Extract transformers

1 files changed, 42 insertions, 0 deletions

diff --git a/activestorage/lib/active_storage/transformers/transformer.rb b/activestorage/lib/active_storage/transformers/transformer.rb
new file mode 100644
index 0000000000..2e21201004
--- /dev/null
+++ b/activestorage/lib/active_storage/transformers/transformer.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module ActiveStorage
+  module Transformers
+    # A Transformer applies a set of transformations to an image.
+    #
+    # The following concrete subclasses are included in Active Storage:
+    #
+    # * ActiveStorage::Transformers::ImageProcessingTransformer:
+    #   backed by ImageProcessing, a common interface for MiniMagick and ruby-vips
+    #
+    # * ActiveStorage::Transformers::MiniMagickTransformer:
+    #   backed by MiniMagick, a wrapper around the ImageMagick CLI
+    class Transformer
+      attr_reader :transformations
+
+      def initialize(transformations)
+        @transformations = transformations
+      end
+
+      # Applies the transformations to the source image in +file+, producing a target image in the
+      # specified +format+. Yields an open Tempfile containing the target image. Closes and unlinks
+      # the output tempfile after yielding to the given block. Returns the result of the block.
+      def transform(file, format:)
+        output = process(file, format: format)
+
+        begin
+          yield output
+        ensure
+          output.close!
+        end
+      end
+
+      private
+        # Returns an open Tempfile containing a transformed image in the given +format+.
+        # All subclasses implement this method.
+        def process(file, format:) #:doc:
+          raise NotImplementedError
+        end
+    end
+  end
+end