Add Widget and BoxedWidget

showbits-common/src/widget.rs

@@ -0,0 +1,98 @@
+use crate::{Rect, Vec2, View};
+
+pub trait Widget<C> {
+    /// Size that the widget wants to be, given the width and height
+    /// constraints.
+    fn size(&self, max_width: Option<i32>, max_height: Option<i32>) -> Vec2;
+
+    /// Recalculate the size of all inner widgets given the widget's own size.
+    ///
+    /// # Implement if...
+    ///
+    /// - There are inner widgets
+    fn resize(&mut self, _area: Rect) {}
+
+    /// Perform any updates (e.g. fetching map tiles) that require the widget's
+    /// size and may fail.
+    ///
+    /// # Implement if...
+    ///
+    /// - There are inner widgets
+    /// - This widget needs to perform updates
+    fn update(&mut self, _area: Rect) -> anyhow::Result<()> {
+        Ok(())
+    }
+
+    fn draw(self, view: &mut View<'_, C>);
+}
+
+/// Wrapper trait around [`Widget`] that turns `Box<Self>` into a `Self` to get
+/// around the "size cannot be statically determined" error with the naïve
+/// approach of `Box<Widget>`.
+trait WidgetWrapper<C> {
+    fn size(&self, max_width: Option<i32>, max_height: Option<i32>) -> Vec2;
+    fn resize(&mut self, _area: Rect);
+    fn update(&mut self, _area: Rect) -> anyhow::Result<()>;
+    fn draw(self: Box<Self>, view: &mut View<'_, C>);
+}
+
+impl<C, W: Widget<C>> WidgetWrapper<C> for W {
+    // These implementations explicitly use `Widget::*` to call the widget
+    // methods even though they have priority over the `WidgetWrapper::*`
+    // methods for some reason. Just a bit of rustc magic, I guess.
+
+    fn size(&self, max_width: Option<i32>, max_height: Option<i32>) -> Vec2 {
+        Widget::size(self, max_width, max_height)
+    }
+
+    fn resize(&mut self, area: Rect) {
+        Widget::resize(self, area);
+    }
+
+    fn update(&mut self, area: Rect) -> anyhow::Result<()> {
+        Widget::update(self, area)
+    }
+
+    fn draw(self: Box<Self>, view: &mut View<'_, C>) {
+        Widget::draw(*self, view);
+    }
+}
+
+pub struct BoxedWidget<C> {
+    area: Rect,
+    widget: Box<dyn WidgetWrapper<C>>,
+}
+
+impl<C> BoxedWidget<C> {
+    pub fn new<W>(widget: W) -> Self
+    where
+        W: Widget<C> + 'static,
+    {
+        Self {
+            area: Rect::ZERO,
+            widget: Box::new(widget),
+        }
+    }
+
+    pub fn area(&self) -> Rect {
+        self.area
+    }
+}
+
+impl<C> Widget<C> for BoxedWidget<C> {
+    fn size(&self, max_width: Option<i32>, max_height: Option<i32>) -> Vec2 {
+        self.widget.size(max_width, max_height)
+    }
+
+    fn resize(&mut self, area: Rect) {
+        self.widget.resize(area);
+    }
+
+    fn update(&mut self, area: Rect) -> anyhow::Result<()> {
+        self.widget.update(area)
+    }
+
+    fn draw(self, view: &mut View<'_, C>) {
+        self.widget.draw(view);
+    }
+}