using System;
using System.Security.Cryptography;
using System.Text;

namespace BeWoDatabaseTerminator.Security
{
    public static class PasswordHelper
    {
        private const string _LowerCaseLetters = "abcdefghijklmnopqrstuvwxyz";
        private const string _UpperCaseLetters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        private const string _Numbers          = "0123456789";

        /// <summary>
        /// Erzeugt das zufällige, zehnstellige, alphanumerisches Initialpasswort
        /// </summary>
        /// <param name="random">Random zur Erzeugung zufälliger Indizes</param>
        /// <returns></returns>
        public static string GenerateInitialPassword(Random random)
        {
            var password = "";

            for(var i = 0; i < 10; i++)
            {
                var r1 = random.Next(0, 3);

                switch(r1)
                {
                    case 0:
                        password += _LowerCaseLetters[random.Next(0, 26)];
                        break;
                    case 1:
                        password += _UpperCaseLetters[random.Next(0, 26)];
                        break;
                    case 2:
                        password += _Numbers[random.Next(0, 10)];
                        break;
                    default:
                        password += _LowerCaseLetters[i];
                        break;
                }
            }

            return password;
        }

        /// <summary>
        /// Erzeugt das Passwort für die neuangelegte Datenbank.
        /// </summary>
        /// <param name="initialPassword">Das 10-stellige Initialpasswort</param>
        /// <returns>Ein ApplicationUserCredentials-Objekt mit den für die Datenbank notwendigen strings.</returns>
        public static ApplicationUserCredentials GenerateUserCredentials(string initialPassword)
        {
            if(string.IsNullOrWhiteSpace(initialPassword) || initialPassword.Length < 10)
            {
                throw new ArgumentException("Das Initialpasswort ist ungültig!", nameof(initialPassword));
            }

            var salt = BitConverter.ToString(new MD5CryptoServiceProvider().ComputeHash(Encoding.UTF8.GetBytes(Guid.NewGuid().ToString())));
            var md5 = new MD5CryptoServiceProvider();
            var hashedPassword = BitConverter.ToString(md5.ComputeHash(Encoding.UTF8.GetBytes($"{salt}_{initialPassword}_o238rRndguK4Fh8dsfkhwon54H8n3qo4itv8nz3o4LvnzQs0npmwEp")));
            var bCryptSalt = BCrypt.GenerateSalt();
            var bCryptPassword = BCrypt.HashPassword(initialPassword, bCryptSalt);

            return new ApplicationUserCredentials(salt, hashedPassword, bCryptPassword);
        }
    }

    public class ApplicationUserCredentials
    {
        public string Salt { get; }
        public string HashedPassword { get; }
        public string BCryptPassword { get; }

        public ApplicationUserCredentials(string salt, string hashedPassword, string bCryptPassword)
        {
            Salt = salt;
            HashedPassword = hashedPassword;
            BCryptPassword = bCryptPassword;
        }
    }
}