use crate::{

    collision::{fppoint_round, CircleBounds, DetectedCollisions},

    common::GearId,

};

use fpnum::FPPoint;

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

struct GridBin {

    static_refs: Vec<GearId>,

    static_entries: Vec<CircleBounds>,

    dynamic_refs: Vec<GearId>,

    dynamic_entries: Vec<CircleBounds>,

}

impl GridBin {

    fn new() -> Self {

        Self {

            static_refs: vec![],

            static_entries: vec![],

            dynamic_refs: 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 get_bin(&mut self, index: Point) -> &mut GridBin {

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

    }

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

        self.get_bin(self.bin_index(position))

    }

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

        let bin = self.lookup_bin(&bounds.center);

        bin.static_refs.push(gear_id);

        bin.static_entries.push(*bounds)

    }

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

        let bin = self.lookup_bin(&bounds.center);

        bin.dynamic_refs.push(gear_id);

        bin.dynamic_entries.push(*bounds);

    }

    pub fn update_position(

        &mut self,

        gear_id: GearId,

        old_position: &FPPoint,

        new_position: &FPPoint,

    ) {

        let old_bin_index = self.bin_index(old_position);

        let new_bin_index = self.bin_index(new_position);

        let old_bin = self.lookup_bin(old_position);

        if let Some(index) = old_bin.dynamic_refs.iter().position(|id| *id == gear_id) {

            if old_bin_index == new_bin_index {

                old_bin.dynamic_entries[index].center = *new_position

            } else {

                let bounds = old_bin.dynamic_entries.swap_remove(index);

                let new_bin = self.get_bin(new_bin_index);

                new_bin.dynamic_refs.push(gear_id);

                new_bin.dynamic_entries.push(CircleBounds {

                    center: *new_position,

                    ..bounds

                });

            }

        } else if let Some(index) = old_bin.static_refs.iter().position(|id| *id == gear_id) {

            let bounds = old_bin.static_entries.swap_remove(index);

            old_bin.static_refs.swap_remove(index);

            let new_bin = if old_bin_index == new_bin_index {

                old_bin

            } else {

                self.get_bin(new_bin_index)

            };

            new_bin.dynamic_refs.push(gear_id);

            new_bin.dynamic_entries.push(CircleBounds {

                center: *new_position,

                ..bounds

            });

        }

    }

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

        for bin in &self.bins {

            for (index, bounds) in bin.dynamic_entries.iter().enumerate() {

                for (other_index, other) in bin.dynamic_entries.iter().enumerate().skip(index + 1) {

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

                        collisions.push(

                            bin.dynamic_refs[index],

                            Some(bin.dynamic_refs[other_index]),

                        )

                    }

                }

                for (other_index, other) in bin.static_entries.iter().enumerate() {

                    if bounds.intersects(other) {

                        collisions.push(

                            bin.dynamic_refs[index],

                            Some(bin.static_refs[other_index]),

                        )

                    }

                }

            }

        }

    }

}