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use crate::render_resource::CachedComputePipelineId;
use crate::{
    mesh::{InnerMeshVertexBufferLayout, MeshVertexBufferLayout, MissingVertexAttributeError},
    render_resource::{
        CachedRenderPipelineId, ComputePipelineDescriptor, PipelineCache, RenderPipelineDescriptor,
        VertexBufferLayout,
    },
};
use bevy_ecs::system::Resource;
use bevy_utils::{
    default, hashbrown::hash_map::RawEntryMut, tracing::error, Entry, HashMap, PreHashMap,
    PreHashMapExt,
};
use std::{fmt::Debug, hash::Hash};
use thiserror::Error;

pub trait SpecializedRenderPipeline {
    type Key: Clone + Hash + PartialEq + Eq;
    fn specialize(&self, key: Self::Key) -> RenderPipelineDescriptor;
}

#[derive(Resource)]
pub struct SpecializedRenderPipelines<S: SpecializedRenderPipeline> {
    cache: HashMap<S::Key, CachedRenderPipelineId>,
}

impl<S: SpecializedRenderPipeline> Default for SpecializedRenderPipelines<S> {
    fn default() -> Self {
        Self { cache: default() }
    }
}

impl<S: SpecializedRenderPipeline> SpecializedRenderPipelines<S> {
    pub fn specialize(
        &mut self,
        cache: &PipelineCache,
        specialize_pipeline: &S,
        key: S::Key,
    ) -> CachedRenderPipelineId {
        *self.cache.entry(key.clone()).or_insert_with(|| {
            let descriptor = specialize_pipeline.specialize(key);
            cache.queue_render_pipeline(descriptor)
        })
    }
}

pub trait SpecializedComputePipeline {
    type Key: Clone + Hash + PartialEq + Eq;
    fn specialize(&self, key: Self::Key) -> ComputePipelineDescriptor;
}

#[derive(Resource)]
pub struct SpecializedComputePipelines<S: SpecializedComputePipeline> {
    cache: HashMap<S::Key, CachedComputePipelineId>,
}

impl<S: SpecializedComputePipeline> Default for SpecializedComputePipelines<S> {
    fn default() -> Self {
        Self { cache: default() }
    }
}

impl<S: SpecializedComputePipeline> SpecializedComputePipelines<S> {
    pub fn specialize(
        &mut self,
        cache: &PipelineCache,
        specialize_pipeline: &S,
        key: S::Key,
    ) -> CachedComputePipelineId {
        *self.cache.entry(key.clone()).or_insert_with(|| {
            let descriptor = specialize_pipeline.specialize(key);
            cache.queue_compute_pipeline(descriptor)
        })
    }
}

pub trait SpecializedMeshPipeline {
    type Key: Clone + Hash + PartialEq + Eq;
    fn specialize(
        &self,
        key: Self::Key,
        layout: &MeshVertexBufferLayout,
    ) -> Result<RenderPipelineDescriptor, SpecializedMeshPipelineError>;
}

#[derive(Resource)]
pub struct SpecializedMeshPipelines<S: SpecializedMeshPipeline> {
    mesh_layout_cache:
        PreHashMap<InnerMeshVertexBufferLayout, HashMap<S::Key, CachedRenderPipelineId>>,
    vertex_layout_cache: HashMap<VertexBufferLayout, HashMap<S::Key, CachedRenderPipelineId>>,
}

impl<S: SpecializedMeshPipeline> Default for SpecializedMeshPipelines<S> {
    fn default() -> Self {
        Self {
            mesh_layout_cache: Default::default(),
            vertex_layout_cache: Default::default(),
        }
    }
}

impl<S: SpecializedMeshPipeline> SpecializedMeshPipelines<S> {
    #[inline]
    pub fn specialize(
        &mut self,
        cache: &PipelineCache,
        specialize_pipeline: &S,
        key: S::Key,
        layout: &MeshVertexBufferLayout,
    ) -> Result<CachedRenderPipelineId, SpecializedMeshPipelineError> {
        let map = self
            .mesh_layout_cache
            .get_or_insert_with(layout, Default::default);
        match map.entry(key.clone()) {
            Entry::Occupied(entry) => Ok(*entry.into_mut()),
            Entry::Vacant(entry) => {
                let descriptor = specialize_pipeline
                    .specialize(key.clone(), layout)
                    .map_err(|mut err| {
                        {
                            let SpecializedMeshPipelineError::MissingVertexAttribute(err) =
                                &mut err;
                            err.pipeline_type = Some(std::any::type_name::<S>());
                        }
                        err
                    })?;
                // Different MeshVertexBufferLayouts can produce the same final VertexBufferLayout
                // We want compatible vertex buffer layouts to use the same pipelines, so we must "deduplicate" them
                let layout_map = match self
                    .vertex_layout_cache
                    .raw_entry_mut()
                    .from_key(&descriptor.vertex.buffers[0])
                {
                    RawEntryMut::Occupied(entry) => entry.into_mut(),
                    RawEntryMut::Vacant(entry) => {
                        entry
                            .insert(descriptor.vertex.buffers[0].clone(), Default::default())
                            .1
                    }
                };
                Ok(*entry.insert(match layout_map.entry(key) {
                    Entry::Occupied(entry) => {
                        if cfg!(debug_assertions) {
                            let stored_descriptor =
                                cache.get_render_pipeline_descriptor(*entry.get());
                            if stored_descriptor != &descriptor {
                                error!(
                                    "The cached pipeline descriptor for {} is not \
                                equal to the generated descriptor for the given key. \
                                This means the SpecializePipeline implementation uses \
                                unused' MeshVertexBufferLayout information to specialize \
                                the pipeline. This is not allowed because it would invalidate \
                                the pipeline cache.",
                                    std::any::type_name::<S>()
                                );
                            }
                        }
                        *entry.into_mut()
                    }
                    Entry::Vacant(entry) => *entry.insert(cache.queue_render_pipeline(descriptor)),
                }))
            }
        }
    }
}

#[derive(Error, Debug)]
pub enum SpecializedMeshPipelineError {
    #[error(transparent)]
    MissingVertexAttribute(#[from] MissingVertexAttributeError),
}