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diff --git a/activestorage/app/models/active_storage/variation.rb b/activestorage/app/models/active_storage/variation.rb
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+++ b/activestorage/app/models/active_storage/variation.rb
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+# frozen_string_literal: true
+
+# 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 based on the given variator. If the variator is a Variation, it is
+    # returned unmodified. If it is a String, it is passed to ActiveStorage::Variation.decode. Otherwise,
+    # it is assumed to be a transformations Hash and is passed directly to the constructor.
+    def wrap(variator)
+      case variator
+      when self
+        variator
+      when String
+        decode variator
+      else
+        new variator
+      end
+    end
+
+    # 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 <tt>ActiveStorage::Variant#key</tt>).
+    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 returned by <tt>MiniMagick::Image.read(io)</tt>,
+  # and performs the +transformations+ against it. The transformed image instance is then returned.
+  def transform(image)
+    transformations.each do |name, argument_or_subtransformations|
+      image.mogrify do |command|
+        if name.to_s == "combine_options"
+          argument_or_subtransformations.each do |subtransformation_name, subtransformation_argument|
+            pass_transform_argument(command, subtransformation_name, subtransformation_argument)
+          end
+        else
+          pass_transform_argument(command, name, argument_or_subtransformations)
+        end
+      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 pass_transform_argument(command, method, argument)
+      if eligible_argument?(argument)
+        command.public_send(method, argument)
+      else
+        command.public_send(method)
+      end
+    end
+
+    def eligible_argument?(argument)
+      argument.present? && argument != true
+    end
+end