use glam::{IVec2, Vec2};

use crate::{
    config::PIXELS_TO_METRES,
    sim::{
        cell::{
            cell::Cell,
            materials::{MaterialForm, MaterialId},
        },
        cell_sim::world::World,
        particle_sim::particle::Particle,
    },
};

pub mod particle;

pub struct ParticleManager {
    pub particles: Vec<Particle>,
}

const PARTICLE_GRAVITY: f32 = 9.81 * PIXELS_TO_METRES;

impl ParticleManager {
    pub fn particle_tick(&mut self, world: &mut World, delta_time: f32) {
        let mut i = 0;
        'outer: while i < self.particles.len() {
            let p = &mut self.particles[i];

            p.life -= delta_time;
            if p.life <= 0.0 {
                self.particles.swap_remove(i);
                continue 'outer;
            }

            p.velocity.y += PARTICLE_GRAVITY * delta_time;
            let dt_velocity = p.velocity * delta_time;

            // Amanatides and Woo's fast Voxel Traversal
            {
                let mut cur = IVec2::new(p.position.x.round() as i32, p.position.y.round() as i32);
                // direction we step for each component on each iteration
                let step_sign =
                    IVec2::new(dt_velocity.x.signum() as i32, dt_velocity.y.signum() as i32);
                let delta = Vec2::new(1.0 / dt_velocity.x.abs(), 1.0 / dt_velocity.y.abs());

                let frac = Vec2::new(
                    if step_sign.x > 0 {
                        (cur.x as f32 + 0.5) - p.position.x
                    } else {
                        p.position.x - (cur.x as f32 - 0.5)
                    },
                    if step_sign.y > 0 {
                        (cur.y as f32 + 0.5) - p.position.y
                    } else {
                        p.position.y - (cur.y as f32 - 0.5)
                    },
                );
                let mut t_max = frac * delta;

                let mut prev = cur;
                if let Some(cell) = world.get_cell_from_game_position(prev.x, prev.y)
                    && [MaterialForm::Solid, MaterialForm::Powder]
                        .contains(&cell.material.def().form)
                {
                    // already occupied, die
                    self.particles.swap_remove(i);
                    continue 'outer;
                }
                while t_max.min_element() <= 1.0 {
                    if t_max.x < t_max.y {
                        cur.x += step_sign.x;
                        t_max.x += delta.x;
                    } else {
                        cur.y += step_sign.y;
                        t_max.y += delta.y;
                    }
                    if let Some(cell) = world.get_cell_from_game_position(cur.x, cur.y)
                        && [MaterialForm::Solid, MaterialForm::Powder]
                            .contains(&cell.material.def().form)
                    {
                        // write ourselves to the board
                        world.set_cell_from_game_position(
                            prev.x,
                            prev.y,
                            Cell::from_material(p.material),
                            false,
                        );
                        self.particles.swap_remove(i);
                        continue 'outer;
                    }
                    prev = cur;
                }
            }

            // no collision, just move
            p.position = p.position + dt_velocity;
            i += 1;
        }
    }

    pub fn new() -> Self {
        ParticleManager {
            particles: Vec::new(),
        }
    }
}