using Org.BouncyCastle.Bcpg;
using Org.BouncyCastle.Bcpg.OpenPgp;
using Org.BouncyCastle.Security;
using System;
using System.IO;
using System.Text;
using Org.BouncyCastle.Utilities.IO;

namespace LCU.Api.Internal.FileOperations.Services
{
    public static class CryptoHelper
    {
        private static PgpPublicKey ReadPublicKey(Stream inputStream)
        {
            inputStream = PgpUtilities.GetDecoderStream(inputStream);
            PgpPublicKeyRingBundle pgpPub = new PgpPublicKeyRingBundle(inputStream);

            foreach (PgpPublicKeyRing keyRing in pgpPub.GetKeyRings())
            {
                foreach (PgpPublicKey key in keyRing.GetPublicKeys())
                {
                    if (key.IsEncryptionKey)
                    {
                        return key;
                    }
                }
            }

            throw new ArgumentException("Can't find encryption key in key ring.");
        }

        private static PgpPrivateKey FindSecretKey(PgpSecretKeyRingBundle pgpSec, long keyId, char[] pass)
        {
            PgpSecretKey pgpSecKey = pgpSec.GetSecretKey(keyId);
            return pgpSecKey?.ExtractPrivateKey(pass);
        }

        public static void DecryptPgpFile(string inputFile, string outputFile, string keyFile, string passPhrase)
        {
            var encryptedFileData = File.ReadAllBytes(inputFile);
            var secretKeyData = File.ReadAllBytes(keyFile);
            var decryptedData = DecryptPgpData(encryptedFileData, secretKeyData, passPhrase);

            File.WriteAllText(outputFile, decryptedData);
        }

        public static string DecryptPgpData(byte[] inputData, byte[] secretKeyData, string passPhrase)
        {
            Stream inputStream = new MemoryStream(inputData);
            Stream secretKeyStream = new MemoryStream(secretKeyData);

            string output;

            PgpObjectFactory pgpFactory = new PgpObjectFactory(PgpUtilities.GetDecoderStream(inputStream));
            // find secret key
            PgpSecretKeyRingBundle pgpKeyRing = new PgpSecretKeyRingBundle(PgpUtilities.GetDecoderStream(secretKeyStream));

            PgpObject pgp = null;
            if (pgpFactory != null)
            {
                pgp = pgpFactory.NextPgpObject();
            }

            // the first object might be a PGP marker packet.
            PgpEncryptedDataList encryptedData = null;
            if (pgp is PgpEncryptedDataList)
            {
                encryptedData = (PgpEncryptedDataList)pgp;
            }
            else
            {
                encryptedData = (PgpEncryptedDataList)pgpFactory.NextPgpObject();
            }

            // decrypt
            PgpPrivateKey privateKey = null;
            PgpPublicKeyEncryptedData pubKeyData = null;
            foreach (PgpPublicKeyEncryptedData pubKeyDataItem in encryptedData.GetEncryptedDataObjects())
            {
                privateKey = FindSecretKey(pgpKeyRing, pubKeyDataItem.KeyId, passPhrase.ToCharArray());

                if (privateKey != null)
                {
                    pubKeyData = pubKeyDataItem;
                    break;
                }
            }

            if (privateKey == null)
            {
                throw new ArgumentException("Secret key for message not found.");
            }

            PgpObjectFactory plainFact = null;
            using (Stream clear = pubKeyData.GetDataStream(privateKey))
            {
                plainFact = new PgpObjectFactory(clear);
            }

            PgpObject message = plainFact.NextPgpObject();

            switch (message)
            {
                case PgpCompressedData data:
                {
                    PgpCompressedData compressedData = data;
                    PgpObjectFactory pgpCompressedFactory = null;

                    using (Stream compDataIn = compressedData.GetDataStream())
                    {
                        pgpCompressedFactory = new PgpObjectFactory(compDataIn);
                    }

                    message = pgpCompressedFactory.NextPgpObject();
                    PgpLiteralData literalData = null;
                    if (message is PgpOnePassSignatureList)
                    {
                        message = pgpCompressedFactory.NextPgpObject();
                    }

                    literalData = (PgpLiteralData)message;
                    using (Stream unc = literalData.GetInputStream())
                    {
                        output = GetString(unc);
                    }

                    break;
                }
                case PgpLiteralData data:
                {
                    PgpLiteralData literalData = data;
                    using (Stream unc = literalData.GetInputStream())
                    {
                        output = GetString(unc);
                    }

                    break;
                }
                case PgpOnePassSignatureList _:
                    throw new PgpException("Encrypted message contains a signed message - not literal data.");
                default:
                    throw new PgpException("Message is not a simple encrypted file - type unknown.");
            }

            return output;
        }

        public static void EncryptPgpFile(string inputFile, string outputFile, string publicKeyFile, bool applyArmor, bool withIntegrityCheck)
        {
            using (Stream publicKeyStream = File.OpenRead(publicKeyFile))
            {
                PgpPublicKey pubKey = ReadPublicKey(publicKeyStream);

                using (MemoryStream outputBytes = new MemoryStream())
                {
                    PgpCompressedDataGenerator dataCompressor = new PgpCompressedDataGenerator(CompressionAlgorithmTag.Zip);
                    PgpUtilities.WriteFileToLiteralData(dataCompressor.Open(outputBytes), PgpLiteralData.Binary, new FileInfo(inputFile));

                    dataCompressor.Close();
                    PgpEncryptedDataGenerator dataGenerator =
                        new PgpEncryptedDataGenerator(SymmetricKeyAlgorithmTag.Cast5, withIntegrityCheck, new SecureRandom());

                    dataGenerator.AddMethod(pubKey);
                    byte[] dataBytes = outputBytes.ToArray();

                    using (Stream outputStream = File.Create(outputFile))
                    {
                        if (applyArmor)
                        {
                            using (ArmoredOutputStream armoredStream = new ArmoredOutputStream(outputStream))
                            {
                                WriteStream(dataGenerator.Open(armoredStream, dataBytes.Length), ref dataBytes);
                            }
                        }
                        else
                        {
                            WriteStream(dataGenerator.Open(outputStream, dataBytes.Length), ref dataBytes);
                        }
                    }
                }
            }
        }

        public static void WriteStream(Stream inputStream, ref byte[] dataBytes)
        {
            using (Stream outputStream = inputStream)
            {
                outputStream.Write(dataBytes, 0, dataBytes.Length);
            }
        }

        public static string GetString(Stream inputStream)
        {
            string output;
            using (StreamReader reader = new StreamReader(inputStream))
            {
                output = reader.ReadToEnd();
            }

            return output;
        }

        public static Stream GetStream(string stringData)
        {
            MemoryStream stream = new MemoryStream();
            StreamWriter writer = new StreamWriter(stream);
            writer.Write(stringData);
            writer.Flush();
            stream.Position = 0;
            return stream;
        }
    }
}