post versions: add ability to search post versions by tags.

* Add ability to search /post_versions by added tags, removed tags, or
  changed tags (added or removed).

* Add 'History' link to the sidebar of the /posts index. This is a
  shortcut for a /post_versions search of the current tag.

app/models/application_record.rb

@@ -39,10 +39,14 @@ class ApplicationRecord < ActiveRecord::Base
         where.not("#{qualified_column_for(attr)} ~ ?", "(?e)" + value)
       end
 
-      def where_array_includes(attr, values)
+      def where_array_includes_any(attr, values)
         where("#{qualified_column_for(attr)} && ARRAY[?]", values)
       end
 
+      def where_array_includes_all(attr, values)
+        where("#{qualified_column_for(attr)} @> ARRAY[?]", values)
+      end
+
       def where_array_count(attr, value)
         relation = all
         qualified_column = "cardinality(#{qualified_column_for(attr)})"
@@ -100,6 +104,10 @@ class ApplicationRecord < ActiveRecord::Base
         column = column_for_attribute(name)
         type = column.type || reflect_on_association(name)&.class_name
 
+        if column.array?
+          return search_array_attribute(name, type, params)
+        end
+
         case type
         when "User"
           search_user_attribute(name, params)
@@ -110,11 +118,7 @@ class ApplicationRecord < ActiveRecord::Base
         when :boolean
           search_boolean_attribute(name, params)
         when :integer, :datetime
-          if column.array?
-            search_array_attribute(name, type, params)
-          else
-            numeric_attribute_matches(name, params[name])
-          end
+          numeric_attribute_matches(name, params[name])
         else
           raise NotImplementedError, "unhandled attribute type"
         end
@@ -173,9 +177,16 @@ class ApplicationRecord < ActiveRecord::Base
       def search_array_attribute(name, type, params)
         relation = all
 
-        if params[:"#{name}_include"] && type == :integer
-          items = params[:"#{name}_include"].to_s.scan(/\d+/).map(&:to_i)
-          relation = relation.where_array_includes(name, items)
+        if params[:"#{name}_include_any"]
+          items = params[:"#{name}_include_any"].to_s.scan(/[^[:space:]]+/)
+          items = items.map(&:to_i) if type == :integer
+
+          relation = relation.where_array_includes_any(name, items)
+        elsif params[:"#{name}_include_all"]
+          items = params[:"#{name}_include_any"].to_s.scan(/[^[:space:]]+/)
+          items = items.map(&:to_i) if type == :integer
+
+          relation = relation.where_array_includes_all(name, items)
         end
 
         if params[:"#{name.to_s.singularize}_count"]

app/models/pool_archive.rb

@@ -19,7 +19,7 @@ class PoolArchive < ApplicationRecord
     end
 
     def for_post_id(post_id)
-      where_array_includes(:added_post_ids, [post_id]).or(where_array_includes(:removed_post_ids, [post_id]))
+      where_array_includes_any(:added_post_ids, [post_id]).or(where_array_includes_any(:removed_post_ids, [post_id]))
     end
 
     def search(params)

app/models/post_archive.rb

@@ -18,9 +18,23 @@ class PostArchive < ApplicationRecord
   end
 
   module SearchMethods
+    def changed_tags_include(tag)
+      where_array_includes_all(:added_tags, [tag]).or(where_array_includes_all(:removed_tags, [tag]))
+    end
+
+    def changed_tags_include_all(tags)
+      tags.reduce(all) do |relation, tag|
+        relation.changed_tags_include(tag)
+      end
+    end
+
     def search(params)
       q = super
-      q = q.search_attributes(params, :updater_id, :post_id, :rating, :rating_changed, :parent_id, :parent_changed, :source, :source_changed, :version)
+      q = q.search_attributes(params, :updater_id, :post_id, :tags, :added_tags, :removed_tags, :rating, :rating_changed, :parent_id, :parent_changed, :source, :source_changed, :version)
+
+      if params[:changed_tags]
+        q = q.changed_tags_include_all(params[:changed_tags].scan(/[^[:space:]]+/))
+      end
 
       if params[:updater_name].present?
         q = q.where(updater_id: User.name_to_id(params[:updater_name]))