feat: focusable segmented items in segmented button

src/widget/segmented_button/selection_modes.rs

@@ -0,0 +1,59 @@
+// Copyright 2022 System76 <info@system76.com>
+// SPDX-License-Identifier: MPL-2.0
+
+//! Describes logic specific to the single-select and multi-select modes of a model.
+
+use super::Key;
+use std::collections::HashSet;
+
+/// Describes a type that has selectable components.
+pub trait Selectable: Default {
+    /// Activate a component.
+    fn activate(&mut self, key: Key);
+
+    /// Deactivate a component.
+    fn deactivate(&mut self, key: Key);
+
+    /// Checks if the component is active.
+    fn is_active(&self, key: Key) -> bool;
+}
+
+/// Ensures that only one key may be selected.
+#[derive(Default)]
+pub struct SingleSelect {
+    pub active: Key,
+}
+
+impl Selectable for SingleSelect {
+    fn activate(&mut self, key: Key) {
+        self.active = key;
+    }
+
+    fn deactivate(&mut self, _key: Key) {
+        self.active = Key::default();
+    }
+
+    fn is_active(&self, key: Key) -> bool {
+        self.active == key
+    }
+}
+
+/// Permits multiple keys to be active at a time.
+#[derive(Default)]
+pub struct MultiSelect {
+    pub active: HashSet<Key>,
+}
+
+impl Selectable for MultiSelect {
+    fn activate(&mut self, key: Key) {
+        self.active.insert(key);
+    }
+
+    fn deactivate(&mut self, key: Key) {
+        self.active.remove(&key);
+    }
+
+    fn is_active(&self, key: Key) -> bool {
+        self.active.contains(&key)
+    }
+}