extern crate sdl2;
extern crate gl;

use sdl2::video::GLProfile;
use gl::types::*;

use std;

/*enum Vattr {
	VATTR_VERTEX,
	VATTR_TEXCOORD
}*/

static WIN_W : u32 = 800;
static WIN_H : u32 = 600;

static VERTEX_DATA : [GLfloat; 12] = [
	-0.5, -0.5,
	0.5, -0.5,
	0.5, 0.5,

	-0.5, -0.5,
	0.5, 0.5,
	-0.5, 0.5
];

static NUM_VERTICES : GLint = 6;
static VERTEX_LOC : u32 = 0;

let tex : u32 = 0;

static VS : &'static str =
"#version 130\n\
 attribute vec4 pos;\n\
 void main() {\n\
    gl_Position = pos;\n\
 }";

static FS : &'static str =
"#version 130\n\
 out vec4 color;\n\
 void main() {\n\
    color = vec4(0.0, 0.5, 0.8, 1.0);\n\
 }";

fn compile_sdr(src: &str, stage:GLenum) -> GLuint {
    let shader;
    unsafe {
        shader = gl::CreateShader(stage);

        let s = std::ffi::CString::new(src).expect("CString::new failed");;

        gl::ShaderSource(shader, 1, &s.as_ptr(), std::ptr::null());
        gl::CompileShader(shader);
        // status
        let mut status = gl::FALSE as GLint;
        gl::GetShaderiv(shader, gl::COMPILE_STATUS, &mut status);

        // error handling
        if status != (gl::TRUE as GLint) {
            let mut len = 0;
            gl::GetShaderiv(shader, gl::INFO_LOG_LENGTH, &mut len);

            let mut buf: Vec<u8> = Vec::with_capacity((len + 1) as usize);
            buf.extend([b' '].iter().cycle().take(len as usize));
            let err: std::ffi::CString = std::ffi::CString::from_vec_unchecked(buf);

            gl::GetShaderInfoLog(shader, len, std::ptr::null_mut(),
                                err.as_ptr() as *mut GLchar);
            println!("{}", err.to_str().unwrap());

        }
    }
    shader
}

fn link_sdr_prog(vs: GLuint, fs: GLuint) -> GLuint {
    unsafe {
        let sdr_prog = gl::CreateProgram();
        gl::AttachShader(sdr_prog, vs);
        gl::AttachShader(sdr_prog, fs);
        gl::LinkProgram(sdr_prog);

        let mut status = gl::FALSE as GLint;
        gl::GetProgramiv(sdr_prog, gl::LINK_STATUS, &mut status);
        if status != (gl::TRUE as GLint) {
            let mut len: GLint = 0;
            gl::GetProgramiv(sdr_prog, gl::INFO_LOG_LENGTH, &mut len);


            let mut buf: Vec<u8> = Vec::with_capacity((len + 1) as usize);
            buf.extend([b' '].iter().cycle().take(len as usize));
            let err: std::ffi::CString = std::ffi::CString::from_vec_unchecked(buf);

            gl::GetProgramInfoLog(sdr_prog, len, std::ptr::null_mut(), err.as_ptr() as *mut GLchar);
            println!("{}", err.to_str().unwrap());
        }
        sdr_prog
    }
}

fn main() {
    let sdl_ctx = sdl2::init().unwrap();
    let vid_sys = sdl_ctx.video().unwrap();
    let gl_attr = vid_sys.gl_attr();

    gl_attr.set_context_profile(GLProfile::Core);

    let win = vid_sys
        .window("foobar", WIN_W, WIN_H)
        .opengl() // add opengl flag
        .resizable()
        .build()
        .unwrap();

    let _gl_ctx = win.gl_create_context().unwrap();
    let _gl = gl::load_with(|s| vid_sys.gl_get_proc_address(s) as
                            *const std::os::raw::c_void);

    let mut vao = 0;
    let mut vbo = 0;

    let mut sprog;
    let fs;
    let vs;

    unsafe {
        gl::ClearColor(0.3, 0.1, 0.1, 1.0);
        gl::GenVertexArrays(1, &mut vao);
        gl::BindVertexArray(vao);

        gl::GenBuffers(1, &mut vbo);
        gl::BindBuffer(gl::ARRAY_BUFFER, vbo);
        gl::BufferData(gl::ARRAY_BUFFER, (VERTEX_DATA.len() * std::mem::size_of::<GLfloat>()) as GLsizeiptr,
                       std::mem::transmute(&VERTEX_DATA[0]),
                       gl::STATIC_DRAW);
        gl::BindBuffer(gl::ARRAY_BUFFER, 0);

        vs = compile_sdr(VS, gl::VERTEX_SHADER);
        fs = compile_sdr(FS, gl::FRAGMENT_SHADER);

        sprog = link_sdr_prog(vs, fs);
        let att_str = std::ffi::CString::new("position").unwrap();

        gl::BindAttribLocation(sprog, VERTEX_LOC, att_str.as_ptr());
        sprog = link_sdr_prog(vs, fs);

        gl::UseProgram(sprog);
    }

    let mut event_pump = sdl_ctx.event_pump().unwrap();
    'main: loop {
        for event in event_pump.poll_iter() {
            // handle user input here
            match event {
                sdl2::event::Event::Quit {..} |
                sdl2::event::Event::KeyDown {keycode:
                    Some(sdl2::keyboard::Keycode::Escape), ..} =>
                        break 'main,
                _ => {},
            }
        }

        unsafe {
            gl::Clear(gl::COLOR_BUFFER_BIT);
            gl::Viewport(0, 0, WIN_W as i32, WIN_H as i32);

            gl::EnableVertexAttribArray(VERTEX_LOC);
            gl::BindBuffer(gl::ARRAY_BUFFER, vbo);
            gl::VertexAttribPointer(VERTEX_LOC, 2,
                                    gl::FLOAT, gl::FALSE,
                                    0 as i32, std::ptr::null());

            gl::DrawArrays(gl::TRIANGLES, 0, NUM_VERTICES);
        }

        win.gl_swap_window();
    }

    unsafe {
        gl::DeleteProgram(sprog);
        gl::DeleteShader(vs);
        gl::DeleteShader(fs);
        gl::DeleteBuffers(1, &vbo);
        gl::DeleteVertexArrays(1, &vao);
    }
}