storage managers: add mirror storage manager.

Add a storage manager that allows mirroring files to multiple storage
backends.

app/logical/storage_manager.rb

@@ -17,9 +17,9 @@ class StorageManager
   # @param base_url [String] the base URL where images are stored (ex: "https://cdn.donmai.us/")
   # @param base_dir [String] the base directory where images are stored (ex: "/var/www/danbooru/public/images")
   # @param tagged_filenames [Boolean] whether image URLs can include tags
-  def initialize(base_url:, base_dir:, tagged_filenames: Danbooru.config.enable_seo_post_urls)
-    @base_url = base_url.chomp("/")
-    @base_dir = base_dir
+  def initialize(base_url: nil, base_dir: nil, tagged_filenames: Danbooru.config.enable_seo_post_urls)
+    @base_url = base_url.to_s.chomp("/")
+    @base_dir = base_dir.to_s
     @tagged_filenames = tagged_filenames
   end
 

app/logical/storage_manager/mirror.rb

@@ -0,0 +1,29 @@
+# A StorageManager that mirrors files across multiple storage backends.
+class StorageManager::Mirror < StorageManager
+  attr_reader :services
+
+  def initialize(services, **options)
+    @services = services
+    super(**options)
+  end
+
+  def store(io, dest_path)
+    services.each do |service|
+      service.store(io, dest_path)
+    end
+  end
+
+  def delete(path)
+    services.each do |service|
+      service.delete(path)
+    end
+  end
+
+  def open(path)
+    services.first.open(path)
+  end
+
+  def file_url(path)
+    services.first.file_url(path)
+  end
+end