using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Security.Cryptography;
using DistributedPasswordCracker.Client.Models;
using DistributedPasswordCracker.Client.Utilities;

namespace DistributedPasswordCracker.Client
{
    public class Cracking
    {
        /// <summary>
        /// The algorithm used for encryption.
        /// Must be exactly the same algorithm that was used to encrypt the passwords in the password file
        /// </summary>
        private readonly HashAlgorithm _messageDigest;

        public Cracking()
        {
            _messageDigest = new SHA1CryptoServiceProvider();
            //_messageDigest = new MD5CryptoServiceProvider();
            // seems to be same speed
        }

        /// <summary>
        /// Runs the password cracking algorithm
        /// </summary>
        public string RunCracking(string [] dictionary)
        {
            Stopwatch stopwatch = Stopwatch.StartNew();

            List<UserInfo> userInfos =
                PasswordFileHandler.ReadPasswordFile("passwords.txt");
            //Console.WriteLine("passwd opeend");

            List<UserInfoClearText> results = new List<UserInfoClearText>();
            
           for(int i = 0; i < dictionary.Length; i++)
           {
                    String dictionaryEntry = dictionary[i];
                    IEnumerable<UserInfoClearText> partialResult = CheckWordWithVariations(dictionaryEntry, userInfos);
                    results.AddRange(partialResult);
           }
  
            stopwatch.Stop();
            //Console.WriteLine(string.Join(", ", results));
            //Console.WriteLine("Out of {0} password {1} was found ", userInfos.Count, results.Count);
            //Console.WriteLine();
            //Console.WriteLine("Time elapsed: {0}", stopwatch.Elapsed);

            string output = "";
            for(int i = 0; i < results.Count; i++)
                output += $"{results[i].UserName}:{results[i].Password}|";

            return output;
        }

        /// <summary>
        /// Generates a lot of variations, encrypts each of the and compares it to all entries in the password file
        /// </summary>
        /// <param name="dictionaryEntry">A single word from the dictionary</param>
        /// <param name="userInfos">List of (username, encrypted password) pairs from the password file</param>
        /// <returns>A list of (username, readable password) pairs. The list might be empty</returns>
        private IEnumerable<UserInfoClearText> CheckWordWithVariations(String dictionaryEntry, List<UserInfo> userInfos)
        {
            List<UserInfoClearText> result = new List<UserInfoClearText>(); //might be empty

            String possiblePassword = dictionaryEntry;
            IEnumerable<UserInfoClearText> partialResult = CheckSingleWord(userInfos, possiblePassword);
            result.AddRange(partialResult);

            String possiblePasswordUpperCase = dictionaryEntry.ToUpper();
            IEnumerable<UserInfoClearText> partialResultUpperCase = CheckSingleWord(userInfos, possiblePasswordUpperCase);
            result.AddRange(partialResultUpperCase);

            String possiblePasswordCapitalized = StringUtilities.Capitalize(dictionaryEntry);
            IEnumerable<UserInfoClearText> partialResultCapitalized = CheckSingleWord(userInfos, possiblePasswordCapitalized);
            result.AddRange(partialResultCapitalized);

            String possiblePasswordReverse = StringUtilities.Reverse(dictionaryEntry);
            IEnumerable<UserInfoClearText> partialResultReverse = CheckSingleWord(userInfos, possiblePasswordReverse);
            result.AddRange(partialResultReverse);

            for (int i = 0; i < 100; i++)
            {
                String possiblePasswordEndDigit = dictionaryEntry + i;
                IEnumerable<UserInfoClearText> partialResultEndDigit = CheckSingleWord(userInfos, possiblePasswordEndDigit);
                result.AddRange(partialResultEndDigit);
            }

            for (int i = 0; i < 100; i++)
            {
                String possiblePasswordStartDigit = i + dictionaryEntry;
                IEnumerable<UserInfoClearText> partialResultStartDigit = CheckSingleWord(userInfos, possiblePasswordStartDigit);
                result.AddRange(partialResultStartDigit);
            }

            for (int i = 0; i < 10; i++)
            {
                for (int j = 0; j < 10; j++)
                {
                    String possiblePasswordStartEndDigit = i + dictionaryEntry + j;
                    IEnumerable<UserInfoClearText> partialResultStartEndDigit = CheckSingleWord(userInfos, possiblePasswordStartEndDigit);
                    result.AddRange(partialResultStartEndDigit);
                }
            }

            return result;
        }

        /// <summary>
        /// Checks a single word (or rather a variation of a word): Encrypts and compares to all entries in the password file
        /// </summary>
        /// <param name="userInfos"></param>
        /// <param name="possiblePassword">List of (username, encrypted password) pairs from the password file</param>
        /// <returns>A list of (username, readable password) pairs. The list might be empty</returns>
        private IEnumerable<UserInfoClearText> CheckSingleWord(IEnumerable<UserInfo> userInfos, String possiblePassword)
        {
            char[] charArray = possiblePassword.ToCharArray();
            byte[] passwordAsBytes = Array.ConvertAll(charArray, PasswordFileHandler.GetConverter());

            byte[] encryptedPassword = _messageDigest.ComputeHash(passwordAsBytes);
            //string encryptedPasswordBase64 = System.Convert.ToBase64String(encryptedPassword);

            List<UserInfoClearText> results = new List<UserInfoClearText>();

            foreach (UserInfo userInfo in userInfos)
            {
                if (CompareBytes(userInfo.EntryptedPassword, encryptedPassword))  //compares byte arrays
                {
                    results.Add(new UserInfoClearText(userInfo.Username, possiblePassword));
                    Console.WriteLine(userInfo.Username + " " + possiblePassword);
                }
            }
            return results;
        }

        /// <summary>
        /// Compares to byte arrays. Encrypted words are byte arrays
        /// </summary>
        /// <param name="firstArray"></param>
        /// <param name="secondArray"></param>
        /// <returns></returns>
        private static bool CompareBytes(IList<byte> firstArray, IList<byte> secondArray)
        {
            //if (secondArray == null)
            //{
            //    throw new ArgumentNullException("firstArray");
            //}
            //if (secondArray == null)
            //{
            //    throw new ArgumentNullException("secondArray");
            //}
            if (firstArray.Count != secondArray.Count)
            {
                return false;
            }
            for (int i = 0; i < firstArray.Count; i++)
            {
                if (firstArray[i] != secondArray[i])
                    return false;
            }
            return true;
        }

    }
}