bevy_lagrange 0.0.2

use bevy::prelude::*;
use bevy_kana::Position;

use crate::constants::EPSILON;
use crate::constants::MIN_ORBIT_RADIUS;
use crate::constants::SMOOTHNESS_EXPONENT;

pub(crate) fn calculate_from_translation_and_focus(
    translation: impl Into<Position>,
    focus: impl Into<Position>,
    axis: [Vec3; 3],
) -> (f32, f32, f32) {
    let translation = translation.into();
    let focus = focus.into();
    let axis = Mat3::from_cols(axis[0], axis[1], axis[2]);
    let comp_vec = *translation - *focus;
    let mut radius = comp_vec.length();
    if radius < f32::EPSILON {
        radius = MIN_ORBIT_RADIUS;
    }
    let comp_vec = axis * comp_vec;
    let yaw = comp_vec.x.atan2(comp_vec.z);
    let pitch = (comp_vec.y / radius).asin();
    (yaw, pitch, radius)
}

/// Update `transform` based on yaw, pitch, and the camera's focus and radius
pub(crate) fn update_orbit_transform(
    yaw: f32,
    pitch: f32,
    mut radius: f32,
    focus: impl Into<Position>,
    transform: &mut Transform,
    projection: &mut Projection,
    axis: [Vec3; 3],
) {
    let focus = focus.into();
    let mut new_transform = Transform::IDENTITY;
    if let Projection::Orthographic(ref mut p) = *projection {
        p.scale = radius;
        // IMPORTANT: Do NOT replace this with `f32::midpoint()`.
        // On aarch64, `midpoint()` promotes to f64 intermediate precision:
        //   ((self as f64 + other as f64) / 2.0) as f32
        // This produces a subtly different camera distance than plain f32 arithmetic.
        // That tiny difference shifts the projected screen-space bounds just enough
        // to flip the fit overlay balance check (tolerance: 0.001) — causing
        // all margin labels to show green/balanced when they should show red/unbalanced.
        #[expect(
            clippy::manual_midpoint,
            reason = "f32::midpoint uses f64 on aarch64, breaking fit visualization balance detection"
        )]
        {
            radius = (p.near + p.far) / 2.0;
        }
    }
    let yaw_rot = Quat::from_axis_angle(axis[1], yaw);
    let pitch_rot = Quat::from_axis_angle(axis[0], -pitch);
    new_transform.rotation *= yaw_rot * pitch_rot;
    new_transform.translation += *focus + new_transform.rotation * Vec3::new(0.0, 0.0, radius);
    *transform = new_transform;
}

pub(crate) fn approx_equal(a: f32, b: f32) -> bool { (a - b).abs() < EPSILON }

pub(crate) fn lerp_and_snap_f32(from: f32, to: f32, smoothness: f32, dt: f32) -> f32 {
    let t = smoothness.powi(SMOOTHNESS_EXPONENT);
    let mut new_value = from.lerp(to, 1.0 - t.powf(dt));
    if smoothness < 1.0 && approx_equal(new_value, to) {
        new_value = to;
    }
    new_value
}

pub(crate) fn lerp_and_snap_position(
    from: impl Into<Position>,
    to: impl Into<Position>,
    smoothness: f32,
    dt: f32,
) -> Position {
    let from = from.into();
    let to = to.into();
    let t = smoothness.powi(SMOOTHNESS_EXPONENT);
    let mut new_value = (*from).lerp(*to, 1.0 - t.powf(dt));
    if smoothness < 1.0 && approx_equal((new_value - *to).length(), 0.0) {
        new_value.x = to.x;
    }
    Position(new_value)
}

#[cfg(test)]
#[allow(
    clippy::unreadable_literal,
    clippy::float_cmp,
    reason = "test assertions verify deterministic bitwise-exact float results"
)]
mod calculate_from_translation_and_focus_tests {
    use std::f32::consts::PI;

    use float_cmp::approx_eq;

    use super::*;
    const AXIS: [Vec3; 3] = [Vec3::X, Vec3::Y, Vec3::Z];
    const AXIS_Z_UP: [Vec3; 3] = [Vec3::X, Vec3::Z, Vec3::Y];

    #[test]
    fn zero() {
        let translation = Position::new(0.0, 0.0, 0.0);
        let focus = Position::default();
        let (yaw, pitch, radius) = calculate_from_translation_and_focus(translation, focus, AXIS);
        assert_eq!(yaw, 0.0);
        assert_eq!(pitch, 0.0);
        assert_eq!(radius, MIN_ORBIT_RADIUS);
    }

    #[test]
    fn zero_z_up_axis() {
        let translation = Position::new(0.0, 0.0, 0.0);
        let focus = Position::default();
        let (yaw, pitch, radius) =
            calculate_from_translation_and_focus(translation, focus, AXIS_Z_UP);
        assert_eq!(yaw, 0.0);
        assert_eq!(pitch, 0.0);
        assert_eq!(radius, MIN_ORBIT_RADIUS);
    }

    #[test]
    fn in_front() {
        let translation = Position::new(0.0, 0.0, 5.0);
        let focus = Position::default();
        let (yaw, pitch, radius) = calculate_from_translation_and_focus(translation, focus, AXIS);
        assert_eq!(yaw, 0.0);
        assert_eq!(pitch, 0.0);
        assert_eq!(radius, 5.0);
    }

    #[test]
    fn in_front_z_up_axis() {
        let translation = Position::new(0.0, 5.0, 0.0);
        let axis = [Vec3::X, Vec3::Z, Vec3::Y];
        let focus = Position::default();
        let (yaw, pitch, radius) = calculate_from_translation_and_focus(translation, focus, axis);
        assert_eq!(yaw, 0.0);
        assert_eq!(pitch, 0.0);
        assert_eq!(radius, 5.0);
    }

