carrierwave_meta.rb

# DRAFT
module CarrierWave::Meta
  extend ActiveSupport::Concern

  included do
    before :cache, :store_original_meta

    [:width, :height, :content_type, :size, :filename].each do |m|
      define_method :"meta_#{m}" do |*args|
        style = args.first
        style ||= :original
        meta[style][m] unless meta.blank?
      end
    end
  end
  
  module ClassMethods
    def store_meta
      process :store_meta
    end
  end
  
  module InstanceMethods
    def meta
      raise "Can not read carrierwave metadata for #{mounted_as}: #{meta_column} attribute is not defined" unless has_meta_column?
      meta = self.model[meta_column]
      meta = unless meta.blank?
        Marshal.load(ActiveSupport::Base64.decode64(meta)) rescue nil
      end
      meta || {}
    end
    
    private
    def meta_column
      :"#{self.mounted_as}_meta"
    end

    def has_meta_column?
      self.model.has_attribute?(meta_column)    
    end

    def save_meta(meta)
      self.model[meta_column] = ActiveSupport::Base64.encode64(Marshal.dump(meta))    
    end

    # This is used to determine original file name && content type, because the first call of 
    # store_meta processor recieves the sanitized file name and so on.
    def store_original_meta(file)
      @original ||= {
        :filename => file.original_filename,
        :size => file.size,
        :content_type => file.content_type
      }
    end

    def store_meta
      if has_meta_column?
        version_meta = {
          :content_type => self.file.content_type,
          :size => self.file.size
        }

        if self.respond_to?(:manipulate!) && self.file.content_type =~ /image/
          version_meta[:width], version_meta[:height] = get_dimensions
        end

        version_name = (self.version_name || :undefined).to_sym

        meta = self.meta
        meta[:original] = @original unless @original.blank?
        meta[version_name] = version_meta
        save_meta(meta)
      end    
    end

    def get_dimensions
      width = 0
      height = 0
      manipulate! do |img|
        if img.is_a?(::Magick::Image)
          width = img.columns
          height = img.rows
        else
          raise "Processor is not supported. Fork me and update me."
        end        
        img
      end
      [width, height]    
    end    
  end  
end