module QrcodeHelper
  def qrcode(data='', options = {})
    # Google API: https://google-developers.appspot.com/chart/infographics/docs/qr_codes
    width = pop_value :width, options, '200'
    output_encoding = pop_value :output_encoding, options
    error_correction_level = pop_value :error_correction_level, options
    margin = pop_value :margin, options

    qrcode_url = 'https://chart.googleapis.com/chart?cht=qr'
    qrcode_url += "&chl=#{data}"
    qrcode_url += "&chs=#{width}x#{width}"
    qrcode_url += "&choe=#{output_encoding}" unless output_encoding.nil?
    if error_correction_level.nil? or margin.nil?
      qrcode_url += "&chld=#{error_correction_level}" unless error_correction_level.nil?
      qrcode_url += "&chld=|#{margin}" unless margin.nil?
    else
      qrcode_url += "&chld=#{error_correction_level}|#{margin}"
    end
    image_tag qrcode_url, alt: data
  end
end