Prompt an instructor to write up her teaching experience as a retrospective on CaseLog

.rubocop.yml

@@ -28,6 +28,7 @@ Layout/ClassStructure:
       - attr_writer
       - attr_accessor
       - alias_attribute
+      - time_for_a_boolean
       - translates
     associations:
       - has_one

Gemfile

@@ -16,7 +16,7 @@ gem 'redis', '~> 3.0'
 gem 'acts_as_list'
 gem 'kaminari'
 gem 'memoist'
-gem 'time_for_a_boolean', git: 'https://github.com/calebthompson/time_for_a_boolean'
+gem 'time_for_a_boolean', '~> 0.2.0'
 gem 'virtus'
 
 # Authentication and Authorization

Gemfile.lock

@@ -14,14 +14,6 @@ GIT
       user_agent_parser
       uuidtools
 
-GIT
-  remote: https://github.com/calebthompson/time_for_a_boolean
-  revision: 636a4c6b4645f9888402ff49b40b7f42c270d946
-  specs:
-    time_for_a_boolean (0.1.0)
-      activerecord
-      railties
-
 GIT
   remote: https://github.com/cbothner/omniauth-lti
   revision: 578245b0cabb755a209221ce1682667d9154ac4d
@@ -395,6 +387,9 @@ GEM
     thor (0.19.4)
     thread_safe (0.3.6)
     tilt (2.0.8)
+    time_for_a_boolean (0.2.0)
+      activerecord
+      railties
     tzinfo (1.2.3)
       thread_safe (~> 0.1)
     uglifier (3.2.0)
@@ -487,7 +482,7 @@ DEPENDENCIES
   spring-commands-rspec
   spring-watcher-listen (~> 2.0.0)
   table_print
-  time_for_a_boolean!
+  time_for_a_boolean (~> 0.2.0)
   uglifier (>= 1.3.0)
   virtus
   web-console

app/models/deployment.rb

@@ -11,11 +11,16 @@
 #   - 0 means no quiz (and assumes quiz == nil)
 # @attr key [String] a random URL safe string used as the hard-to-guess
 #   identifier that allows the {MagicLink} to work
+# @attr retrospective_prompt_sent_at [DateTime] at most once after a professor
+#   has deployed a case, we want to prompt them to write up their experience
+#   teaching with the case as a post in CaseLog
 #
 # @see GenericDeployment GenericDeployment: this model’s null object
 class Deployment < ApplicationRecord
   include Authority::Abilities
 
+  time_for_a_boolean :retrospective_prompt_sent
+
   belongs_to :case
   belongs_to :group
   belongs_to :quiz

app/services/send_retrospective_prompts.rb

@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+# After a professor has deployed a case in their classroom, we want to invite
+# them to write up a retrospective of their experience as a post in the
+# instructors-only community “CaseLog.” This service sends such notifications.
+#
+# Running once a week, on Wednesdays at noon (Eastern), we look for deployments
+# whose members were much more active in the case 14 to 7 days ago than they
+# were in the last 7 days. This is defined as an 80% drop-off of use from week
+# to week, where the previous week measured over 500 events. This was chosen
+# empirically based on recorded data at an early stage and should be subject to
+# review. We exclude any deployments with fewer than five readers as a sanity
+# check. When we send prompts to the instructors, we set the
+# `retrospective_prompt_sent` flag so never to bug people more than once.
+class SendRetrospectivePrompts
+  def self.call(time_basis: Time.zone.now)
+    new(time_basis).call
+  end
+
+  def initialize(now)
+    @now = now
+  end
+
+  def call
+    deployments_needing_prompts.map { |x| [x.group.name, x.case.slug] }
+    # deployments_needing_prompts.each do |deployment|
+    #   deployment.update retrospective_prompt_set: true
+    #   DeploymentMailer.retrospective_prompt(deployment).deliver
+    # end
+  end
+
+  private
+
+  def deployments_needing_prompts
+    candidate_deployments_with_enough_readers
+      .select { |d| much_more_use_two_weeks_ago d }
+  end
+
+  def candidate_deployments_with_enough_readers
+    count_readers_by_group = GroupMembership.group(:group_id).count(:reader_id)
+    Deployment.where(retrospective_prompt_sent_at: nil)
+              .select { |d| count_readers_by_group[d.group_id] > 5 }
+  end
+
+  def much_more_use_two_weeks_ago(deployment)
+    two_weeks_ago = count_interesting_events(
+      deployment,
+      (@now - 2.weeks)..(@now - 1.week)
+    )
+    last_week = count_interesting_events(
+      deployment,
+      (@now - 1.week)..@now
+    )
+
+    two_weeks_ago > 500 && (two_weeks_ago - last_week) / two_weeks_ago > -0.8
+  end
+
+  def count_interesting_events(deployment, range)
+    Ahoy::Event.interesting
+               .where(user_id: deployment.group.readers.pluck(:id))
+               .where_properties(case_slug: deployment.case.slug)
+               .where(time: range)
+               .count
+  end
+end

db/migrate/20180129162300_add_retrospective_prompt_sent_at_to_deployments.rb

@@ -0,0 +1,5 @@
+class AddRetrospectivePromptSentAtToDeployments < ActiveRecord::Migration[5.1]
+  def change
+    add_column :deployments, :retrospective_prompt_sent_at, :timestamp
+  end
+end

db/structure.sql

@@ -423,7 +423,8 @@ CREATE TABLE deployments (
     created_at timestamp without time zone NOT NULL,
     updated_at timestamp without time zone NOT NULL,
     answers_needed integer DEFAULT 1,
-    key character varying
+    key character varying,
+    retrospective_prompt_sent_at timestamp without time zone
 );
 
 
@@ -2309,6 +2310,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20171113192541'),
 ('20171220165301'),
 ('20180119170858'),
-('20180129143420');
+('20180129143420'),
+('20180129162300');