From ba68e34d0d61936404d27a61add4c0f19a0ea0c9 Mon Sep 17 00:00:00 2001
From: Joscha <joscha@plugh.de>
Date: Sun, 3 Mar 2024 23:33:42 +0100
Subject: [PATCH] Add Widget and BoxedWidget

---
 Cargo.lock                    |  9 ++++
 showbits-common/Cargo.toml    |  3 ++
 showbits-common/src/lib.rs    |  3 +-
 showbits-common/src/widget.rs | 98 +++++++++++++++++++++++++++++++++++
 4 files changed, 112 insertions(+), 1 deletion(-)
 create mode 100644 showbits-common/src/widget.rs

diff --git a/Cargo.lock b/Cargo.lock
index 44847ac..3c7da6b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,9 +2,18 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "anyhow"
+version = "1.0.80"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5ad32ce52e4161730f7098c077cd2ed6229b5804ccf99e5366be1ab72a98b4e1"
+
 [[package]]
 name = "showbits-common"
 version = "0.0.0"
+dependencies = [
+ "anyhow",
+]
 
 [[package]]
 name = "showbits-thermal-printer"
diff --git a/showbits-common/Cargo.toml b/showbits-common/Cargo.toml
index ec7ce3b..ecc8221 100644
--- a/showbits-common/Cargo.toml
+++ b/showbits-common/Cargo.toml
@@ -3,5 +3,8 @@ name = "showbits-common"
 version.workspace = true
 edition.workspace = true
 
+[dependencies]
+anyhow = "1.0.80"
+
 [lints]
 workspace = true
diff --git a/showbits-common/src/lib.rs b/showbits-common/src/lib.rs
index 605350f..4b1f0b5 100644
--- a/showbits-common/src/lib.rs
+++ b/showbits-common/src/lib.rs
@@ -1,6 +1,7 @@
-pub use crate::{buffer::Buffer, rect::Rect, vec2::Vec2, view::View};
+pub use crate::{buffer::*, rect::*, vec2::*, view::*, widget::*};
 
 mod buffer;
 mod rect;
 mod vec2;
 mod view;
+mod widget;
diff --git a/showbits-common/src/widget.rs b/showbits-common/src/widget.rs
new file mode 100644
index 0000000..942754b
--- /dev/null
+++ b/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);
+    }
+}