add-watermark.rb

require "prawn"

class AddWatermarkService
  def initialize(cv)
    @cv = cv
  end

  def perform
    begin
      return { cv: @cv, success: false } if File.extname(@cv.original_filename) != ".pdf"

      @random_uid = SecureRandom.hex

      pdf = @cv.read
      save_path = Rails.root.join("tmp", "#{@random_uid}.pdf")
      File.open(save_path, "wb") { |file| file << pdf }

      # Get size of the CV
      reader = PDF::Reader.new("#{Rails.root}/tmp/#{@random_uid}.pdf")
      bbox = reader.pages.first.attributes[:MediaBox]
      width = bbox[2] - bbox[0]
      height = bbox[3] - bbox[1]

      # Generate watermark
      header_img = "#{Rails.root}/share/header.png"
      watermark_img = "#{Rails.root}/share/center.png"
      save_path = Rails.root.join("tmp", "watermark_#{@random_uid}.pdf")

      Prawn::Document.generate(save_path, page_size: [width, height], margin: 0) do
        image header_img, vposition: :top, position: :left, width: 130, height: 20
        image watermark_img, vposition: :center, position: :center
      end

      # Add watermark
      company_logo = CombinePDF.load("#{Rails.root}/tmp/watermark_#{@random_uid}.pdf").pages[0]
      pdf = CombinePDF.load("#{Rails.root}/tmp/#{@random_uid}.pdf")

      pdf.pages.each { |page| page << company_logo }

      # Remove tmp file
      File.delete("#{Rails.root}/tmp/watermark_#{@random_uid}.pdf")
      File.delete("#{Rails.root}/tmp/#{@random_uid}.pdf")

      return { cv: pdf, success: true }
    rescue StandardError => e
      return { cv: @cv, success: false }
    end
  end

  private

  def pt2mm(pt)
    (pt2in(pt) * BigDecimal("25.4")).round(2)
  end

  def pt2in(pt)
    (pt / BigDecimal("72")).round(2)
  end
end