Implement periodic email digest (forem#123)

* Create EmailDigest WIP

* Add email_digest_periodic to User model

* Add email digest setting to notification

* Draft thoughts (?)  WIP

* Implement EmailDigest's features

* Remove hard-coded email digest vars

* Create spec for EmailDigest

* Fix something

* Temp work

* Run migration & Yarn

* Move email logic out of EmailDigest

* Improve email logic

* Improve EmailLogic'specs

* Update copy

* Change positive_reactions_count limit

For non-followed articles we should have a higher limit. So this change modifies that.

Guardfile

@@ -36,7 +36,7 @@ rspec_options = {
   # fast but no coverage
   cmd: "bin/spring rspec -p",
   #############################
-  failed_mode: :none,
+  failed_mode: :focus,
   bundler_env: :clean_env
 }
 

app/controllers/users_controller.rb

@@ -154,6 +154,7 @@ def user_params
                     website_url
                     summary
                     email_newsletter
+                    email_digest_periodic
                     email_membership_newsletter
                     email_comment_notifications
                     email_mention_notifications

app/labor/email_digest.rb

@@ -0,0 +1,29 @@
+# Usecase would be
+# EmailDigest.send_periodic_digest_email
+# OR
+# EmailDigets.send_periodic_digest_email(Users.first(4))
+
+class EmailDigest
+  def self.send_periodic_digest_email(users = [])
+    new(users).send_periodic_digest_email
+  end
+
+  def initialize(users = [])
+    @users = users.empty? ? get_users : users
+  end
+
+  def send_periodic_digest_email
+    @users.each do |user|
+      user_email_heuristic = EmailLogic.new(user).analyze
+      next unless user_email_heuristic.should_receive_email?
+      articles = user_email_heuristic.articles_to_send
+      DigestMailer.daily_digest(user, articles).deliver
+    end
+  end
+
+  private
+
+  def get_users
+    User.where(email_digest_periodic: true)
+  end
+end

app/labor/email_logic.rb

@@ -0,0 +1,92 @@
+class EmailLogic
+  attr_reader :open_percentage, :last_email_sent_at,
+    :days_until_next_email, :articles_to_send
+
+  def initialize(user)
+    @user = user
+    @open_percentage = nil
+    @ready_to_receive_email = nil
+    @last_email_sent_at = nil
+    @days_until_next_email = nil
+    @articles_to_send = []
+  end
+
+  def analyze
+    @last_email_sent_at = get_last_digest_email_user_recieved
+    @open_percentage = get_open_rate
+    @days_until_next_email = get_days_until_next_email
+    @ready_to_receive_email = get_user_readiness
+    if @ready_to_receive_email
+      @articles_to_send = get_articles_to_send
+    end
+    self
+  end
+
+  def should_receive_email?
+    @ready_to_receive_email
+  end
+
+  private
+
+  def get_articles_to_send
+    fresh_date = get_fresh_date
+    articles = if user_has_followings?
+                 @user.followed_articles.
+                   where("created_at > ?", fresh_date).
+                   where("positive_reactions_count > ?", 15).
+                   order("positive_reactions_count DESC").
+                   limit(6)
+               else
+                 Article.
+                   where("positive_reactions_count > ?", 30).
+                   order("positive_reactions_count DESC").
+                   limit(6)
+               end
+    if articles.length < 3
+      @ready_to_receive_email = false
+    end
+    articles
+  end
+
+  def get_days_until_next_email
+    # Relies on hyperbolic tangent function to model the frequency of the digest email
+    max_day = ENV["PERIODIC_EMAIL_DIGEST_MAX"].to_i
+    min_day = ENV["PERIODIC_EMAIL_DIGEST_MIN"].to_i
+    result = max_day * (1 - Math.tanh(2 * @open_percentage))
+    result = result.round
+    result < min_day ? min_day : result
+  end
+
+  def get_open_rate
+    past_sent_emails = @user.email_messages.where(mailer: "DigestMailer#daily_digest").limit(10)
+
+    # Will stick with 50% open rate if @user has no/not-enough email digest history
+    return 0.5 if past_sent_emails.length < 10
+
+    past_sent_emails_count = past_sent_emails.count
+    past_opened_emails_count = past_sent_emails.where("opened_at IS NOT NULL").count
+    past_opened_emails_count / past_sent_emails_count
+  end
+
+  def get_user_readiness
+    return true unless @last_email_sent_at
+    # Has it been atleast x days since @user receive an email?
+    (Time.now.utc - @last_email_sent_at) >= @days_until_next_email.days.to_i
+  end
+
+  def get_last_digest_email_user_recieved
+    @user.email_messages.where(mailer: "DigestMailer#daily_digest").last&.sent_at
+  end
+
+  def get_fresh_date
+    a_month_ago = 1.month.ago.utc
+    return a_month_ago unless @last_email_sent_at
+    a_month_ago > @last_email_sent_at ? a_month_ago : @last_email_sent_at
+  end
+
+  def user_has_followings?
+    following_users = @user.cached_following_users_ids
+    following_tags = @user.cached_followed_tag_names
+    !following_users.empty? || !following_tags.empty?
+  end
+end

