//! Additional [`Gizmos`] Functions -- Arcs
//!
//! Includes the implementation of [`Gizmos::arc_2d`],
//! and assorted support items.

use crate::circles::DEFAULT_CIRCLE_SEGMENTS;
use crate::prelude::{GizmoConfigGroup, Gizmos};
use bevy_math::{Quat, Vec2, Vec3};
use bevy_render::color::Color;
use std::f32::consts::TAU;

// === 2D ===

impl<'w, 's, T: GizmoConfigGroup> Gizmos<'w, 's, T> {
    /// Draw an arc, which is a part of the circumference of a circle, in 2D.
    ///
    /// This should be called for each frame the arc needs to be rendered.
    ///
    /// # Arguments
    /// - `position` sets the center of this circle.
    /// - `radius` controls the distance from `position` to this arc, and thus its curvature.
    /// - `direction_angle` sets the clockwise  angle in radians between `Vec2::Y` and
    /// the vector from `position` to the midpoint of the arc.
    /// - `arc_angle` sets the length of this arc, in radians.
    ///
    /// # Example
    /// ```
    /// # use bevy_gizmos::prelude::*;
    /// # use bevy_render::prelude::*;
    /// # use bevy_math::prelude::*;
    /// # use std::f32::consts::PI;
    /// fn system(mut gizmos: Gizmos) {
    ///     gizmos.arc_2d(Vec2::ZERO, 0., PI / 4., 1., Color::GREEN);
    ///
    ///     // Arcs have 32 line-segments by default.
    ///     // You may want to increase this for larger arcs.
    ///     gizmos
    ///         .arc_2d(Vec2::ZERO, 0., PI / 4., 5., Color::RED)
    ///         .segments(64);
    /// }
    /// # bevy_ecs::system::assert_is_system(system);
    /// ```
    #[inline]
    pub fn arc_2d(
        &mut self,
        position: Vec2,
        direction_angle: f32,
        arc_angle: f32,
        radius: f32,
        color: Color,
    ) -> Arc2dBuilder<'_, 'w, 's, T> {
        Arc2dBuilder {
            gizmos: self,
            position,
            direction_angle,
            arc_angle,
            radius,
            color,
            segments: None,
        }
    }
}

/// A builder returned by [`Gizmos::arc_2d`].
pub struct Arc2dBuilder<'a, 'w, 's, T: GizmoConfigGroup> {
    gizmos: &'a mut Gizmos<'w, 's, T>,
    position: Vec2,
    direction_angle: f32,
    arc_angle: f32,
    radius: f32,
    color: Color,
    segments: Option<usize>,
}

impl<T: GizmoConfigGroup> Arc2dBuilder<'_, '_, '_, T> {
    /// Set the number of line-segments for this arc.
    pub fn segments(mut self, segments: usize) -> Self {
        self.segments.replace(segments);
        self
    }
}

impl<T: GizmoConfigGroup> Drop for Arc2dBuilder<'_, '_, '_, T> {
    fn drop(&mut self) {
        if !self.gizmos.enabled {
            return;
        }

        let segments = self
            .segments
            .unwrap_or_else(|| segments_from_angle(self.arc_angle));

        let positions = arc_2d_inner(self.direction_angle, self.arc_angle, self.radius, segments)
            .map(|vec2| (vec2 + self.position));
        self.gizmos.linestrip_2d(positions, self.color);
    }
}

fn arc_2d_inner(
    direction_angle: f32,
    arc_angle: f32,
    radius: f32,
    segments: usize,
) -> impl Iterator<Item = Vec2> {
    (0..segments + 1).map(move |i| {
        let start = direction_angle - arc_angle / 2.;

        let angle = start + (i as f32 * (arc_angle / segments as f32));
        Vec2::from(angle.sin_cos()) * radius
    })
}

