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use crate::astronomy::*;
use crate::helpers::{i64_to_saturated_i32, next};
use crate::rata_die::{Moment, RataDie};
#[allow(unused_imports)]
use core_maths::*;
pub use crate::astronomy::Location;
/// The average length of an Islamic year, equal to 12 moon cycles
pub const MEAN_YEAR_LENGTH: f64 = MEAN_SYNODIC_MONTH * 12.;
/// Different islamic calendars use different epochs (Thursday vs Friday) due to disagreement on the exact date of Mohammed's migration to Mecca.
pub const ISLAMIC_EPOCH_FRIDAY: RataDie = crate::julian::fixed_from_julian(622, 7, 16);
/// Different islamic calendars use different epochs (Thursday vs Friday) due to disagreement on the exact date of Mohammed's migration to Mecca.
pub const ISLAMIC_EPOCH_THURSDAY: RataDie = crate::julian::fixed_from_julian(622, 7, 15);
pub const CAIRO: Location = Location {
latitude: 30.1,
longitude: 31.3,
elevation: 200.0,
utc_offset: (1_f64 / 12_f64),
};
/// The location of Mecca; used for Islamic calendar calculations.
pub const MECCA: Location = Location {
latitude: 6427.0 / 300.0,
longitude: 11947.0 / 300.0,
elevation: 298.0,
utc_offset: (1_f64 / 8_f64),
};
pub fn fixed_from_observational_islamic(
year: i32,
month: u8,
day: u8,
location: Location,
) -> RataDie {
let year = i64::from(year);
let month = i64::from(month);
let day = i64::from(day);
let midmonth = ISLAMIC_EPOCH_FRIDAY.to_f64_date()
+ (((year - 1) as f64) * 12.0 + month as f64 - 0.5) * MEAN_SYNODIC_MONTH;
let lunar_phase = Astronomical::calculate_new_moon_at_or_before(RataDie::new(midmonth as i64));
Astronomical::phasis_on_or_before(RataDie::new(midmonth as i64), location, Some(lunar_phase))
+ day
- 1
}
/// Lisp code reference: <https://github.com/EdReingold/calendar-code2/blob/1ee51ecfaae6f856b0d7de3e36e9042100b4f424/calendar.l#L6983-L6995>
pub fn observational_islamic_from_fixed(date: RataDie, location: Location) -> (i32, u8, u8) {
let lunar_phase = Astronomical::calculate_new_moon_at_or_before(date);
let crescent = Astronomical::phasis_on_or_before(date, location, Some(lunar_phase));
let elapsed_months =
((crescent - ISLAMIC_EPOCH_FRIDAY) as f64 / MEAN_SYNODIC_MONTH).round() as i32;
let year = elapsed_months.div_euclid(12) + 1;
let month = elapsed_months.rem_euclid(12) + 1;
let day = (date - crescent + 1) as u8;
(year, month as u8, day)
}
// Saudi visibility criterion on eve of fixed date in Mecca.
// The start of the new month only happens if both of these criteria are met: The moon is a waxing crescent at sunset of the previous day
// and the moon sets after the sun on that same evening.
fn saudi_criterion(date: RataDie) -> Option<bool> {
let sunset = Astronomical::sunset((date - 1).as_moment(), MECCA)?;
let tee = Location::universal_from_standard(sunset, MECCA);
let phase = Astronomical::lunar_phase(tee, Astronomical::julian_centuries(tee));
let moonlag = Astronomical::moonlag((date - 1).as_moment(), MECCA)?;
Some(phase > 0.0 && phase < 90.0 && moonlag > 0.0)
}
fn adjusted_saudi_criterion(date: RataDie) -> bool {
saudi_criterion(date).unwrap_or_default()
}
// Closest fixed date on or before date when Saudi visibility criterion is held.
