[feature] Enable template variables in messages (#143)

Fixes #139

Author: sman591

Gemfile

@@ -28,6 +28,8 @@ gem 'redis', '~> 4.0'
 # Use ActiveModel has_secure_password
 # gem 'bcrypt', '~> 3.1.7'
 
+gem 'mustache', '~> 1.0'
+
 # Use ActiveStorage variant
 # gem 'mini_magick', '~> 4.8'
 

Gemfile.lock

@@ -239,6 +239,7 @@ GEM
     multi_json (1.13.1)
     multi_xml (0.6.0)
     multipart-post (2.0.0)
+    mustache (1.1.0)
     mysql2 (0.5.2)
     nenv (0.3.0)
     nio4r (2.3.1)
@@ -480,6 +481,7 @@ DEPENDENCIES
   jquery-ui-sass-rails
   listen (>= 3.0.5, < 3.2)
   minitest-reporters
+  mustache (~> 1.0)
   mysql2 (>= 0.4.4, < 0.6.0)
   omniauth-mlh (~> 0.1)
   paperclip (~> 6.0)

app/controllers/manage/messages_controller.rb

@@ -58,14 +58,14 @@ def deliver
   end
 
   def preview
-    email = Mailer.bulk_message_email(@message.id, current_user.id)
+    email = Mailer.bulk_message_email(@message.id, current_user.id, nil, true)
     render html: email.body.raw_source.html_safe
   end
 
   def live_preview
     body = params[:body] || ''
     message = Message.new(body: body)
-    email = Mailer.bulk_message_email(nil, current_user.id, message)
+    email = Mailer.bulk_message_email(nil, current_user.id, message, true)
     render html: email.body.raw_source.html_safe
   end
 

app/mailers/mailer.rb

@@ -4,9 +4,10 @@ class Mailer < ApplicationMailer
 
   default from: -> { HackathonConfig['email_from'] }
 
-  def bulk_message_email(message_id, user_id, message = nil)
-    @message = message || Message.find_by_id(message_id)
-    @user    = User.find_by_id(user_id)
+  def bulk_message_email(message_id, user_id, message = nil, use_examples = false)
+    @message      = message || Message.find_by_id(message_id)
+    @user         = User.find_by_id(user_id)
+    @use_examples = use_examples
     return if @user.blank? || @message.blank?
     mail(
       to: pretty_email(@user.full_name, @user.email),

app/models/message.rb

@@ -4,6 +4,8 @@ class Message < ApplicationRecord
   validates_presence_of :name, :subject, :template
   validates_presence_of :body, if: :using_default_template?
 
+  validate :body_successfully_parses
+
   strip_attributes
 
   POSSIBLE_TEMPLATES = ["default"].freeze
@@ -40,6 +42,29 @@ class Message < ApplicationRecord
   validates_inclusion_of :template, in: POSSIBLE_TEMPLATES
   validates_inclusion_of :type, in: POSSIBLE_TYPES
 
+  def parsed_body(context, use_examples = false)
+    return body if body.blank?
+
+    message_template = MessageTemplate.new(context, use_examples)
+    message_template.template = body
+    message_template.render
+  end
+
+  def valid_body?
+    begin
+      parsed_body(nil, true)
+    rescue Mustache::Parser::SyntaxError
+      return false
+    end
+    true
+  end
+
+  def body_successfully_parses
+    unless valid_body?
+      errors.add(:body, 'failed to parse template variables')
+    end
+  end
+
   def recipients=(values)
     values.present? ? super(values.reject(&:blank?)) : super(values)
   end

