedPwd);

            // compare the values
            return CompareByteArray(dbPwd, saltedPassword);


        }


        /// <summary>
        /// 
        /// </summary>
        /// <param name="str"></param>
        /// <param name="code">16与32位加密</param>
        /// <returns></returns>
        public static string MD5_Encrypt(string str, int code)
        {
            if (code == 16) //16位MD5加密（取32位加密的9~25字符）
            {
                return FormsAuthentication.HashPasswordForStoringInConfigFile(str, "MD5").ToLower().Substring(8, 16);
            }
            if (code == 32)
            {
                return FormsAuthentication.HashPasswordForStoringInConfigFile(str, "MD5").ToLower();
            }
            return str;
        }


        /// <summary>
        /// 创建用户的数据库密码
        /// </summary>
        /// <param name="password"></param>
        /// <returns></returns>
		public static string CreateDbPassword(string userPassword)
        {
            byte[] unsaltedPassword = HashString(userPassword);

            //Create a salt value
            byte[] saltValue = new byte[saltLength];
            RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
            rng.GetBytes(saltValue);

            byte[] saltedPassword = CreateSaltedPassword(saltValue, unsaltedPassword);

            return Convert.ToBase64String(saltedPassword);

        }

        #region 私有函数
        /// <summary>
        /// 将一个字符串哈希化
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        private static byte[] HashString(string str)
        {
            byte[] pwd = System.Text.Encoding.UTF8.GetBytes(str);

            SHA1 sha1 = SHA1.Create();
            byte[] saltedPassword = sha1.ComputeHash(pwd);
            return saltedPassword;
        }
        private static bool CompareByteArray(byte[] array1, byte[] array2)
        {
            if (array1.Length != array2.Length)
                return false;
            for (int i = 0; i < array1.Length; i++)
            {
                if (array1[i] != array2[i])
                    return false;
            }
            return true;
        }
        // create a salted password given the salt value
        private static byte[] CreateSaltedPassword(byte[] saltValue, byte[] unsaltedPassword)
        {
            // add the salt to the hash
            byte[] rawSalted = new byte[unsaltedPassword.Length + saltValue.Length];
            unsaltedPassword.CopyTo(rawSalted, 0);
            saltValue.CopyTo(rawSalted, unsaltedPassword.Length);

            //Create the salted hash			
            SHA1 sha1 = SHA1.Create();
            byte[] saltedPassword = sha1.ComputeHash(rawSalted);

            // add the salt value to the salted hash
            byte[] dbPassword = new byte[saltedPassword.Length + saltValue.Length];
            saltedPassword.CopyTo(dbPassword, 0);
            saltValue.CopyTo(dbPassword, saltedPassword.Length);

            return dbPassword;
        }
        #endregion

    }
}