use crate::{

    collision::{fppoint_round, CircleBounds, DetectedCollisions},

    common::GearId,

};

use fpnum::FPPoint;

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

struct GridBin {

    refs: Vec<GearId>,

    entries: Vec<CircleBounds>,

}

impl GridBin {

    fn new() -> Self {

        Self {

            refs: vec![],

            entries: vec![],

        }

    }

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

        self.refs.push(gear_id);

        self.entries.push(*bounds);

    }

    fn remove(&mut self, gear_id: GearId) -> bool {

        if let Some(pos) = self.refs.iter().position(|id| *id == gear_id) {

            self.refs.swap_remove(pos);

            self.entries.swap_remove(pos);

            true

        } else {

            false

        }

    }

}

const GRID_BIN_SIZE: usize = 128;

pub struct Grid {

    bins: Vec<GridBin>,

    space_size: PotSize,

    bins_count: PotSize,

    index: GridIndex,

}

impl Grid {

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

        let bins_count =

            PotSize::new(size.width() / GRID_BIN_SIZE, size.height() / GRID_BIN_SIZE).unwrap();

        Self {

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

            space_size: size,

            bins_count,

            index: PotSize::square(GRID_BIN_SIZE).unwrap().to_grid_index(),

        }

    }

    fn linear_bin_index(&self, index: Point) -> usize {

        self.bins_count

            .linear_index(index.x as usize, index.y as usize)

    }

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

        self.index.map(fppoint_round(position))

    }

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

        let index = self.linear_bin_index(index);

        &mut self.bins[index]

    }

    fn try_get_bin(&mut self, index: Point) -> Option<&mut GridBin> {

        let index = self.linear_bin_index(index);

        self.bins.get_mut(index)

    }

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

        self.get_bin(self.bin_index(position))

    }

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

        self.lookup_bin(&bounds.center).add(gear_id, bounds);

    }

    fn remove_all(&mut self, gear_id: GearId) {

        for bin in &mut self.bins {

            if bin.remove(gear_id) {

                break;

            }

        }

    }

    pub fn remove(&mut self, gear_id: GearId, bounds: Option<&CircleBounds>) {

        if let Some(bounds) = bounds {

            if !self.lookup_bin(&bounds.center).remove(gear_id) {

                self.remove_all(gear_id);

            }

        } else {

            self.remove_all(gear_id);

        }

    }

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

        for bin in &self.bins {

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

        }

    }

}