//! The international fixed calendar is a 13-month calendar with each month
//! containing exactly 28 days. There is an extra day at the end of the year
//! called the year day.
//!
//! In leap-years there is an extra day inserted at the end of June called the
//! leap day. It is directly after the fourth week of june and is given to june,
//! so it becomes June 29th. The day after June 29th starts the new month, Sol,
//! with Sol 1.
//!
//! [Wikipedia: International Fixed Calendar][wp-ifc]
//! [wp-ifc]: https://en.wikipedia.org/wiki/International_Fixed_Calendar

use time::Date as TimeDate;

const MONTHS: [[&str; 2]; 13] = [
	["January", "Jan"],
	["February", "Feb"],
	["March", "Mar"],
	["April", "Apr"],
	["May", "May"],
	["June", "Jun"],
	["Sol", "Sol"],
	["July", "Jul"],
	["August", "Aug"],
	["September", "Sep"],
	["October", "Oct"],
	["November", "Nov"],
	["December", "Dec"],
];

pub struct Calendar {
	pub year: usize,
	pub ordinal: usize,
}

impl Calendar {
	pub fn from_year(year: usize) -> Self {
		Self { year, ordinal: 0 }
	}

	pub fn from_time_date(date: TimeDate) -> Self {
		let year = date.year() as usize;
		let ord = date.ordinal() as usize;

		Self { year, ordinal: ord }
	}
}

pub struct Date {
	pub year: u32,
	pub month: u8,
	pub day: u8,
}

impl Date {
	pub fn from_time_date(date: TimeDate) -> Self {
		let year = date.year() as u32;
		let ord = date.ordinal();

		if !year_leaps(year) || ord <= 168 {
			// not a leap year path
			// also the "leap year but before the leap-day" path
			Self {
				year,
				month: (ord / 28) as u8,
				day: (ord % 28) as u8,
			}
		} else if ord == 169 {
			Self {
				year,
				month: 6,
				day: 29,
			}
		} else {
			todo!()
		}
	}

	pub fn is_leap(&self) -> bool {
		year_leaps(self.year)
	}
}

/// Whether or not a year is a leap year
fn year_leaps(year: u32) -> bool {
	let four = year % 4 == 0;
	let hundreds = year % 100 == 0;
	let fourhund = year % 400 == 0;

	// leap if:
	// - four AND NOT hundred
	// - four AND hundred AND fourhund

	// `fourhund` here checks `hundreds` by virtue of 100 being a multiple of 400
	four && (!hundreds || fourhund)
}

mod test {
	use crate::ifc::year_leaps;

	#[test]
	fn leap_years() {
		// the examples given by wikipedia
		assert!(year_leaps(2000));
		assert!(!year_leaps(1700));
		assert!(!year_leaps(1800));
		assert!(!year_leaps(1900));

		// testing the four rule
		assert!(year_leaps(2024));
	}
}