Next dump

app/controllers/unsubscribes_controller.rb

@@ -0,0 +1,15 @@
+class UnsubscribesController < ApplicationController
+  allow_unauthenticated_access
+  before_action :set_subscriber
+
+  def show
+    @subscriber.destroy
+    redirect_to root_path, notice: "Unsubscribed successfully."
+  end
+
+  private
+
+    def set_subscriber
+      @subscriber = Subscriber.find_by_token_for(:unsubscribe, params[:token])
+    end
+end

app/mailers/product_mailer.rb

@@ -0,0 +1,11 @@
+class ProductMailer < ApplicationMailer
+  # Subject can be set in your I18n file at config/locales/en.yml
+  # with the following lookup:
+  #
+  #   en.product_mailer.in_stock.subject
+  #
+  def in_stock
+    @product = params[:product]
+    mail to: params[:subscriber].email
+  end
+end

app/models/product.rb

@@ -1,5 +1,5 @@
 class Product < ApplicationRecord
-  has_many :subscribers, dependent: :destroy
+  include Notifications
 
   has_one_attached :featured_image
   has_rich_text :description

app/models/product/notifications.rb

@@ -0,0 +1,18 @@
+module Product::Notifications
+  extend ActiveSupport::Concern
+
+  included do
+    has_many :subscribers, dependent: :destroy
+    after_update_commit :notify_subscribers, if: :back_in_stock?
+
+    def back_in_stock?
+      inventory_count_previously_was.zero? && inventory_count > 0
+    end
+
+    def notify_subscribers
+      subscribers.each do |sub|
+        ProductMailer.with(product: self, subscriber: sub).in_stock.deliver_later
+      end
+    end
+  end
+end

app/models/subscriber.rb

@@ -1,3 +1,4 @@
 class Subscriber < ApplicationRecord
   belongs_to :product
+  generates_token_for :unsubscribe
 end

app/views/product_mailer/in_stock.html.erb

@@ -0,0 +1,7 @@
+<h1>Good News!</h1>
+
+<p>
+  <%= link_to @product.name, product_url(@product) %> is back in stock!
+</p>
+
+<%= link_to "Unsubscribe", unsubscribe_url(token: params[:subscriber].generate_token_for(:unsubscribe) %>

app/views/product_mailer/in_stock.text.erb

@@ -0,0 +1,6 @@
+Good News!
+
+<%= @product.name %> is back in stock!
+<%= product_url(@product) %>
+
+Unsubscribe: <%= unsubscribe_url(token: params[:subscriber].generate_token_for(:unsubscribe) %>

app/views/products/_inventory.html.erb

@@ -0,0 +1,11 @@
+<% if product.inventory_count? %>
+  <p><%= product.inventory_count %> in stock</p>
+<% else %>
+  <p>Out of Stock</p>
+  <p>Notify me when more is stocked:</p>
+
+  <%= form_with model: [product, Subscriber.new] do |form| %>
+    <%= form.email_field :email, placeholder: "you@example.com", required: true %>
+    <%= form.submit %>
+  <% end %>
+<% end %>

app/views/products/show.html.erb

@@ -5,6 +5,8 @@
   <%= @product.description %>
 <% end %>
 
+<%= render "inventory", product: @product %>
+
 <% if authenticated? %>
   <%= link_to "Edit", edit_product_path(@product) %>
   <%= button_to "Delete", @product, method: :delete, 

config/routes.rb

@@ -1,6 +1,7 @@
 Rails.application.routes.draw do
   resource :session
   resources :passwords, param: :token
+  resources :unsubscribe, only: [ :show ]
   # Define your application routes per the DSL in https://guides.rubyonrails.org/routing.html
   resources :products do
     resources :subscribers, only: [ :create ]

test/mailers/previews/product_mailer_preview.rb

@@ -0,0 +1,7 @@
+# Preview all emails at http://localhost:3000/rails/mailers/product_mailer
+class ProductMailerPreview < ActionMailer::Preview
+  # Preview this email at http://localhost:3000/rails/mailers/product_mailer/in_stock
+  def in_stock
+    ProductMailer.in_stock
+  end
+end

test/mailers/product_mailer_test.rb

@@ -0,0 +1,11 @@
+require "test_helper"
+
+class ProductMailerTest < ActionMailer::TestCase
+  test "in_stock" do
+    mail = ProductMailer.in_stock
+    assert_equal "In stock", mail.subject
+    assert_equal [ "to@example.org" ], mail.to
+    assert_equal [ "from@example.com" ], mail.from
+    assert_match "Hi", mail.body.encoded
+  end
+end