use crate::{

    common::{GearId, Millis},

    data::GearDataManager,

};

use fpnum::*;

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

#[repr(transparent)]

pub struct PositionData(pub FPPoint);

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

#[repr(transparent)]

pub struct VelocityData(pub FPPoint);

pub struct AffectedByWind;

pub struct PositionUpdates {

    pub gear_ids: Vec<GearId>,

    pub shifts: Vec<(FPPoint, FPPoint)>,

}

impl PositionUpdates {

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

        Self {

            gear_ids: Vec::with_capacity(capacity),

            shifts: Vec::with_capacity(capacity),

        }

    }

    pub fn push(&mut self, gear_id: GearId, old_position: &FPPoint, new_position: &FPPoint) {

        self.gear_ids.push(gear_id);

        self.shifts.push((*old_position, *new_position));

    }

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

        self.gear_ids

            .iter()

            .cloned()

            .zip(self.shifts.iter())

            .map(|(id, (from, to))| (id, from, to))

    }

    pub fn clear(&mut self) {

        self.gear_ids.clear();

        self.shifts.clear();

    }

}

pub struct PhysicsProcessor {

    gravity: FPNum,

    wind: FPNum,

    position_updates: PositionUpdates,

}

impl PhysicsProcessor {

    pub fn register_components(data: &mut GearDataManager) {

        data.register::<PositionData>();

        data.register::<VelocityData>();

        data.register::<AffectedByWind>();

    }

    pub fn new() -> Self {

        Self {

            gravity: fp!(1 / 10),

            wind: fp!(0),

            position_updates: PositionUpdates::new(64),

        }

    }

    pub fn process(

        &mut self,

        data: &mut GearDataManager,

        time_step: Millis,

    ) -> &PositionUpdates {

        if time_step == Millis::new(1) {

            self.process_impl::<true>(data, time_step)

        } else {

            self.process_impl::<false>(data, time_step)

        }

    }

    fn process_impl<const SINGLE_TICK: bool>(

        &mut self,

        data: &mut GearDataManager,

        time_step: Millis,

    ) -> &PositionUpdates {

        let fp_step = if SINGLE_TICK {

            fp!(1)

        } else {

            time_step.to_fixed()

        };

        let gravity = FPPoint::unit_y() * (self.gravity * fp_step);

        let wind = FPPoint::unit_x() * (self.wind * fp_step);

        self.position_updates.clear();

        data.iter()

            .with_tags::<&AffectedByWind>()

            .run(|(vel,): (&mut VelocityData,)| {

                vel.0 += wind;

            });

        data.iter().run_id(

            |gear_id, (pos, vel): (&mut PositionData, &mut VelocityData)| {

                let old_pos = pos.0;

                vel.0 += gravity;

                pos.0 += if SINGLE_TICK { vel.0 } else { vel.0 * fp_step };

                self.position_updates.push(gear_id, &old_pos, &pos.0)

            },

        );

        &self.position_updates

    }

}