package calendar;

import java.util.Scanner;
class Calendar {
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);

    // prompt the user to enter the year
    System.out.print("Enter full year (eg., 2001)");
    int year = input.nextInt();

     // promt the user to enter the month
     System.out.print("Enter the month as a number (eg., 6 for June) ");
     int month = input.nextInt ();

    // Print Calendar for the month of the year
    printMonth(year, month);
  }

  // print the calendar for a month in a year
  public static void printMonth(int year, int month){
      // print the headings of the calendar
      printMonthTitle(year,month);
      // print the body of the calenda
      printMonthBody (year,month);
  }

  // printh the month title, eg., March 2012
  public static void printMonthTitle(int year, int month){
      System.out.println("        " + getMonthName(month)+ " " +year);
      System.out.println("-----------------------------");
      System.out.println(" Sun Mon Tue Wed Thu Fri Sat ");
  }
  // get the name for the month
  public static String getMonthName(int month) {
      String monthName = "";
      switch (month){
      case 1:monthName = "January"; break;
      case 2:monthName = "February"; break;
      case 3:monthName = "March"; break;
      case 4:monthName = "April"; break;
      case 5:monthName = "May"; break;
      case 6:monthName = "June"; break;
      case 7:monthName= "July"; break;
      case 8:monthName = "August"; break;
      case 9:monthName = "September"; break;
      case 10:monthName = "October"; break;
      case 11:monthName = "November"; break;
      case 12:monthName = "December";
  }
  return monthName;
  }

  // Print month body
  public static void printMonthBody(int year, int month){
      // Get start day of the week for the first date in the month
      int startDay = getStartDay(year, month);
      // Get number of days in the month
      int numberOfDaysInMonth = getNumberOfDaysInMonth(year, month);
      // pad space before the first day of the month
      int i=0;
      for (i=0; i< startDay; i++)
          System.out.print("   ");
      for (i=1; i<=numberOfDaysInMonth; i++){
          System.out.printf("%4d",i);
          if ((i + startDay)% 7 == 0)
              System.out.println();
      }
      System.out.println();
  }
  // Get the start day of month/1/year
  public static int getStartDay(int year, int month){
      final int START_DAY_FOR_JAN_1_1800 = 3;
      // get total number of days from 1/1/1800 to month/1/year
      int totalNumberOfDays = getTotalNumberOfDays(year,month);
      // return the start day for month/1/year
      return (totalNumberOfDays + START_DAY_FOR_JAN_1_1800) % 7;
  }
  // Get the total number of days since January 1, 1800
  public static int getTotalNumberOfDays(int year, int month){
      int total = 0;
      // get the total days from 1800 to 1/1/year
      for (int i = 1800; i < year; i++)
          if (isleapYear(i))
              total = total + 366;
          else
              total = total + 365;
      // add days from Jan to the month prior to the calendar month
      for (int i =1; i < month; i++)
        total = total + getNumberOfDaysInMonth(year,i);
    return total;
  }
  // Get the number of days in a month
  public static int getNumberOfDaysInMonth(int year, int month){
      if (month ==1 || month ==3 || month ==5 || month == 7 || month ==8 ||
              month == 10 || month == 12)
          return 31;
      if (month == 4 || month == 6 || month == 9 || month == 11)
          return 30;
      if (month == 2) return isleapYear(year) ? 29:28;
      return 0; // if month is incorrect
  }
  // Determine if it is a leap year
  public static boolean isleapYear(int year){
      return year % 400 == 0 || (year % 4 == 0 && year % 100 != 0);
  }
}