guise-ui 1.5.3

//! `Signal` — an observable state cell backed by a gpui entity.

use gpui::{App, AppContext, Entity};

/// A clonable handle to a piece of reactive state. React's `useState` value:
/// reading is cheap, writing notifies every observer (see [`super::watch`]).
///
/// All clones share one backing entity, so passing a `Signal` around — or
/// providing it as context — gives every holder the same live value.
pub struct Signal<T> {
  entity: Entity<T>,
}

impl<T: 'static> Signal<T> {
  /// Create a new signal holding `value`.
  pub fn new(cx: &mut App, value: T) -> Self {
    Signal {
      entity: cx.new(|_cx| value),
    }
  }

  /// The backing entity — pass to `cx.observe(...)` or [`super::watch`].
  pub fn entity(&self) -> &Entity<T> {
    &self.entity
  }

  /// Borrow the current value.
  pub fn read<'a>(&self, cx: &'a App) -> &'a T {
    self.entity.read(cx)
  }

  /// Clone out the current value.
  pub fn get(&self, cx: &App) -> T
  where
    T: Clone,
  {
    self.entity.read(cx).clone()
  }

  /// Replace the value and notify observers.
  pub fn set(&self, cx: &mut App, value: T) {
    self.entity.update(cx, |slot, cx| {
      *slot = value;
      cx.notify();
    });
  }

  /// Replace the value and notify observers, unless the new value equals
  /// the current one — then nothing happens (no notify).
  pub fn set_if_changed(&self, cx: &mut App, value: T)
  where
    T: PartialEq,
  {
    self.entity.update(cx, |slot, cx| {
      if *slot != value {
        *slot = value;
        cx.notify();
      }
    });
  }

  /// Mutate the value in place and notify observers.
  pub fn update(&self, cx: &mut App, f: impl FnOnce(&mut T)) {
    self.entity.update(cx, |slot, cx| {
      f(slot);
      cx.notify();
    });
  }
}

impl<T> Clone for Signal<T> {
  fn clone(&self) -> Self {
    Signal {
      entity: self.entity.clone(),
    }
  }
}