using System;
using System.Text;

/*
 * Code by: Christopher Ardelean
 * Version 1.0
 * 2015-01-29
 *
 * I had far too much fun with this one...
 */

namespace Password_Generation
{
    class Program
    {
        static char[] ALPHA = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();
        static char[] alpha = "abcdefghijklmnopqrstuvwxyz".ToCharArray();
        static char[] numeric = "0123456789".ToCharArray();
        static char[] symbol = "!@#$%^&*()[]{};:'\",.<>/?\\|_+-=`~".ToCharArray();

        static string keyboard = "`1234567890-=qwertyuiop[]\\asdfghjkl;'zxcvbnm,./";
        static string KEYBOARD = "~!@#$%^&*()_+QWERTYUIOP{}|ASDFGHJKL:\"ZXCVBNM<>?";

        static string[] units = { "Seconds", "Minutes", "Hours", "Days", "Weeks", "Years", "Decades", "Centuries", "Millenia" };
        static double[] unitValues = { 1, 60, 60, 24, 7, (365.242196 / 7), 10, 10, 10 }; // 365.242196 is a reasonable estimate for leap years

        static void Main(string[] args)
        {
            int length = 0;
            int numberOfPass = 1;
            bool uppercase = false;
            bool lowercase = false;
            bool num = false;
            bool sym = false;
            bool ASCII = false;
            bool again = true;

            while (again)
            {
                Console.Clear();
                Console.WriteLine("Welcome to the password generator.\n");
                Console.WriteLine("Your current character sets are as follows:");
                Console.WriteLine("-------------------------------------------");
                ShowArray("Uppercase", ALPHA);
                ShowArray("Lowercase", alpha);
                ShowArray("Numerics", numeric);
                ShowArray("Symbols", symbol);

                AskInt("How long would you like your password to be", ref length, 1, 32);
                AskInt("How many passwords would you like to generate", ref numberOfPass, 1, 20);
                AskBool("the full ASCII page", ref ASCII);

                if (!ASCII)
                {
                    Console.WriteLine();
                    AskBool("uppercase", ref uppercase);
                    AskBool("lowercase", ref lowercase);
                    AskBool("numerics", ref num);
                    AskBool("symbols", ref sym);
                }

                generatePassword(ASCII, uppercase, lowercase, num, sym, length, numberOfPass);
                AskBool("this tool again", ref again);
            }

            Console.WriteLine("Goodbye!");
        }

        static void ShowArray(string name, char[] array)
        {
            StringBuilder sb = new StringBuilder(80);
            sb.Append(name);
            sb.Append(":\t");

            for (int i = 0; i < array.Length; i++)
                sb.Append(array[i]);

            Console.WriteLine(sb.ToString());
        }

        static void AskBool(string subject, ref bool test)
        {
            Console.Write("Would you like to use {0}? (y|n): ", subject);

            ConsoleKeyInfo key = Console.ReadKey(true);

            while (key.Key != ConsoleKey.Y && key.Key != ConsoleKey.N)
                key = Console.ReadKey(true);

            Console.WriteLine(key.Key);

            test = key.Key == ConsoleKey.Y;
        }

        static void AskInt(string question, ref int response, int lower, int upper)
        {
            if (upper > lower) // Make sure a coder hooking into this library doesn't accidently create an infinite loop.  Defensive coding!
            {
                Console.WriteLine("\n{0}? (Valid Range: {1}-{2})", question, lower, upper);

                while (!Int32.TryParse(Console.ReadLine(), out response) || response > upper || response < lower)
                {
                    Console.WriteLine("That input didn't make sense.  Please type a numeric value between {0} and {1}.", lower, upper);
                }
            }
            else
                throw new Exception("AskInt requires that your upper bound be higher than your lower bound.");
        }

        static void generatePassword(bool ASCII, bool upper, bool lower, bool num, bool sym, int length, int numOfPass)
        {
            StringBuilder sb = new StringBuilder();
            Random r = new Random();
            int RandomLength = 0;
            char[] charset;

            if (length > 0 && length < 33 && (ASCII || upper || lower || num || sym)) // Length should never be either of these values, but this is good defensive coding.  You never know when someone else might mess up your main method.
            {
                for (int j = 0; j < numOfPass; j++)
                {
                    if (ASCII)
                    {
                        RandomLength = 255;

