sunrise 3.0.0

// The MIT License (MIT)
//
// Copyright (c) 2018 Nathan Osman
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to
// deal in the Software without restriction, including without limitation the
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
// sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
// IN THE SOFTWARE.

use core::f64::consts::PI;

use crate::math::rem_euclid;

const J2000: f64 = 2451545.;

/// Calculates the angle of the sun relative to the earth for the specified
/// Julian day.
pub(crate) fn solar_mean_anomaly(day: f64) -> f64 {
    rem_euclid(
        (357.5291 + 0.98560028 * (day - J2000)).to_radians(),
        2. * PI,
    )
}

#[cfg(test)]
mod tests {
    use super::*;
    use approx::assert_relative_eq;

    #[test]
    fn test_prime_meridian() {
        assert_relative_eq!(
            solar_mean_anomaly(2440588.),
            f64::to_radians(358.30683),
            epsilon = 0.00001
        )
    }
}