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use euclid::Size2D;
use crate::{event::Event, unit::Cell, Printer};
/// A UI element
pub trait View<T, M> {
/// Draws this element
fn draw(&self, printer: &Printer, focused: bool);
/// Calculate the view's content-based size with minimum width
///
/// This is not necessarily the view's *absolute* minimum width; in most
/// cases that would end up being zero, which isn't useful. Instead, the
/// value computed is a *sensible* minimum that, if [`draw`](View::draw)
/// were called with this function's return value as the
/// [`Printer`](crate::Printer)'s size, would produce a visually-acceptable
/// result.
///
/// # Examples
///
/// The [`text`](crate::view::text) view finds the visual length of the
/// [visually-longest](unicode_segmentation::UnicodeSegmentation::graphemes)
/// sequence of [non-whitespace](std::str.split_whitespace) characters (or
/// in other words, longest word including punctuation) and reports that
/// length as its width. The height value is computed by
/// [`textwrap`](textwrap)ing with that width and reporting the amount of
/// lines it would take to display the text.
fn width(&self) -> Size2D<u16, Cell>;
/// Calculate the view's content-based size with minimum height
///
/// This is not necessarily the view's *absolute* minimum height; in most
/// cases that would end up being zero, which isn't useful. Instead, the
/// value computed is a *sensible* minimum that, if [`draw`](View::draw)
/// were called with this function's return value as the
/// [`Printer`](crate::Printer)'s size, would produce a visually-acceptable
/// result.
///
/// # Examples
///
/// The [`text`](crate::view::text) view reports its height as the number of
/// lines in its content and its width as the visual length of the visually
/// longest line.
fn height(&self) -> Size2D<u16, Cell>;
/// Given a constraint, calculate the size of this view
fn layout(&self, constraint: Size2D<u16, Cell>) -> Size2D<u16, Cell>;
/// Process an event and optionally produce messages
fn event(
&mut self,
event: &Event<T>,
focused: bool,
) -> Box<dyn Iterator<Item = M>>;
/// Whether this element can be interacted with by the user
///
/// Returning `false` from this method does not opt the implementor out of
/// receiving events, only from acquiring focus. In other words, the
/// `focused` argument to [`event()`] will be `false` after returning
/// `false` from this function. Also, returning `true` doesn't imply that
/// `focused` will be `true`, only that it may eventually be `true` when the
/// user focuses this element.
///
/// [`event()`]: View::event
fn interactive(&self) -> bool;
}