#include <iostream>
#include <string>
#include <iomanip>
#include <fstream>

using namespace std;

const string FILE_NAME = "message.txt";

const size_t LETTERS = 26;

const size_t  TOP_COUNT = 10;
// the bard 
const char TOP_LETTERS[TOP_COUNT] {'e','t','o','a','h','i','s','r','n','l'};
// dictioniary (wikipedia)
//const char TOP_LETTERS[TOP_COUNT] {'e','s','i','a','r','n','t','o','l','c'};
// text (wikipedia)
//const char TOP_LETTERS[TOP_COUNT] {'e','t','a','o','i','n','s','h','r','d'};

void ReadMessage(string & message);
void FrequencyAnalysis(string message, int counts[LETTERS]);
void PrintFrequencyTable(int counts[]);
void Decode(string & message, int counts[]);
size_t FindMax(int counts[]);
void SubLetter(string message, string & newMessage, char letter, char replace);

int main() {

    int counts[LETTERS]{};
    string message;


    ReadMessage(message);
    cout << "The Message is: " << endl << endl;
    cout << message << endl;

    FrequencyAnalysis(message, counts);

    cout << "Frequency Analysis " << endl;
    PrintFrequencyTable(counts);
    cout << endl;

    Decode(message, counts);
    cout << "The decoded message is: " << endl << endl;
    cout << message << endl;
    cout << endl;

    return 0;
}

void  ReadMessage(string & message){

    ifstream messageFile;
    string line;

    message = "";

    messageFile.open(FILE_NAME);

    getline(messageFile, line);
    while (messageFile) {
        message += line + '\n';
        getline(messageFile, line);
    }

    messageFile.close();
}

void PrintFrequencyTable(int counts[]){
   size_t i;

   for(i=0;i<13;i++) {
      cout << setw(2) << static_cast<char>(i+'a') << setw(5) << counts[i] 
           << setw(5) <<  static_cast<char>(i + 'a' + 13)
           << setw(5) << counts[i+13] << endl;
   }
   cout << endl;

   return;
}

size_t FindMax(int counts[]) {
   int max = 0;
   size_t maxPos = 0;
   size_t i;

   for(i = 0; i < LETTERS; i++) {
      if (counts[i] > max) {
         max = counts[i];
         maxPos = i;
      }
   }

   return maxPos;
}

void SubLetter(string message, string & newMessage, char letter, char replace){
   size_t i;

   for(i = 0; i < message.size(); i++) {
      if (static_cast<char>(tolower(message[i]) == letter)) {
         if (isupper(message[i])) {
            newMessage[i] = static_cast<char>(toupper(replace));
         } else {
             newMessage[i] = replace;
         }
      }
   }

   return;
}

void Decode(string & message, int counts[]){
    size_t pos;
    size_t i;
    char letter;
    string newMessage = message;

    for(i = 0; i< TOP_COUNT; i++) {
        pos = FindMax(counts);

        // so we don't use it again.
        counts[pos] = 0;

        letter = static_cast<char> (pos + 'a');
        cout << "Replacing " << letter << " with " << TOP_LETTERS[i] << endl;
        SubLetter(message, newMessage, letter, TOP_LETTERS[i]);
    }

    cout << endl;

    message = newMessage;

    return;
}

void FrequencyAnalysis(string message, int counts[LETTERS]){
    size_t i;
    size_t offset;

    for (i = 0; i < message.size(); i++) {
        if (isalpha(message[i])) {
           offset = tolower(message[i]) - 'a';
           counts[offset]++;
        }
    }

    return;
}