(This commit introduces a dependency on the patch in bug 289483, which adds

a <deck> to tbird for controlling the main display mode.)

Overlay the world's simplest lightning-deck into tbird, and switch to it when
our pane gets the user's attention. r=pavlov, though I will note his objection
to the Ltn prefix in my function. NPOTB > NKOTB.

calendar/lightning/content/messenger-overlay-sidebar.js

@@ -0,0 +1,23 @@
+function selectedCalendarPane(event)
+{
+    dump("selecting calendar pane\n");
+    document.getElementById("displayDeck").selectedPanel =
+        document.getElementById("calendarViewBox");
+}
+
+function LtnObserveDisplayDeckChange(event)
+{
+    var deck = event.target;
+    if (deck.selectedPanel.id == "calendarViewBox") {
+        GetMessagePane().collapsed = true;
+        document.getElementById("threadpane-splitter").collapsed = true;
+        gSearchBox.collapsed = true;
+    } else {
+        // nothing to "undo" for now
+        // Later: mark the view as not needing reflow due to new events coming
+        // in, for better performance and batching.
+    }
+}
+
+document.getElementById("displayDeck").
+    addEventListener("select", LtnObserveDisplayDeckChange, true);

calendar/lightning/content/messenger-overlay-sidebar.xul

@@ -7,6 +7,7 @@
 <script type="application/x-javascript" src="chrome://calendar/content/calendarUtils.js"/>
 <script type="application/x-javascript" src="chrome://calendar/content/calendarCreation.js"/>
 <script type="application/x-javascript" src="chrome://lightning/content/calendar-management.js"/>
+<script type="application/x-javascript" src="chrome://lightning/content/messenger-overlay-sidebar.js"/>
 
 <vbox id="folderPaneBox">
   <splitter id="folderpaneCalendarSplitter" collapse="after" persist="state"/>
@@ -19,7 +20,8 @@
     </popup>
   </popupset>
 
-  <tree id="calendarTree" flex="1" context="ltnCalendarTreeContext">
+  <tree id="calendarTree" onfocus="selectedCalendarPane(event)" flex="1"
+        context="ltnCalendarTreeContext">
     <treecols>
       <treecol label="Calendar" id="col-calendar-Calendar" flex="1"/>
     </treecols>
@@ -28,4 +30,9 @@
   </tree>
 </vbox>
 
+<deck id="displayDeck">
+  <vbox id="calendarViewBox" flex="1">
+    <iframe name="calendarViewTempIframe" width="150" flex="1" src="javascript:'Lightning'"/>
+  </vbox>
+</deck>
 </overlay>

calendar/lightning/jar.mn

@@ -1,5 +1,6 @@
 lightning.jar:
   content/lightning/messenger-overlay-sidebar.xul	(content/messenger-overlay-sidebar.xul)
+  content/lightning/messenger-overlay-sidebar.js	(content/messenger-overlay-sidebar.js)
   content/lightning/calendar-management.js		(content/calendar-management.js)
   content/lightning/weekView.xul	(content/weekView.xul)
   content/lightning/weekView.js		(content/weekView.js)