use std::{

    ops::RangeInclusive

};

use crate::{

    common::{GearId, GearData, GearDataProcessor},

    physics::PhysicsData,

    grid::Grid

};

use fpnum::*;

use integral_geometry::{

    Point, Size, GridIndex

};

use land2d::Land2D;

pub fn fppoint_round(point: &FPPoint) -> Point {

    Point::new(point.x().round() as i32, point.y().round() as i32)

}

#[derive(PartialEq, Eq, Clone, Copy, Debug)]

pub struct CircleBounds {

    pub center: FPPoint,

    pub radius: FPNum

}

impl CircleBounds {

    pub fn intersects(&self, other: &CircleBounds) -> bool {

        (other.center - self.center).is_in_range(self.radius + other.radius)

    }

    pub fn rows(&self) -> impl Iterator<Item = (usize, RangeInclusive<usize>)> {

        let radius = self.radius.abs_round() as usize;

        let center = Point::from_fppoint(&self.center);

        (center.y as usize - radius..=center.y as usize + radius)

            .map(move |row| (row, center.x as usize - radius..=center.x as usize + radius))

    }

}

#[derive(PartialEq, Eq, Clone, Copy, Debug)]

pub struct CollisionData {

    pub bounds: CircleBounds

}

impl GearData for CollisionData {}

#[derive(PartialEq, Eq, Clone, Copy, Debug)]

pub struct ContactData {

    pub elasticity: FPNum,

    pub friction: FPNum

}

impl GearData for ContactData {}

struct EnabledCollisionsCollection {

    gear_ids: Vec<GearId>,

    collisions: Vec<CollisionData>

}

impl EnabledCollisionsCollection {

    fn new() -> Self {

        Self {

            gear_ids: Vec::new(),

            collisions: Vec::new()

        }

    }

    fn push(&mut self, gear_id: GearId, collision: CollisionData) {

        self.gear_ids.push(gear_id);

        self.collisions.push(collision);

    }

    fn iter(&self) -> impl Iterator<Item = (GearId, &CollisionData)> {

        self.gear_ids.iter().cloned().zip(self.collisions.iter())

    }

}

pub struct CollisionProcessor {

    grid: Grid,

    enabled_collisions: EnabledCollisionsCollection,

    detected_collisions: DetectedCollisions,

}

pub struct DetectedCollisions {

    pub pairs: Vec<(GearId, GearId)>,

    pub positions: Vec<Point>

}

impl DetectedCollisions {

    pub fn new(capacity: usize) -> Self {

        Self {

            pairs: Vec::with_capacity(capacity),

            positions: Vec::with_capacity(capacity),

        }

    }

    pub fn push(&mut self, contact_gear_id1: GearId, contact_gear_id2: GearId, position: &FPPoint) {

        self.pairs.push((contact_gear_id1, contact_gear_id2));

        self.positions.push(fppoint_round(&position));

    }

}

impl CollisionProcessor {

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

        Self {

            grid: Grid::new(size),

            enabled_collisions: EnabledCollisionsCollection::new(),

            detected_collisions: DetectedCollisions::new(0)

        }

    }

    pub fn process(&mut self, land: &Land2D<u32>, updates: &crate::physics::PositionUpdates) {

        self.grid.check_collisions(&mut self.detected_collisions);

        for (gear_id, collision) in self.enabled_collisions.iter() {

            if collision.bounds.rows().any(|(y, r)| (&land[y][r]).iter().any(|v| *v != 0)) {

                self.detected_collisions.push(gear_id, 0, &collision.bounds.center)

            }

        }

    }

}

impl GearDataProcessor<CollisionData> for CollisionProcessor {

    fn add(&mut self, gear_id: GearId, gear_data: CollisionData) {

        self.grid.insert_static(gear_id, &gear_data.bounds);

    }

}