use crate::render_resource::CachedComputePipelineId;
use crate::{
    mesh::{InnerMeshVertexBufferLayout, MeshVertexBufferLayout, MissingVertexAttributeError},
    render_resource::{
        CachedRenderPipelineId, ComputePipelineDescriptor, PipelineCache, RenderPipelineDescriptor,
        VertexBufferLayout,
    },
};
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;
}

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: &mut 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;
}

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: &mut 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>;
}

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: &mut 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),
}