pub fn saudi_new_month_on_or_before(date: RataDie) -> RataDie {
let last_new_moon = (Astronomical::lunar_phase_at_or_before(0.0, date.as_moment()))
.inner()
.floor(); // Gets the R.D Date of the prior new moon
let age = date.to_f64_date() - last_new_moon;
// Explanation of why the value 3.0 is chosen: https://github.com/unicode-org/icu4x/pull/3673/files#r1267460916
let tau = if age <= 3.0 && !adjusted_saudi_criterion(date) {
// Checks if the criterion is not yet visible on the evening of date
last_new_moon - 30.0 // Goes back a month
} else {
last_new_moon
};
next(RataDie::new(tau as i64), adjusted_saudi_criterion) // Loop that increments the day and checks if the criterion is now visible
}
pub fn saudi_islamic_from_fixed(date: RataDie) -> (i32, u8, u8) {
let crescent = saudi_new_month_on_or_before(date);
let elapsed_months =
((crescent - ISLAMIC_EPOCH_FRIDAY) as f64 / MEAN_SYNODIC_MONTH).round() as i64;
let year = i64_to_saturated_i32(elapsed_months.div_euclid(12) + 1);
let month = (elapsed_months.rem_euclid(12) + 1) as u8;
let day = ((date - crescent) + 1) as u8;
(year, month, day)
}
pub fn fixed_from_saudi_islamic(year: i32, month: u8, day: u8) -> RataDie {
let midmonth = RataDie::new(
ISLAMIC_EPOCH_FRIDAY.to_i64_date()
+ (((year as f64 - 1.0) * 12.0 + month as f64 - 0.5) * MEAN_SYNODIC_MONTH).floor()
as i64,
);
let first_day_of_month = saudi_new_month_on_or_before(midmonth).to_i64_date();
RataDie::new(first_day_of_month + day as i64 - 1)
}
pub fn fixed_from_tabular_islamic(year: i32, month: u8, day: u8, epoch: RataDie) -> RataDie {
let year = i64::from(year);
let month = i64::from(month);
let day = i64::from(day);
RataDie::new(
(epoch.to_i64_date() - 1)
+ (year - 1) * 354
+ (3 + year * 11).div_euclid(30)
+ 29 * (month - 1)
+ month.div_euclid(2)
+ day,
)
}
pub fn tabular_islamic_from_fixed(date: RataDie, epoch: RataDie) -> (i32, u8, u8) {
let year = i64_to_saturated_i32(((date - epoch) * 30 + 10646).div_euclid(10631));
let prior_days =
date.to_f64_date() - fixed_from_tabular_islamic(year, 1, 1, epoch).to_f64_date();
debug_assert!(prior_days >= 0.0);
debug_assert!(prior_days <= 354.);
let month = (((prior_days * 11.0) + 330.0) / 325.0) as u8; // Prior days is maximum 354 (when year length is 355), making the value always less than 12
debug_assert!(month <= 12);
let day = (date.to_f64_date() - fixed_from_tabular_islamic(year, month, 1, epoch).to_f64_date()
+ 1.0) as u8; // The value will always be number between 1-30 because of the difference between the date and lunar ordinals function.