app/mailers/digest_mailer.rb

@@ -0,0 +1,5 @@
+class DigestMailer < ApplicationMailer
+  def daily_digest(recipient)
+    @recipient = recipient
+  end
+end

app/views/users/_notifications.html.erb

@@ -3,12 +3,16 @@
   <div class="checkbox-field">
     <div class="sub-field">
       <%= f.check_box :email_newsletter %>
-      <%= f.label :email_newsletter, "Send me periodic newsletter emails" %>
+      <%= f.label :email_newsletter, "Send me weekly newsletter emails" %>
+    </div>
+    <div class="sub-field">
+      <%= f.check_box :email_digest_periodic %>
+      <%= f.label :email_digest_periodic, "Send me a periodic digest of top posts from my tags" %>
     </div>
     <% if current_user.a_sustaining_member? %>
       <div class="sub-field">
         <%= f.check_box :email_membership_newsletter %>
-        <%= f.label :email_membership_newsletter, "Send me membership newsletter emails" %>
+        <%= f.label :email_membership_newsletter, "Send me sustaining membership newsletter emails" %>
       </div>
     <% end %>
     <div class="sub-field">

config/initializers/_env_checker.rb

@@ -37,6 +37,8 @@
   "KEEN_WRITE_KEY",
   "MAILCHIMP_API_KEY",
   "MAILCHIMP_NEWSLETTER_ID",
+  "PERIODIC_EMAIL_DIGEST_MAX",
+  "PERIODIC_EMAIL_DIGEST_MIN",
   "RECAPTCHA_SECRET",
   "RECAPTCHA_SITE",
   "SERVICE_TIMEOUT",

db/migrate/20180321170500_add_email_digest_periodic_to_user.rb

@@ -0,0 +1,5 @@
+class AddEmailDigestPeriodicToUser < ActiveRecord::Migration[5.1]
+  def change
+    add_column :users, :email_digest_periodic, :boolean, default: true, null: false
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20180316174324) do
+ActiveRecord::Schema.define(version: 20180321170500) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -618,6 +618,7 @@
     t.string "website_url"
     t.datetime "workshop_expiration"
     t.boolean "permit_adjacent_sponsors", default: true
+    t.boolean "email_digest_periodic", default: true, null: false
     t.index ["confirmation_token"], name: "index_users_on_confirmation_token", unique: true
     t.index ["language_settings"], name: "index_users_on_language_settings", using: :gin
     t.index ["organization_id"], name: "index_users_on_organization_id"

spec/factories/users.rb

@@ -16,6 +16,7 @@
     confirmed_at       { Time.now }
     saw_onboarding     { true }
     signup_cta_variant { "navbar_basic" }
+    email_digest_periodic { false }
 
     trait :super_admin do
       after(:build) { |user| user.add_role(:super_admin) }

