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use crate::prelude::*;
use crate::Context;

use glow::HasContext;

use crate::Program;
use crate::FragmentShader;
use crate::VertexShader;
use crate::VertexArrayObject;
use crate::Framebuffer;

/// A program for rasterizing `VertexArrayObject`s in a target `Framebuffer`.

#[derive(Shrinkwrap)]
#[shrinkwrap(mutable)]
pub struct RasterProgram {
    /// Program base object.

    #[shrinkwrap(main_field)]
    pub program : Program,
}

/// Kinds of raster geometries.

pub enum RasterGeometry {
    /// Raster three consecutive vertices as a triangle.

    Triangles = glow::TRIANGLES as isize,
    /// Raster each vertex as a point.

    Points    = glow::POINTS as isize
}

impl RasterProgram {
    /// Creates a new `RasterProgram` with a `FragmentShader` and ` VertexShader`.

    pub fn new(context:&Context, fragment_shader:&FragmentShader, vertex_shader:&VertexShader) -> Result<Self, String> {
        let program = Program::new(context);
        let gl      = context.gl_context();
        unsafe {
            gl.attach_shader(program.resource(), vertex_shader.resource());
            gl.attach_shader(program.resource(), fragment_shader.resource());
            gl.link_program(program.resource());

            // Check for linking errors

            if !gl.get_program_link_status(program.resource()) {
                return Err(gl.get_program_info_log(program.resource()))
            }
        }

        Ok(Self {program})
    }

    pub(crate) fn use_(&self) {
        unsafe {
            self.gl.use_program(Some(self.resource()));
        }
    }

    /// Draws the `n_vertices` in a `VertexArrayObject` as the specified `RasterGeometry` on the target `Framebuffer`.

    pub fn raster(&self, framebuffer: &Framebuffer, vertex_array_object: &VertexArrayObject, raster_geometry: RasterGeometry, n_vertices: u32) {
        let gl = &self.gl;
        unsafe {
            framebuffer.bind();
            self.use_();
            vertex_array_object.bind();
            gl.enable(glow::PROGRAM_POINT_SIZE);
            let (width,height) = framebuffer.dimensions();
            gl.viewport(0, 0, width as i32, height as i32);
            gl.draw_arrays(raster_geometry as u32, 0, n_vertices as i32);
        }
    }
}