// Trivial wrappers around GLESv2 C functions that should be safe

use byteorder::{LittleEndian, ReadBytesExt};
use glam::{Mat4, Vec3, Vec4};
use std::collections::*;
use std::convert::TryInto;
use std::cmp;
use std::io::Cursor;
use std::ffi::c_void;

use crate::iqm;

pub fn clear_color (r: f32, g: f32, b: f32, a: f32) {
	unsafe {
		gl::ClearColor (1.0f32, 1.0f32, 1.0f32, 1.0f32);
	}
}

pub fn clear (flags: u32) {
	unsafe {
		gl::Clear (flags);
	}
}

pub fn disable (constant: u32) {
	unsafe {
		gl::Disable (constant);
	}
}

pub fn enable (constant: u32) {
	unsafe {
		gl::Enable (constant);
	}
}

pub fn enable_vertex_attrib_array (id: Option <u32>) {
	if let Some (id) = id {
		// Are safety checks really needed here?
		unsafe {
			gl::EnableVertexAttribArray (id);
		}
	}
}

pub fn uniform_1i (uni: i32, x: i32) {
	unsafe {
		gl::Uniform1i (uni, x);
	}
}

pub fn uniform_3fv (uni: i32, v: &Vec3) {
	unsafe {
		gl::Uniform3fv (uni, 1, v as *const Vec3 as *const f32);
	}
}

pub fn uniform_4fv (uni: i32, v: &Vec4) {
	unsafe {
		gl::Uniform4fv (uni, 1, v as *const Vec4 as *const f32);
	}
}

pub fn uniform_matrix_4fv (uni: i32, m: &Mat4) {
	const FALSE_U8: u8 = 0;
	
	unsafe {
		gl::UniformMatrix4fv (uni, 1, FALSE_U8, m as *const Mat4 as *const f32);
	}
}

// More abstract stuff

unsafe fn vertex_attrib_pointer (id: Option <u32>, num_coords: i32, slice: &[u8]) {
	const FALSE_U8: u8 = 0;
	const FLOAT_SIZE: i32 = 4;
	
	if let Some (id) = id {
		gl::VertexAttribPointer (id, num_coords, gl::FLOAT, FALSE_U8, FLOAT_SIZE * num_coords, &slice [0] as *const u8 as *const c_void);
	}
}

pub fn draw_model (
	attrs: &HashMap <String, Option <u32>>,
	model: &iqm::Model, 
	mesh_number: usize
) {
	let index_slice: &[u8] = model.get_index_slice (mesh_number);
	let num_indexes = model.meshes [mesh_number].num_triangles * 3;
	
	unsafe {
		vertex_attrib_pointer (attrs ["pos"], 3, model.get_vertex_slice (0));
		vertex_attrib_pointer (attrs ["uv"], 2, model.get_vertex_slice (1));
		vertex_attrib_pointer (attrs ["normal"], 3, model.get_vertex_slice (2));
		
		gl::DrawElements (gl::TRIANGLES, (num_indexes) as i32, gl::UNSIGNED_INT, &index_slice [0] as *const u8 as *const c_void);
	}
}

pub struct VertexBuffer {
	id: u32,
	len: usize,
}

impl VertexBuffer {
	pub fn from_slice (slice: &[u8]) -> Self {
		let id = {
			let mut id = 0;
			unsafe {
				gl::GenBuffers (1, &mut id);
				gl::BindBuffer (gl::ARRAY_BUFFER, id);
				
				gl::BufferData (gl::ARRAY_BUFFER, slice.len ().try_into ().unwrap (), &slice [0] as *const u8 as *const c_void, gl::STATIC_DRAW);
			}
			assert! (id != 0);
			id
		};
		
		Self {
			id,
			len: slice.len (),
		}
	}
	
	pub fn bind (&self) {
		unsafe {
			gl::BindBuffer (gl::ARRAY_BUFFER, self.id);
		}
	}
}
impl Drop for VertexBuffer {
	fn drop (&mut self) {
		if self.id == 0 {
			return;
		}
		
		unsafe {
			gl::DeleteBuffers (1, &self.id);
		}
		
		self.id = 0;
	}
}


pub struct IndexBuffer {
	id: u32,
	len: usize,
	min: u32,
	max: u32,
}

impl IndexBuffer {
	pub fn from_slice (slice: &[u8]) -> Self {
		let mut rdr = Cursor::new (slice);
		
		let mut min = None;
		let mut max = None;
		
		assert_eq! (slice.len () % 4, 0);
		
		for _ in 0..slice.len () / 4 {
			let idx = rdr.read_u32::<LittleEndian> ().unwrap ();
			
			min = match min {
				None => Some (idx),
				Some (min) => Some (cmp::min (min, idx)),
			};
			
			max = match max {
				None => Some (idx),
				Some (max) => Some (cmp::max (max, idx)),
			};
		}
		
		let id = {
			let mut id = 0;
			unsafe {
				gl::GenBuffers (1, &mut id);
				gl::BindBuffer (gl::ELEMENT_ARRAY_BUFFER, id);
				
				gl::BufferData (gl::ELEMENT_ARRAY_BUFFER, slice.len ().try_into ().unwrap (), &slice [0] as *const u8 as *const c_void, gl::STATIC_DRAW);
			}
			assert! (id != 0);
			id
		};
		
		Self {
			id,
			len: slice.len () / 4,
			min: min.unwrap (),
			max: max.unwrap (),
		}
	}
	
	pub fn bind (&self) {
		unsafe {
			gl::BindBuffer (gl::ELEMENT_ARRAY_BUFFER, self.id);
		}
	}
}

impl Drop for IndexBuffer {
	fn drop (&mut self) {
		if self.id == 0 {
			return;
		}
		
		unsafe {
			gl::DeleteBuffers (1, &self.id);
		}
		
		self.id = 0;
	}
}