// date.C
#include <iostream> // for the object cout
#include <cstdlib>
#include <chrono>   // for class system_clock
#include <ctime>    // for the function localtime and structure tm
#include "date.h"   // The implementation file always includes the header file.
using namespace std;

// Definition of static data member
const int date::length[] {
     0,   // dummy, so that January will have subscript 1
    31,   // January
    28,   // February. Pretend there are no leap years.
    31,   // March
    30,   // April
    31,   // May
    30,   // June
    31,   // July
    31,   // August
    30,   // September
    31,   // October
    30,   // November
    31    // December
};

// The constructor installs 3 valid values into a newborn date object,
// or it throws an exception.
date::date(int init_month, int init_day, int init_year)
    : year {init_year}, month {init_month}, day {init_day}
{
    if (month < 1 || month > 12) {
        cerr << "Bad month " << init_month << "\n";
        exit(EXIT_FAILURE);
    }

    if (day < 1 || day > length[month]) {
        cerr << "Bad month " << init_month << " and day " << init_day << "\n";
        exit(EXIT_FAILURE);
    }
}

date::date()    // Default constructor puts today's date into the newborn object.
{
    const auto now {chrono::system_clock::now()};
    const time_t t {chrono::system_clock::to_time_t(now)};
    const tm *const p {localtime(&t)};

    year = p->tm_year + 1900;
    month = p->tm_mon + 1;
    day = p->tm_mday;
}

int date::monthsInYear()
{
    return size(length) - 1;   // number of months in a year
}

void date::print() const  // This member function can't change the date object.
{
    cout << month << "/" << day << "/" << year;
}

void date::next(int n)    // Move forward n days (or backward if n is negative).
{
    if (n >= 0) {
        for (int i {0}; i < n; ++i) {
            next(); // Call the other next function, the one with no argument
        }
    } else {
        for (int i {0}; i < -n; ++i) {
            prev(); // Move backward one day
        }
    }
}

void date::next()   // Move this date object one day into the future.
{
    if (day < length[month]) {
        ++day;
    } else {
        day = 1;             // Advance into the next month.
        if (month < 12) {
            ++month;
        } else {
            month = 1;       // Advance into the next year.
            ++year;
        }
    }
}

void date::prev(int n)    // Move backward n days.
{
    for (int i {0}; i < n; ++i) {
        prev();
    }
}

void date::prev()   // Move this date object one day into the past.
{
    if (day > 1) {
        --day;
    } else {
        // Move to last day of previous month
        if (month > 1) {
            --month;
        } else {
            month = 12;  // Move to previous year
            --year;
        }
        day = length[month];
    }
}