// === 3D ===

impl<'w, 's, T: GizmoConfigGroup> Gizmos<'w, 's, T> {
    /// Draw an arc, which is a part of the circumference of a circle, in 3D. For default values
    /// this is drawing a standard arc. A standard arc is defined as
    ///
    /// - an arc with a center at `Vec3::ZERO`
    /// - starting at `Vec3::X`
    /// - embedded in the XZ plane
    /// - rotates counterclockwise
    ///
    /// This should be called for each frame the arc needs to be rendered.
    ///
    /// # Arguments
    /// - `angle`: sets how much of a circle circumference is passed, e.g. PI is half a circle. This
    /// value should be in the range (-2 * PI..=2 * PI)
    /// - `radius`: distance between the arc and it's center point
    /// - `position`: position of the arcs center point
    /// - `rotation`: defines orientation of the arc, by default we assume the arc is contained in a
    /// plane parallel to the XZ plane and the default starting point is (`position + Vec3::X`)
    /// - `color`: color of the arc
    ///
    /// # Builder methods
    /// The number of segments of the arc (i.e. the level of detail) can be adjusted with the
    /// `.segments(...)` method.
    ///
    /// # Example
    /// ```
    /// # use bevy_gizmos::prelude::*;
    /// # use bevy_render::prelude::*;
    /// # use bevy_math::prelude::*;
    /// # use std::f32::consts::PI;
    /// fn system(mut gizmos: Gizmos) {
    ///     // rotation rotates normal to point in the direction of `Vec3::NEG_ONE`
    ///     let rotation = Quat::from_rotation_arc(Vec3::Y, Vec3::NEG_ONE.normalize());
    ///
    ///     gizmos
    ///        .arc_3d(
    ///          270.0_f32.to_radians(),
    ///          0.25,
    ///          Vec3::ONE,
    ///          rotation,
    ///          Color::ORANGE
    ///          )
    ///          .segments(100);
    /// }
    /// # bevy_ecs::system::assert_is_system(system);
    /// ```
    #[inline]
    pub fn arc_3d(
        &mut self,
        angle: f32,
        radius: f32,
        position: Vec3,
        rotation: Quat,
        color: Color,
    ) -> Arc3dBuilder<'_, 'w, 's, T> {
        Arc3dBuilder {
            gizmos: self,
            start_vertex: Vec3::X,
            center: position,
            rotation,
            angle,
            radius,
            color,
            segments: None,
        }
    }

    /// Draws the shortest arc between two points (`from` and `to`) relative to a specified `center` point.
    ///
    /// # Arguments
    ///
    /// - `center`: The center point around which the arc is drawn.
    /// - `from`: The starting point of the arc.
    /// - `to`: The ending point of the arc.
    /// - `color`: color of the arc
    ///
    /// # Builder methods
    /// The number of segments of the arc (i.e. the level of detail) can be adjusted with the
    /// `.segments(...)` method.
    ///
    /// # Examples
    /// ```
    /// # use bevy_gizmos::prelude::*;
    /// # use bevy_render::prelude::*;
    /// # use bevy_math::prelude::*;
    /// fn system(mut gizmos: Gizmos) {
    ///     gizmos.short_arc_3d_between(
    ///        Vec3::ONE,
    ///        Vec3::ONE + Vec3::NEG_ONE,
    ///        Vec3::ZERO,
    ///        Color::ORANGE
    ///        )
    ///        .segments(100);
    /// }
    /// # bevy_ecs::system::assert_is_system(system);
    /// ```
    ///
    /// # Notes
    /// - This method assumes that the points `from` and `to` are distinct from `center`. If one of
    /// the points is coincident with `center`, nothing is rendered.
    /// - The arc is drawn as a portion of a circle with a radius equal to the distance from the
    /// `center` to `from`. If the distance from `center` to `to` is not equal to the radius, then
    /// the results will behave as if this were the case
    #[inline]
    pub fn short_arc_3d_between(
        &mut self,
        center: Vec3,
        from: Vec3,
        to: Vec3,
        color: Color,
    ) -> Arc3dBuilder<'_, 'w, 's, T> {
        self.arc_from_to(center, from, to, color, |x| x)
    }

    /// Draws the longest arc between two points (`from` and `to`) relative to a specified `center` point.
    ///
    /// # Arguments
    /// - `center`: The center point around which the arc is drawn.
    /// - `from`: The starting point of the arc.
    /// - `to`: The ending point of the arc.
    /// - `color`: color of the arc
    ///
    /// # Builder methods
    /// The number of segments of the arc (i.e. the level of detail) can be adjusted with the
    /// `.segments(...)` method.
    ///
    /// # Examples
    /// ```
    /// # use bevy_gizmos::prelude::*;
    /// # use bevy_render::prelude::*;
    /// # use bevy_math::prelude::*;
    /// fn system(mut gizmos: Gizmos) {
    ///     gizmos.long_arc_3d_between(
    ///        Vec3::ONE,
    ///        Vec3::ONE + Vec3::NEG_ONE,
    ///        Vec3::ZERO,
    ///        Color::ORANGE
    ///        )
    ///        .segments(100);
    /// }
    /// # bevy_ecs::system::assert_is_system(system);
    /// ```
    ///
    /// # Notes
    /// - This method assumes that the points `from` and `to` are distinct from `center`. If one of
    /// the points is coincident with `center`, nothing is rendered.
    /// - The arc is drawn as a portion of a circle with a radius equal to the distance from the
    /// `center` to `from`. If the distance from `center` to `to` is not equal to the radius, then
    /// the results will behave as if this were the case.
    #[inline]
    pub fn long_arc_3d_between(
        &mut self,
        center: Vec3,
        from: Vec3,
        to: Vec3,
        color: Color,
    ) -> Arc3dBuilder<'_, 'w, 's, T> {
        self.arc_from_to(center, from, to, color, |angle| {
            if angle > 0.0 {
                TAU - angle
            } else if angle < 0.0 {
                -TAU - angle
            } else {
                0.0
            }
        })
    }

