module CustomFields

  class CustomField
    include Mongoid::Document
    include Mongoid::Timestamps
  
    ## fields ##
    field :label, :type => String
    field :_alias, :type => String # need it for instance in: > asset.description (description being a custom field)
    field :_name, :type => String
    field :kind, :type => String
    field :position, :type => Integer, :default => 0
      
    ## validations ##
    validates_presence_of :label, :kind
    validate :uniqueness_of_label
      
    ## methods ##
    
    %w{String Text Email Boolean Date File}.each do |kind|
      define_method "#{kind.downcase}?" do
        self.kind == kind
      end
    end
  
    def field_type
      case self.kind
        when 'String', 'Text', 'Email' then String
        else
          self.kind.constantize
      end
    end
  
    def apply(object, association_name)
      return unless self.valid?
      
      # trick mongoid
      object.class_eval { def meta; (class << self; self; end); end }
      object.meta.fields = object.fields.clone 
      object.meta.send(:define_method, :fields) { self.meta.fields }
      
      object.meta.field self._name, :type => self.field_type
      object.class_eval <<-EOF
        alias :#{self.safe_alias} :#{self._name}
        alias :#{self.safe_alias}= :#{self._name}=
      EOF
    end
  
    def safe_alias
      self.set_alias
      self._alias 
    end
  
    protected
    
    def uniqueness_of_label
      duplicate = self.siblings.detect { |f| f.label == self.label && f._id != self._id }
      if not duplicate.nil?
        self.errors.add(:label, :taken)
      end
    end
  
    def set_unique_name!
      self._name ||= "custom_field_#{self.increment_counter!}"
    end
    
    def set_alias
      return if self.label.blank? && self._alias.blank?
      self._alias ||= self.label.clone
      self._alias.slugify!(:downcase => true, :underscore => true)
    end
  
    def increment_counter!
      next_value = (self._parent.send(:"#{self.association_name}_counter") || 0) + 1
      self._parent.send(:"#{self.association_name}_counter=", next_value)
      next_value
    end
  
    def siblings
      self._parent.send(self.association_name)
    end
  end
  
end