FEATURE: Load fewer topics in the topic list on slow platforms (Android)

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

@@ -171,7 +171,7 @@ Discourse.TopicList.reopenClass({
 
   from: function(result, filter, params) {
     var topicList = Discourse.TopicList.create({
-      inserted: Em.A(),
+      inserted: [],
       filter: filter,
       params: params || {},
       topics: Discourse.TopicList.topicsFrom(result),
@@ -181,7 +181,8 @@ Discourse.TopicList.reopenClass({
       draft_sequence: result.topic_list.draft_sequence,
       draft: result.topic_list.draft,
       for_period: result.topic_list.for_period,
-      loaded: true
+      loaded: true,
+      per_page: result.topic_list.per_page
     });
 
     if (result.topic_list.filtered_category) {
@@ -212,7 +213,7 @@ Discourse.TopicList.reopenClass({
 
         // Try to use the cached version if it exists and is greater than the topics per page
         if (cachedList && (cachedList.get('filter') === filter) &&
-            (cachedList.get('topics.length') || 0) > Discourse.SiteSettings.topics_per_page &&
+            (cachedList.get('topics.length') || 0) > cachedList.get('per_page') &&
             _.isEqual(cachedList.get('listParams'), filterParams)) {
           cachedList.set('loaded', true);
 

app/controllers/application_controller.rb

@@ -51,6 +51,10 @@ class ApplicationController < ActionController::Base
     @use_crawler_layout ||= (has_escaped_fragment? || CrawlerDetection.crawler?(request.user_agent))
   end
 
+  def slow_platform?
+    request.user_agent =~ /Android/
+  end
+
   def set_layout
     use_crawler_layout? ? 'crawler' : 'application'
   end

app/controllers/list_controller.rb

@@ -264,6 +264,7 @@ class ListController < ApplicationController
       search: params[:search]
     }
     options[:no_subcategories] = true if params[:no_subcategories] == 'true'
+    options[:slow_platform] = true if slow_platform?
 
     options
   end

app/controllers/topics_controller.rb

@@ -47,7 +47,7 @@ class TopicsController < ApplicationController
     opts = params.slice(:username_filters, :filter, :page, :post_number, :show_deleted)
     username_filters = opts[:username_filters]
 
-    opts[:slow_platform] = true if request.user_agent =~ /Android/
+    opts[:slow_platform] = true if slow_platform?
     opts[:username_filters] = username_filters.split(',') if username_filters.is_a?(String)
 
     begin

app/models/topic_list.rb

@@ -9,7 +9,8 @@ class TopicList
                 :draft_key,
                 :draft_sequence,
                 :filter,
-                :for_period
+                :for_period,
+                :per_page
 
   def initialize(filter, current_user, topics, opts=nil)
     @filter = filter

app/serializers/topic_list_serializer.rb

@@ -5,7 +5,8 @@ class TopicListSerializer < ApplicationSerializer
              :draft,
              :draft_key,
              :draft_sequence,
-             :for_period
+             :for_period,
+             :per_page
 
   has_many :topics, serializer: TopicListItemSerializer, embed: :objects
 
@@ -18,7 +19,7 @@ class TopicListSerializer < ApplicationSerializer
   end
 
   def include_more_topics_url?
-    object.more_topics_url.present? && (object.topics.size == SiteSetting.topics_per_page)
+    object.more_topics_url.present? && (object.topics.size == object.per_page)
   end
 
 end

config/locales/server.en.yml

@@ -738,6 +738,7 @@ en:
     share_links: "Determine which items appear on the share dialog, and in what order."
     track_external_right_clicks: "Track external links that are right clicked (eg: open in new tab) disabled by default because it rewrites URLs"
     topics_per_page: "How many topics are loaded by default on the topic list, and when scrolling down to load more topics"
+    slow_topics_per_page: "The amount of topics per page on slow devices such as Android"
     posts_chunksize: "How many posts are loaded by default on a topic, and when scrolling down to load more posts"
     posts_slow_chunksize: "Like `posts_chunksize` but for slow platforms (such as Android)"
     site_contact_username: "All automated private messages will be from this user; if left blank the default System account will be used."

config/site_settings.yml

@@ -154,7 +154,9 @@ basic:
   topics_per_page:
     default: 30
     min: 1
-    client: true
+  slow_topics_per_page:
+    default: 15
+    min: 1
   show_subcategory_list:
     default: false
     client: true

lib/topic_query.rb

@@ -25,6 +25,7 @@ class TopicQuery
                      status
                      state
                      search
+                     slow_platform
                      ).map(&:to_sym)
 
   # Maps `order` to a columns in `topics`
@@ -155,15 +156,21 @@ class TopicQuery
 
   protected
 
+    def per_page_setting
+      @options[:slow_platform] ? SiteSetting.slow_topics_per_page : SiteSetting.topics_per_page
+    end
+
     def create_list(filter, options={}, topics = nil)
       topics ||= default_results(options)
       topics = yield(topics) if block_given?
-      TopicList.new(filter, @user, topics, options.merge(@options))
+      list = TopicList.new(filter, @user, topics, options.merge(@options))
+      list.per_page = per_page_setting
+      list
     end
 
     def private_messages_for(user)
       options = @options
-      options.reverse_merge!(per_page: SiteSetting.topics_per_page)
+      options.reverse_merge!(per_page: per_page_setting)
 
       # Start with a list of all topics
       result = Topic.includes(:allowed_users)
@@ -230,7 +237,7 @@ class TopicQuery
     # Create results based on a bunch of default options
     def default_results(options={})
       options.reverse_merge!(@options)
-      options.reverse_merge!(per_page: SiteSetting.topics_per_page)
+      options.reverse_merge!(per_page: per_page_setting)
 
       # Start with a list of all topics
       result = Topic.unscoped