//! An animated solar system.
//!
//! This example showcases how to use a `Canvas` widget with transforms to draw
//! using different coordinate systems.
//!
//! Inspired by the example found in the MDN docs[1].
//!
//! [1]: https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API/Tutorial/Basic_animations#An_animated_solar_system
use iced::{
    canvas, executor, window, Application, Canvas, Color, Command, Container,
    Element, Length, Point, Settings, Size, Subscription, Vector,
};

use std::time::Instant;

pub fn main() {
    SolarSystem::run(Settings {
        antialiasing: true,
        ..Settings::default()
    })
}

struct SolarSystem {
    state: State,
    solar_system: canvas::layer::Cache<State>,
}

#[derive(Debug, Clone, Copy)]
enum Message {
    Tick(Instant),
}

impl Application for SolarSystem {
    type Executor = executor::Default;
    type Message = Message;
    type Flags = ();

    fn new(_flags: ()) -> (Self, Command<Message>) {
        (
            SolarSystem {
                state: State::new(),
                solar_system: canvas::layer::Cache::new(),
            },
            Command::none(),
        )
    }

    fn title(&self) -> String {
        String::from("Solar system - Iced")
    }

    fn update(&mut self, message: Message) -> Command<Message> {
        match message {
            Message::Tick(instant) => {
                self.state.update(instant);
                self.solar_system.clear();
            }
        }

        Command::none()
    }

    fn subscription(&self) -> Subscription<Message> {
        time::every(std::time::Duration::from_millis(10))
            .map(|instant| Message::Tick(instant))
    }

    fn view(&mut self) -> Element<Message> {
        let canvas = Canvas::new()
            .width(Length::Fill)
            .height(Length::Fill)
            .push(self.solar_system.with(&self.state));

        Container::new(canvas)
            .width(Length::Fill)
            .height(Length::Fill)
            .center_x()
            .center_y()
            .into()
    }
}

#[derive(Debug)]
struct State {
    start: Instant,
    current: Instant,
    stars: Vec<(Point, f32)>,
}

impl State {
    const SUN_RADIUS: f32 = 70.0;
    const ORBIT_RADIUS: f32 = 150.0;
    const EARTH_RADIUS: f32 = 12.0;
    const MOON_RADIUS: f32 = 4.0;
    const MOON_DISTANCE: f32 = 28.0;

    pub fn new() -> State {
        let now = Instant::now();
        let (width, height) = window::Settings::default().size;

        State {
            start: now,
            current: now,
            stars: {
                use rand::Rng;

                let mut rng = rand::thread_rng();

                (0..100)
                    .map(|_| {
                        (
                            Point::new(
                                rng.gen_range(0.0, width as f32),
                                rng.gen_range(0.0, height as f32),
                            ),
                            rng.gen_range(0.5, 1.0),
                        )
                    })
                    .collect()
            },
        }
    }

    pub fn update(&mut self, now: Instant) {
        self.current = now;
    }
}

impl canvas::Drawable for State {
    fn draw(&self, frame: &mut canvas::Frame) {
        use canvas::{Fill, Path, Stroke};
        use std::f32::consts::PI;

        let center = frame.center();

        let space = Path::new(|path| {
            path.rectangle(Point::new(0.0, 0.0), frame.size())
        });

        let stars = Path::new(|path| {
            for (p, size) in &self.stars {
                path.rectangle(*p, Size::new(*size, *size));
            }
        });

        let sun = Path::new(|path| path.circle(center, Self::SUN_RADIUS));
        let orbit = Path::new(|path| path.circle(center, Self::ORBIT_RADIUS));

        frame.fill(&space, Fill::Color(Color::BLACK));
        frame.fill(&stars, Fill::Color(Color::WHITE));
        frame.fill(&sun, Fill::Color(Color::from_rgb8(0xF9, 0xD7, 0x1C)));
        frame.stroke(
            &orbit,
            Stroke {
                width: 1.0,
                color: Color::from_rgba8(0, 153, 255, 0.1),
                ..Stroke::default()
            },
        );

        let elapsed = self.current - self.start;
        let elapsed_seconds = elapsed.as_secs() as f32;
        let elapsed_millis = elapsed.subsec_millis() as f32;

        frame.with_save(|frame| {
            frame.translate(Vector::new(center.x, center.y));
            frame.rotate(
                (2.0 * PI / 60.0) * elapsed_seconds
                    + (2.0 * PI / 60_000.0) * elapsed_millis,
            );
            frame.translate(Vector::new(Self::ORBIT_RADIUS, 0.0));

            let earth = Path::new(|path| {
                path.circle(Point::ORIGIN, Self::EARTH_RADIUS)
            });

            let shadow = Path::new(|path| {
                path.rectangle(
                    Point::new(0.0, -Self::EARTH_RADIUS),
                    Size::new(
                        Self::EARTH_RADIUS * 4.0,
                        Self::EARTH_RADIUS * 2.0,
                    ),
                )
            });

            frame.fill(&earth, Fill::Color(Color::from_rgb8(0x6B, 0x93, 0xD6)));

            frame.with_save(|frame| {
                frame.rotate(
                    ((2.0 * PI) / 6.0) * elapsed_seconds
                        + ((2.0 * PI) / 6_000.0) * elapsed_millis,
                );
                frame.translate(Vector::new(0.0, Self::MOON_DISTANCE));

                let moon = Path::new(|path| {
                    path.circle(Point::ORIGIN, Self::MOON_RADIUS)
                });

                frame.fill(&moon, Fill::Color(Color::WHITE));
            });

            frame.fill(
                &shadow,
                Fill::Color(Color {
                    a: 0.7,
                    ..Color::BLACK
                }),
            );
        });
    }
}

mod time {
    use iced::futures;
    use std::time::Instant;

    pub fn every(duration: std::time::Duration) -> iced::Subscription<Instant> {
        iced::Subscription::from_recipe(Every(duration))
    }

    struct Every(std::time::Duration);

    impl<H, I> iced_native::subscription::Recipe<H, I> for Every
    where
        H: std::hash::Hasher,
    {
        type Output = Instant;

        fn hash(&self, state: &mut H) {
            use std::hash::Hash;

            std::any::TypeId::of::<Self>().hash(state);
            self.0.hash(state);
        }

        fn stream(
            self: Box<Self>,
            _input: futures::stream::BoxStream<'static, I>,
        ) -> futures::stream::BoxStream<'static, Self::Output> {
            use futures::stream::StreamExt;

            async_std::stream::interval(self.0)
                .map(|_| Instant::now())
                .boxed()
        }
    }
}