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# frozen_string_literal: true
module ActiveStorage::Blob::Representable
extend ActiveSupport::Concern
included do
has_one_attached :preview_image
end
# Returns an ActiveStorage::Variant instance with the set of +transformations+ provided. This is only relevant for image
# files, and it allows any image to be transformed for size, colors, and the like. Example:
#
# avatar.variant(resize: "100x100").processed.service_url
#
# This will create and process a variant of the avatar blob that's constrained to a height and width of 100px.
# Then it'll upload said variant to the service according to a derivative key of the blob and the transformations.
#
# Frequently, though, you don't actually want to transform the variant right away. But rather simply refer to a
# specific variant that can be created by a controller on-demand. Like so:
#
# <%= image_tag Current.user.avatar.variant(resize: "100x100") %>
#
# This will create a URL for that specific blob with that specific variant, which the ActiveStorage::VariantsController
# can then produce on-demand.
#
# Raises ActiveStorage::InvariableError if ImageMagick cannot transform the blob. To determine whether a blob is
# variable, call ActiveStorage::Blob#variable?.
def variant(transformations)
if variable?
ActiveStorage::Variant.new(self, ActiveStorage::Variation.wrap(transformations))
else
raise ActiveStorage::InvariableError
end
end
# Returns true if ImageMagick can transform the blob (its content type is in +ActiveStorage.variable_content_types+).
def variable?
ActiveStorage.variable_content_types.include?(content_type)
end
# Returns an ActiveStorage::Preview instance with the set of +transformations+ provided. A preview is an image generated
# from a non-image blob. Active Storage comes with built-in previewers for videos and PDF documents. The video previewer
# extracts the first frame from a video and the PDF previewer extracts the first page from a PDF document.
#
# blob.preview(resize: "100x100").processed.service_url
#
# Avoid processing previews synchronously in views. Instead, link to a controller action that processes them on demand.
# Active Storage provides one, but you may want to create your own (for example, if you need authentication). Here’s
# how to use the built-in version:
#
# <%= image_tag video.preview(resize: "100x100") %>
#
# This method raises ActiveStorage::UnpreviewableError if no previewer accepts the receiving blob. To determine
# whether a blob is accepted by any previewer, call ActiveStorage::Blob#previewable?.
def preview(transformations)
if previewable?
ActiveStorage::Preview.new(self, ActiveStorage::Variation.wrap(transformations))
else
raise ActiveStorage::UnpreviewableError
end
end
# Returns true if any registered previewer accepts the blob. By default, this will return true for videos and PDF documents.
def previewable?
ActiveStorage.previewers.any? { |klass| klass.accept?(self) }
end
# Returns an ActiveStorage::Preview for a previewable blob or an ActiveStorage::Variant for a variable image blob.
#
# blob.representation(resize: "100x100").processed.service_url
#
# Raises ActiveStorage::UnrepresentableError if the receiving blob is neither variable 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 variable?
variant transformations
else
raise ActiveStorage::UnrepresentableError
end
end
# Returns true if the blob is variable or previewable.
def representable?
variable? || previewable?
end
end
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