use std::collections::HashMap;

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

use crate::{
    components::{Fleet, FleetOwned, Ship},
    misc::{ComponentEvent, StorageHelper, StorageHelperMut},
};

pub struct FleetOwnedUpdate {
    fleet_ids: BitSet,
    fleet_owned_ids: BitSet,
    old_fleet_ids: HashMap<Index, Entity>,
    fleet_owned_event_id: ReaderId<ComponentEvent<FleetOwned>>,
}

impl FleetOwnedUpdate {
    pub fn new(world: &mut World) -> Self {
        WriteStorage::<FleetOwned>::setup(world);

        let fleet_ids = BitSet::new();
        let fleet_owned_ids = BitSet::new();
        let old_fleet_ids = HashMap::new();
        let fleet_owned_event_id = world
            .system_data::<WriteStorage<FleetOwned>>()
            .register_event_reader();

        Self {
            fleet_ids,
            fleet_owned_ids,
            old_fleet_ids,
            fleet_owned_event_id,
        }
    }
}

#[derive(SystemData)]
pub struct FleetOwnedUpdateData<'a> {
    entities: Entities<'a>,
    ships: ReadStorage<'a, Ship>,
    fleets: WriteStorage<'a, Fleet>,
    fleet_owned: ReadStorage<'a, FleetOwned>,
}

impl<'a> System<'a> for FleetOwnedUpdate {
    type SystemData = FleetOwnedUpdateData<'a>;

    fn run(&mut self, data: Self::SystemData) {
        let FleetOwnedUpdateData {
            entities,
            ships,
            mut fleets,
            fleet_owned,
        } = data;

        self.fleet_ids.clear();
        self.fleet_owned_ids.clear();
        self.old_fleet_ids.clear();

        /* handle events */
        let events = fleet_owned.channel().read(&mut self.fleet_owned_event_id);
        for event in events {
            match event {
                ComponentEvent::Inserted(id, fleet_owned) => {
                    self.fleet_ids.add(fleet_owned.owner().id());
                    self.fleet_owned_ids.add(*id);
                }
                ComponentEvent::Modified(id, fleet_owned) => {
                    self.fleet_ids.add(fleet_owned.owner().id());
                    self.fleet_owned_ids.add(*id);
                    *self
                        .old_fleet_ids
                        .entry(*id)
                        .or_insert_with(|| fleet_owned.owner()) = fleet_owned.owner();
                }
                ComponentEvent::Removed(id, fleet_owned) => {
                    self.fleet_ids.add(fleet_owned.owner().id());
                    self.fleet_owned_ids.add(*id);
                    *self
                        .old_fleet_ids
                        .entry(*id)
                        .or_insert_with(|| fleet_owned.owner()) = fleet_owned.owner();
                }
            }
        }

        /* find new fleet ids */
        for (fleet_owned, _) in (&fleet_owned, &self.fleet_owned_ids).join() {
            self.fleet_ids.add(fleet_owned.owner().id());
        }

        /* update fleets */
        for (fleet_id, fleet, _) in (&entities, &mut fleets, &self.fleet_ids).join() {
            let data = (&entities, &ships, &fleet_owned, &self.fleet_owned_ids);

            for (ship_id, ship, fleet_owned, _) in data.join() {
                let new_match = fleet_id == fleet_owned.owner();
                let old_match = match self.old_fleet_ids.get(&ship_id.id()) {
                    Some(old_fleet_id) => fleet_id == *old_fleet_id,
                    None => false,
                };

                if old_match && !new_match {
                    fleet.remove_ship(ship_id, ship);
                } else if !old_match && new_match {
                    fleet.add_ship(ship_id, ship);
                }
            }
        }
    }
}