backups: add stub backup service.

app/logical/backup_service.rb

@@ -0,0 +1,5 @@
+class BackupService
+  def backup(file_path, options = {})
+    raise NotImplementedError.new("#{self.class}.backup not implemented")
+  end
+end

app/logical/null_backup_service.rb

@@ -0,0 +1,5 @@
+class NullBackupService
+  def backup(file_path, options = {})
+    # do nothing
+  end
+end

app/models/post.rb

@@ -23,6 +23,7 @@ class Post < ActiveRecord::Base
   before_save :set_tag_counts
   before_save :set_pool_category_pseudo_tags
   before_create :autoban
+  after_save :queue_backup, if: :md5_changed?
   after_save :create_version
   after_save :update_parent_on_save
   after_save :apply_post_metatags
@@ -229,6 +230,23 @@ class Post < ActiveRecord::Base
     end
   end
 
+  module BackupMethods
+    extend ActiveSupport::Concern
+
+    def queue_backup
+      Post.delay(queue: "default", priority: -1).backup_file(file_path, id: id, type: :original)
+      Post.delay(queue: "default", priority: -1).backup_file(large_file_path, id: id, type: :large) if has_large?
+      Post.delay(queue: "default", priority: -1).backup_file(preview_file_path, id: id, type: :preview) if has_preview?
+    end
+
+    module ClassMethods
+      def backup_file(file_path, options = {})
+        backup_service = Danbooru.config.backup_service
+        backup_service.backup(file_path, options)
+      end
+    end
+  end
+
   module ImageMethods
     def device_scale
       if large_image_width > 320
@@ -1701,6 +1719,7 @@ class Post < ActiveRecord::Base
   end
   
   include FileMethods
+  include BackupMethods
   include ImageMethods
   include ApprovalMethods
   include PresenterMethods

config/danbooru_default_config.rb

@@ -90,6 +90,10 @@ module Danbooru
       true
     end
 
+    def backup_service
+      NullBackupService.new
+    end
+
     # What method to use to store images.
     # local_flat: Store every image in one directory.
     # local_hierarchy: Store every image in a hierarchical directory, based on the post's MD5 hash. On some file systems this may be faster.
@@ -477,6 +481,7 @@ module Danbooru
       false
     end
 
+    # Used for backing up images to S3. Must be changed to your own S3 bucket.
     def aws_s3_bucket_name
       "danbooru"
     end