/* 
* @file
* @brief Determines the date of Easter after 1582
* 
* @details
* The date of Easter is determined in each year through a calculation known as "computus."
* Easter is celebrated on the first Sunday after the Paschal full moon, which is the first full moon on or after 21 March. 
* Determining this date in advance requires a correlation between the lunar months and the solar year, while also accounting for the month, date, and weekday of the Julian or Gregorian calendar.
* The complexity of the algorithm arises because of the desire to associate the date of Easter with the date of the Jewish feast of Passover which, Christians believe, is when Jesus was crucified.
* 
* You can read more about the date of Easter here:
* https://en.wikipedia.org/wiki/Date_of_Easter
* 
* @author [AlternateWalls](https://github.com/AlternateWalls)
*/ 

#include <cassert>    /// for assert
#include <iostream>   /// for IO operations

/*
* @brief Contains information for Easter date 
*/
class EasterYearMonthDay 
{
public:
    int year;   ///< year Easter is on
    int month;  ///< month Easter is on
    int day;    ///< day Easter is on

    EasterYearMonthDay(int newYear, int newMonth, int newDay) 
    {
        year = newYear;  // Assigns year to class
        month = newMonth;
        day = newDay;
    }
};

/*
 * @brief Function that finds the month and day of Easter
 * @params param1 An int "y" of the year you want to find Easter on after
 * 1582
 * @returns An instance of the easterYearMonthDay calss that contains the
 * information (Ex. 420 - 4/20 or April 20th)
 */

EasterYearMonthDay findEaster(int y) {
    if (y > 1582)
    {
        int a = y % 19;   // Year's location on Metonic Calendar
        int b = y / 100;  // Century index
        int c = y % 100;
        int d = b / 4;
        int e = b % 4;  // Takes into account leap years
        int f = (b + 8) / 25;
        int g = (b - f + 1) / 3;
        int h = (19 * a + b - d - g + 15) % 30;  // Days from Mar. 21st until the full moon
        int i = c / 4;
        int k = c % 4;
        int r = (32 + 2 * e + 2 * i - h - k) % 7;  // The number of days from Paschal full moon to next Sunday
        int m = (a + 11 * h + 22 * r) / 451;
        int n = (h + r - 7 * m + 114) / 31;  // Month of Easter
        int p = (h + r - 7 * m + 114) % 31;  // p + 1 is the day of Easter

        // Assign values
        EasterYearMonthDay date(y, n, p + 1);  // Assign values to new instance of class

        //Return date
        return date;
    } 
    else 
    {
        EasterYearMonthDay date(0, 0, 0);

        //Return date
        return date;
    }
}


    static void test() 
    { 
        /*
        * @brief Inputting different year values and comparing the outputs to a calendar
        */

        //2003 | April 20th
        assert(findEaster(2003).month == 4); //Should return true
        assert(findEaster(2003).day == 20); //Should return true

        //1910 | March 27th 
        assert(findEaster(1910).month == 3); //Should return true
        assert(findEaster(1910).day == 27); //Should return true

        //1877 | April 1st
        assert(findEaster(1877).month != 3);  // Should return true
        assert(findEaster(1877).day != 22);   // Should return true

        //1400 | Invalid date
        assert(findEaster(1400).month == 0);  // Should return true
        assert(findEaster(1400).day == 0);   // Should return true
    }

    //Main 
    int main() 
    { 
        test();
        return 0;
    }