validation for image dimesion with MiniMagick and CarrierWave

imageability_validator.rb

require 'mini_magick'

class ImageabilityValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    if image_changed?(record, attribute, value)
      pic = MiniMagick::Image.open(value.path)

      if pic[:height] < options[:min][1] || pic[:width] < options[:min][0]
        record.errors.add(attribute, "should be greater than #{options[:min][0]}x#{options[:min][1]} pixels")
      end

      if options[:wide]
        if pic[:height] > pic[:width]
          record.errors.add(attribute, "should be wider")
        end
      end

      if value.size > options[:size]
        record.errors.add(attribute, "should be less than #{size options[:size]}MB")
      end
    end
  end

  protected
    def image_changed?(record, attribute, value)
      (!value.file.nil? && record.changed? && record.changed.include?(attribute)) || record.try("#{attribute.to_s}_cache")
    end

    def size(bytes)
      bytes / 1.megabyte
    end
end