Show Gaps in the post stream when filters are active

Conflicts:
	app/assets/javascripts/discourse/templates/topic.js.handlebars

lib/gaps.rb

@@ -0,0 +1,54 @@
+#
+# This is used for finding the gaps between a subset of elements in an array
+# and the original layout. We use this in Discourse to find gaps between posts.
+#
+# Note that we will only return a gap as 'before' or 'after', not both. We only
+# want to display the gap once.
+#
+class Gaps
+
+  attr_reader :before, :after
+
+  def initialize(subset, original)
+    @before = {}
+    @after = {}
+    @subset = subset
+    @original = original
+
+    find_gaps
+  end
+
+  def empty?
+    @before.size == 0 && @after.size == 0
+  end
+
+  def find_gaps
+    return if @subset.nil? or @original.nil?
+
+    i = j = 0
+    gaps = {}
+    current_gap = []
+
+    while
+      e1 = @subset[i]
+      e2 = @original[j]
+
+      if (e1 == e2)
+        if current_gap.size > 0
+          @before[e1] = current_gap.dup
+          current_gap = []
+        end
+
+        i = i + 1
+      else
+        current_gap << e2
+      end
+      j = j + 1
+
+      break if (i == @subset.size) || (j == @original.size)
+    end
+
+    @after[@subset[i-1]] = @original[j..-1] if j < @original.size
+  end
+
+end