using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Security;
using System.Configuration;
using System.Security.Principal;
using System.Collections.Generic;
using System.Security.Cryptography;

namespace FileComparer
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                /*Validating the folder names*/
                if (!Directory.Exists(ConfigurationManager.AppSettings["folder1"]) || !Directory.Exists(ConfigurationManager.AppSettings["folder2"]))
                    throw new Exception("Folder(s) do not exist!");
                else
                {
                    /*Load the Dictionaries*/
                    Diff.loadDictionaries(ConfigurationManager.AppSettings["folder1"], Diff.table1);
                    Diff.loadDictionaries(ConfigurationManager.AppSettings["folder2"], Diff.table2);

                    /*Compare & combine the data*/
                    Diff.processItems();

                    /*Print information*/
                    Diff.printData();
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message + "\n\nException Message>> " + e + "\n" + e.Source + "\n" + e.StackTrace + "\n" + e.InnerException);
            }
            finally
            {
                Console.WriteLine("Press any key to continue...");
                Console.ReadLine();
            }
        }
    }

    class Diff
    {
        public static Dictionary<String, String> table1 = null, table2 = null;
        private static HashSet<String> set = null;
        private static String origPath = null;
        private static MD5 md5 = null;

        static Diff()
        {
            table1 = new Dictionary<string, string>();
            table2 = new Dictionary<string, string>();
            md5 = new MD5CryptoServiceProvider();
            set = new HashSet<string>();
            origPath = string.Empty;
        }

        public static void loadDictionaries(String path, Dictionary<String, String> dict)
        {
            try
            {
                origPath = path;
                dfs(path, dict);
            }
            catch(Exception e)
            {
                throw e;
            }
        }

        public static void dfs(String path, Dictionary<String, String> dict)
        {
            foreach (var x in Directory.GetFiles(path))
                using (FileStream file = new FileStream(x, FileMode.Open))
                {
                    byte[] retVal = md5.ComputeHash(file);

                    StringBuilder sb = new StringBuilder();
                    for (int i = 0; i < retVal.Length; i++)
                        sb.Append(retVal[i].ToString("x2"));

                    dict.Add(x.Replace(origPath, string.Empty), sb.ToString());
                }

            foreach (var y in Directory.GetDirectories(path))
                dfs(y, dict);
        }

        public static void processItems()
        {
            HashSet<String> common = new HashSet<string>(table1.Keys.Intersect(table2.Keys));

            foreach (var x in table1.Keys)
                if (common.Contains(x))
                {
                    if (table1[x] != table2[x])
                        set.Add(x);
                }
                else
                    set.Add(x);

            table1 = null;

            foreach(var y in table2.Keys)
                if (!common.Contains(y))
                    set.Add(y);

            table2 = null;
        }

        public static void printData()
        {
            if (set.Count > 0)
            {
                Console.WriteLine("Items include: ");
                foreach (var x in set)
                    Console.WriteLine(x);
                Console.WriteLine("\nTotal number of changed files: " + set.Count);
            }
            else
                Console.WriteLine("No changes noticed");
        }
    }
}