master courses: create master content tags

gives a place for us to keep track of changed items for now
(and soon the restrictions for content after copy)

closes #MC-7

Change-Id: I7bbd6e371528a06ea93181b0f4d91f451ae99d52
Reviewed-on: https://gerrit.instructure.com/95502
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Tested-by: Jenkins
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>

app/models/master_courses.rb

@@ -2,4 +2,10 @@ module MasterCourses
   def self.table_name_prefix
     'master_courses_'
   end
+
+  # probably not be a comprehensive list but oh well
+  ALLOWED_CONTENT_TYPES = %w{
+    Announcement AssessmentQuestionBank Assignment Attachment CalendarEvent
+    DiscussionTopic ContextExternalTool ContextModule LearningOutcome Quizzes::Quiz Rubric WikiPage
+  }.freeze
 end

app/models/master_courses/master_content_tag.rb

@@ -0,0 +1,9 @@
+class MasterCourses::MasterContentTag < ActiveRecord::Base
+  # i want to get off content tag's wild ride
+
+  belongs_to :master_template, :class_name => "MasterCourses::MasterTemplate"
+  belongs_to :content, :polymorphic => true
+  validates_inclusion_of :content_type, :allow_nil => false, :in => MasterCourses::ALLOWED_CONTENT_TYPES
+
+  strong_params
+end

app/models/master_courses/master_template.rb

@@ -3,6 +3,7 @@ class MasterCourses::MasterTemplate < ActiveRecord::Base
   # instead of the entire course, but for now that's what we'll roll with
 
   belongs_to :course
+  has_many :master_content_tags, :class_name => "MasterCourses::MasterContentTag", :inverse_of => :master_template
 
   strong_params
 
@@ -19,4 +20,31 @@ class MasterCourses::MasterTemplate < ActiveRecord::Base
   def self.full_template_for(course)
     course.master_course_templates.active.for_full_course.first
   end
+
+  # load all the tags into a nested index for fast searching in content_tag_for
+  def load_tags!
+    @content_tag_index = {}
+    self.master_content_tags.to_a.group_by(&:content_type).each do |content_type, typed_tags|
+      @content_tag_index[content_type] = typed_tags.index_by(&:content_id)
+    end
+    true
+  end
+
+  def content_tag_for(content)
+    if @content_tag_index
+      (@content_tag_index[content.class.base_class.name] || {})[content.id] || create_content_tag_for!(content)
+    else
+      self.master_content_tags.polymorphic_where(:content => content).first || create_content_tag_for!(content)
+    end
+  end
+
+  def create_content_tag_for!(content)
+    self.class.unique_constraint_retry do |retry_count|
+      tag = nil
+      tag = self.master_content_tags.polymorphic_where(:content => content).first if retry_count > 0
+      tag ||= self.master_content_tags.create!(:content => content)
+      tag
+    end
+
+  end
 end

config/initializers/active_record.rb

@@ -780,7 +780,7 @@ ActiveRecord::Relation.class_eval do
     raise ArgumentError unless args.length == 1
 
     column = args.first.first
-    values = args.first.last
+    values = Array(args.first.last)
     original_length = values.length
     values = values.compact
 

db/migrate/20161116211024_create_master_content_tags.rb

@@ -0,0 +1,25 @@
+class CreateMasterContentTags < ActiveRecord::Migration[4.2]
+  tag :predeploy
+
+  def change
+    create_table :master_courses_master_content_tags do |t|
+      t.integer :master_template_id, limit: 8, null: false
+
+      # should we add a workflow state and make this soft-deletable? meh methinks
+      # maybe someday if we decide to use these to define the template content aets
+
+      t.string :content_type, null: false
+      t.integer :content_id, limit: 8, null: false
+
+      # here i was originally going to have a boolean column to keep track whether any changes had been made
+      # since last export but i think i want to tie it directly to a master course 'migration'
+      # to make it more robust against failure (i.e. we'll know that we'll need to re-export if the export failed)
+      # so i'm going to add a column later when i have a new table
+    end
+
+    add_foreign_key :master_courses_master_content_tags, :master_courses_master_templates, column: "master_template_id"
+    add_index :master_courses_master_content_tags, :master_template_id
+    add_index :master_courses_master_content_tags, [:master_template_id, :content_type, :content_id], :unique => true,
+      :name => "index_master_content_tags_on_template_id_and_content"
+  end
+end

spec/models/master_courses/master_template_spec.rb

@@ -26,4 +26,42 @@ describe MasterCourses::MasterTemplate do
       expect(template2).to be_active
     end
   end
+
+  describe "content_tag_for" do
+    before :once do
+      @template = MasterCourses::MasterTemplate.set_as_master_course(@course)
+      @assignment = @course.assignments.create!
+    end
+
+    it "should create tags for course content" do
+      tag = @template.content_tag_for(@assignment)
+      expect(tag.reload.content).to eq @assignment
+    end
+
+    it "should find tags" do
+      tag = @template.create_content_tag_for!(@assignment)
+      @template.expects(:create_content_tag_for!).never # don't try to recreate
+      expect(@template.content_tag_for(@assignment)).to eq tag
+    end
+
+    it "should not fail on double-create" do
+      tag = @template.create_content_tag_for!(@assignment)
+      expect(@template.create_content_tag_for!(@assignment)).to eq tag # should retry on unique constraint failure
+    end
+
+    it "should be able to load tags for fast searching" do
+      tag = @template.create_content_tag_for!(@assignment)
+      @template.load_tags!
+
+      old_tag_id = tag.id
+      tag.destroy! # delete in the db - proves that we cached them
+
+      expect(@template.content_tag_for(@assignment).id).to eq old_tag_id
+
+      # should still create a tag even if it's not found in the index
+      @page = @course.wiki.wiki_pages.create!(:title => "title")
+      page_tag = @template.content_tag_for(@page)
+      expect(page_tag.reload.content).to eq @page
+    end
+  end
 end