1 files changed, 53 insertions, 0 deletions
diff --git a/activestorage/app/models/active_storage/variation.rb b/activestorage/app/models/active_storage/variation.rb
new file mode 100644
index 0000000000..e784506b4c
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+++ b/activestorage/app/models/active_storage/variation.rb
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+require "active_support/core_ext/object/inclusion"
+
+# A set of transformations that can be applied to a blob to create a variant. This class is exposed via
+# the `ActiveStorage::Blob#variant` method and should rarely be used directly.
+#
+# In case you do need to use this directly, it's instantiated using a hash of transformations where
+# the key is the command and the value is the arguments. Example:
+#
+#   ActiveStorage::Variation.new(resize: "100x100", monochrome: true, trim: true, rotate: "-90")
+#
+# A list of all possible transformations is available at https://www.imagemagick.org/script/mogrify.php.
+class ActiveStorage::Variation
+  attr_reader :transformations
+
+  class << self
+    # Returns a variation instance with the transformations that were encoded by `#encode`.
+    def decode(key)
+      new ActiveStorage.verifier.verify(key, purpose: :variation)
+    end
+
+    # Returns a signed key for the `transformations`, which can be used to refer to a specific
+    # variation in a URL or combined key (like `ActiveStorage::Variant#key`).
+    def encode(transformations)
+      ActiveStorage.verifier.generate(transformations, purpose: :variation)
+    end
+  end
+
+  def initialize(transformations)
+    @transformations = transformations
+  end
+
+  # Accepts an open MiniMagick image instance, like what's return by `MiniMagick::Image.read(io)`,
+  # and performs the `transformations` against it. The transformed image instance is then returned.
+  def transform(image)
+    transformations.each do |(method, argument)|
+      if eligible_argument?(argument)
+        image.public_send(method, argument)
+      else
+        image.public_send(method)
+      end
+    end
+  end
+
+  # Returns a signed key for all the `transformations` that this variation was instantiated with.
+  def key
+    self.class.encode(transformations)
+  end
+
+  private
+    def eligible_argument?(argument)
+      argument.present? && argument != true
+    end
+end