app/models/message_template.rb

@@ -0,0 +1,58 @@
+class MessageTemplate < Mustache
+  def initialize(context, use_examples = false)
+    @var_context = context
+    @use_examples = use_examples
+  end
+
+  def method_missing(method_name, *arguments, &block)
+    variable = MessageTemplate.variables[method_name.to_s]
+    return evaluate(variable) if variable
+
+    super
+  end
+
+  def respond_to_missing?(method_name, include_private = false)
+    MessageTemplate.variables.key?(method_name.to_s) || super
+  end
+
+  class << self
+    def variables
+      config["variables"]
+    end
+
+    def config
+      @config ||= reload_config
+    end
+
+    def reload_config
+      @config = YAML.load_file('config/template_variables.yml')
+    end
+  end
+
+  private
+
+  def evaluate(variable)
+    return variable["example"] if @use_examples && !variable["use_value_as_example"]
+
+    value = variable["value"]
+    instance_eval(value)
+  end
+
+  def user
+    @user ||= begin
+      user_id = @var_context[:user_id]
+      return nil if user_id.blank?
+
+      User.find_by_id(user_id)
+    end
+  end
+
+  def bus_list
+    @bus_list ||= begin
+      bus_list_id = @var_context[:bus_list_id] || user&.questionnaire&.bus_list_id
+      return nil if bus_list_id.blank?
+
+      BusList.find_by_id(bus_list_id)
+    end
+  end
+end

app/views/mailer/bulk_templates/_default.html.erb

@@ -1 +1,9 @@
-<%= markdown(@message.body) %>
+<%
+  begin
+    parsed_body = @message.parsed_body({ user_id: @user.id }, @use_examples)
+  rescue Mustache::Parser::SyntaxError
+    raise unless @use_examples
+    parsed_body = @message.body
+  end
+%>
+<%= markdown(parsed_body) %>

app/views/manage/messages/_form.html.haml

@@ -19,3 +19,5 @@
 
     .form-actions.mb-3
       = f.button :submit, class: 'btn-primary'
+
+= render 'templating'

app/views/manage/messages/_templating.haml

@@ -0,0 +1,22 @@
+%h3.mt-5.pb-2#triggered-email-overview Templating
+
+%p
+  Message bodies can make use of template variables to help personalize and streamline emails.
+  Templating is powered by <a target="_blank" href="https://mustache.github.io/mustache.5.html">mustache</a>.
+
+%table.table.table-striped
+  %thead
+    %tr
+      %th Variable
+      %th About
+      %th Example
+  %tbody
+    - example = MessageTemplate.new(nil, true)
+    - MessageTemplate.variables.each do |variable, config|
+      %tr
+        %td
+          %pre {{#{variable}}}
+        %td
+          %span= config["description"]
+        %td
+          %pre= example.send(variable)

config/template_variables.yml

@@ -0,0 +1,52 @@
+sections:
+  user:
+    description: The email recipient
+  buslist:
+    description: The bus list specified for the email, or the bus list a recipient is signed up for.
+variables:
+  first_name:
+    description: The recipient's first name, if it exists
+    example: John
+    value: user&.first_name
+  last_name:
+    description: The recipient's last name, if it exists
+    example: Smith
+    value: user&.last_name
+
+  bus_list_exists?:
+    description: True/false if bus list information is available. Useful for optionally including bus content in emails.
+    example: true
+    value: bus_list.present?
+  bus_list_name:
+    description: The bus list's name.
+    example: Toronto & Buffalo Bus
+    value: bus_list&.name
+  bus_list_notes:
+    description: The bus list's bus notes
+    example: |
+      **Some notes for your bus:**
+
+      Picks up at 8:00am
+    value: bus_list&.name
+
+  hackathon_name:
+    description: Name of the hackathon
+    use_value_as_example: true
+    value: HackathonConfig['name']
+
+  apply_url:
+    description: Full URL of the apply page. Useful for links.
+    use_value_as_example: true
+    value: Rails.application.routes.url_helpers.root_url(Rails.application.config.action_mailer.default_url_options)
+  rsvp_url:
+    description: Full URL of RSVP page. Useful for links.
+    use_value_as_example: true
+    value: Rails.application.routes.url_helpers.rsvp_url(Rails.application.config.action_mailer.default_url_options)
+  rsvp_accept_url:
+    description: Full URL to the RSVP acceptance page. Useful for a one-click RSVP link.
+    use_value_as_example: true
+    value: Rails.application.routes.url_helpers.accept_rsvp_url(Rails.application.config.action_mailer.default_url_options)
+  rsvp_deny_url:
+    description: Full URL to the RSVP denial page. Useful for a one-click RSVP link.
+    use_value_as_example: true
+    value: Rails.application.routes.url_helpers.deny_rsvp_url(Rails.application.config.action_mailer.default_url_options)