//! Render pass data structures and interfaces.

use crate::phase::Phase;
use std::sync::Arc;

pub mod debug;
pub mod mesh;

/// Viewport data shared by all passes, once the [ViewportPhase] group is
/// entered.
pub struct ViewportData;

/// Data passed to each render pass's recording phases.
pub struct PhaseData<'a, T> {
    pub phase: Phase,
    pub frame_data: T,
    pub viewport_data: &'a ViewportData,
    pub bind_viewport: &'a wgpu::BindGroup,
}

pub type IndexedPhaseData<'a> = PhaseData<'a, usize>;

/// The render pass interface trait.
///
/// Render passes are persistent structures that share GPU resources, user data,
/// and more across both phases and frames.
///
/// Rendering functions record their GPU commands using the [gpu::RenderBundleEncoder]
/// passed to them.
pub trait RenderPass: Send + Sync {
    /// A structure that contains a pass's per-frame data.
    type FrameData: Send + Sync;

    /// Gets a short name for this pass.
    fn get_name(&self) -> &str {
        std::any::type_name::<Self>()
    }

    /// Sets up a new instance of [Self::FrameData].
    ///
    /// Called when a render pass is added to [crate::Renderer].
    fn create_frame_data(&self) -> Self::FrameData;

    /// Initializes this frame's [Self::FrameData], and queries the pass for
    /// which phases to execute.
    ///
    /// This is the only opportunity the render pass has to mutate this frame's
    /// data this frame, so all setup for future phases should be done here.
    ///
    /// The render pass is also given access to the [queue][wgpu::Queue] this
    /// frame will be submitted on, and can be used to transfer image or buffer
    /// data to the GPU.
    fn begin_frame(&self, data: &mut Self::FrameData, phases: &mut Vec<Phase>, queue: &wgpu::Queue);

    fn record_commands(
        &self,
        _data: PhaseData<&Self::FrameData>,
        _cmds: &mut wgpu::CommandEncoder,
    ) {
    }

    fn record_compute<'a>(
        &'a self,
        _data: PhaseData<&'a Self::FrameData>,
        _cmds: &mut wgpu::ComputePass<'a>,
    ) {
    }

    fn record_render(&self, _data: PhaseData<&Self::FrameData>) -> Option<wgpu::RenderBundle> {
        None
    }
}

/// The interface trait for [RenderPassBox], allowing use of a statically-sized
/// [Box] for storage.
///
/// Functions on this trait map one-to-one with [RenderPass], except that
/// frame data is passed by index and not by reference.
pub trait RenderPassBoxTrait: Send + Sync {
    fn begin_frame(&mut self, data_index: usize, phases: &mut Vec<Phase>, queue: &wgpu::Queue);

    fn record_commands(&self, data: IndexedPhaseData, cmds: &mut wgpu::CommandEncoder);

    fn record_compute<'a>(&'a self, data: IndexedPhaseData<'a>, cmds: &mut wgpu::ComputePass<'a>);

    fn record_render(&self, data: IndexedPhaseData) -> Option<wgpu::RenderBundle>;
}

/// A container for a reference-counted render pass instance and its frame data.
pub struct RenderPassBox<T: RenderPass> {
    render_pass: Arc<T>,
    frame_data: Vec<T::FrameData>,
}

impl<T: 'static + RenderPass> RenderPassBox<T> {
    /// Creates a new boxed render pass.
    ///
    /// Calls to [RenderPassBoxTrait] functions with frame indices greater
    /// than or equal to `frame_num` are out-of-bounds and will panic.
    pub fn new(render_pass: Arc<T>, frame_num: usize) -> Self {
        let frame_data = {
            (0..frame_num)
                .map(|_| render_pass.create_frame_data())
                .collect()
        };

        Self {
            render_pass,
            frame_data,
        }
    }

    /// Same as [Self::new], but creates a boxed [RenderPassBoxTrait] in a
    /// generic-friendly interface.
    pub fn new_boxed(render_pass: Arc<T>, frame_num: usize) -> Box<dyn RenderPassBoxTrait> {
        Box::new(Self::new(render_pass, frame_num))
    }
}

impl<T: RenderPass> RenderPassBox<T> {
    fn get_frame_data<'a>(
        &'a self,
        index: IndexedPhaseData<'a>,
    ) -> PhaseData<'a, &'a T::FrameData> {
        let PhaseData {
            phase,
            frame_data,
            viewport_data,
            bind_viewport,
        } = index;

        let frame_data = self.frame_data.get(frame_data).unwrap();

        PhaseData {
            phase,
            frame_data,
            viewport_data,
            bind_viewport,
        }
    }
}

impl<T: RenderPass> std::ops::Deref for RenderPassBox<T> {
    type Target = T;
    fn deref(&self) -> &T {
        self.render_pass.as_ref()
    }
}

impl<T: RenderPass> RenderPassBoxTrait for RenderPassBox<T> {
    fn begin_frame(&mut self, data_index: usize, phases: &mut Vec<Phase>, queue: &wgpu::Queue) {
        let rp = &self.render_pass;
        let name = rp.get_name();
        puffin::profile_scope!("RenderPass::begin_frame(...)", name);
        let frame_data = &mut self.frame_data[data_index];
        rp.begin_frame(frame_data, phases, queue)
    }

    fn record_commands(&self, data: IndexedPhaseData, cmds: &mut wgpu::CommandEncoder) {
        let rp = &self.render_pass;
        let name = rp.get_name();
        let scope = format!("{} (phase: {:?})", name, data.phase);
        puffin::profile_scope!("RenderPass::record_commands(...)", scope);
        let frame_data = self.get_frame_data(data);
        rp.record_commands(frame_data, cmds)
    }

    fn record_compute<'a>(&'a self, data: IndexedPhaseData<'a>, cmds: &mut wgpu::ComputePass<'a>) {
        let rp = &self.render_pass;
        let name = rp.get_name();
        let scope = format!("{} (phase: {:?})", name, data.phase);
        puffin::profile_scope!("RenderPass::record_compute(...)", scope);
        let frame_data = self.get_frame_data(data);
        rp.record_compute(frame_data, cmds)
    }

    fn record_render(&self, data: IndexedPhaseData) -> Option<wgpu::RenderBundle> {
        let rp = &self.render_pass;
        let name = rp.get_name();
        let scope = format!("{} (phase: {:?})", name, data.phase);
        puffin::profile_scope!("RenderPass::record_render(...)", scope);
        let frame_data = self.get_frame_data(data);
        rp.record_render(frame_data)
    }
}