                        for (int i = 0; i < length; i++)
                        {
                            sb.Append((char)(r.Next(RandomLength)+1)); // 0 is NULL terminator, and not alt-able. 255 total values, 1-255.
                        }
                    }
                    else
                    {
                        RandomLength = 0;
                        RandomLength += upper ? ALPHA.Length : 0;
                        RandomLength += lower ? alpha.Length : 0;
                        RandomLength += num ? numeric.Length : 0;
                        RandomLength += sym ? symbol.Length : 0;

                        charset = new char[RandomLength];
                        int curLength = 0;

                        BuildCharset(upper, ref curLength, ref charset, ref ALPHA);
                        BuildCharset(lower, ref curLength, ref charset, ref alpha);
                        BuildCharset(num, ref curLength, ref charset, ref numeric);
                        BuildCharset(sym, ref curLength, ref charset, ref symbol);

                        for (int i = 0; i < length; i++)
                        {
                            int pos = r.Next(RandomLength);
                            sb.Append(charset[pos]);
                        }
                    }

                    Console.WriteLine("\nYour generated password is: {0}", ASCII ? KeyCombo(sb.ToString()) : sb.ToString());
                    if (!ASCII)
                        Console.WriteLine(KeyCombo(sb.ToString()));

                    sb.Clear();
                }

                double stats = Math.Pow((double)RandomLength, (double)length);
                double result1 = Math.Ceiling(stats / 1000);
                double result2 = Math.Ceiling(stats / 10000000);
                double result3 = Math.Ceiling(stats / 100000000000);
                string unit1 = "";
                string unit2 = "";
                string unit3 = "";

                FriendlyUnits(ref result1, ref unit1);
                FriendlyUnits(ref result2, ref unit2);
                FriendlyUnits(ref result3, ref unit3);

                Console.WriteLine("\nPassword Statistics:");
                Console.WriteLine("---------------------");

                if (stats < Int64.MaxValue)
                    Console.WriteLine("\nYour password's uniqueness is 1 in {0:N0}", stats);
                else
                    Console.WriteLine("\nYour password's uniqueness is 1 in {0}", stats);

                if (result1 < 100)
                    Console.WriteLine("At 1,000 guesses per second it would take\t{0:N1}\t{1} to guess.", result1, unit1);
                else
                    Console.WriteLine("At 1,000 guesses per second it would take:\n{0:F1} {1} to guess.", result1, unit1);

                if (result2 < 100)
                    Console.WriteLine("At 10,000,000 guesses per second it would take\t{0:N1}\t{1} to guess.", result2, unit2);
                else
                    Console.WriteLine("At 10,000,000 guesses per second it would take:\n{0:F1} {1} to guess.", result2, unit2);

                if (result3 < 100)
                    Console.WriteLine("At 100 Billion guesses per second it would take\t{0:N1}\t{1} to guess.\n", result3, unit3);
                else
                    Console.WriteLine("At 100 Billion guesses per second it would take:\n{0:F1} {1} to guess.\n", result3, unit3);
            }
            else
            {
                Console.WriteLine("\nNo valid passwords could be generated. Check your criteria, and try again.\n");
            }
        }

        static string KeyCombo (string password)
        {
            StringBuilder sb = new StringBuilder(80);

            for (int i = 0; i < password.Length; i++ )
            {
                char c = password.Substring(i, 1).ToCharArray()[0];
                int k = keyboard.IndexOf(c);
                int K = KEYBOARD.IndexOf(c);

                if (k > 0)
                    sb.Append(string.Format("{0}  ", keyboard.Substring(k, 1).ToUpper()));
                else if (K > 0)
                    sb.Append(string.Format("Shift+{0}  ", keyboard.Substring(K, 1).ToUpper()));
                else if (c == ' ')
                    sb.Append("Spacebar  ");
                else
                    sb.Append(string.Format("Alt+{0}  ", (byte)c));
            }

            return sb.ToString();
        }

        static void FriendlyUnits (ref double d, ref string unit)
        {
            double result = d;
            int i = 0;

            // This code might never run if the result is already within range.
            while (result >= 1 && i < units.Length - 1)
            {
                i++;
                result = result / unitValues[i];

                if (result >= 1) // only assign the result if it's in the right range
                    d = result;
                else // This is the final run of the loop, because the result is too coarse. Reduce i so that the appropriate unit is selected.
                    i--;
            }

            unit = units[i];
        }

        static void BuildCharset (bool test, ref int curLength, ref char[] charset, ref char[] chars)
        {
            if (test)
            {
                chars.CopyTo(charset, curLength);
                curLength += chars.Length;
            }
        }
    }
}