ui: add experimental list view element (not used)

Signed-off-by: Fabrizio Iannetti <fabrizio.iannetti@gmail.com>

src/ui.rs

@@ -1,2 +1,3 @@
 pub mod calendar;
-pub mod basics;
+pub mod basics;
+pub mod list;

src/ui/list.rs

@@ -0,0 +1,65 @@
+
+trait ListContentProvider<Item> {
+
+    /// Get the number of items provided
+    fn get_count(&self) -> i64;
+
+    fn get_item(&self, index: i64) -> Item;
+}
+
+trait ListLabelProvider<Item> {
+
+    fn get_label(&self, item: &Item) -> str;
+}
+
+trait CellRenderer {
+    fn new() -> Self;
+
+    /// Get the height of a single cell
+    fn height(&self) -> i64;
+}
+
+
+struct ListView<'a, Item, R: CellRenderer> {
+    content_provider: &'a dyn ListContentProvider<Item>,
+    label_provider: &'a dyn ListLabelProvider<Item>,
+    cell_renderer: R,
+    x: i64,
+}
+
+
+
+/// A ListView is responsible for:
+/// - get number of objects from the content provider
+/// - manage the range of visible objects
+/// - retrieve objects to be rendered from the content provider
+///
+impl<'a, Item, R: CellRenderer> ListView<'a, Item, R> {
+    pub fn new(content_provider: &'a dyn ListContentProvider<Item>, label_provider: &'a dyn ListLabelProvider<Item>) -> Self {
+        ListView::<'a, Item, R> {
+            content_provider,
+            label_provider,
+            cell_renderer: CellRenderer::new(),
+            x: 0,
+        }
+    }
+
+    pub fn refresh(&mut self) {
+        let list_height = self.content_provider.get_count() * self.cell_renderer.height();
+        if self.x > list_height {
+            self.x = list_height;
+        }
+    }
+
+    pub fn top_item(&self) -> Item {
+        let index = self.x / self.cell_renderer.height();
+        self.content_provider.get_item(index)
+    }
+
+    /// move the viewport on the list by the given amount
+    pub fn move_by(&mut self, delta: i64) {
+        self.x += delta;
+        self.refresh();
+    }
+
+}