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

lib/topic_view.rb

@@ -2,6 +2,7 @@ require_dependency 'guardian'
 require_dependency 'topic_query'
 require_dependency 'filter_best_posts'
 require_dependency 'summarize'
+require_dependency 'gaps'
 
 class TopicView
 
@@ -44,6 +45,15 @@ class TopicView
     path
   end
 
+  def contains_gaps?
+    @contains_gaps
+  end
+
+  def gaps
+    return unless @contains_gaps
+    Gaps.new(filtered_post_ids, unfiltered_posts.order(:sort_order).pluck(:id))
+  end
+
   def last_post
     return nil if @posts.blank?
     @last_post ||= @posts.last
@@ -113,9 +123,7 @@ class TopicView
 
   # Filter to all posts near a particular post number
   def filter_posts_near(post_number)
-
     min_idx, max_idx = get_minmax_ids(post_number)
-
     filter_posts_in_range(min_idx, max_idx)
   end
 
@@ -255,14 +263,36 @@ class TopicView
     finder.first
   end
 
+  def unfiltered_posts
+    result = @topic.posts.where(hidden: false)
+    result = result.with_deleted if @user.try(:staff?)
+    result
+  end
+
   def setup_filtered_posts
-    @filtered_posts = @topic.posts.where(hidden: false)
+
+    # Certain filters might leave gaps between posts. If that's true, we can return a gap structure
+    @contains_gaps = false
+    @filtered_posts = unfiltered_posts
     @filtered_posts = @filtered_posts.with_deleted if @user.try(:staff?)
-    @filtered_posts = @filtered_posts.summary if @filter == 'summary'
-    @filtered_posts = @filtered_posts.where('posts.post_type <> ?', Post.types[:moderator_action]) if @best.present?
-    return unless @username_filters.present?
-    usernames = @username_filters.map{|u| u.downcase}
-    @filtered_posts = @filtered_posts.where('post_number = 1 or user_id in (select u.id from users u where username_lower in (?))', usernames)
+
+    # Filters
+    if @filter == 'summary'
+      @filtered_posts = @filtered_posts.summary
+      @contains_gaps = true
+    end
+
+    if @best.present?
+      @filtered_posts = @filtered_posts.where('posts.post_type <> ?', Post.types[:moderator_action])
+      @contains_gaps = true
+    end
+
+    if @username_filters.present?
+      usernames = @username_filters.map{|u| u.downcase}
+      @filtered_posts = @filtered_posts.where('post_number = 1 or user_id in (select u.id from users u where username_lower in (?))', usernames)
+      @contains_gaps = true
+    end
+
   end
 
   def check_and_raise_exceptions