use std::marker::PhantomData;

use crate::{ComponentColumn, Tick, DynTypeId, World};

use super::{Query, Fetch, AsQuery};

#[derive(Clone, Copy, Debug, Default)]
pub struct TickOf<T> {
    tick: Tick,
    _phantom: PhantomData<T>,
}

impl<T> std::ops::Deref for TickOf<T> {
    type Target = Tick;

    fn deref(&self) -> &Self::Target {
        &self.tick
    }
}

/// Fetcher for borrowing components from archetypes.
pub struct FetchTickOf<'a, T> {
    col: &'a ComponentColumn,
    _phantom: PhantomData<&'a T>
}

impl<'a, T> Fetch<'a> for FetchTickOf<'a, T>
where
    T: 'a,
{
    type Item = Tick;

    fn dangling() -> Self {
        unreachable!()
    }

    unsafe fn get_item(&mut self, entity: crate::world::ArchetypeEntityId) -> Self::Item {
        self.col.entity_ticks[entity.0 as usize]
    }
}

/// A Query for borrowing components from archetypes.
/// 
/// Since [`AsQuery`] is implemented for `&T`, you can use this query like this:
/// ```nobuild
/// for ts in world.view::<&T>() {
///     println!("Got a &T!");
/// }
/// ```
pub struct QueryTickOf<T> {
    type_id: DynTypeId,
    _phantom: PhantomData<T>
}

impl<T: 'static> Default for QueryTickOf<T> {
    fn default() -> Self {
        Self {
            type_id: DynTypeId::of::<T>(),
            _phantom: PhantomData,
        }
    }
}

// manually implemented to avoid a Copy bound on T
impl<T> Copy for QueryTickOf<T> {}

// manually implemented to avoid a Clone bound on T
impl<T> Clone for QueryTickOf<T> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<T: 'static> QueryTickOf<T> {
    pub fn new() -> Self {
        Self::default()
    }
}

impl<T> Query for QueryTickOf<T>
where
    T: 'static
{
    type Item<'a> = Tick;

    type Fetch<'a> = FetchTickOf<'a, T>;

    fn new() -> Self {
        QueryTickOf::<T>::new()
    }

    fn can_visit_archetype(&self, archetype: &crate::archetype::Archetype) -> bool {
        archetype.has_column(self.type_id)
    }

    unsafe fn fetch<'a>(&self, _world: &'a World, archetype: &'a crate::archetype::Archetype, _tick: crate::Tick) -> Self::Fetch<'a> {
        let col = archetype.get_column(self.type_id)
            .expect("You ignored 'can_visit_archetype'!");

        FetchTickOf {
            col,
            _phantom: PhantomData,
        }
    }
}

impl<T: 'static> AsQuery for QueryTickOf<T> {
    type Query = Self;
}

impl<T: 'static> AsQuery for TickOf<T> {
    type Query = QueryTickOf<T>;
}