module FacebookCoverResize

# File lib/facebook_cover_resize.rb, line 5
def self.compute(args)
  ow = args[:width].to_f
  oh = (ow / args[:ratio])

  if args[:original].any? && args[:offsets].any?
    nw = args[:original].first.to_f
    nh = args[:original].last.to_f
    ox = args[:offsets].first.to_f
    oy = args[:offsets].last.to_f

    if ox == 0 && oy == 0
      w = ow
      h = nh * (ow / nw)
      if h < oh
        h = oh
        w = nw * (oh / nh)
        offset_x = ow - w
        offset_y = 0
      else
        offset_x = 0
        if w < h
          offset_y = 0
        else
          offset_y = oh - h
        end
      end
    else
      if oy > 0
        w = ow
        h = nh * (ow / nw)
        offset_x = 0
        offset_y = (oh - h) * (oy / 100.0)
        if h < oh
          h = oh
          w = nw * (oh / nh)
          offset_x = (ow - w) / 2
          offset_y = 0
        end
      elsif ox > 0
        h = oh
        w = nw * (oh / nh)
        offset_x = (ow - w) / 2
        offset_y = 0
      else
        w = ow
        h = nh * (ow / nw)
        offset_x = 0
        offset_y = 0
      end
    end
  else
    w = ow
    h = oh
    offset_x = 0
    offset_y = 0
  end

  # [margin-top, margin-left, image width, image height]
  out = [
    offset_y.ceil,
    offset_x.ceil,
    w.ceil,
    h.ceil
  ]

  return out
end