Work in progress: detect gaps in post stream

Author: eviltrout

app/assets/javascripts/discourse/models/post_stream.js

@@ -522,9 +522,9 @@ Discourse.PostStream = Em.Object.extend({
     @method updateFromJson
   **/
   updateFromJson: function(postStreamData) {
-    var postStream = this;
+    var postStream = this,
+        posts = this.get('posts');
 
-    var posts = this.get('posts');
     posts.clear();
     if (postStreamData) {
       // Load posts if present

app/serializers/post_stream_serializer_mixin.rb

@@ -5,17 +5,18 @@ def self.included(klass)
   end
 
   def post_stream
-    { posts: posts,
-      stream: object.filtered_post_ids }
+    result = { posts: posts, stream: object.filtered_post_ids }
+    result[:gaps] = object.gaps if object.gaps.present?
+    result
   end
 
   def posts
     return @posts if @posts.present?
     @posts = []
-    @highest_number_in_posts = 0
+    highest_number_in_posts = 0
     if object.posts
       object.posts.each_with_index do |p, idx|
-        @highest_number_in_posts = p.post_number if p.post_number > @highest_number_in_posts
+        highest_number_in_posts = p.post_number if p.post_number > highest_number_in_posts
         ps = PostSerializer.new(p, scope: scope, root: false)
         ps.topic_slug = object.topic.slug
         ps.topic_view = object

lib/gap_finder.rb

@@ -0,0 +1,48 @@
+#
+# This is used for finding the gaps between a subset of elements in an array
+# and the original layout. We use this is Discourse to find gaps between posts.
+#
+module GapFinder
+
+  def self.find(subset, original)
+    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
+          gaps[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
+    # if current_gap.size > 0
+    #   gaps[e1] = current_gap.dup
+    # end
+
+    if j < original.size
+      current_gap = gaps[original.last] = gaps[original.last] || []
+      while j < original.size
+        current_gap << original[j]
+        j = j + 1
+      end
+    end
+
+    # If we have no gaps, return nil
+    gaps.keys.size > 0 ? gaps : nil
+  end
+
+end

lib/topic_view.rb

@@ -2,6 +2,7 @@
 require_dependency 'topic_query'
 require_dependency 'filter_best_posts'
 require_dependency 'summarize'
+require_dependency 'gap_finder'
 
 class TopicView
 
@@ -44,6 +45,15 @@ def canonical_path
     path
   end
 
+  def contains_gaps?
+    @contains_gaps
+  end
+
+  def gaps
+    return unless @contains_gaps
+    GapFinder.find(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 @@ def sort_order_for_post_number(post_number)
 
   # 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 @@ def find_topic(topic_id)
     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

spec/components/gap_finder_spec.rb

@@ -0,0 +1,42 @@
+require 'spec_helper'
+require 'cache'
+
+describe GapFinder do
+
+  it 'returns no gaps for empty data' do
+    GapFinder.find(nil, nil).should be_nil
+  end
+
+  it 'returns no gaps with one element' do
+    GapFinder.find([1], [1]).should be_nil
+  end
+
+  it 'returns no gaps when all elements are present' do
+    GapFinder.find([1,2,3], [1,2,3]).should be_nil
+  end
+
+  it 'returns a single element gap' do
+    GapFinder.find([1,3], [1,2,3]).should == {3 => [2]}
+  end
+
+  it 'returns a gap when one is present' do
+    GapFinder.find([1,2,3,6,7], [1,2,3,4,5,6,7]).should == {6 => [4, 5]}
+  end
+
+  it 'returns multiple gaps' do
+    GapFinder.find([1,5,6,7,10], [1,2,3,4,5,6,7,8,9,10]).should == {5 => [2,3,4], 10 => [8, 9]}
+  end
+
+  it 'returns a gap in the beginning' do
+    GapFinder.find([2,3,4], [1,2,3,4]).should == {2 => [1]}
+  end
+
+  it 'returns a gap in the ending' do
+    GapFinder.find([1,2,3], [1,2,3,4]).should == {4 => [4]}
+  end
+
+  it 'returns a large gap in the ending' do
+    GapFinder.find([1,2,3], [1,2,3,4,5,6]).should == {6 => [4,5,6]}
+  end
+
+end

spec/components/topic_view_spec.rb

@@ -89,7 +89,6 @@
 
     end
 
-
     it "raises NotLoggedIn if the user isn't logged in and is trying to view a private message" do
       Topic.any_instance.expects(:private_message?).returns(true)
       lambda { TopicView.new(topic.id, nil) }.should raise_error(Discourse::NotLoggedIn)
@@ -233,6 +232,26 @@
       p6.save!
     end
 
+    describe "contains_gaps?" do
+      it "does not contain contains_gaps with default filtering" do
+        topic_view.contains_gaps?.should be_false
+      end
+
+      it "contains contains_gaps when filtered by username" do
+        TopicView.new(topic.id, coding_horror, username_filters: ['eviltrout']).contains_gaps?.should be_true
+      end
+
+      it "contains contains_gaps when filtered by summary" do
+        TopicView.new(topic.id, coding_horror, filter: 'summary').contains_gaps?.should be_true
+      end
+
+      it "contains contains_gaps when filtered by best" do
+        TopicView.new(topic.id, coding_horror, best: 5).contains_gaps?.should be_true
+      end
+
+    end
+
+
     describe '#filter_posts_paged' do
       before { SiteSetting.stubs(:posts_per_page).returns(2) }