aboutsummaryrefslogtreecommitdiffstats
path: root/activestorage/app/models/active_storage/blob/representable.rb
blob: 0ad2e2fd77bf9424c27de99680eb59b02f942b01 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
# 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