using Scrypt;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;

namespace Manager.Framework.Helpers
{
    /// <summary>
    /// Password utils
    /// </summary>
    public static class PasswordUtils
    {
        private const int DefaultIterationCount = 16384;
        private const int DefaultBlockSize = 8;
        private const int DefaultThreadCount = 1;

        private static readonly Random s_random = new Random((int)(DateTimeOffset.Now.Ticks % 100000));

        #region Secure password management

        /// <summary>
        /// Generate a random key of the specified length (source: https://stackoverflow.com/a/31959204/249000)
        /// </summary>
        /// <param name="length">Length of the resulting key</param>
        /// <param name="chars">Allowed characters for the resulting key</param>
        /// <returns></returns>
        public static string GetUniqueKey(int length = 32, string chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890")
        {
            using (var crypto = new RNGCryptoServiceProvider())
            {
                var data = new byte[length];

                // If chars.Length isn't a power of 2 then there is a bias if
                // we simply use the modulus operator. The first characters of
                // chars will be more probable than the last ones.

                // buffer used if we encounter an unusable random byte. We will
                // regenerate it in this buffer
                byte[] smallBuffer = null;

                // Maximum random number that can be used without introducing a
                // bias
                int maxRandom = byte.MaxValue - ((byte.MaxValue + 1) % chars.Length);

                crypto.GetBytes(data);

                var result = new char[length];

                for (int i = 0; i < length; i++)
                {
                    byte v = data[i];

                    while (v > maxRandom)
                    {
                        if (smallBuffer == null)
                        {
                            smallBuffer = new byte[1];
                        }

                        crypto.GetBytes(smallBuffer);
                        v = smallBuffer[0];
                    }

                    result[i] = chars[v % chars.Length];
                }

                return new string(result);
            }
        }

        /// <summary>
        /// Encode the specified password with the specified pepper with the scrypt algorithm
        /// </summary>
        /// <param name="password">Password to encode</param>
        /// <param name="pepper">Pepper to use</param>
        /// <param name="iterationCount">scrypt algorithm iteration count</param>
        /// <param name="blockSize">scrypt algorithm  block size</param>
        /// <param name="threadCount">scrypt algorithm thread count</param>
        /// <returns>Encoded password</returns>
        public static string Encode(string password, string pepper = "", int iterationCount = DefaultIterationCount, int blockSize = DefaultBlockSize, int threadCount = DefaultThreadCount)
        {
            var encoder = new ScryptEncoder(iterationCount, blockSize, threadCount);
            return encoder.Encode(pepper + password);
        }

        /// <summary>
        /// Compare the specified encoded password with the specified password with the specified pepper with the scrypt algorithm
        /// </summary>
        /// <param name="hashedPassword">Hashed password</param>
        /// <param name="password">Password to compare</param>
        /// <param name="pepper">Pepper to use</param>
        /// <param name="iterationCount">scrypt algorithm iteration count</param>
        /// <param name="blockSize">scrypt algorithm  block size</param>
        /// <param name="threadCount">scrypt algorithm thread count</param>
        /// <returns></returns>
        public static bool Compare(string hashedPassword, string password, string pepper = "", int iterationCount = DefaultIterationCount, int blockSize = DefaultBlockSize, int threadCount = DefaultThreadCount)
        {
            var encoder = new ScryptEncoder(iterationCount, blockSize, threadCount);
            return encoder.Compare(pepper + password, hashedPassword);
        }

        /// <summary>
        /// Generate a random password
        /// </summary>
        /// <param name="pepper">Pepper to use</param>
        /// <param name="iterationCount">scrypt algorithm iteration count</param>
        /// <param name="blockSize">scrypt algorithm  block size</param>
        /// <param name="threadCount">scrypt algorithm thread count</param>
        /// <returns>Generated password</returns>
        public static string Generate(string pepper = "", int iterationCount = DefaultIterationCount, int blockSize = DefaultBlockSize, int threadCount = DefaultThreadCount)
        {
            return Encode(GetUniqueKey(), pepper, iterationCount, blockSize, threadCount);
        }

        #endregion

        /// <summary>
        /// Get a random string of the specified length
        /// </summary>
        /// <param name="length">Number of characters</param>
        /// <returns>Random string of the specified length</returns>
        public static string GetRandomString(int length)
        {
            string pass = "";
            for (int i = 0; i < length; i++)
            {
                int r = s_random.Next(10 + 26 + 26);
                char c;
                if (r < 10) c = (char)(r + 48);
                else if (r < 10 + 26) c = (char)((r - 10) + 65);
                else c = (char)((r - 10 - 26) + 97);
                pass += c;
            }
            return pass;
        }

        /// <summary>
        /// Get a random number with the specified maximum number of digits
        /// </summary>
        /// <param name="maxDigits">Maximum number of digits</param>
        /// <returns>Random number with the specified maximum number of digits</returns>
        public static int GetRandomNumber(int maxDigits)
        {
            return s_random.Next((int)Math.Pow(10, maxDigits));
        }

        /// <summary>
        /// Calculate the MD5 sum of the specified byte array and remove potential dashes
        /// </summary>
        /// <param name="source">Source array</param>
        /// <returns>Source array MD5 sum</returns>
        public static string MD5Sum(byte[] source)
        {
            return BitConverter.ToString(new MD5CryptoServiceProvider().ComputeHash(source)).Replace("-", "").ToLower();
        }

        /// <summary>
        /// Calculate the MD5 sum of the specified string and remove potential dashes
        /// </summary>
        /// <param name="source">Source string</param>
        /// <returns>Source string MD5 sum</returns>
        public static string MD5Sum(string source)
        {
            return MD5Sum(Encoding.ASCII.GetBytes(source));
        }
    }
}