class ActiveStorage::Previewer::PopplerPDFPreviewer

def accept?(blob)
  blob.content_type == "application/pdf" && pdftoppm_exists?
end

def draw_first_page_from(file, &block)
  # use 72 dpi to match thumbnail dimensions of the PDF
  draw self.class.pdftoppm_path, "-singlefile", "-cropbox", "-r", "72", "-png", file.path, &block
end

def pdftoppm_exists?
  return @pdftoppm_exists if defined?(@pdftoppm_exists)
  @pdftoppm_exists = system(pdftoppm_path, "-v", out: File::NULL, err: File::NULL)
end

def pdftoppm_path
  ActiveStorage.paths[:pdftoppm] || "pdftoppm"
end

def preview(**options)
  download_blob_to_tempfile do |input|
    draw_first_page_from input do |output|
      yield io: output, filename: "#{blob.filename.base}.png", content_type: "image/png", **options
    end
  end
end