Show estimated reading time near summarize button.

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

@@ -160,6 +160,15 @@ Discourse.Topic = Discourse.Model.extend({
     return I18n.t(this.get('favoriteTooltipKey'));
   }.property('favoriteTooltipKey'),
 
+  estimatedReadingTime: function() {
+    var wordCount = this.get('word_count');
+    if (!wordCount) return;
+
+    // Avg for 250 words per minute.
+    var minutes = Math.floor(wordCount / 250.0);
+    return minutes;
+  }.property('word_count'),
+
   toggleStar: function() {
     var topic = this;
     topic.toggleProperty('starred');

app/assets/javascripts/discourse/templates/components/toggle-summary.js.handlebars

@@ -2,6 +2,11 @@
   <p>{{{i18n summary.enabled_description}}}</p>
   <button class='btn' {{action toggleSummary}}>{{i18n summary.disable}}</button>
 {{else}}
-  <p>{{{i18n summary.description count="topic.posts_count"}}}</p>
+  {{#if topic.estimatedReadingTime}}
+    <p>{{{i18n summary.description_time count="topic.posts_count" readingTime="topic.estimatedReadingTime"}}}</p>
+  {{else}}
+    <p>{{{i18n summary.description count="topic.posts_count"}}}</p>
+  {{/if}}
+
   <button class='btn' {{action toggleSummary}}>{{i18n summary.enable}}</button>
 {{/if}}

app/serializers/topic_view_serializer.rb

@@ -22,6 +22,7 @@ class TopicViewSerializer < ApplicationSerializer
      :archetype,
      :slug,
      :category_id,
+     :word_count,
      :deleted_at]
   end
 

config/locales/client.en.yml

@@ -384,6 +384,7 @@ en:
     summary:
       enabled_description: "You're viewing a summary of this topic. To see all posts again, click below."
       description: "There are <b>{{count}}</b> replies. Save reading time by displaying only the most relevant replies?"
+      description_time: "There are <b>{{count}}</b> replies with an estimated read time of <b>{{readingTime}} minutes</b>. Save reading time by displaying only the most relevant replies?"
       enable: 'Summarize This Topic'
       disable: 'Show All Posts'
 

db/migrate/20131210163702_add_word_count_to_posts.rb

@@ -0,0 +1,11 @@
+class AddWordCountToPosts < ActiveRecord::Migration
+  def up
+    add_column :posts, :word_count, :integer
+    add_column :topics, :word_count, :integer
+  end
+
+  def down
+    remove_column :posts, :word_count, :integer
+    remove_column :topics, :word_count, :integer
+  end
+end

db/migrate/20131210181901_migrate_word_counts.rb

@@ -0,0 +1,20 @@
+class MigrateWordCounts < ActiveRecord::Migration
+  def up
+
+    disable_ddl_transaction
+
+    post_ids = execute("SELECT id FROM posts WHERE word_count IS NULL LIMIT 500").map {|r| r['id'].to_i }
+    while post_ids.length > 0
+      execute "UPDATE posts SET word_count = array_length(regexp_split_to_array(raw, ' '),1) WHERE id IN (#{post_ids.join(',')})"
+      post_ids = execute("SELECT id FROM posts WHERE word_count IS NULL LIMIT 500").map {|r| r['id'].to_i }
+    end
+
+    topic_ids = execute("SELECT id FROM topics WHERE word_count IS NULL LIMIT 500").map {|r| r['id'].to_i }
+    while topic_ids.length > 0
+      execute "UPDATE topics SET word_count = (SELECT SUM(COALESCE(posts.word_count, 0)) FROM posts WHERE posts.topic_id = topics.id) WHERE topics.id IN (#{topic_ids.join(',')})"
+      topic_ids = execute("SELECT id FROM topics WHERE word_count IS NULL LIMIT 500").map {|r| r['id'].to_i }
+    end
+
+  end
+
+end

lib/post_creator.rb

@@ -96,6 +96,7 @@ class PostCreator
       post.reply_to_user_id ||= Post.select(:user_id).where(topic_id: post.topic_id, post_number: post.reply_to_post_number).first.try(:user_id)
     end
 
+    post.word_count = post.raw.scan(/\w+/).size
     post.post_number ||= Topic.next_post_number(post.topic_id, post.reply_to_post_number.present?)
 
     cooking_options = post.cooking_options || {}
@@ -198,6 +199,7 @@ class PostCreator
     # Update attributes on the topic - featured users and last posted.
     attrs = {last_posted_at: @post.created_at, last_post_user_id: @post.user_id}
     attrs[:bumped_at] = @post.created_at unless @post.no_bump
+    attrs[:word_count] = (@topic.word_count || 0) + @post.word_count
     @topic.update_attributes(attrs)
   end
 

lib/post_revisor.rb

@@ -16,6 +16,7 @@ class PostRevisor
     revise_post
     update_category_description
     post_process_post
+    update_topic_word_counts
     @post.advance_draft_sequence
     true
   end
@@ -66,8 +67,15 @@ class PostRevisor
     end
   end
 
+  def update_topic_word_counts
+    Topic.exec_sql("UPDATE topics SET word_count = (SELECT SUM(COALESCE(posts.word_count, 0))
+                                                    FROM posts WHERE posts.topic_id = :topic_id)
+                    WHERE topics.id = :topic_id", topic_id: @post.topic_id)
+  end
+
   def update_post
     @post.raw = @new_raw
+    @post.word_count = @new_raw.scan(/\w+/).size
     @post.updated_by = @user
     @post.last_editor_id = @user.id
     @post.edit_reason = @opts[:edit_reason] if @opts[:edit_reason]

spec/components/post_creator_spec.rb

@@ -394,5 +394,17 @@ describe PostCreator do
       creator.errors.should be_nil
     end
   end
+
+  describe "word_count" do
+    it "has a word count" do
+      creator = PostCreator.new(user, title: 'some inspired poetry for a rainy day', raw: 'mary had a little lamb, little lamb, little lamb. mary had a little lamb')
+      post = creator.create
+      post.word_count.should == 14
+
+      post.topic.reload
+      post.topic.word_count.should == 14
+    end
+  end
+
 end
 

spec/components/post_revisor_spec.rb

@@ -222,14 +222,14 @@ describe PostRevisor do
 
     describe 'with a new body' do
       let(:changed_by) { Fabricate(:coding_horror) }
-      let!(:result) { subject.revise!(changed_by, 'updated body') }
+      let!(:result) { subject.revise!(changed_by, "lets update the body") }
 
       it 'returns true' do
         result.should be_true
       end
 
       it 'updates the body' do
-        post.raw.should == 'updated body'
+        post.raw.should == "lets update the body"
       end
 
       it 'sets the invalidate oneboxes attribute' do
@@ -252,6 +252,12 @@ describe PostRevisor do
         post.versions.first.user.should be_present
       end
 
+      it "updates the word count" do
+        post.word_count.should == 4
+        post.topic.reload
+        post.topic.word_count.should == 4
+      end
+
       context 'second poster posts again quickly' do
         before do
           SiteSetting.expects(:ninja_edit_window).returns(1.minute.to_i)