TagSetPresenter: refactor *_tag_list_html to avoid memcache calls.

Refactor the tag set presenter to get both the tag categories and the
tag counts in the same call to the database, instead of getting the
counts from the db and the categories from memcache.

app/models/tag.rb

@@ -56,10 +56,6 @@ class Tag < ApplicationRecord
     extend ActiveSupport::Concern
 
     module ClassMethods
-      def counts_for(tag_names)
-        select_all_sql("SELECT name, post_count FROM tags WHERE name IN (?)", tag_names)
-      end
-
       def highest_post_count
         Cache.get("highest-post-count", 4.hours) do
           select("post_count").order("post_count DESC").first.post_count

app/presenters/tag_set_presenter.rb

@@ -5,7 +5,8 @@
 =end
 
 class TagSetPresenter < Presenter
-  attr_reader :tag_names, :tags
+  extend Memoist
+  attr_reader :tag_names
 
   def initialize(tag_names)
     @tag_names = tag_names
@@ -13,9 +14,10 @@ class TagSetPresenter < Presenter
 
   def tag_list_html(current_query: "", show_extra_links: false, name_only: false)
     html = ""
-    if tag_names.present?
+
+    if ordered_tags.present?
       html << '<ul itemscope itemtype="http://schema.org/ImageObject">'
-      tag_names.each do |tag|
+      ordered_tags.each do |tag|
         html << build_list_item(tag, current_query: current_query, show_extra_links: show_extra_links, name_only: name_only)
       end
       html << "</ul>"
@@ -28,7 +30,8 @@ class TagSetPresenter < Presenter
     html = ""
 
     category_list.each do |category|
-      typetags = typed_tags(category)
+      typetags = ordered_tags.select { |tag| tag.category == Tag.categories.value_for(category) }
+
       if typetags.any?
         html << TagCategory.header_mapping[category] if headers
         html << %{<ul class="#{category}-tag-list">}
@@ -50,60 +53,54 @@ class TagSetPresenter < Presenter
 
   private
 
-  def typed_tags(name)
-    @typed_tags ||= {}
-    @typed_tags[name] ||= begin
-      tag_names.select do |tag|
-        categories[tag] == TagCategory.mapping[name]
-      end
-    end
-  end
-
-  def categories
-    @categories ||= Tag.categories_for(tag_names)
-  end
-
-  def counts
-    @counts ||= Tag.counts_for(tag_names).inject({}) do |hash, x|
-      hash[x["name"]] = x["post_count"]
-      hash
+  def tags
+    Tag.where(name: tag_names).select(:name, :post_count, :category)
+  end
+  memoize :tags
+
+  def ordered_tags
+    names_to_tags = tags.map { |tag| [tag.name, tag] }.to_h
+
+    tag_names.map do |name|
+      names_to_tags[name] || Tag.new(name: name).freeze
     end
   end
+  memoize :ordered_tags
 
   def build_list_item(tag, name_only: false, humanize_tags: true, show_extra_links: false, current_query: "")
-    html = %{<li class="category-#{categories[tag]}">}
+    name = tag.name
+    count = tag.post_count
+    category = tag.category
+
+    html = %{<li class="category-#{tag.category}">}
 
     unless name_only
-      if categories[tag] == Tag.categories.artist
-        html << %{<a class="wiki-link" href="/artists/show_or_new?name=#{u(tag)}">?</a> }
+      if category == Tag.categories.artist
+        html << %{<a class="wiki-link" href="/artists/show_or_new?name=#{u(name)}">?</a> }
       else
-        html << %{<a class="wiki-link" href="/wiki_pages/show_or_new?title=#{u(tag)}">?</a> }
+        html << %{<a class="wiki-link" href="/wiki_pages/show_or_new?title=#{u(name)}">?</a> }
       end
 
       if show_extra_links && current_query.present?
-        html << %{<a rel="nofollow" href="/posts?tags=#{u(current_query)}+#{u(tag)}" class="search-inc-tag">+</a> }
-        html << %{<a rel="nofollow" href="/posts?tags=#{u(current_query)}+-#{u(tag)}" class="search-exl-tag">&ndash;</a> }
+        html << %{<a rel="nofollow" href="/posts?tags=#{u(current_query)}+#{u(name)}" class="search-inc-tag">+</a> }
+        html << %{<a rel="nofollow" href="/posts?tags=#{u(current_query)}+-#{u(name)}" class="search-exl-tag">&ndash;</a> }
       end
     end
 
-    humanized_tag = humanize_tags ? tag.tr("_", " ") : tag
-    if categories[tag] == Tag.categories.artist
-      itemprop = 'itemprop="author"'
-    else
-      itemprop = nil
-    end
-    html << %{<a class="search-tag" #{itemprop} href="/posts?tags=#{u(tag)}">#{h(humanized_tag)}</a> }
+    humanized_tag = humanize_tags ? name.tr("_", " ") : name
+    itemprop = 'itemprop="author"' if category == Tag.categories.artist
+    html << %{<a class="search-tag" #{itemprop} href="/posts?tags=#{u(name)}">#{h(humanized_tag)}</a> }
 
-    unless name_only
-      if counts[tag].to_i >= 10_000
-        post_count = "#{counts[tag].to_i / 1_000}k"
-      elsif counts[tag].to_i >= 1_000
-        post_count = "%.1fk" % (counts[tag].to_f / 1_000)
+    unless name_only || tag.new_record?
+      if count >= 10_000
+        post_count = "#{count / 1_000}k"
+      elsif count >= 1_000
+        post_count = "%.1fk" % (count / 1_000.0)
       else
-        post_count = counts[tag].to_s
+        post_count = count
       end
 
-      is_underused_tag = counts[tag].to_i <= 1 && categories[tag] == Tag.categories.general
+      is_underused_tag = count <= 1 && category == Tag.categories.general
       klass = "post-count#{is_underused_tag ? " low-post-count" : ""}"
       title = "New general tag detected. Check the spelling or populate it now."