class ActiveStorage::Variation

The options map directly to ImageProcessing commands.
ActiveStorage::Variation.new(resize_to_limit: [100, 100], colourspace: “b-w”, rotate: “-90”, saver: { trim: true })
the key is the command and the value is the arguments. Example:
In case you do need to use this directly, it’s instantiated using a hash of transformations where
the ActiveStorage::Blob#variant method and should rarely be used directly.
A set of transformations that can be applied to a blob to create a variant. This class is exposed via
= Active Storage Variation

def content_type 

def content_type
  Marcel::MimeType.for(extension: format.to_s)
end

def decode(key)

Returns a Variation instance with the transformations that were encoded by +encode+. 
def decode(key)
  new ActiveStorage.verifier.verify(key, purpose: :variation)
end

def default_to(defaults) 

def default_to(defaults)
  self.class.new transformations.reverse_merge(defaults)
end

def digest 

def digest
  OpenSSL::Digest::SHA1.base64digest Marshal.dump(transformations)
end

def encode(transformations)

variation in a URL or combined key (like ActiveStorage::Variant#key).
Returns a signed key for the +transformations+, which can be used to refer to a specific 
def encode(transformations)
  ActiveStorage.verifier.generate(transformations, purpose: :variation)
end

def format 

def format
  transformations.fetch(:format, :png).tap do |format|
    if Marcel::Magic.by_extension(format.to_s).nil?
      raise ArgumentError, "Invalid variant format (#{format.inspect})"
    end
  end
end

def initialize(transformations) 

def initialize(transformations)
  @transformations = transformations.deep_symbolize_keys
end

def key

Returns a signed key for all the +transformations+ that this variation was instantiated with. 
def key
  self.class.encode(transformations)
end

def transform(file, &block)

saves the transformed image into a temporary file.
Accepts a File object, performs the +transformations+ against it, and 
def transform(file, &block)
  ActiveSupport::Notifications.instrument("transform.active_storage") do
    transformer.transform(file, format: format, &block)
  end
end

def transformer 

def transformer
  ActiveStorage::Transformers::ImageProcessingTransformer.new(transformations.except(:format))
end

def wrap(variator)

it is assumed to be a transformations Hash and is passed directly to the constructor.
returned unmodified. If it is a String, it is passed to ActiveStorage::Variation.decode. Otherwise,
Returns a Variation instance based on the given variator. If the variator is a Variation, it is 
def wrap(variator)
  case variator
  when self
    variator
  when String
    decode variator
  else
    new variator
  end
end