using Isopoh.Cryptography.Argon2;
using Isopoh.Cryptography.SecureArray;
using System;
using System.Buffers.Binary;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace Akari.Prototype.Server.Utils
{
    public static class Security
    {
        public const int DefaultHashLength = 32;
        public const int DefaultSaltLength = 12;

        public static string NewArgon2idHash(byte[] password, int hashLength = DefaultHashLength, int saltLength = DefaultSaltLength, bool clear = false, int? threads = null)
        {
            int t = threads ?? Environment.ProcessorCount / 2;

            if (t < 1)
            {
                t = 1;
            }

            var salt = new byte[saltLength];

            RandomNumberGenerator.Fill(salt);

            var config = new Argon2Config()
            {
                HashLength = hashLength,
                Password = password,
                Salt = salt,
                Lanes = t,
                Threads = t,
                ClearPassword = clear,
                ClearSecret = clear,
                Type = Argon2Type.HybridAddressing,
                Version = Argon2Version.Nineteen
            };

            return Argon2.Hash(config);
        }
        public static string NewArgon2idHash(string password, int hashLength = DefaultHashLength, int saltLength = DefaultSaltLength, bool clear = false, int? threads = null)
        {
            return NewArgon2idHash(Encoding.UTF8.GetBytes(password), hashLength, saltLength, clear, threads);
        }

        public static SecureArray<byte> Argon2idDeriveBytes(byte[] password, byte[] salt, int length, bool clear = false, int? threads = null)
        {
            int t = threads ?? Environment.ProcessorCount / 2;

            if (t < 1)
            {
                t = 1;
            }

            var config = new Argon2Config()
            {
                HashLength = length,
                Password = password,
                Salt = salt,
                Lanes = t,
                Threads = t,
                ClearPassword = clear,
                ClearSecret = clear,
                Type = Argon2Type.HybridAddressing,
                Version = Argon2Version.Nineteen
            };

            return new Argon2(config).Hash();
        }
        public static SecureArray<byte> Argon2idDeriveBytes(string password, string salt, int length, bool clear = false, int? threads = null)
        {
            return Argon2idDeriveBytes(Encoding.UTF8.GetBytes(password), Encoding.UTF8.GetBytes(salt), length, clear, threads);
        }

        // Source: https://stackoverflow.com/a/60891115/7465768
        public static byte[] AesGcmEncrypt(AesGcm key, Span<byte> plain)
        {
            // Get parameter sizes
            int nonceSize = AesGcm.NonceByteSizes.MaxSize;
            int tagSize = AesGcm.TagByteSizes.MaxSize;
            int cipherSize = plain.Length;

            // We write everything into one big array for easier encoding
            int encryptedDataLength = 4 + nonceSize + 4 + tagSize + cipherSize;
            Span<byte> encryptedData = encryptedDataLength <= 1024
                                     ? stackalloc byte[encryptedDataLength]
                                     : new byte[encryptedDataLength];

            // Copy parameters
            BinaryPrimitives.WriteInt32LittleEndian(encryptedData.Slice(0, 4), nonceSize);
            BinaryPrimitives.WriteInt32LittleEndian(encryptedData.Slice(4 + nonceSize, 4), tagSize);

            var nonce = encryptedData.Slice(4, nonceSize);
            var tag = encryptedData.Slice(4 + nonceSize + 4, tagSize);
            var cipherBytes = encryptedData.Slice(4 + nonceSize + 4 + tagSize, cipherSize);

            // Generate secure nonce
            RandomNumberGenerator.Fill(nonce);

            // Encrypt
            key.Encrypt(nonce, plain, cipherBytes, tag);

            // Encode for transmission
            return encryptedData.ToArray();
        }

        public static byte[] AesGcmDecrypt(AesGcm key, Span<byte> encryptedData)
        {
            // Extract parameter sizes
            int nonceSize = BinaryPrimitives.ReadInt32LittleEndian(encryptedData.Slice(0, 4));
            int tagSize = BinaryPrimitives.ReadInt32LittleEndian(encryptedData.Slice(4 + nonceSize, 4));
            int cipherSize = encryptedData.Length - 4 - nonceSize - 4 - tagSize;

            // Extract parameters
            var nonce = encryptedData.Slice(4, nonceSize);
            var tag = encryptedData.Slice(4 + nonceSize + 4, tagSize);
            var cipherBytes = encryptedData.Slice(4 + nonceSize + 4 + tagSize, cipherSize);

            // Decrypt
            Span<byte> plainBytes = cipherSize <= 1024
                                  ? stackalloc byte[cipherSize]
                                  : new byte[cipherSize];

            key.Decrypt(nonce, cipherBytes, tag, plainBytes);

            // Convert plain bytes back into string
            return plainBytes.ToArray();
        }
    }
}