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use crate::components::Component;
use crate::group::GroupInfo;
use crate::query::{Contains, QueryElementFilter};
use crate::storage::{Entity, SparseArrayView};
use crate::utils::{ChangeTicks, Ticks};
use std::marker::PhantomData;

/// Trait implement by types which can be part of a query.
pub unsafe trait QueryElement<'a> {
    type Item: 'a;
    type Component: Component;
    type Filter: QueryElementFilter<Self::Component>;

    fn get(self, entity: Entity) -> Option<Self::Item>;

    fn get_with_ticks(&self, entity: Entity) -> Option<(&Self::Component, &ChangeTicks)>;

    fn contains(&self, entity: Entity) -> bool;

    fn group_info(&self) -> Option<GroupInfo<'a>>;

    fn world_tick(&self) -> Ticks;

    fn change_tick(&self) -> Ticks;

    fn split(self) -> SplitQueryElement<'a, Self::Component, Self::Filter>;

    unsafe fn get_from_parts(
        component: *mut Self::Component,
        ticks: *mut ChangeTicks,
        world_tick: Ticks,
        change_tick: Ticks,
    ) -> Self::Item;
}

/// Trait implemented by immutable `QueryElement`s.
pub unsafe trait ImmutableQueryElement<'a>
where
    Self: QueryElement<'a>,
{
    // Empty
}

/// Trait implemented by unfiltered `QueryElement`s.
pub trait UnfilteredQueryElement<'a>
where
    Self: QueryElement<'a, Filter = Contains>,
{
    // Empty
}

impl<'a, E> UnfilteredQueryElement<'a> for E
where
    E: QueryElement<'a, Filter = Contains>,
{
    // Empty
}

/// Trait implemented by unfiltered immutable `QueryElement`s.
pub unsafe trait UnfilteredImmutableQueryElement<'a>
where
    Self: ImmutableQueryElement<'a> + UnfilteredQueryElement<'a>,
{
    fn entities(&self) -> &'a [Entity];

    fn components(&self) -> &'a [Self::Component];
}

/// Type returned by `QueryElement::split`.
#[non_exhaustive]
pub struct SplitQueryElement<'a, T, F> {
    pub sparse: SparseArrayView<'a>,
    pub entities: &'a [Entity],
    pub components: *mut T,
    pub ticks: *mut ChangeTicks,
    pub filter: F,
}

impl<'a, T, F> SplitQueryElement<'a, T, F> {
    /// Creates a new `SplitQueryElement`.
    pub fn new(
        sparse: SparseArrayView<'a>,
        entities: &'a [Entity],
        components: *mut T,
        ticks: *mut ChangeTicks,
        filter: F,
    ) -> Self {
        Self {
            sparse,
            entities,
            components,
            ticks,
            filter,
        }
    }

    pub fn into_sparse_split(self) -> (&'a [Entity], SparseSplitQueryElement<'a, T, F>) {
        (
            self.entities,
            SparseSplitQueryElement {
                sparse: self.sparse,
                components: self.components,
                ticks: self.ticks,
                filter: self.filter,
            },
        )
    }

    pub fn into_dense_split(self) -> (&'a [Entity], DenseSplitQueryElement<'a, T, F>) {
        (
            self.entities,
            DenseSplitQueryElement {
                components: self.components,
                ticks: self.ticks,
                filter: self.filter,
                lifetime: PhantomData,
            },
        )
    }

    pub fn into_modifier_split(self) -> (&'a [Entity], SparseArrayView<'a>) {
        (self.entities, self.sparse)
    }
}

/// Used to form `QueryBase::SparseSplit`.
#[non_exhaustive]
pub struct SparseSplitQueryElement<'a, T, F> {
    pub sparse: SparseArrayView<'a>,
    pub components: *mut T,
    pub ticks: *mut ChangeTicks,
    pub filter: F,
}

impl<'a, T, F> SparseSplitQueryElement<'a, T, F> {
    pub unsafe fn get<E>(
        &mut self,
        entity: Entity,
        world_tick: Ticks,
        change_tick: Ticks,
    ) -> Option<E::Item>
    where
        T: Component,
        E: QueryElement<'a, Component = T>,
        F: QueryElementFilter<T>,
    {
        let index = self.sparse.get_index(entity)?;
        let component = self.components.add(index);
        let ticks = self.ticks.add(index);

        self.filter
            .matches(&*component, &*ticks, world_tick, change_tick)
            .then(|| E::get_from_parts(component, ticks, world_tick, change_tick))
    }
}

/// Used to form `QueryBase::DenseSplit`.
pub struct DenseSplitQueryElement<'a, T, F> {
    pub components: *mut T,
    pub ticks: *mut ChangeTicks,
    pub filter: F,
    lifetime: PhantomData<&'a ()>,
}

impl<'a, T, F> DenseSplitQueryElement<'a, T, F> {
    pub unsafe fn get<E>(
        &mut self,
        index: usize,
        world_tick: Ticks,
        change_tick: Ticks,
    ) -> Option<E::Item>
    where
        T: Component,
        E: QueryElement<'a, Component = T>,
        F: QueryElementFilter<T>,
    {
        let component = self.components.add(index);
        let ticks = self.ticks.add(index);

        self.filter
            .matches(&*component, &*ticks, world_tick, change_tick)
            .then(|| E::get_from_parts(component, ticks, world_tick, change_tick))
    }
}