/*
 * Program: Password Manager/Generator
 * This program will generate a password corresponding to a string that a user type in
 * Summer 08 - CS 31 Bridge
 * by Chuong Nguyen
 * version 1.0
 *
 * Exercise: think of and implement a simple rule that maps a long password to one
 *   of fixed length (say all password generated must be 8-character long).
 */

#include <iostream>
#include <string>
#include <cassert> // for the "assert" function used when testing
#include <cstdlib> // for the "exit" function
using namespace std;

/*
 * generatePass will generate a password corresponding to a key, given a master password
 *   and a list of allowed characters
 * -input key: a string representing a domain/site/account (ex: facebook, gmail)
 * -input masterPass: the master password
 * -input charList: a string representing allowed characters for the generated password
 * -output: a password corresponding to the key
 */
string generatePass(string key, string masterPass, string charList);

/*
 * patchToSize will repeat a string until its length is up to a certain size
 * -input str: a string to patch
 * -input size: a desired size
 * -output: a new string of size 'size' that contains repetitions of str
 *   if str's length is <= size, return str
 * ex: patchTosize("abc", 5) => "abcab"
 */
string patchToSize(string str, int size);

/*
 * test helper functions
 */
void test();


// ============================== MAIN PROGRAM ==============================

int main() {

  // uncomment these 2 lines to test our helper functions
  //test();
  //exit(0);

  //at least 8 characters for the master password
  const string MASTER_PASS = "YourVerySecretMasterPassword";

  // allowed characters for the generated password
  const string CHAR_LIST = "abcdefghigklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

  // repeating till the user type 'q'
  string key;
  do {
    cout << "Enter a string for a site/account to generate its password (type 'q' to quit): ";
    getline(cin, key);

    // generate a password corresponding to the key and display it
    cout << generatePass(key, MASTER_PASS, CHAR_LIST) << endl;

  } while ( key != "q" );

}// end main()


// ============================== HELPER FUNCTIONS ==============================

/*
 * generatePass will generate a password corresponding to a key, given a master password
 *   and a list of allowed characters
 * -input key: a string representing a domain/site/account (ex: facebook, gmail)
 * -input masterPass: the master password
 * -input charList: a string representing allowed characters for the generated password
 * -output: a password corresponding to the key
 */
string generatePass(string key, string masterPass, string charList) {

  // if masterPass is shorter than the key, repeat it until its length
  // is the same as the key's length
  int masterPassLen = masterPass.length();
  int keyLen = key.length();
  if ( masterPassLen < keyLen ) {
    masterPass = patchToSize(masterPass, keyLen);
  }

  // generate password by mapping a character in the key to a new character (of charList)
  // simple rule: add the ASCII code of a key[i] and a masterPass[i] together
  // use that number to pick which character in the charList
  // by reducing that number to the range of 0 to charList.length()-1
  string pass;
  int charListLen = charList.length();
  for (int i = 0; i < keyLen; i++) {
    int index = (masterPass[i] + key[i]) % charListLen;
    pass += charList[index];
  }

  return pass;

}// end generatePass(key,masterPass,charList)


/*
 * patchToSize will repeat a string until its length is up to a certain size
 * -input str: a string to patch
 * -input size: a desired size
 * -output: a new string of size 'size' that contains repetitions of str
 *   if str's length is <= size, return str
 * ex: patchTosize("abc", 5) => "abcab"
 */
string patchToSize(string str, int size) {

  int strSize = str.length();

  if ( strSize >= size )
    return str;

  //how many times should str appears evenly in a new string 'newStr' of size 'size'
  int numOfAppearances = size / strSize;
  string newStr;
  for (int i = 0; i < numOfAppearances; i++) {
    newStr += str;
  }

  //how many remaining characters needed to fill up 'newStr'
  int numOfRemainingChars = size % strSize;
  newStr += str.substr(0, numOfRemainingChars);

  return newStr;

}// end patchToSize(str,size)


/*
 * test helper functions
 */
void test() {
  assert( 1
	  && patchToSize("abc", 2) == "abc"
	  && patchToSize("abc", 3) == "abc"
	  && patchToSize("abc", 4) == "abca"
	  && patchToSize("abc", 5) == "abcab"
	  && patchToSize("abc", 6) == "abcabc"
	  && patchToSize("abc", 7) == "abcabca"
	  && patchToSize("abc", 8) == "abcabcab"
	  && patchToSize("abc", 9) == "abcabcabc" );
  cerr << "=== All tests passed ===" << endl;
}// end test()