use crate::{
    render_resource::DynamicUniformVec,
    renderer::{RenderDevice, RenderQueue},
    RenderApp, RenderStage,
};
use bevy_app::{App, Plugin};
use bevy_asset::{Asset, Handle};
use bevy_ecs::{
    component::Component,
    prelude::*,
    query::{FilterFetch, QueryItem, ReadOnlyFetch, WorldQuery},
    system::{
        lifetimeless::{Read, SCommands, SQuery},
        RunSystem, SystemParamItem,
    },
};
use crevice::std140::AsStd140;
use std::{marker::PhantomData, ops::Deref};

/// Stores the index of a uniform inside of [`ComponentUniforms`].
#[derive(Component)]
pub struct DynamicUniformIndex<C: Component> {
    index: u32,
    marker: PhantomData<C>,
}

impl<C: Component> DynamicUniformIndex<C> {
    #[inline]
    pub fn index(&self) -> u32 {
        self.index
    }
}

/// Describes how a component gets extracted for rendering.
///
/// Therefore the component is transferred from the "app world" into the "render world"
/// in the [`RenderStage::Extract`](crate::RenderStage::Extract) step.
pub trait ExtractComponent: Component {
    /// ECS [`WorldQuery`] to fetch the components to extract.
    type Query: WorldQuery;
    /// Filters the entities with additional constraints.
    type Filter: WorldQuery;
    /// Defines how the component is transferred into the "render world".
    fn extract_component(item: QueryItem<Self::Query>) -> Self;
}

/// This plugin prepares the components of the corresponding type for the GPU
/// by transforming them into uniforms.
///
/// They can then be accessed from the [`ComponentUniforms`] resource.
/// For referencing the newly created uniforms a [`DynamicUniformIndex`] is inserted
/// for every processed entity.
///
/// Therefore it sets up the [`RenderStage::Prepare`](crate::RenderStage::Prepare) step
/// for the specified [`ExtractComponent`].
pub struct UniformComponentPlugin<C>(PhantomData<fn() -> C>);

impl<C> Default for UniformComponentPlugin<C> {
    fn default() -> Self {
        Self(PhantomData)
    }
}

impl<C: Component + AsStd140 + Clone> Plugin for UniformComponentPlugin<C> {
    fn build(&self, app: &mut App) {
        app.sub_app(RenderApp)
            .insert_resource(ComponentUniforms::<C>::default())
            .add_system_to_stage(
                RenderStage::Prepare,
                prepare_uniform_components::<C>.system(),
            );
    }
}

/// Stores all uniforms of the component type.
pub struct ComponentUniforms<C: Component + AsStd140> {
    uniforms: DynamicUniformVec<C>,
}

impl<C: Component + AsStd140> Deref for ComponentUniforms<C> {
    type Target = DynamicUniformVec<C>;

    #[inline]
    fn deref(&self) -> &Self::Target {
        &self.uniforms
    }
}

impl<C: Component + AsStd140> ComponentUniforms<C> {
    #[inline]
    pub fn uniforms(&self) -> &DynamicUniformVec<C> {
        &self.uniforms
    }
}

impl<C: Component + AsStd140> Default for ComponentUniforms<C> {
    fn default() -> Self {
        Self {
            uniforms: Default::default(),
        }
    }
}

/// This system prepares all components of the corresponding component type.
/// They are transformed into uniforms and stored in the [`ComponentUniforms`] resource.
fn prepare_uniform_components<C: Component>(
    mut commands: Commands,
    render_device: Res<RenderDevice>,
    render_queue: Res<RenderQueue>,
    mut component_uniforms: ResMut<ComponentUniforms<C>>,
    components: Query<(Entity, &C)>,
) where
    C: AsStd140 + Clone,
{
    component_uniforms.uniforms.clear();
    for (entity, component) in components.iter() {
        commands
            .get_or_spawn(entity)
            .insert(DynamicUniformIndex::<C> {
                index: component_uniforms.uniforms.push(component.clone()),
                marker: PhantomData,
            });
    }

    component_uniforms
        .uniforms
        .write_buffer(&render_device, &render_queue);
}

/// This plugin extracts the components into the "render world".
///
/// Therefore it sets up the [`RenderStage::Extract`](crate::RenderStage::Extract) step
/// for the specified [`ExtractComponent`].
pub struct ExtractComponentPlugin<C, F = ()>(PhantomData<fn() -> (C, F)>);

impl<C, F> Default for ExtractComponentPlugin<C, F> {
    fn default() -> Self {
        Self(PhantomData)
    }
}

impl<C: ExtractComponent> Plugin for ExtractComponentPlugin<C>
where
    <C::Query as WorldQuery>::Fetch: ReadOnlyFetch,
    <C::Filter as WorldQuery>::Fetch: FilterFetch,
{
    fn build(&self, app: &mut App) {
        let system = ExtractComponentSystem::<C>::system(&mut app.world);
        let render_app = app.sub_app(RenderApp);
        render_app.add_system_to_stage(RenderStage::Extract, system);
    }
}

impl<T: Asset> ExtractComponent for Handle<T> {
    type Query = Read<Handle<T>>;
    type Filter = ();

    #[inline]
    fn extract_component(handle: QueryItem<Self::Query>) -> Self {
        handle.clone_weak()
    }
}

/// This system extracts all components of the corresponding [`ExtractComponent`] type.
pub struct ExtractComponentSystem<C: ExtractComponent>(PhantomData<C>);

impl<C: ExtractComponent> RunSystem for ExtractComponentSystem<C>
where
    <C::Filter as WorldQuery>::Fetch: FilterFetch,
    <C::Query as WorldQuery>::Fetch: ReadOnlyFetch,
{
    type Param = (
        SCommands,
        // the previous amount of extracted components
        Local<'static, usize>,
        SQuery<(Entity, C::Query), C::Filter>,
    );

    fn run((mut commands, mut previous_len, query): SystemParamItem<Self::Param>) {
        let mut values = Vec::with_capacity(*previous_len);
        for (entity, query_item) in query.iter() {
            values.push((entity, (C::extract_component(query_item),)));
        }
        *previous_len = values.len();
        commands.insert_or_spawn_batch(values);
    }
}