use std::collections::{HashMap, VecDeque};

use crate::Record;

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub struct EntityId(pub u64);

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub struct Entity {
    pub(crate) id: EntityId,
    pub(crate) generation: u64,
}

pub struct Entities {
    pub(crate) arch_index: HashMap<EntityId, Record>,
    dead: VecDeque<Entity>,
    next_id: EntityId,
}

impl Default for Entities {
    fn default() -> Self {
        Self {
            arch_index: Default::default(),
            dead: Default::default(),
            next_id: EntityId(0),
        }
    }
}

impl Entities {
    pub fn reserve(&mut self) -> Entity {
        match self.dead.pop_front() {
            Some(mut e) => {
                e.generation += 1;
                e
            }
            None => {
                let new_id = self.next_id;
                self.next_id.0 += 1;

                Entity {
                    id: new_id,
                    generation: 0,
                }
            }
        }
    }

    /// Returns the number of spawned entities
    pub fn len(&self) -> usize {
        self.next_id.0 as usize - self.dead.len()
    }

    /// Retrieves the Archetype Record for the entity
    pub(crate) fn entity_record(&self, entity: Entity) -> Option<Record> {
        self.arch_index.get(&entity.id).cloned()
    }

    pub(crate) fn insert_entity_record(&mut self, entity: Entity, record: Record) {
        self.arch_index.insert(entity.id, record);
    }
}