require 'dynamic_image'

module DynamicImage

  @@filtersets = Hash.new
  
  # Singleton methods for the filtersets hash.
  class << @@filtersets
    def names; keys; end
  end
  
  # Accessor for the filtersets hash. Installed filter names are available through the <tt>names</tt> method. Example:
  #   @filter_names = DynamicImage.filtersets.names
  def self.filtersets
    @@filtersets
  end
  
  # Base class for filter sets. Extending this with your own subclasses will automatically enable them for use.
  # You'll need to overwrite <tt>Filterset.process</tt> in order to make your filter useful. Note that it's a class
  # method.
  #
  # === Example
  #
  #   class BlogThumbnailsFilterset < DynamicImage::Filterset
  #     def self.process(image)
  #       image = image.sepiatone     # convert the image to sepia tones
  #     end
  #   end
  #
  # The filter set is now available for use in your application:
  #
  #   <%= dynamic_image_tag( @blog_post.image, :size => "120x100", :filterset => 'blog_thumbnails' ) %>
  #
  # === Applying effects by default
  #
  # If <tt>Image.get_oricessed</tt> is called without filters, it will look for a set named 'default'.
  # This means that you can automatically apply effects on resized images by defining a class called <tt>DefaultFilterset</tt>:
  #
  #   class DefaultFilterset < DynamicImage::Filterset
  #     def self.process(image)
  #       image = image.unsharp_mask  # apply unsharp mask on images by default.
  #     end
  #   end
  #
  # === Chaining filters
  #
  # You can only apply one filterset on an image, but compound filters can easily be created:
  #
  #   class CompoundFilterset < DynamicImage::Filterset
  #     def self.process(image)
  #       image = MyFirstFilterset.process(image)
  #       image = SomeOtherFilterset.process(image)
  #       image = DefaultFilterset.process(image)
  #     end
  #   end
  #
  class Filterset
    include ::Magick

    # Detect inheritance and store the new filterset in the lookup table.
    def self.inherited(sub)
      filter_name = sub.name.gsub!( /Filterset$/, '' ).underscore
      DynamicImage.filtersets[filter_name] = sub
    end

    # Get a Filterset class by name. Accepts a symbol or string, CamelCase and under_scores both work.
    def self.[](filter_name)
      filter_name = filter_name.to_s if filter_name.kind_of? Symbol
      filter_name = filter_name.underscore
      DynamicImage.filtersets[filter_name] || nil
    end

    # Process the image. This is a dummy method, you should overwrite it in your subclass.
    def self.process(image)
      # This is a stub
    end
    
  end
end