rmagick with active_storage and active_record

Gemfile

@@ -70,3 +70,5 @@ group :test do
   gem "selenium-webdriver"
   gem "webdrivers"
 end
+
+gem "rmagick", "~> 4.3"

Gemfile.lock

@@ -163,6 +163,7 @@ GEM
     reline (0.3.1)
       io-console (~> 0.5)
     rexml (3.2.5)
+    rmagick (4.3.0)
     rubyzip (2.3.2)
     selenium-webdriver (4.5.0)
       childprocess (>= 0.5, < 5.0)
@@ -216,6 +217,7 @@ DEPENDENCIES
   puma (~> 5.0)
   rails (~> 7.0.4)
   redis (~> 4.0)
+  rmagick (~> 4.3)
   selenium-webdriver
   sprockets-rails
   stimulus-rails

app/models/post.rb

@@ -1,2 +1,11 @@
 class Post < ApplicationRecord
+  has_one_attached :thumbnail
+
+  after_create :attach_thumbnail
+
+  private
+
+  def attach_thumbnail
+    GenerateThumbnailService.new(self)
+  end
 end

app/services/generate_thumbnail_service.rb

@@ -0,0 +1,46 @@
+class GenerateThumbnailService
+  require 'RMagick'
+  include Magick
+
+  attr_reader :post
+
+  def initialize(post)
+    @post = post
+    call
+  end
+
+  def call
+    image = Magick::Image.new(800, 400) do |img|
+      img.background_color = 'yellow'
+    end
+
+    logo_path = Rails.root.join('app/assets/images/logo.png')
+    logo = Magick::Image.read(logo_path).first
+    logo = logo.scale(0.2)
+    image = image.composite(logo, SouthEastGravity, 5, 5, OverCompositeOp)
+
+    text = Magick::Draw.new
+    text.annotate(image, 0, 0, 0, -50, post.title) do |txt|
+      txt.pointsize = 48
+      txt.font_weight = BoldWeight
+      txt.fill = 'blue'
+      txt.gravity = CenterGravity
+    end
+
+    text.annotate(image, 0, 0, 0, 50, post.body) do |txt|
+      txt.pointsize = 24
+      txt.font_weight = NormalWeight
+      txt.fill = 'green'
+      txt.gravity = CenterGravity
+    end
+
+    filename = [post.model_name.human, post.id].join.downcase
+    # FileUtils.mkdir_p 'app/assets/images/generator'
+    image.write("app/assets/images/generator/#{filename}.png")
+
+    image_io = File.open("app/assets/images/generator/#{filename}.png")
+    post.thumbnail.attach(io: image_io, filename:, content_type: 'image/png')
+
+    File.delete(image_io)
+  end
+end

app/views/posts/_post.html.erb

@@ -1,4 +1,5 @@
 <div id="<%= dom_id post %>">
+  <%= image_tag post.thumbnail %>
   <p>
     <strong>Title:</strong>
     <%= post.title %>

db/migrate/20221003205919_create_active_storage_tables.active_storage.rb

@@ -0,0 +1,57 @@
+# This migration comes from active_storage (originally 20170806125915)
+class CreateActiveStorageTables < ActiveRecord::Migration[5.2]
+  def change
+    # Use Active Record's configured type for primary and foreign keys
+    primary_key_type, foreign_key_type = primary_and_foreign_key_types
+
+    create_table :active_storage_blobs, id: primary_key_type do |t|
+      t.string   :key,          null: false
+      t.string   :filename,     null: false
+      t.string   :content_type
+      t.text     :metadata
+      t.string   :service_name, null: false
+      t.bigint   :byte_size,    null: false
+      t.string   :checksum
+
+      if connection.supports_datetime_with_precision?
+        t.datetime :created_at, precision: 6, null: false
+      else
+        t.datetime :created_at, null: false
+      end
+
+      t.index [ :key ], unique: true
+    end
+
+    create_table :active_storage_attachments, id: primary_key_type do |t|
+      t.string     :name,     null: false
+      t.references :record,   null: false, polymorphic: true, index: false, type: foreign_key_type
+      t.references :blob,     null: false, type: foreign_key_type
+
+      if connection.supports_datetime_with_precision?
+        t.datetime :created_at, precision: 6, null: false
+      else
+        t.datetime :created_at, null: false
+      end
+
+      t.index [ :record_type, :record_id, :name, :blob_id ], name: :index_active_storage_attachments_uniqueness, unique: true
+      t.foreign_key :active_storage_blobs, column: :blob_id
+    end
+
+    create_table :active_storage_variant_records, id: primary_key_type do |t|
+      t.belongs_to :blob, null: false, index: false, type: foreign_key_type
+      t.string :variation_digest, null: false
+
+      t.index [ :blob_id, :variation_digest ], name: :index_active_storage_variant_records_uniqueness, unique: true
+      t.foreign_key :active_storage_blobs, column: :blob_id
+    end
+  end
+
+  private
+    def primary_and_foreign_key_types
+      config = Rails.configuration.generators
+      setting = config.options[config.orm][:primary_key_type]
+      primary_key_type = setting || :primary_key
+      foreign_key_type = setting || :bigint
+      [primary_key_type, foreign_key_type]
+    end
+end