#![deny(clippy::all, clippy::pedantic)]

use std::any::TypeId;
use std::collections::{HashMap, HashSet};
use std::fmt::Debug;
use std::hash::Hash;
use std::marker::PhantomData;
use std::slice::IterMut as SliceIterMut;

use crate::component::{Component, Sequence as ComponentSequence};
use crate::system::{System, TypeErased as TypeErasedSystem};

pub mod component;
pub mod system;

#[derive(Debug)]
struct Entity
{
    components: Vec<Box<dyn Component>>,
}

#[derive(Debug)]
pub struct World<Event>
{
    systems: Vec<TypeErasedSystem>,
    events: HashMap<Event, Vec<usize>>,
    component_storage: ComponentStorage,
}

impl<Event> World<Event>
{
    #[must_use]
    pub fn new() -> Self
    {
        Self {
            systems: Vec::new(),
            component_storage: ComponentStorage { entities: Vec::new() },
            events: HashMap::new(),
        }
    }

    pub fn create_entity<Comps>(&mut self, components: Comps)
    where
        Comps: ComponentSequence,
    {
        self.component_storage
            .entities
            .push(Entity { components: components.into_vec() });
    }

    pub fn register_system<TSystem, SystemImpl>(&mut self, event: Event, system: TSystem)
    where
        Event: Hash + PartialEq + Eq,
        TSystem: System<SystemImpl>,
    {
        self.systems.push(system.into_type_erased());

        self.events
            .entry(event)
            .or_default()
            .push(self.systems.len() - 1);
    }

    /// Emits a event, running all systems listening to the event for each compatible
    /// entity.
    ///
    /// # Panics
    /// Will panic if a system has dissapeared.
    pub fn emit(&mut self, event: &Event)
    where
        Event: Hash + PartialEq + Eq,
    {
        let Some(system_indices) = self.events.get(event).cloned() else {
            return;
        };

        for system_index in system_indices {
            let system = self.systems.get_mut(system_index).unwrap();

            system.run(&mut self.component_storage);
        }
    }

    pub fn query<Comps>(&mut self) -> Query<Comps>
    where
        Comps: ComponentSequence,
    {
        Query::new(&mut self.component_storage)
    }
}

impl<Event> Default for World<Event>
{
    fn default() -> Self
    {
        Self::new()
    }
}

#[derive(Debug)]
pub struct Query<'world, Comps>
{
    component_storage: &'world mut ComponentStorage,
    comps_pd: PhantomData<Comps>,
}

impl<'world, Comps> Query<'world, Comps>
{
    fn new(component_storage: &'world mut ComponentStorage) -> Self
    {
        Self {
            component_storage,
            comps_pd: PhantomData,
        }
    }
}

impl<'world, Comps> Query<'world, Comps>
where
    Comps: ComponentSequence,
{
    pub fn iter_mut(&mut self) -> QueryComponentIter<Comps>
    {
        QueryComponentIter {
            entity_iter: self.component_storage.entities.iter_mut(),
            component_type_ids: Comps::type_ids(),
            comps_pd: PhantomData,
        }
    }
}

impl<'world, Comps> IntoIterator for &'world mut Query<'world, Comps>
where
    Comps: ComponentSequence + 'world,
{
    type IntoIter = QueryComponentIter<'world, Comps>;
    type Item = Comps::MutRefs<'world>;

    fn into_iter(self) -> Self::IntoIter
    {
        self.iter_mut()
    }
}

pub struct QueryComponentIter<'world, Comps>
{
    entity_iter: SliceIterMut<'world, Entity>,
    component_type_ids: Vec<TypeId>,
    comps_pd: PhantomData<Comps>,
}

impl<'world, Comps> Iterator for QueryComponentIter<'world, Comps>
where
    Comps: ComponentSequence + 'world,
{
    type Item = Comps::MutRefs<'world>;

    fn next(&mut self) -> Option<Self::Item>
    {
        // TODO: This is a really dumb and slow way to do this. Refactor the world
        // to store components in archetypes
        let entity =
            self.entity_iter.find(|entity| {
                let entity_components: HashSet<_> = entity
                    .components
                    .iter()
                    .map(|component| component.as_ref().type_id())
                    .collect();

                if self.component_type_ids.iter().all(|component_type_id| {
                    entity_components.contains(component_type_id)
                }) {
                    return true;
                }

                false
            })?;

        Some(Comps::from_components(&mut entity.components))
    }
}

#[derive(Debug)]
pub struct ComponentStorage
{
    entities: Vec<Entity>,
}