Extract variation value object

1 files changed, 53 insertions, 0 deletions

diff --git a/lib/active_storage/variation.rb b/lib/active_storage/variation.rb
new file mode 100644
index 0000000000..abff288ac1
--- /dev/null
+++ b/lib/active_storage/variation.rb
@@ -0,0 +1,53 @@
+require "active_support/core_ext/object/inclusion"
+
+# A set of transformations that can be applied to a blob to create a variant.
+class ActiveStorage::Variation
+  class_attribute :verifier
+
+  ALLOWED_TRANSFORMATIONS = %i(
+    resize rotate format flip fill monochrome orient quality roll scale sharpen shave shear size thumbnail
+    transparent transpose transverse trim background bordercolor compress crop
+  )
+
+  attr_reader :transformations
+
+  class << self
+    def decode(key)
+      new verifier.verify(key)
+    end
+    
+    def encode(transformations)
+      verifier.generate(transformations)
+    end
+  end
+
+  def initialize(transformations)
+    @transformations = transformations
+  end
+
+  def transform(image)
+    transformations.each do |(method, argument)|
+      next unless eligible_transformation?(method)
+
+      if eligible_argument?(argument)
+        image.public_send(method, argument)
+      else
+        image.public_send(method)
+      end
+    end
+  end
+
+  def key
+    self.class.encode(transformations)
+  end
+
+  private
+    def eligible_transformation?(method)
+      method.to_sym.in?(ALLOWED_TRANSFORMATIONS)
+    end
+
+    # FIXME: Consider whitelisting allowed arguments as well?
+    def eligible_argument?(argument)
+      argument.present? && argument != true
+    end
+end