(year, month, day)
}
/// The number of days in a month for the observational islamic calendar
pub fn observational_islamic_month_days(year: i32, month: u8, location: Location) -> u8 {
let midmonth = ISLAMIC_EPOCH_FRIDAY.to_f64_date()
+ (((year - 1) as f64) * 12.0 + month as f64 - 0.5) * MEAN_SYNODIC_MONTH;
let lunar_phase: f64 =
Astronomical::calculate_new_moon_at_or_before(RataDie::new(midmonth as i64));
let f_date = Astronomical::phasis_on_or_before(
RataDie::new(midmonth as i64),
location,
Some(lunar_phase),
);
Astronomical::month_length(f_date, location)
}
/// The number of days in a month for the Saudi (Umm Al-Qura) calendar
pub fn saudi_islamic_month_days(year: i32, month: u8) -> u8 {
// We cannot use month_days from the book here, that is for the observational calendar
//
// Instead we subtract the two new months calculated using the saudi criterion
let midmonth = Moment::new(
ISLAMIC_EPOCH_FRIDAY.to_f64_date()
+ (((year - 1) as f64) * 12.0 + month as f64 - 0.5) * MEAN_SYNODIC_MONTH,
);
let midmonth_next = midmonth + MEAN_SYNODIC_MONTH;
let month_start = saudi_new_month_on_or_before(midmonth.as_rata_die());
let next_month_start = saudi_new_month_on_or_before(midmonth_next.as_rata_die());
let diff = next_month_start - month_start;
debug_assert!(
diff <= 30,
"umm-al-qura months must not be more than 30 days"
);
u8::try_from(diff).unwrap_or(30)
}
#[cfg(test)]
mod tests {
use super::*;
static TEST_FIXED_DATE: [i64; 33] = [
-214193, -61387, 25469, 49217, 171307, 210155, 253427, 369740, 400085, 434355, 452605,
470160, 473837, 507850, 524156, 544676, 567118, 569477, 601716, 613424, 626596, 645554,
664224, 671401, 694799, 704424, 708842, 709409, 709580, 727274, 728714, 744313, 764652,
];
// Removed: 601716 and 727274 fixed dates
static TEST_FIXED_DATE_UMMALQURA: [i64; 31] = [
-214193, -61387, 25469, 49217, 171307, 210155, 253427, 369740, 400085, 434355, 452605,
470160, 473837, 507850, 524156, 544676, 567118, 569477, 613424, 626596, 645554, 664224,
671401, 694799, 704424, 708842, 709409, 709580, 728714, 744313, 764652,
];
// Values from lisp code
static SAUDI_CRITERION_EXPECTED: [bool; 33] = [
false, false, true, false, false, true, false, true, false, false, true, false, false,
true, true, true, true, false, false, true, true, true, false, false, false, false, false,
false, true, false, true, false, true,
];
// Values from lisp code, removed two expected months.
static SAUDI_NEW_MONTH_OR_BEFORE_EXPECTED: [f64; 31] = [
-214203.0, -61412.0, 25467.0, 49210.0, 171290.0, 210152.0, 253414.0, 369735.0, 400063.0,
434348.0, 452598.0, 470139.0, 473830.0, 507850.0, 524150.0, 544674.0, 567118.0, 569450.0,
613421.0, 626592.0, 645551.0, 664214.0, 671391.0, 694779.0, 704405.0, 708835.0, 709396.0,
709573.0, 728709.0, 744301.0, 764647.0,
];
#[test]
fn test_islamic_epoch_friday() {
let epoch = ISLAMIC_EPOCH_FRIDAY.to_i64_date();
// Iso year of Islamic Epoch
let epoch_year_from_fixed = crate::iso::iso_year_from_fixed(RataDie::new(epoch));
// 622 is the correct ISO year for the Islamic Epoch
assert_eq!(epoch_year_from_fixed, 622);
}
#[test]
fn test_islamic_epoch_thursday() {
let epoch = ISLAMIC_EPOCH_THURSDAY.to_i64_date();
// Iso year of Islamic Epoch
let epoch_year_from_fixed = crate::iso::iso_year_from_fixed(RataDie::new(epoch));
// 622 is the correct ISO year for the Islamic Epoch
assert_eq!(epoch_year_from_fixed, 622);
}
#[test]
fn test_saudi_criterion() {
for (boolean, f_date) in SAUDI_CRITERION_EXPECTED.iter().zip(TEST_FIXED_DATE.iter()) {
let bool_result = saudi_criterion(RataDie::new(*f_date)).unwrap();
assert_eq!(*boolean, bool_result, "{f_date:?}");
}
}
#[test]
fn test_saudi_new_month_or_before() {
for (date, f_date) in SAUDI_NEW_MONTH_OR_BEFORE_EXPECTED
.iter()
.zip(TEST_FIXED_DATE_UMMALQURA.iter())
{
let date_result = saudi_new_month_on_or_before(RataDie::new(*f_date)).to_f64_date();
assert_eq!(*date, date_result, "{f_date:?}");
}
}
}