Add task to migrate files to Active Storage

This task was copied from Thoughtbot's migration guide [1]. They use a
migration file, but we usually use rake tasks to migrate data.

[1] https://github.com/thoughtbot/paperclip/blob/master/MIGRATING.md

lib/tasks/active_storage.rake

@@ -0,0 +1,78 @@
+# This code is based on Thoughtbot's guide to migrating from Paperclip
+# to Active Storage:
+# https://github.com/thoughtbot/paperclip/blob/master/MIGRATING.md
+namespace :active_storage do
+  desc "Copy paperclip's attachment database columns to active storage"
+  task migrate_from_paperclip: :environment do
+    logger = ApplicationLogger.new
+    get_blob_id = "LASTVAL()"
+
+    ActiveRecord::Base.connection.raw_connection.prepare("active_storage_blob_statement", <<-SQL)
+    INSERT INTO active_storage_blobs (
+      key, filename, content_type, metadata, byte_size, checksum, created_at
+    ) VALUES ($1, $2, $3, '{}', $4, $5, $6)
+    SQL
+
+    ActiveRecord::Base.connection.raw_connection.prepare("active_storage_attachment_statement", <<-SQL)
+    INSERT INTO active_storage_attachments (
+      name, record_type, record_id, blob_id, created_at
+    ) VALUES ($1, $2, $3, #{get_blob_id}, $4)
+    SQL
+
+    Rails.application.eager_load!
+    models = ActiveRecord::Base.descendants.reject(&:abstract_class?)
+
+    ActiveRecord::Base.transaction do
+      models.each do |model|
+        attachments = model.column_names.map do |c|
+          if c =~ /(.+)_file_name$/
+            $1
+          end
+        end.compact
+
+        if attachments.blank?
+          next
+        end
+
+        model.find_each.each do |instance|
+          attachments.each do |attachment|
+            next if instance.send(attachment).path.blank?
+
+            ActiveRecord::Base.connection.raw_connection.exec_prepared(
+              "active_storage_blob_statement", [
+                SecureRandom.uuid, # Alternatively instance.send("#{attachment}_file_name"),
+                instance.send("#{attachment}_file_name"),
+                instance.send("#{attachment}_content_type"),
+                instance.send("#{attachment}_file_size"),
+                Digest::MD5.base64digest(File.read(instance.send(attachment).path)),
+                instance.updated_at.iso8601
+              ])
+
+            ActiveRecord::Base.connection.raw_connection.exec_prepared(
+              "active_storage_attachment_statement", [
+                attachment,
+                model.name,
+                instance.id,
+                instance.updated_at.iso8601
+              ])
+          end
+        end
+      end
+    end
+
+    ActiveStorage::Attachment.find_each do |attachment|
+      name = attachment.name
+      source = attachment.record.send(name).path
+
+      dest_dir = File.join(
+        "storage",
+        attachment.blob.key.first(2),
+        attachment.blob.key.first(4).last(2))
+      dest = File.join(dest_dir, attachment.blob.key)
+
+      FileUtils.mkdir_p(dest_dir)
+      logger.info "Copying #{source} to #{dest}"
+      FileUtils.cp(source, dest)
+    end
+  end
+end

lib/tasks/consul.rake

@@ -1,7 +1,13 @@
 namespace :consul do
   desc "Runs tasks needed to upgrade to the latest version"
   task execute_release_tasks: ["settings:rename_setting_keys",
-                               "settings:add_new_settings"]
+                               "settings:add_new_settings",
+                               "execute_release_1.4.0_tasks"]
+
+  desc "Runs tasks needed to upgrade from 1.3.0 to 1.4.0"
+  task "execute_release_1.4.0_tasks": [
+    "active_storage:migrate_from_paperclip"
+  ]
 
   desc "Runs tasks needed to upgrade from 1.2.0 to 1.3.0"
   task "execute_release_1.3.0_tasks": [