module NSWTopo::Font::Chrome

def self.extended(instance)
  instance.start_chrome
end

def glyph_length(string, attributes)
  validate attributes
  style = attributes.slice(*ATTRIBUTES).map do |pair|
    pair.join ?:
  end.join(?;)
  @text[:style] = style
  @text.value = string
  @text.width / @scale
end

def start_chrome
  @families = Set[]
  NSWTopo::Chrome.new("data:image/svg+xml;base64,#{Base64.encode64 SVG}").tap do |browser|
    @scale = browser.query_selector("rect").width
    @text = browser.query_selector "text"
  end
end

def validate(attributes)
  return unless family = attributes["font-family"]
  return unless @families.add? family
  @text.value = "abcdefghijklmnopqrstuvwxyz"
  @text[:style] = "font-family:#{family}"
  styled_width = @text.width
  @text[:style] = nil
  unstyled_width = @text.width
  log_neutral "font '#{family}' doesn't appear to be available" if styled_width == unstyled_width
end