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

namespace Common.Helper.Encryption
{
    public class RsaHelper
    {
        private RSACryptoServiceProvider Csp { get; set; }
        private RSAParameters PrivateKey { get; set; }
        private RSAParameters PublicKey { get; set; }
        
        /// <summary>
        /// 公钥字符串
        /// </summary>
        public string PublicKeyString { get; set; }

        private RsaHelper()
        {
            Csp = new RSACryptoServiceProvider(2048);

            //how to get the private key
            PrivateKey = Csp.ExportParameters(true);

            //and the public key ...
            PublicKey = Csp.ExportParameters(false);

            //converting the public key into a string representation
            {
                //we need some buffer
                var sw = new System.IO.StringWriter();
                //we need a serializer
                var xs = new System.Xml.Serialization.XmlSerializer(typeof(RSAParameters));
                //serialize the key into the stream
                xs.Serialize(sw, PublicKey);
                //get the string from the stream
                PublicKeyString = sw.ToString();
            }

            //converting it back
            {
                //get a stream from the string
                var sr = new System.IO.StringReader(PublicKeyString);
                //we need a deserializer
                var xs = new System.Xml.Serialization.XmlSerializer(typeof(RSAParameters));
                //get the object back from the stream
                PublicKey = (RSAParameters)xs.Deserialize(sr);
            }

        }
        static RsaHelper(){}

        public static RsaHelper Instance { get; } = new RsaHelper();
        /// <summary>
        /// 加密数据
        /// </summary>
        /// <param name="keyWord"></param>
        /// <returns></returns>
        public string DesEncrypt(string keyWord)
        {
            //lets take a new CSP with a new 2048 bit rsa key pair
            
            //conversion for the private key is no black magic either ... omitted

            //we have a public key ... let's get a new csp and load that key
            Csp = new RSACryptoServiceProvider();
            Csp.ImportParameters(PublicKey);
            

            //for encryption, always handle bytes...
            var bytesPlainTextData = System.Text.Encoding.Unicode.GetBytes(keyWord);

            //apply pkcs#1.5 padding and encrypt our data 
            var bytesCypherText = Csp.Encrypt(bytesPlainTextData, false);

            //we might want a string representation of our cypher text... base64 will do
            return Convert.ToBase64String(bytesCypherText);

        }
        /// <summary>
        /// 解密数据
        /// </summary>
        /// <param name="keyWord"></param>
        /// <returns></returns>

        public string DesDecrypt(string keyWord)
        {

            //first, get our bytes back from the base64 string ...
            var bytesCypherText = Convert.FromBase64String(keyWord);

            //we want to decrypt, therefore we need a csp and load our private key
            var csp = new RSACryptoServiceProvider();
            csp.ImportParameters(PrivateKey);

            //decrypt and strip pkcs#1.5 padding
            var bytesPlainTextData = csp.Decrypt(bytesCypherText, false);

            //get our original plainText back...
            return System.Text.Encoding.Unicode.GetString(bytesPlainTextData);
        }
    }
}