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use bytemuck::{Pod, Zeroable};
use std::{ops::Range, vec::Drain};

#[derive(Debug, Copy, Clone, Pod, Zeroable)]
#[repr(C)]
pub struct SimpleVertex {
    pub position: [f32; 3],
    pub normal: [f32; 3],
    pub uv: [f32; 2],
}

#[derive(Debug, Copy, Clone, Pod, Zeroable)]
#[repr(C)]
pub struct Triangle {
    pub a: u32,
    pub b: u32,
    pub c: u32,
}

impl Default for Triangle {
    fn default() -> Self {
        Self { a: 0, b: 1, c: 2 }
    }
}

impl Triangle {
    pub fn offset(mut self, offset: usize) -> Self {
        self.a += offset as u32;
        self.b += offset as u32;
        self.c += offset as u32;
        self
    }
}

pub struct VertexStream<V: Pod, B> {
    vertices: Vec<V>,
    triangles: Vec<Triangle>,
    batches: Vec<(B, Range<usize>)>,
    resize_count: usize,
}

impl<V: Pod, B> Default for VertexStream<V, B> {
    fn default() -> Self {
        Self {
            vertices: Vec::with_capacity(1024),
            triangles: Vec::with_capacity(1024),
            batches: Vec::with_capacity(1024),
            resize_count: 1024,
        }
    }
}

impl<V: Pod, B> VertexStream<V, B> {
    pub fn new(resize_count: usize) -> Self {
        Self {
            vertices: Vec::with_capacity(resize_count),
            triangles: Vec::with_capacity(resize_count),
            batches: Vec::with_capacity(resize_count),
            resize_count,
        }
    }

    pub fn triangle(&mut self, vertices: [V; 3]) -> &mut Self {
        self.ensure_capacity();
        let offset = self.triangles.len() * 3;
        self.vertices.extend(vertices);
        self.triangles.push(Triangle::default().offset(offset));
        self
    }

    pub fn quad(&mut self, vertices: [V; 4]) -> &mut Self {
        self.ensure_capacity();
        let offset = self.triangles.len() * 3;
        self.vertices.extend(vertices);
        self.triangles
            .push(Triangle { a: 0, b: 1, c: 2 }.offset(offset));
        self.triangles
            .push(Triangle { a: 2, b: 3, c: 0 }.offset(offset));
        self
    }

    pub fn extend(
        &mut self,
        vertices: impl IntoIterator<Item = V>,
        triangles: impl IntoIterator<Item = Triangle>,
    ) -> &mut Self {
        self.ensure_capacity();
        let offset = self.triangles.len() * 3;
        self.vertices.extend(vertices);
        self.triangles.extend(
            triangles
                .into_iter()
                .map(|triangle| triangle.offset(offset)),
        );
        self
    }

    pub fn append(&mut self, other: &mut Self) {
        self.extend(other.vertices.drain(..), other.triangles.drain(..));
        let offset = self.triangles.len();
        self.batches.extend(
            other
                .batches
                .drain(..)
                .map(|(data, range)| (data, (range.start + offset)..(range.end + offset))),
        );
    }

    pub fn clear(&mut self) {
        self.vertices.clear();
        self.triangles.clear();
        self.batches.clear();
    }

    pub fn batch(&mut self, data: B) {
        if self.batches.len() == self.batches.capacity() {
            self.batches.reserve_exact(self.resize_count);
        }
        self.batch_end();
        let start = self.triangles.len();
        self.batches.push((data, start..start))
    }

    pub fn batch_end(&mut self) {
        if let Some(last) = self.batches.last_mut() {
            last.1.end = self.triangles.len();
        }
    }

    pub fn render<R: VertexStreamRenderer<V, B>>(
        &mut self,
        renderer: &mut R,
    ) -> Result<(), R::Error> {
        self.batch_end();
        renderer.render(self)
    }

    pub fn vertices(&self) -> &[V] {
        &self.vertices
    }

    pub fn triangles(&self) -> &[Triangle] {
        &self.triangles
    }

    pub fn batches(&self) -> &[(B, Range<usize>)] {
        &self.batches
    }

    #[allow(clippy::type_complexity)]
    pub fn drain(&mut self) -> (Drain<V>, Drain<Triangle>, Drain<(B, Range<usize>)>) {
        self.batch_end();
        (
            self.vertices.drain(..),
            self.triangles.drain(..),
            self.batches.drain(..),
        )
    }

    fn ensure_capacity(&mut self) {
        if self.vertices.len() == self.vertices.capacity() {
            self.vertices.reserve_exact(self.resize_count);
        }
        if self.triangles.len() == self.triangles.capacity() {
            self.triangles.reserve_exact(self.resize_count);
        }
    }
}

pub trait VertexStreamRenderer<V: Pod, B> {
    type Error;

    fn render(&mut self, stream: &mut VertexStream<V, B>) -> Result<(), Self::Error>;
}

impl<V: Pod, B> VertexStreamRenderer<V, B> for () {
    type Error = ();

    fn render(&mut self, _: &mut VertexStream<V, B>) -> Result<(), Self::Error> {
        Ok(())
    }
}