//! Cyborg is a high-performance, modern, experimental rendering engine written
//! in Rust.

use std::collections::HashMap;
use std::sync::{Arc, RwLock};
use strum::IntoEnumIterator;

#[derive(Copy, Clone, Debug, Hash, Eq, Ord, PartialEq, PartialOrd, strum::EnumIter)]
pub enum PrePhase {}

#[derive(Copy, Clone, Debug, Hash, Eq, Ord, PartialEq, PartialOrd, strum::EnumIter)]
pub enum ViewportPhase {}

#[derive(Debug, Default)]
pub struct PhaseList {
    pub pre: Vec<PrePhase>,
    pub viewport: Vec<ViewportPhase>,
}

impl PhaseList {
    pub fn clear(&mut self) {
        self.pre.clear();
        self.viewport.clear();
    }
}

#[derive(Debug, Default)]
pub struct PhaseMultiMap<T> {
    pub pre: HashMap<PrePhase, Vec<T>>,
    pub viewport: HashMap<ViewportPhase, Vec<T>>,
}

impl<T: Copy + PartialEq> PhaseMultiMap<T> {
    pub fn insert_multi(&mut self, keys: &PhaseList, val: T) {
        for pre in keys.pre.iter() {
            Self::insert(&mut self.pre, pre, val);
        }

        for viewport in keys.viewport.iter() {
            Self::insert(&mut self.viewport, viewport, val);
        }
    }

    pub fn iter_pre<'a>(&'a self, phase: &'a PrePhase) -> std::slice::Iter<'a, T> {
        Self::iter(&self.pre, phase)
    }

    pub fn iter_viewport<'a>(&'a self, phase: &'a ViewportPhase) -> std::slice::Iter<'a, T> {
        Self::iter(&self.viewport, phase)
    }

    fn insert<K>(map: &mut HashMap<K, Vec<T>>, key: &K, val: T)
    where
        K: std::hash::Hash + Eq + Copy,
    {
        if let Some(existing) = map.get_mut(key) {
            if !existing.contains(&val) {
                existing.push(val);
            }
        } else {
            map.insert(*key, vec![val]);
        }
    }

    fn iter<'a, K>(map: &'a HashMap<K, Vec<T>>, key: &'a K) -> std::slice::Iter<'a, T>
    where
        K: std::hash::Hash + Eq + Copy,
    {
        if let Some(vals) = map.get(key) {
            vals.iter()
        } else {
            [].iter()
        }
    }
}

pub struct ViewportData;

pub trait FrameData {}

pub trait RenderPass {
    type FrameData: FrameData;

    fn create_frame_data(&mut self) -> Self::FrameData;

    fn begin_frame(&mut self, data: &mut Self::FrameData, phases: &mut PhaseList);

    fn render_pre(
        &self,
        phase: PrePhase,
        data: &Self::FrameData,
        cmds: &mut gpu::RenderBundleEncoder,
    );

    fn render_viewport(
        &self,
        phase: ViewportPhase,
        data: &Self::FrameData,
        viewport: &ViewportData,
        cmds: &mut gpu::RenderBundleEncoder,
    );
}

pub struct Renderer {
    pub render_passes: Vec<Box<dyn RenderPassBoxTrait>>,
}

impl Renderer {
    pub fn render(&mut self) {
        let frame_index = 0;

        let mut phase_passes = PhaseMultiMap::<usize>::default();

        let mut phases_buf = PhaseList::default();
        for (pass_index, rp) in self.render_passes.iter_mut().enumerate() {
            phases_buf.clear();
            rp.begin_frame(frame_index, &mut phases_buf);
            phase_passes.insert_multi(&phases_buf, pass_index);
        }

        for phase in PrePhase::iter() {
            for pass_index in phase_passes.iter_pre(&phase) {
                let pass = &self.render_passes[*pass_index];
                let mut encoder = gpu::RenderBundleEncoder;
                pass.render_pre(phase, frame_index, &mut encoder);
            }
        }

        let viewport = ViewportData;

        for phase in ViewportPhase::iter() {
            for pass_index in phase_passes.iter_viewport(&phase) {
                let pass = &self.render_passes[*pass_index];
                let mut encoder = gpu::RenderBundleEncoder;
                pass.render_viewport(phase, frame_index, &viewport, &mut encoder);
            }
        }
    }
}

pub trait RenderPassBoxTrait {
    fn begin_frame(&mut self, data_index: usize, phases: &mut PhaseList);

    fn render_pre(&self, phase: PrePhase, data_index: usize, cmds: &mut gpu::RenderBundleEncoder);

    fn render_viewport(
        &self,
        phase: ViewportPhase,
        data_index: usize,
        viewport: &ViewportData,
        cmds: &mut gpu::RenderBundleEncoder,
    );
}

pub struct RenderPassBox<T: RenderPass> {
    render_pass: Arc<RwLock<T>>,
    frame_data: Vec<T::FrameData>,
}

impl<T: RenderPass> RenderPassBox<T> {
    pub fn new(render_pass: Arc<RwLock<T>>, frame_num: usize) -> Self {
        let frame_data = {
            let mut lock = render_pass.write().unwrap();
            (0..frame_num).map(|_| lock.create_frame_data()).collect()
        };

        Self {
            render_pass,
            frame_data,
        }
    }
}

impl<T: RenderPass> RenderPassBoxTrait for RenderPassBox<T> {
    fn begin_frame(&mut self, data_index: usize, phases: &mut PhaseList) {
        let frame_data = &mut self.frame_data[data_index];
        let mut render_pass = self.render_pass.write().unwrap();
        render_pass.begin_frame(frame_data, phases)
    }

    fn render_pre(&self, phase: PrePhase, data_index: usize, cmds: &mut gpu::RenderBundleEncoder) {
        let frame_data = &self.frame_data[data_index];
        let render_pass = self.render_pass.read().unwrap();
        render_pass.render_pre(phase, frame_data, cmds)
    }

    fn render_viewport(
        &self,
        phase: ViewportPhase,
        data_index: usize,
        viewport: &ViewportData,
        cmds: &mut gpu::RenderBundleEncoder,
    ) {
        let frame_data = &self.frame_data[data_index];
        let render_pass = self.render_pass.read().unwrap();
        render_pass.render_viewport(phase, frame_data, viewport, cmds)
    }
}

/// Mock GPU API (like Vulkan, WebGPU, or OpenGL) types for prototyping.
pub mod gpu {
    /// Thread-safe GPU command recorder that's later executed in a command buffer.
    ///
    /// Also known as a:
    /// - RenderBundleEncoder in WebGPU
    /// - secondary command buffer in Vulkan
    pub struct RenderBundleEncoder;
}