use crate::{

    collision::{fppoint_round, CircleBounds, DetectedCollisions},

    common::GearId,

};

use fpnum::FPPoint;

use integral_geometry::{GridIndex, Point, Size};

struct GridBin {

    refs: Vec<GearId>,

    static_entries: Vec<CircleBounds>,

    dynamic_entries: Vec<CircleBounds>,

}

impl GridBin {

    fn new() -> Self {

        Self {

            refs: vec![],

            static_entries: vec![],

            dynamic_entries: vec![],

        }

    }

}

const GRID_BIN_SIZE: usize = 128;

pub struct Grid {

    bins: Vec<GridBin>,

    space_size: Size,

    bins_count: Size,

    index: GridIndex,

}

impl Grid {

    pub fn new(size: Size) -> Self {

        assert!(size.is_power_of_two());

        let bins_count = Size::new(size.width / GRID_BIN_SIZE, size.height / GRID_BIN_SIZE);

        Self {

            bins: (0..bins_count.area()).map(|_| GridBin::new()).collect(),

            space_size: size,

            bins_count,

            index: Size::square(GRID_BIN_SIZE).to_grid_index(),

        }

    }

    fn bin_index(&self, position: &FPPoint) -> Point {

        self.index.map(fppoint_round(position))

    }

    fn lookup_bin(&mut self, position: &FPPoint) -> &mut GridBin {

        let index = self.bin_index(position);

        &mut self.bins[index.x as usize * self.bins_count.width + index.y as usize]

    }

    pub fn insert_static(&mut self, gear_id: GearId, bounds: &CircleBounds) {

        self.lookup_bin(&bounds.center).static_entries.push(*bounds)

    }

    pub fn insert_dynamic(&mut self, gear_id: GearId, bounds: &CircleBounds) {

        self.lookup_bin(&bounds.center)

            .dynamic_entries

            .push(*bounds)

    }

    pub fn check_collisions(&self, collisions: &mut DetectedCollisions) {

        for bin in &self.bins {

            for bounds in &bin.dynamic_entries {

                for other in &bin.dynamic_entries {

                    if bounds.intersects(other) && bounds != other {

                        collisions.push(0, 0, &bounds.center)

                    }

                }

                for other in &bin.static_entries {

                    if bounds.intersects(other) {

                        collisions.push(0, 0, &bounds.center)

                    }

                }

            }

        }

    }

}