Repository: rails/rails
File: activestorage/lib/active_storage/previewer.rb (Ruby)

Code before:
  #
  # This is an abstract base class for previewers, which generate images from blobs. See
  # ActiveStorage::Previewer::MuPDFPreviewer and ActiveStorage::Previewer::VideoPreviewer for
  # examples of concrete subclasses.
  class Previewer
    attr_reader :blob

    # Implement this method in a concrete subclass. Have it return true when given a blob from which
    # the previewer can generate an image.
    def self.accept?(blob)
      false
    end

    def initialize(blob)
      @blob = blob
    end

    # Override this method in a concrete subclass. Have it yield an attachable preview image (i.e.
    # anything accepted by ActiveStorage::Attached::One#attach). Pass the additional options to
    # the underlying blob that is created.
    def preview(**options)
      raise NotImplementedError
    end

    private
      # Downloads the blob to a tempfile on disk. See +ActiveStorage::Blob#open+ for details.
      def download_blob_to_tempfile(&block) # :doc:
        blob.open tmpdir: tmpdir, &block
      end

      # Executes a system command, capturing its binary output in a tempfile. Yields the tempfile.
      #
      # Use this method to shell out to a system library (e.g. muPDF or FFmpeg) for preview image
      # generation. The resulting tempfile can be used as the +:io+ value in an attachable Hash:
      #
      #   def preview
      #     download_blob_to_tempfile do |input|
      #       draw "my-drawing-command", input.path, "--format", "png", "-" do |output|
      #         yield io: output, filename: "#{blob.filename.base}.png", content_type: "image/png"
      #       end
      #     end
      #   end
      #
      # The output tempfile is opened in the directory returned by #tmpdir.
      def draw(*argv) # :doc:
        open_tempfile do |file|
          instrument :preview, key: blob.key do
            capture(*argv, to: file)
          end

          yield file

Review comment (suggestion):
```suggestion
      # Downloads the blob to a tempfile on disk. See ActiveStorage::Blob#open for details.
```

If you want it to auto-link need to remove the fixed-width wrapper.

Code after:
  #
  # This is an abstract base class for previewers, which generate images from blobs. See
  # ActiveStorage::Previewer::MuPDFPreviewer and ActiveStorage::Previewer::VideoPreviewer for
  # examples of concrete subclasses.
  class Previewer
    attr_reader :blob

    # Implement this method in a concrete subclass. Have it return true when given a blob from which
    # the previewer can generate an image.
    def self.accept?(blob)
      false
    end

    def initialize(blob)
      @blob = blob
    end

    # Override this method in a concrete subclass. Have it yield an attachable preview image (i.e.
    # anything accepted by ActiveStorage::Attached::One#attach). Pass the additional options to
    # the underlying blob that is created.
    def preview(**options)
      raise NotImplementedError
    end

    private
      # Downloads the blob to a tempfile on disk. See ActiveStorage::Blob#open for details.
      def download_blob_to_tempfile(&block) # :doc:
        blob.open tmpdir: tmpdir, &block
      end

      # Executes a system command, capturing its binary output in a tempfile. Yields the tempfile.
      #
      # Use this method to shell out to a system library (e.g. muPDF or FFmpeg) for preview image
      # generation. The resulting tempfile can be used as the +:io+ value in an attachable Hash:
      #
      #   def preview
      #     download_blob_to_tempfile do |input|
      #       draw "my-drawing-command", input.path, "--format", "png", "-" do |output|
      #         yield io: output, filename: "#{blob.filename.base}.png", content_type: "image/png"
      #       end
      #     end
      #   end
      #
      # The output tempfile is opened in the directory returned by #tmpdir.
      def draw(*argv) # :doc:
        open_tempfile do |file|
          instrument :preview, key: blob.key do
            capture(*argv, to: file)
          end

          yield file