require 'cgi'

module ActiveMerchant
  class PostData < Hash
    class_inheritable_accessor :required_fields, :instance_writer => false
    self.required_fields = []
  
    def []=(key, value)
      return if value.blank? && !required?(key)
      super
    end
  
    def to_post_data
      collect { |key, value| "#{key}=#{CGI.escape(value.to_s)}" }.join("&")  
    end
  
    alias_method :to_s, :to_post_data
  
    private
    def required?(key)
      required_fields.include?(key)
    end
  end
end