feat: implement SegmentedButton widget

src/widget/segmented_button/state.rs

@@ -0,0 +1,82 @@
+/// Copyright 2022 System76 <info@system76.com>
+// SPDX-License-Identifier: MPL-2.0
+
+use slotmap::{SecondaryMap, SlotMap};
+
+slotmap::new_key_type! {
+    pub struct Key;
+}
+
+/// Contains all state for interacting with a [`SegmentedButton`].
+pub struct State<Data> {
+    pub inner: WidgetState,
+    pub data: SecondaryState<Data>,
+}
+
+impl<Data> Default for State<Data> {
+    fn default() -> Self {
+        Self {
+            inner: WidgetState::default(),
+            data: SecondaryState::default(),
+        }
+    }
+}
+
+/// State which is most useful to the widget.
+#[derive(Default)]
+pub struct WidgetState {
+    pub buttons: SlotMap<Key, ButtonContent>,
+    pub active: Key,
+}
+
+/// State which is most useful to the application.
+pub type SecondaryState<Data> = SecondaryMap<Key, Data>;
+
+impl<Data> State<Data> {
+    /// The ID of the active button.
+    #[must_use]
+    pub fn active(&self) -> Key {
+        self.inner.active
+    }
+
+    /// Get the application data for the active button.
+    #[must_use]
+    pub fn active_data(&self) -> Option<&Data> {
+        self.data(self.active())
+    }
+
+    /// Get the application data for a button.
+    #[must_use]
+    pub fn data(&self, key: Key) -> Option<&Data> {
+        self.data.get(key)
+    }
+
+    /// Insert a new button.
+    pub fn insert(&mut self, content: impl Into<ButtonContent>, data: Data) -> Key {
+        let key = self.inner.buttons.insert(content.into());
+        self.data.insert(key, data);
+        key
+    }
+
+    /// Removes a button.
+    pub fn remove(&mut self, key: Key) -> Option<Data> {
+        self.inner.buttons.remove(key);
+        self.data.remove(key)
+    }
+
+    /// Activates this button.
+    pub fn activate(&mut self, key: Key) {
+        self.inner.active = key;
+    }
+}
+
+/// Data to be drawn in a [`SegmentedButton`] button.
+pub struct ButtonContent {
+    pub text: String,
+}
+
+impl From<String> for ButtonContent {
+    fn from(text: String) -> Self {
+        ButtonContent { text }
+    }
+}