use ::std::f32::consts::PI;

const C4: f32 = (2.0 * PI) / 3.0;
const C5: f32 = (2.0 * PI) / 4.5;

/// <https://easings.net/#easeInElastic>
#[inline]
#[must_use]
pub fn elastic_in(t: f32) -> f32 {
	if t <= 0.0 {
		0.0
	} else if 1.0 <= t {
		1.0
	} else {
		-10.0f32.mul_add(t, -10.0).exp2() * (t.mul_add(10.0, -10.75) * C4).sin()
	}
}

/// <https://easings.net/#easeOutElastic>
#[inline]
#[must_use]
pub fn elastic_out(t: f32) -> f32 {
	if t <= 0.0 {
		0.0
	} else if 1.0 <= t {
		1.0
	} else {
		(-10.0 * t)
			.exp2()
			.mul_add((t.mul_add(10.0, -0.75) * C4).sin(), 1.0)
	}
}

/// <https://easings.net/#easeInOutElastic>
#[inline]
#[must_use]
pub fn elastic_in_out(t: f32) -> f32 {
	if t <= 0.0 {
		0.0
	} else if 1.0 <= t {
		1.0
	} else if t < 0.5 {
		-(20.0f32.mul_add(t, -10.0).exp2() * (20.0f32.mul_add(t, -11.125) * C5).sin()) / 2.0
	} else {
		((-20.0f32).mul_add(t, 10.0).exp2() * (20.0f32.mul_add(t, -11.125) * C5).sin()) / 2.0 + 1.0
	}
}