add support for a sidebar

* button to toggle the sidebar
* currently no content, in future a list of calendars will
  be displayed, with options to show/hide single calendars

src/app.rs

@@ -23,6 +23,9 @@ use iced::{
     widget::{
 	    Column,
 	    Container,
+	    button,
+	    text,
+	    pane_grid::{self, PaneGrid}
 	},
 };
 
@@ -35,15 +38,41 @@ pub enum Message {
     NextYear,
     PrevYear,
     ViewModeSelected(ViewMode),
+    ToggleSidebar,
+    Resized(pane_grid::ResizeEvent),
+}
+
+#[derive(PartialEq, Eq)]
+enum PaneType {
+	Calendar,
+	Sidebar,
+}
+
+struct PaneGridState {
+	pane_type: PaneType,
 }
 
-#[derive(Default)]
 pub struct CalendarApp {
     view_date: NaiveDate,
     controls: Controls,
+    grid_state: pane_grid::State<PaneGridState>,
     events: EventsCollection,
 }
 
+impl Default for CalendarApp {
+
+    fn default() -> Self {
+		let (grid_state, _) = pane_grid::State::new(PaneGridState{pane_type: PaneType::Calendar});
+
+        CalendarApp {
+			view_date: NaiveDate::default(),
+			controls: Controls::default(),
+			grid_state,
+			events: EventsCollection::default(),
+			}
+    }
+}
+
 impl CalendarApp {
 	pub fn with_files(calendar_paths: std::vec::Vec<path::PathBuf>) -> Self {
         let view_date = Utc::now().date_naive();
@@ -81,18 +110,69 @@ impl CalendarApp {
             Message::ViewModeSelected(mode) => {
                 self.controls.mode = Some(mode);
             }
+            Message::ToggleSidebar => {
+				self.toggle_sidebar();
+			},
+            Message::Resized(pane_grid::ResizeEvent { split, ratio }) => {
+                self.grid_state.resize(split, ratio);
+            },
         }
         Task::none()
     }
 
+	fn toggle_sidebar(&mut self) {
+		if let Some(sidebar_pane) = self.get_sidebar_pane() {
+			// close the sidebar
+			self.grid_state.close(sidebar_pane);
+		} else {
+			// no sidebar: split the main pane (calendar) and move the new pane to the left
+			let pane = self.get_main_pane();
+			if let Some((new_pane, split)) = self.grid_state.split(pane_grid::Axis::Vertical, pane, PaneGridState{pane_type: PaneType::Sidebar}) {
+				self.grid_state.move_to_edge(new_pane, pane_grid::Edge::Left);
+				self.grid_state.resize(split, 0.25);
+			};
+		}
+	}
+
+	fn get_sidebar_pane(&self) -> Option<pane_grid::Pane> {
+		let sb_pane = self.grid_state.iter().find(|&(_, pgs)| {pgs.pane_type == PaneType::Sidebar});
+		if let Some((pane, _)) = sb_pane {
+			Some(*pane)
+		} else {
+			None
+		}
+	}
+
+	fn get_main_pane(&self) -> pane_grid::Pane {
+		// TODO: assuming there is always a calendar pane
+		*(self.grid_state.iter().find(|&(_, pgs)| {pgs.pane_type == PaneType::Calendar}).unwrap().0)
+	}
+
+	fn get_calendar_view(&self) -> CalendarView {
+		CalendarView::new(
+			self.controls.mode.unwrap_or(ViewMode::Year),
+			&CalendarParams::new(),
+			self.view_date,
+			&self.events)
+	}
+
+	fn get_sidebar_view(&self) -> Container<Message> {
+		Container::new(text("TODO"))
+	}
+
     pub fn view(&self) -> Element<Message> {
         #[cfg(feature = "tracing")]
         tracepoints::calendar::view_entry();
+        let main_content = PaneGrid::new(&self.grid_state, |id, pane, is_maximized| {
+			match pane.pane_type {
+			    PaneType::Calendar => pane_grid::Content::new(self.get_calendar_view()),
+			    PaneType::Sidebar => pane_grid::Content::new(self.get_sidebar_view()),
+			}
+		}).on_resize(10, Message::Resized);
         let content = Column::new()
             .align_x(Alignment::Center)
             .push(self.controls.view(self.view_date))
-            .push(CalendarView::new(self.controls.mode.unwrap_or(ViewMode::Year), &CalendarParams::new(), self.view_date, &self.events))
-            ;
+            .push(main_content);
 
         let container = Container::new(content)
             .width(Length::Fill)

src/ui/controls.rs

@@ -16,7 +16,7 @@ use iced::{
 	alignment,
 	theme::palette,
 	border,
-	widget::{Button, Row, Text, button::{Status, Style, secondary}, row, text}
+	widget::{Row, button::{Status, Style, secondary}, row, text, button}
 };
 
 //#[derive(Default)]
@@ -45,24 +45,25 @@ impl Controls {
             .align_y(Alignment::Center)
             .padding(5)
             .spacing(10)
+			.push(button(text("=")).on_press(Message::ToggleSidebar).style(secondary))
         	.push(row![
-				Button::new(text("Week")).on_press(Message::ViewModeSelected(ViewMode::Week)).style(self.get_mode_style(ViewMode::Week)),
-				Button::new(text("Month")).on_press(Message::ViewModeSelected(ViewMode::Month)).style(self.get_mode_style(ViewMode::Month)),
-				Button::new(text("Year")).on_press(Message::ViewModeSelected(ViewMode::Year)).style(self.get_mode_style(ViewMode::Year)),
+				button(text("Week")).on_press(Message::ViewModeSelected(ViewMode::Week)).style(self.get_mode_style(ViewMode::Week)),
+				button(text("Month")).on_press(Message::ViewModeSelected(ViewMode::Month)).style(self.get_mode_style(ViewMode::Month)),
+				button(text("Year")).on_press(Message::ViewModeSelected(ViewMode::Year)).style(self.get_mode_style(ViewMode::Year)),
 			])
 			.push(row![
-	                Button::new(Text::new("<")).on_press(self.get_msg_prev()).style(secondary),
-	                Button::new(Text::new(">")).on_press(self.get_msg_next()).style(secondary),
+	                button(text("<")).on_press(self.get_msg_prev()).style(secondary),
+	                button(text(">")).on_press(self.get_msg_next()).style(secondary),
 				].spacing(0).padding(0)
 			)
             .push(
-                Text::new(description)
+                text(description)
                     .width(Length::Fill)
                     .align_x(alignment::Horizontal::Left)
                     .size(24),
             )
             .push(
-                Text::new(view_date.year().to_string())
+                text(view_date.year().to_string())
                     .width(Length::Fill)
                     .align_x(alignment::Horizontal::Right)
                     .size(40),