use std::ffi::CStr;
use std::mem;
use std::ptr;
use glutin;

mod gl {
    pub use self::Gles2 as Gl;
    include!(concat!(env!("OUT_DIR"), "/test_gl_bindings.rs"));
}

pub struct Context {
    gl: gl::Gl
}

pub fn load(window: &glutin::Window) -> Context {
    let gl = gl::Gl::load_with(|ptr| window.get_proc_address(ptr) as *const _);

    let version = unsafe {
        let data = CStr::from_ptr(gl.GetString(gl::VERSION) as *const _).to_bytes().to_vec();
        String::from_utf8(data).unwrap()
    };

    println!("OpenGL version {}", version);

    unsafe {
        let vs = gl.CreateShader(gl::VERTEX_SHADER);
        gl.ShaderSource(vs, 1, [VS_SRC.as_ptr() as *const _].as_ptr(), ptr::null());
        gl.CompileShader(vs);

        let fs = gl.CreateShader(gl::FRAGMENT_SHADER);
        gl.ShaderSource(fs, 1, [FS_SRC.as_ptr() as *const _].as_ptr(), ptr::null());
        gl.CompileShader(fs);

        let program = gl.CreateProgram();
        gl.AttachShader(program, vs);
        gl.AttachShader(program, fs);
        gl.LinkProgram(program);
        gl.UseProgram(program);

        let mut vb = mem::uninitialized();
        gl.GenBuffers(1, &mut vb);
        gl.BindBuffer(gl::ARRAY_BUFFER, vb);
        gl.BufferData(gl::ARRAY_BUFFER,
                           (VERTEX_DATA.len() * mem::size_of::<f32>()) as gl::types::GLsizeiptr,
                           VERTEX_DATA.as_ptr() as *const _, gl::STATIC_DRAW);

        if gl.BindVertexArray.is_loaded() {
            let mut vao = mem::uninitialized();
            gl.GenVertexArrays(1, &mut vao);
            gl.BindVertexArray(vao);
        }

        let pos_attrib = gl.GetAttribLocation(program, b"position\0".as_ptr() as *const _);
        let color_attrib = gl.GetAttribLocation(program, b"color\0".as_ptr() as *const _);
        gl.VertexAttribPointer(pos_attrib as gl::types::GLuint, 2, gl::FLOAT, 0,
                                    5 * mem::size_of::<f32>() as gl::types::GLsizei,
                                    ptr::null());
        gl.VertexAttribPointer(color_attrib as gl::types::GLuint, 3, gl::FLOAT, 0,
                                    5 * mem::size_of::<f32>() as gl::types::GLsizei,
                                    (2 * mem::size_of::<f32>()) as *const () as *const _);
        gl.EnableVertexAttribArray(pos_attrib as gl::types::GLuint);
        gl.EnableVertexAttribArray(color_attrib as gl::types::GLuint);
    }

    Context { gl: gl }
}

impl Context {
    pub fn draw_frame(&self, color: (f32, f32, f32, f32)) {
        unsafe {
            self.gl.ClearColor(color.0, color.1, color.2, color.3);
            self.gl.Clear(gl::COLOR_BUFFER_BIT);

            self.gl.DrawArrays(gl::TRIANGLES, 0, 3);
        }
    }
}

static VERTEX_DATA: [f32; 15] = [
    -0.5, -0.5, 1.0, 0.0, 0.0,
    0.0, 0.5, 0.0, 1.0, 0.0,
    0.5, -0.5, 0.0, 0.0, 1.0
];

const VS_SRC: &'static [u8] = b"
#version 100
precision mediump float;

attribute vec2 position;
attribute vec3 color;

varying vec3 v_color;

void main() {
    gl_Position = vec4(position, 0.0, 1.0);
    v_color = color;
}
\0";

const FS_SRC: &'static [u8] = b"
#version 100
precision mediump float;

varying vec3 v_color;

void main() {
    gl_FragColor = vec4(v_color, 1.0);
}
\0";