3 files changed, 43 insertions, 8 deletions
diff --git a/activestorage/app/models/active_storage/blob.rb b/activestorage/app/models/active_storage/blob.rb
index ff785d4f61..84b8f3827b 100644
--- a/activestorage/app/models/active_storage/blob.rb
+++ b/activestorage/app/models/active_storage/blob.rb
@@ -15,6 +15,7 @@
 # If you need to create a derivative or otherwise change the blob, simply create a new blob and purge the old one.
 class ActiveStorage::Blob < ActiveRecord::Base
   class UnpreviewableError < StandardError; end
+  class UnrepresentableError < StandardError; end
 
   self.table_name = "active_storage_blobs"
 
@@ -123,7 +124,7 @@ class ActiveStorage::Blob < ActiveRecord::Base
   # This will create a URL for that specific blob with that specific variant, which the ActiveStorage::VariantsController
   # can then produce on-demand.
   def variant(transformations)
-    ActiveStorage::Variant.new(self, ActiveStorage::Variation.new(transformations))
+    ActiveStorage::Variant.new(self, ActiveStorage::Variation.wrap(transformations))
   end
 
 
@@ -143,7 +144,7 @@ class ActiveStorage::Blob < ActiveRecord::Base
   # whether a blob is accepted by any previewer, call ActiveStorage::Blob#previewable?.
   def preview(transformations)
     if previewable?
-      ActiveStorage::Preview.new(self, ActiveStorage::Variation.new(transformations))
+      ActiveStorage::Preview.new(self, ActiveStorage::Variation.wrap(transformations))
     else
       raise UnpreviewableError
     end
@@ -155,6 +156,31 @@ class ActiveStorage::Blob < ActiveRecord::Base
   end
 
 
+  # Returns an ActiveStorage::Preview instance for a previewable blob or an ActiveStorage::Variant instance for an image blob.
+  #
+  #   blob.representation(resize: "100x100").processed.service_url
+  #
+  # Raises ActiveStorage::Blob::UnrepresentableError if the receiving blob is neither an image nor previewable. Call
+  # ActiveStorage::Blob#representable? to determine whether a blob is representable.
+  #
+  # See ActiveStorage::Blob#preview and ActiveStorage::Blob#variant for more information.
+  def representation(transformations)
+    case
+    when previewable?
+      preview transformations
+    when image?
+      variant transformations
+    else
+      raise UnrepresentableError
+    end
+  end
+
+  # Returns true if the blob is an image or is previewable.
+  def representable?
+    image? || previewable?
+  end
+
+
   # Returns the URL of the blob on the service. This URL is intended to be short-lived for security and not used directly
   # with users. Instead, the +service_url+ should only be exposed as a redirect from a stable, possibly authenticated URL.
   # Hiding the +service_url+ behind a redirect also gives you the power to change services without updating all URLs. And
diff --git a/activestorage/app/models/active_storage/variant.rb b/activestorage/app/models/active_storage/variant.rb
index 54685b4c0e..fa5aa69bd3 100644
--- a/activestorage/app/models/active_storage/variant.rb
+++ b/activestorage/app/models/active_storage/variant.rb
@@ -50,7 +50,7 @@ class ActiveStorage::Variant
 
   # Returns a combination key of the blob and the variation that together identifies a specific variant.
   def key
-    "variants/#{blob.key}/#{variation.key}"
+    "variants/#{blob.key}/#{Digest::SHA256.hexdigest(variation.key)}"
   end
 
   # Returns the URL of the variant on the service. This URL is intended to be short-lived for security and not used directly
@@ -65,6 +65,10 @@ class ActiveStorage::Variant
     service.url key, expires_in: expires_in, disposition: disposition, filename: blob.filename, content_type: blob.content_type
   end
 
+  # Returns the receiving variant. Allows ActiveStorage::Variant and ActiveStorage::Preview instances to be used interchangeably.
+  def image
+    self
+  end
 
   private
     def processed?
diff --git a/activestorage/app/models/active_storage/variation.rb b/activestorage/app/models/active_storage/variation.rb
index df2643442a..13bad87cac 100644
--- a/activestorage/app/models/active_storage/variation.rb
+++ b/activestorage/app/models/active_storage/variation.rb
@@ -13,16 +13,21 @@ class ActiveStorage::Variation
   attr_reader :transformations
 
   class << self
-    def wrap(variation_or_key)
-      case variation_or_key
+    # 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
-        variation_or_key
+        variator
+      when String
+        decode variator
       else
-        decode variation_or_key
+        new variator
       end
     end
 
-    # Returns a variation instance with the transformations that were encoded by +encode+.
+    # Returns a Variation instance with the transformations that were encoded by +encode+.
     def decode(key)
       new ActiveStorage.verifier.verify(key, purpose: :variation)
     end