    #[inline]
    fn arc_from_to(
        &mut self,
        center: Vec3,
        from: Vec3,
        to: Vec3,
        color: Color,
        angle_fn: impl Fn(f32) -> f32,
    ) -> Arc3dBuilder<'_, 'w, 's, T> {
        // `from` and `to` can be the same here since in either case nothing gets rendered and the
        // orientation ambiguity of `up` doesn't matter
        let from_axis = (from - center).normalize_or_zero();
        let to_axis = (to - center).normalize_or_zero();
        let (up, angle) = Quat::from_rotation_arc(from_axis, to_axis).to_axis_angle();

        let angle = angle_fn(angle);
        let radius = center.distance(from);
        let rotation = Quat::from_rotation_arc(Vec3::Y, up);

        let start_vertex = rotation.inverse() * from_axis;

        Arc3dBuilder {
            gizmos: self,
            start_vertex,
            center,
            rotation,
            angle,
            radius,
            color,
            segments: None,
        }
    }
}

/// A builder returned by [`Gizmos::arc_2d`].
pub struct Arc3dBuilder<'a, 'w, 's, T: GizmoConfigGroup> {
    gizmos: &'a mut Gizmos<'w, 's, T>,
    // this is the vertex the arc starts on in the XZ plane. For the normal arc_3d method this is
    // always starting at Vec3::X. For the short/long arc methods we actually need a way to start
    // at the from position and this is where this internal field comes into play. Some implicit
    // assumptions:
    //
    // 1. This is always in the XZ plane
    // 2. This is always normalized
    //
    // DO NOT expose this field to users as it is easy to mess this up
    start_vertex: Vec3,
    center: Vec3,
    rotation: Quat,
    angle: f32,
    radius: f32,
    color: Color,
    segments: Option<usize>,
}

impl<T: GizmoConfigGroup> Arc3dBuilder<'_, '_, '_, T> {
    /// Set the number of line-segments for this arc.
    pub fn segments(mut self, segments: usize) -> Self {
        self.segments.replace(segments);
        self
    }
}

impl<T: GizmoConfigGroup> Drop for Arc3dBuilder<'_, '_, '_, T> {
    fn drop(&mut self) {
        if !self.gizmos.enabled {
            return;
        }

        let segments = self
            .segments
            .unwrap_or_else(|| segments_from_angle(self.angle));

        let positions = arc_3d_inner(
            self.start_vertex,
            self.center,
            self.rotation,
            self.angle,
            self.radius,
            segments,
        );
        self.gizmos.linestrip(positions, self.color);
    }
}

fn arc_3d_inner(
    start_vertex: Vec3,
    center: Vec3,
    rotation: Quat,
    angle: f32,
    radius: f32,
    segments: usize,
) -> impl Iterator<Item = Vec3> {
    // drawing arcs bigger than TAU degrees or smaller than -TAU degrees makes no sense since
    // we won't see the overlap and we would just decrease the level of details since the segments
    // would be larger
    let angle = angle.clamp(-TAU, TAU);
    (0..=segments)
        .map(move |frac| frac as f32 / segments as f32)
        .map(move |percentage| angle * percentage)
        .map(move |frac_angle| Quat::from_axis_angle(Vec3::Y, frac_angle) * start_vertex)
        .map(move |p| rotation * (p * radius) + center)
}

// helper function for getting a default value for the segments parameter
fn segments_from_angle(angle: f32) -> usize {
    ((angle.abs() / TAU) * DEFAULT_CIRCLE_SEGMENTS as f32).ceil() as usize
}