use std::collections::HashMap;

use shrev::ReaderId;
use specs::{
    hibitset::BitSet, prelude::*, world::Index, Entities, Entity, ReadStorage, System, World,
    WriteStorage,
};

use crate::{
    components::{Orbit, OrbitOwned, PlayerOwned},
    misc::ComponentEvent,
};

pub struct OrbitOwnedUpdate {
    orbit_ids: BitSet,
    orbit_owned_ids: BitSet,
    old_orbit_ids: HashMap<Index, Entity>,
    orbit_owned_event_id: ReaderId<crate::misc::ComponentEvent<OrbitOwned>>,
}

impl OrbitOwnedUpdate {
    pub fn new(world: &mut World) -> Self {
        let orbit_ids = BitSet::new();
        let orbit_owned_ids = BitSet::new();
        let old_orbit_ids = HashMap::new();

        let orbit_owned_event_id = unsafe {
            WriteStorage::<OrbitOwned>::setup(world);

            let mut orbit_owned = world.system_data::<WriteStorage<OrbitOwned>>();
            orbit_owned
                .unprotected_storage_mut()
                .channel_mut()
                .register_reader()
        };

        Self {
            orbit_ids,
            orbit_owned_ids,
            old_orbit_ids,
            orbit_owned_event_id,
        }
    }
}

#[derive(SystemData)]
pub struct OrbitOwnedUpdateData<'a> {
    entities: Entities<'a>,
    orbits: WriteStorage<'a, Orbit>,
    player_owned: ReadStorage<'a, PlayerOwned>,
    orbit_owned: ReadStorage<'a, OrbitOwned>,
}

impl<'a> System<'a> for OrbitOwnedUpdate {
    type SystemData = OrbitOwnedUpdateData<'a>;

    fn run(&mut self, data: Self::SystemData) {
        let OrbitOwnedUpdateData {
            entities,
            mut orbits,
            player_owned,
            orbit_owned,
        } = data;

        self.orbit_ids.clear();
        self.orbit_owned_ids.clear();
        self.old_orbit_ids.clear();

        /* handle events */
        let events = orbit_owned
            .unprotected_storage()
            .channel()
            .read(&mut self.orbit_owned_event_id);
        for event in events {
            match event {
                ComponentEvent::Inserted(id, orbit_owned) => {
                    self.orbit_ids.add(orbit_owned.owner.id());
                    self.orbit_owned_ids.add(*id);
                }
                ComponentEvent::Modified(id, orbit_owned) => {
                    self.orbit_ids.add(orbit_owned.owner.id());
                    self.orbit_owned_ids.add(*id);
                    *self.old_orbit_ids.entry(*id).or_insert(orbit_owned.owner) = orbit_owned.owner;
                }
                ComponentEvent::Removed(id, orbit_owned) => {
                    self.orbit_ids.add(orbit_owned.owner.id());
                    self.orbit_owned_ids.add(*id);
                    *self.old_orbit_ids.entry(*id).or_insert(orbit_owned.owner) = orbit_owned.owner;
                }
            }
        }

        /* update orbits */
        for (orbit_id, orbit, _) in (&entities, &mut orbits, &self.orbit_ids).join() {
            let data = (
                &entities,
                &orbit_owned,
                &player_owned,
                &self.orbit_owned_ids,
            );

            for (fleet_id, orbit_owned, player_owned, _) in data.join() {
                let new_match = orbit_id == orbit_owned.owner;
                let old_match = match self.old_orbit_ids.get(&fleet_id.id()) {
                    Some(old_orbit_id) => orbit_id == *old_orbit_id,
                    None => false,
                };

                let player_id = player_owned.owner.id() as usize;
                if old_match && !new_match {
                    if let Some(fleet) = orbit.fleets.get_mut(player_id) {
                        *fleet = None;
                    }
                } else if !old_match && new_match {
                    orbit.fleets.resize_with(player_id + 1, Default::default);
                    orbit.fleets[player_id] = Some(fleet_id);
                }
            }
        }
    }
}