/*   File enumWeek.cpp                  shinnerl@ucla.edu
     Enumerated weekdays.

     Using an enumerated type for weekdays improves the style
     and enhances modularity, at some cost in increased coding.
*/

#include <iostream>
#include <cstdlib>
#include <string>

using namespace std;

enum weekday { UNKNOWN = -1, SUN, MON, TUE, WED, THU, FRI, SAT, };
                                                 // Note: SUN == 0.

string dayToString( weekday day ){
   string answer;
   switch (day) {
      case  SUN:   answer = "SUN";  break;
      case  MON:   answer = "MON";  break;
      case  TUE:   answer = "TUE";  break;
      case  WED:   answer = "WED";  break;
      case  THU:   answer = "THU";  break;
      case  FRI:   answer = "FRI";  break;
      case  SAT:   answer = "SAT";  break;
      default:     answer = "UNKNOWN";
   }
   return answer;
}

weekday stringToDay( string s ){
   weekday answer = UNKNOWN;
   if      (s == "sun" || s == "SUN" )  answer = SUN;
   else if (s == "mon" || s == "MON" )  answer = MON;
   else if (s == "tue" || s == "TUE" )  answer = TUE;
   else if (s == "wed" || s == "WED" )  answer = WED;
   else if (s == "thu" || s == "THU" )  answer = THU;
   else if (s == "fri" || s == "FRI" )  answer = FRI;
   else if (s == "sat" || s == "SAT" )  answer = SAT;
   return answer;
}

void fail( const char* msg ){
   cout << msg << endl;
   exit (EXIT_FAILURE);
}

void checkDate( int date, const char* functionName ){
   if (  date < 1  || date > 31 ){
      string s =   string("\nError in function ") + string(functionName)
                 + string(": invalid date. \n");
      fail (s.c_str());
   }
}

void checkDay( weekday day, const char* functionName ){
   if (  day < SUN  || day > SAT ){
      string s =   string("\nError in function ") + string(functionName)
                 + string(": invalid weekday. \n");
      fail (s.c_str());
   }
}

weekday getDay(){
  const int MAXTRY = 3;
  int count = 0;
  weekday answer;
  string s;
  do {
     cout << " Enter one of the following days: "
	  << " sun mon tue wed thu fri sat :  ";
     cin >> s;
     answer = stringToDay( s );
  } while (answer == UNKNOWN && count++ < MAXTRY );
  return answer;
}

int getDate(){
  const int MAXTRY = 3;
  int count = 0;
  int answer;
  do {
      cout << " Enter an integer between 1 and 31:  ";
      cin >> answer;
  } while ( (answer < 1 || answer > 31) && count++ < MAXTRY );
  return answer;
}

int weekNumber( int dayNum, weekday firstDay ){
   checkDate( dayNum, "weekNumber()");      // Enforce preconditions.
   checkDay( firstDay, "weekNumber()");
   int idealDate = dayNum + firstDay;      // Ideally, the 1st is a Sunday. 
   return  (idealDate - 1) / 7 + 1;
}

weekday dateToDay( int dayNum, weekday firstDay ){
   checkDate( dayNum, "dateToDay()");       // Enforce preconditions.
   checkDay( firstDay, "dateToDay()");
   int idealDate = dayNum + firstDay;      // Ideally, the 1st is a Sunday. 
   return weekday((idealDate - 1) % 7) ;   // Note the explicit cast.
}

int main ()
{
  // ------------------------------------------------
  // Input the first weekday of the month and a date:
  // ------------------------------------------------
  cout << "\n Enter the first weekday of the month. \n"; 
  weekday firstDay = getDay();
  checkDay( firstDay, "getDay()");

  cout << " Enter a month date. \n"; 
  int dayNum = getDate();
  checkDate( dayNum, "getDate()");

  // -------------------------------------
  // Output the day and week for the date:
  // -------------------------------------
  cout << "\n The week number for the date is  "
       <<  weekNumber( dayNum, firstDay ) << ". " << endl;
  cout << " The weekday for the date is      " 
       <<  dayToString( dateToDay(dayNum, firstDay) ) << ". \n" <<  endl; 
  return EXIT_SUCCESS;
}

/*   Sample I/O

Script started on Thu Feb 28 12:16:45 2002
whale.1> weekday

 Enter the first weekday of the month. 
 Enter one of the following days:  sun mon tue wed thu fri sat :  banana
 Enter one of the following days:  sun mon tue wed thu fri sat :  mon
 Enter a month date. 
 Enter an integer between 1 and 31:  437
 Enter an integer between 1 and 31:  -17
 Enter an integer between 1 and 31:  12

 The week number for the date is  2. 
 The weekday for the date is      FRI. 

whale.2> exit
exit

whale.3> cal 4 2002

   April 2002
 S  M Tu  W Th  F  S
    1  2  3  4  5  6
 7  8  9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30

script done on Thu Feb 28 12:17:24 2002
*/