Introduce MarkerLayer.prototype.getLastMarker()

spec/marker-layer-spec.coffee

@@ -75,6 +75,26 @@ describe "MarkerLayer", ->
     expect(createEventCount).toBe 1
     expect(updateEventCount).toBe 2
 
+  describe "::getLastMarker()", ->
+    it "returns the last (in terms of time) non-destroyed marker added to the layer", ->
+      marker1 = layer1.markRange([[0, 0], [0, 3]])
+      marker2 = layer1.markRange([[0, 2], [0, 6]])
+      marker3 = layer1.markRange([[0, 8], [0, 10]])
+      marker4 = layer1.markRange([[1, 0], [1, 10]])
+      expect(layer1.getLastMarker()).toBe(marker4)
+
+      marker4.destroy()
+      expect(layer1.getLastMarker()).toBe(marker3)
+
+      marker1.destroy()
+      expect(layer1.getLastMarker()).toBe(marker3)
+
+      marker3.destroy()
+      expect(layer1.getLastMarker()).toBe(marker2)
+
+      marker2.destroy()
+      expect(layer1.getLastMarker()).toBeFalsy()
+
   describe "when destroyInvalidatedMarkers is enabled for the layer", ->
     it "destroys markers when they are invalidated via a splice", ->
       layer3 = buffer.addMarkerLayer(destroyInvalidatedMarkers: true)

src/display-marker-layer.coffee

@@ -236,6 +236,12 @@ class DisplayMarkerLayer
   getMarkers: ->
     @bufferMarkerLayer.getMarkers().map ({id}) => @getMarker(id)
 
+  # Public: Get the last (in terms of time) non-destroyed marker added to this layer.
+  #
+  # Returns a {DisplayMarker}.
+  getLastMarker: ->
+    @getMarker(@bufferMarkerLayer.getLastMarker()?.id)
+
   # Public: Get the number of markers in the marker layer.
   #
   # Returns a {Number}.

src/marker-layer.coffee

@@ -81,6 +81,12 @@ class MarkerLayer
   getMarker: (id) ->
     @markersById.get(id)
 
+  # Public: Get the last (in terms of time) non-destroyed marker added to this layer.
+  #
+  # Returns a {Marker}.
+  getLastMarker: ->
+    @getMarker(@markers[@markers.length - 1])
+
   # Public: Get all existing markers on the marker layer.
   #
   # Returns an {Array} of {Marker}s.
@@ -334,6 +340,8 @@ class MarkerLayer
   destroyMarker: (id) ->
     if @markersById.has(id)
       @markersById.delete(id)
+      index = @indexForMarkerId(id)
+      @markers.splice(index, 1) if index isnt -1
       @markersIdsWithChangeSubscriptions.delete(id)
       @index.delete(id)
       @destroyedMarkers.add(id)
@@ -382,8 +390,22 @@ class MarkerLayer
     @index.insert(id, range.start, range.end)
     marker = new Marker(id, this, range, params)
     @markersById.set(id, marker)
+    @markers.push(id)
     marker
 
+  indexForMarkerId: (id) ->
+    low = 0
+    high = @markers.length - 1
+    while low <= high
+      index = low + ((high - low) >> 1)
+      if id < @markers[index]
+        high = index - 1
+      else if id is @markers[index]
+        return index
+      else
+        low = index + 1
+    -1
+
   setDisableDidUpdateEvent: (@didUpdateEventDisabled) ->
 
   emitDidUpdateEvent: ->