require 'hari/relation/sorted_set'

module Hari
  class Relation < Entity

    DIRECTIONS = %w(in out)

    attr_accessor :label, :start_node_id, :end_node_id

    validates :label, :start_node_id, :end_node_id, presence: true

    def start_node
      @start_node ||= Hari::Node.find(start_node_id)
    end

    def end_node
      @end_node ||= Hari::Node.find(end_node_id)
    end

    def key(direction = nil)
      case direction.try :to_s
      when nil   then "#{start_node_id}:#{label}:#{end_node_id}"
      when 'out' then "#{start_node_id}:#{label}:out"
      when 'in'  then "#{end_node_id}:#{label}:in"
      end
    end

    alias :generate_id :key

    def self.create(label, start_node, end_node, attrs = {})
      new(attrs).tap do |r|
        r.label = label
        r.start_node_id = Hari.node_key(start_node)
        r.end_node_id   = Hari.node_key(end_node)
        r.save
      end
    end

    def self.use!(backend)
      @backend = backend.kind_of?(Module) ? backend
       : "Hari::Relation::#{backend.to_s.camelize}".constantize
    end

    def self.backend
      @backend ||= Hari::Relation::SortedSet
    end

    def backend
      self.class.backend
    end

    def weight(direction)
      ::Time.now.to_f
    end

    def create
      super
      backend.create self
      self
    end

    def delete
      backend.delete self
      super
      self
    end

  end
end