#include <iostream.h>
#include "roman.h"

istream& getRomanNumeral(istream &i, char buf[]) {
  char c;
  int index = 0;

  buf[index] = '\0';

  while(!index && i.get(c))  {
    switch(c) {
    case 'I':
    case 'V':
    case 'X':
    case 'L':
    case 'C':
    case 'D':
    case 'M':
      buf[index++] = c;
      break;
    }
  }

  // if index is 0, no valid characters were found and eof was reached.
  if(!index) return i;

  int valid = 1;
  while(i.get(c) && valid && index < MAX_ROMAN_LEN) {
    switch(c) {
    case 'I':
    case 'V':
    case 'X': 
    case 'L': 
    case 'C': 
    case 'D': 
    case 'M':
      buf[index++] = c;
      break;
    default:
      valid = 0;
      i.putback(c);
    }
  }
  
  if(index == MAX_ROMAN_LEN) { // we were about to write off the end
    buf[0] = '\0';  // specs demand the empty string be written
    while(valid) {  // now eat up all remaining roman numeral characters
      switch(c) {
      case 'I':
      case 'V':
      case 'X': 
      case 'L': 
      case 'C': 
      case 'D': 
      case 'M':
	i.get(c);
	break;
      default:
	i.putback(c);
	valid = 0;
      }
    }
  } else { // we either reached eof, or the end of the valid string
    buf[index] = '\0';
  }
  
  return i;
}

int thousands(const char roman[], int index, int& sum) {
  while(roman[index] == 'M') {
    sum += 1000;
    index++;
  }

  // sum is now the sum of all M's
  // index is the first non-M character
  return index;
}

int oneFiveTen(const char roman[], int index, int& sum, 
	       char one, char five, char ten, int multiplier) {
  if(roman[index] == one) { // first character is the one character.
                            // check for four or nine
    index++;
    if(roman[index] == ten) {
      sum += (9 * multiplier) ;
      return index + 1;
    } else if (roman[index] == five) {
      sum += (4 * multiplier);
      return index + 1;
    } else {
      sum += multiplier;
    }
  } else if(roman[index] == five) { // first character is the five character
    index++;
    sum += (5 * multiplier);
  }
  // there should be nothing but ones for the remainder of this decimal digit
  while(roman[index] == one) {
    sum += multiplier;
    index++;
  }

  // sum is now correctly accumulated for this digit
  // index should be the first character of the next decimal digit
  // if the input is well formed

  return index;
}
  
int hundreds(const char roman[], int index, int& sum) {
  return oneFiveTen(roman, index, sum, 'C', 'D', 'M', 100);
}

int tens(const char roman[], int index, int& sum) {
  return oneFiveTen(roman, index, sum, 'X', 'L', 'C', 10);
}

int ones(const char roman[], int index, int& sum) {
  return oneFiveTen(roman, index, sum, 'I', 'V', 'X', 1);
}

int romanToInt(const char roman[]) {
  int index = 0, sum = 0;
  
  index = thousands(roman, index, sum);
  index = hundreds(roman, index, sum);
  index = tens(roman, index, sum);
  index = ones(roman, index, sum);

  if(roman[index]) return -1;  // the whole string was not consumed so there
                               // was an error
  return sum;
}