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extern crate gfx;
extern crate gfx_device_gl;
extern crate glutin;
extern crate time;


use std::thread::sleep;
use std::time::{Duration, Instant};
use std::cmp;
const CLEAR_COLOR: [f32; 4] = [0.0, 0., 0., 1.0];
use self::glutin::ElementState;
use self::glutin::GlContext;
pub use self::glutin::VirtualKeyCode as Key;
use gfx::Device;
use graphics::camera::OrthoCamera;
use graphics::context::Context;
use graphics::pipeline::Transform;

#[derive(Copy, Clone, Debug)]
pub struct EventSettings {
    pub max_fps: u64,
    pub ups: u64,
    pub ups_reset: u64,
    pub swap_buffers: bool,
    pub bench_mode: bool,
    pub lazy: bool,
}

impl EventSettings {
    /// Creates new with default settings.
    pub fn new() -> EventSettings {
        EventSettings {
            max_fps: DEFAULT_MAX_FPS,
            ups: DEFAULT_UPS,
            swap_buffers: true,
            bench_mode: false,
            lazy: false,
            ups_reset: DEFAULT_UPS_RESET,
        }
    }
}

impl Default for EventSettings {
    fn default() -> EventSettings {
        EventSettings::new()
    }
}


/// The default updates per second.
pub const DEFAULT_UPS: u64 = 120;
/// The default delayed updates reset.
pub const DEFAULT_UPS_RESET: u64 = 2;
/// The default maximum frames per second.
pub const DEFAULT_MAX_FPS: u64 = 60;


static BILLION: u64 = 1_000_000_000;

fn ns_to_duration(ns: u64) -> Duration {
    let secs = ns / BILLION;
    let nanos = (ns % BILLION) as u32;
    Duration::new(secs, nanos)
}

fn duration_to_secs(dur: Duration) -> f32 {
    dur.as_secs() as f32 + dur.subsec_nanos() as f32 / 1_000_000_000.0
}




/// Do all operations with Window and GameLoop
pub fn run<State>(ctx: &mut Context, state: &mut State, ups: u64)
where
    State: MainLoop,
{
    let mut running = true;
    let mut transform = Transform {
        combined: ctx.camera.combined(),
    };

    let start = Instant::now();

    let mut last_update = start;
    let mut last_frame = start;
    let mut dt_update_in_ns = BILLION / ups;
    let mut dt_frame_in_ns = BILLION  / ups;
    let mut dt = 1.0 / ups as f32;
    let mut first_frame = true;




    while running {
            ctx.events.poll_events(|event| {
                if let glutin::Event::WindowEvent { event, .. } = event {
                    match event {
                        glutin::WindowEvent::CloseRequested
                        | glutin::WindowEvent::KeyboardInput {
                            input:
                                glutin::KeyboardInput {
                                    virtual_keycode: Some(Key::Escape),
                                    ..
                                },
                            ..
                        } => running = false,
                        glutin::WindowEvent::KeyboardInput {
                            input:
                                glutin::KeyboardInput {
                                    virtual_keycode: Some(keycode),
                                    state: ElementState::Pressed,
                                    ..
                                },
                            ..
                        } => {
                            state.button_down(keycode);
                        }
                        glutin::WindowEvent::KeyboardInput {
                            input:
                                glutin::KeyboardInput {
                                    virtual_keycode: Some(keycode),
                                    state: ElementState::Released,
                                    ..
                                },
                            ..
                        } => {
                            state.button_release(keycode);
                        }

                        _ => {}
                    }
                }
            });
            state.update(ctx, 1.0);


            match ctx.encoder
                .update_buffer(&ctx.data.transform, &[transform], 0)
            {
                Err(err) => {
                    println!("Error: {:?}", err);
                }
                _ => {}
            }
            transform.combined = ctx.camera.combined();

            ctx.encoder.clear(&ctx.data.out, CLEAR_COLOR);

            state.draw(ctx);
            ctx.encoder.flush(&mut ctx.device);
            ctx.window.swap_buffers().unwrap();
            ctx.device.cleanup();
            let cur_time = Instant::now();

            let next_frame = last_frame + ns_to_duration(dt_frame_in_ns);
            let next_update = last_update + ns_to_duration(dt_update_in_ns);
            let next_event = cmp::min(next_frame,next_update);

            if next_event > cur_time {
                sleep(next_event - cur_time);
            }
    }
}

///MainLoop
pub trait MainLoop {
    /// Update function, called every time
    fn update(&mut self, ctx: &mut Context, dt: f32);
    /// Draw function, called every time
    fn draw(&mut self, ctx: &mut Context);
    /// Called when keyboard button pressed
    fn button_down(&mut self, _button: Key) {}
    /// Called when keyboard button released
    fn button_release(&mut self, _button: Key) {}
}