extern crate sdl2;

use sdl2::pixels::PixelFormatEnum;
use sdl2::rect::Rect;
use sdl2::event::Event;
use sdl2::keyboard::Keycode;

pub fn main() -> Result<(), String> {
    let sdl_context = sdl2::init()?;
    let video_subsystem = sdl_context.video()?;

    let window = video_subsystem.window("rust-sdl2 demo: Video", 800, 600)
        .position_centered()
        .opengl()
        .build()
        .map_err(|e| e.to_string())?;

    let mut canvas = window.into_canvas().build().map_err(|e| e.to_string())?;
    let texture_creator = canvas.texture_creator();

    let mut texture = texture_creator.create_texture_streaming(PixelFormatEnum::IYUV, 256, 256)
        .map_err(|e| e.to_string())?;
    // Create a U-V gradient
    texture.with_lock(None, |buffer: &mut [u8], pitch: usize| {
        // `pitch` is the width of the Y component
        // The U and V components are half the width and height of Y

        let w = 256;
        let h = 256;

        // Set Y (constant)
        for y in 0..h {
            for x in 0..w {
                let offset = y*pitch + x;
                buffer[offset] = 128;
            }
        }

        let y_size = pitch*h;

        // Set U and V (X and Y)
        for y in 0..h/2 {
            for x in 0..w/2 {
                let u_offset = y_size + y*pitch/2 + x;
                let v_offset = y_size + (pitch/2 * h/2) + y*pitch/2 + x;
                buffer[u_offset] = (x*2) as u8;
                buffer[v_offset] = (y*2) as u8;
            }
        }
    })?;

    canvas.clear();
    canvas.copy(&texture, None, Some(Rect::new(100, 100, 256, 256)))?;
    canvas.present();

    let mut event_pump = sdl_context.event_pump()?;

    'running: loop {
        for event in event_pump.poll_iter() {
            match event {
                Event::Quit {..} | Event::KeyDown { keycode: Some(Keycode::Escape), .. } => {
                    break 'running
                },
                _ => {}
            }
        }
        // The rest of the game loop goes here...
    }

    Ok(())
}