spec/labor/email_digest_spec.rb

@@ -0,0 +1,37 @@
+require "rails_helper"
+
+class FakeDelegator < ActionMailer::MessageDelivery
+  # TODO: we should replace all usage of .deliver to .deliver_now
+  def deliver(*args); super end
+end
+
+RSpec.describe EmailDigest do
+  let(:user) { create(:user, email_digest_periodic: true) }
+  let(:author) { create(:user) }
+  let(:mock_delegator) { instance_double("FakeDelegator") }
+
+  before do
+    allow(DigestMailer).to receive(:daily_digest) { mock_delegator }
+    allow(mock_delegator).to receive(:deliver).and_return(true)
+    Delayed::Worker.delay_jobs = false
+    user
+  end
+
+  after do
+    Delayed::Worker.delay_jobs = true
+  end
+
+  describe "::send_daily_digest" do
+    context "when there's article to be sent" do
+      before { user.follow(author) }
+
+      it "send digest email when there's atleast 3 hot articles" do
+        3.times { create(:article, user_id: author.id, positive_reactions_count: 20) }
+        described_class.send_periodic_digest_email
+        expect(DigestMailer).to have_received(:daily_digest).with(
+          user, [instance_of(Article), instance_of(Article), instance_of(Article)]
+        )
+      end
+    end
+  end
+end

spec/labor/email_logic_spec.rb

@@ -0,0 +1,77 @@
+require "rails_helper"
+
+RSpec.describe EmailLogic do
+  let(:user) { create(:user) }
+
+  # TODO: improve this test suite, and improve it's speed
+
+  describe "#analyze" do
+    context "when user is brand new with no-follow" do
+      it "returns 0.5 for open_percentage" do
+        author = create(:user)
+        user.follow(author)
+        3.times { create(:article, user_id: author.id, positive_reactions_count: 20) }
+        h = described_class.new(user).analyze
+        expect(h.open_percentage).to eq(0.5)
+      end
+
+      it "provides top 3 articles" do
+        3.times { create(:article, positive_reactions_count: 20) }
+        h = described_class.new(user).analyze
+        expect(h.articles_to_send.length).to eq(3)
+      end
+
+      it "marks as not ready if there isn't atleast 3 articles" do
+        2.times { create(:article, positive_reactions_count: 20) }
+        h = described_class.new(user).analyze
+        expect(h.should_receive_email?).to eq(false)
+      end
+    end
+
+    context "when a user's open_percentage is low " do
+      before do
+        author = create(:user)
+        user.follow(author)
+        3.times { create(:article, user_id: author.id, positive_reactions_count: 20) }
+        10.times do
+          Ahoy::Message.create(mailer: "DigestMailer#daily_digest",
+                               user_id: user.id, sent_at: Time.now.utc)
+        end
+      end
+
+      it "will not send email when user shouldn't receive any" do
+        h = described_class.new(user).analyze
+        expect(h.should_receive_email?).to eq(false)
+      end
+    end
+
+    context "when a user's open_percentage is high" do
+      before do
+        10.times do
+          Ahoy::Message.create(mailer: "DigestMailer#daily_digest", user_id: user.id,
+                               sent_at: Time.now.utc, opened_at: Time.now.utc)
+          author = create(:user)
+          user.follow(author)
+          3.times { create(:article, user_id: author.id, positive_reactions_count: 20) }
+        end
+      end
+
+      it "evaluates that user is ready to recieve an email" do
+        Timecop.freeze(Date.today + 3) do
+          h = described_class.new(user).analyze
+          expect(h.should_receive_email?).to eq(true)
+        end
+      end
+    end
+  end
+
+  describe "#should_receive_email?" do
+    it "refelcts @ready_to_receive_email" do
+      author = create(:user)
+      user.follow(author)
+      3.times { create(:article, user_id: author.id, positive_reactions_count: 20) }
+      h = described_class.new(user).analyze
+      expect(h.should_receive_email?).to eq(true)
+    end
+  end
+end