use crate::*;
use std::ops::{Add, Sub};
use std::cmp::{Ord, Eq, PartialEq};

/// Entry point for main loop
pub trait App<T: Engine> {
    fn run (self, context: T) -> Usually<T>;
}

pub trait Number: Send + Sync + Copy
    + Add<Self, Output=Self>
    + Sub<Self, Output=Self>
    + Ord + PartialEq + Eq {}

impl<T> Number for T where
    T: Send + Sync + Copy
        + Add<Self, Output=Self>
        + Sub<Self, Output=Self>
        + Ord + PartialEq + Eq
{}

/// Platform backend.
pub trait Engine: Sized {
    fn setup (&mut self) -> Usually<()> { Ok(()) }
    fn exited (&self) -> bool;
    fn teardown (&mut self) -> Usually<()> { Ok(()) }

    /// Unit of distance.
    type Unit: Number;

    type HandleInput;
    type Handled;
    type RenderInput;
    type Rendered;
}

pub trait HandleContext {}

pub trait RenderContext {}

submod! {
    collect
    component
    exit
    focus
    handle
    keymap
    layered
    layout
    render
    split
}