use std::mem::size_of;

use crate::opengl::currently_bound::CurrentlyBound;
use crate::opengl::vertex_buffer::VertexBuffer;
use crate::vertex::{Attribute, AttributeComponentType, Vertex};

const VERTEX_STRIDE: usize = size_of::<Vertex>();

#[derive(Debug)]
pub struct VertexArray
{
    array: gl::types::GLuint,
}

impl VertexArray
{
    pub fn new() -> Self
    {
        let mut array = 0;

        unsafe {
            gl::GenVertexArrays(1, &mut array);
        }

        Self { array }
    }

    /// Draws the currently bound vertex array.
    pub fn draw(
        _currently_bound: &CurrentlyBound<Self>,
        primitive_kind: PrimitiveKind,
        start_index: u32,
        index_cnt: u32,
    )
    {
        unsafe {
            #[allow(clippy::cast_possible_wrap)]
            gl::DrawArrays(
                primitive_kind.into_gl(),
                start_index as gl::types::GLint,
                index_cnt as gl::types::GLsizei,
            );
        }
    }

    pub fn configure_attrs(
        _currently_bound: &CurrentlyBound<Self>,
        _vert_buf_curr_bound: &CurrentlyBound<VertexBuffer>,
    )
    {
        let mut offset = 0;

        for attr in Vertex::attrs() {
            Self::vertex_attrib_ptr(attr, offset);

            Self::enable_vertex_attrib_array(attr.index);

            offset += attr.component_size * attr.component_cnt as usize;
        }
    }

    #[allow(clippy::inline_always)]
    #[inline(always)]
    pub fn bind(&self, cb: impl FnOnce(CurrentlyBound<'_, Self>))
    {
        unsafe { gl::BindVertexArray(self.array) }

        // SAFETY: A vertex array object is currently bound
        let currently_bound = unsafe { CurrentlyBound::new() };

        cb(currently_bound);
    }

    fn vertex_attrib_ptr(vertex_attr: &Attribute, offset: usize)
    {
        unsafe {
            #[allow(clippy::cast_possible_wrap, clippy::cast_possible_truncation)]
            gl::VertexAttribPointer(
                vertex_attr.index as gl::types::GLuint,
                vertex_attr.component_cnt as i32,
                Self::vertex_attr_type_to_gl(&vertex_attr.component_type),
                gl::FALSE,
                VERTEX_STRIDE as gl::types::GLsizei,
                offset as *const _,
            );
        }
    }

    fn enable_vertex_attrib_array(index: usize)
    {
        unsafe {
            #[allow(clippy::cast_possible_truncation)]
            gl::EnableVertexAttribArray(index as gl::types::GLuint);
        }
    }

    fn vertex_attr_type_to_gl(
        vertex_attr_type: &AttributeComponentType,
    ) -> gl::types::GLenum
    {
        match vertex_attr_type {
            AttributeComponentType::Float => gl::FLOAT,
        }
    }
}

impl Drop for VertexArray
{
    fn drop(&mut self)
    {
        unsafe {
            gl::DeleteVertexArrays(1, &self.array);
        }
    }
}

#[derive(Debug)]
pub enum PrimitiveKind
{
    Triangles,
}

impl PrimitiveKind
{
    fn into_gl(self) -> gl::types::GLenum
    {
        match self {
            Self::Triangles => gl::TRIANGLES,
        }
    }
}