    #[test]
    fn to_the_side() {
        let translation = Position::new(5.0, 0.0, 0.0);
        let focus = Position::default();
        let (yaw, pitch, radius) = calculate_from_translation_and_focus(translation, focus, AXIS);
        assert!(approx_eq!(f32, yaw, PI / 2.0));
        assert_eq!(pitch, 0.0);
        assert_eq!(radius, 5.0);
    }

    #[test]
    fn above() {
        let translation = Position::new(0.0, 5.0, 0.0);
        let focus = Position::default();
        let (yaw, pitch, radius) = calculate_from_translation_and_focus(translation, focus, AXIS);
        assert_eq!(yaw, 0.0);
        assert!(approx_eq!(f32, pitch, PI / 2.0));
        assert_eq!(radius, 5.0);
    }

    #[test]
    fn above_z_as_up_axis() {
        let translation = Position::new(0.0, 0.0, 5.0);
        let focus = Position::default();
        let (yaw, pitch, radius) =
            calculate_from_translation_and_focus(translation, focus, AXIS_Z_UP);
        assert_eq!(yaw, 0.0);
        assert!(approx_eq!(f32, pitch, PI / 2.0));
        assert_eq!(radius, 5.0);
    }

    #[test]
    fn arbitrary() {
        let translation = Position::new(0.92563736, 3.864204, -1.0105048);
        let focus = Position::default();
        let (yaw, pitch, radius) = calculate_from_translation_and_focus(translation, focus, AXIS);
        assert!(approx_eq!(f32, yaw, 2.4));
        assert!(approx_eq!(f32, pitch, 1.23));
        assert_eq!(radius, 4.1);
    }

    #[test]
    fn negative_x() {
        let translation = Position::new(-5.0, 5.0, 9.0);
        let focus = Position::default();
        let (yaw, pitch, radius) = calculate_from_translation_and_focus(translation, focus, AXIS);
        assert!(approx_eq!(f32, yaw, -0.5070985));
        assert!(approx_eq!(f32, pitch, 0.45209613));
        assert!(approx_eq!(f32, radius, 11.445523));
    }
}

#[cfg(test)]
#[allow(
    clippy::unreadable_literal,
    clippy::float_cmp,
    reason = "test assertions verify deterministic bitwise-exact float results"
)]
mod approx_equal_tests {
    use super::*;

    #[test]
    fn same_value_is_approx_equal() {
        assert!(approx_equal(1.0, 1.0));
    }

    #[test]
    fn value_within_threshold_is_approx_equal() {
        assert!(approx_equal(1.0, 1.0000001));
    }

    #[test]
    fn value_outside_threshold_is_not_approx_equal() {
        assert!(!approx_equal(1.0, 1.01));
    }
}

#[cfg(test)]
#[allow(
    clippy::unreadable_literal,
    clippy::float_cmp,
    reason = "test assertions verify deterministic bitwise-exact float results"
)]
mod lerp_and_snap_f32_tests {
    use super::*;

    #[test]
    fn lerps_when_output_outside_snap_threshold() {
        let out = lerp_and_snap_f32(1.0, 2.0, 0.5, 1.0);
        // Due to the frame rate independence, this value is not easily predictable
        assert_eq!(out, 1.9921875);
    }

    #[test]
    fn snaps_to_target_when_inside_threshold() {
        let out = lerp_and_snap_f32(1.9991, 2.0, 0.5, 1.0);
        assert_eq!(out, 2.0);
        let out = lerp_and_snap_f32(1.9991, 2.0, 0.1, 1.0);
        assert_eq!(out, 2.0);
        let out = lerp_and_snap_f32(1.9991, 2.0, 0.9, 1.0);
        assert_eq!(out, 2.0);
    }

    #[test]
    fn does_not_snap_if_smoothness_is_one() {
        // Smoothness of one results in the value not changing, so it doesn't make sense to snap
        let out = lerp_and_snap_f32(1.9991, 2.0, 1.0, 1.0);
        assert_eq!(out, 1.9991);
    }
}

#[cfg(test)]
#[allow(
    clippy::unreadable_literal,
    clippy::float_cmp,
    reason = "test assertions verify deterministic bitwise-exact float results"
)]
mod lerp_and_snap_position_tests {
    use super::*;

    #[test]
    fn lerps_when_output_outside_snap_threshold() {
        let out = lerp_and_snap_position(Position::default(), Position(Vec3::X), 0.5, 1.0);
        // Due to the frame rate independence, this value is not easily predictable
        assert_eq!(out, Position::new(0.9921875, 0.0, 0.0));
    }

    #[test]
    fn snaps_to_target_when_inside_threshold() {
        let out = lerp_and_snap_position(Position(Vec3::X * 0.9991), Position(Vec3::X), 0.5, 1.0);
        assert_eq!(out, Position(Vec3::X));
        let out = lerp_and_snap_position(Position(Vec3::X * 0.9991), Position(Vec3::X), 0.1, 1.0);
        assert_eq!(out, Position(Vec3::X));
        let out = lerp_and_snap_position(Position(Vec3::X * 0.9991), Position(Vec3::X), 0.9, 1.0);
        assert_eq!(out, Position(Vec3::X));
    }

    #[test]
    fn does_not_snap_if_smoothness_is_one() {
        // Smoothness of one results in the value not changing, so it doesn't make sense to snap
        let out = lerp_and_snap_position(Position(Vec3::X * 0.9991), Position(Vec3::X), 1.0, 1.0);
        assert_eq!(out, Position(Vec3::X * 0.9991));
    }
}