require "neoteric-navigator/version"

module Neoteric
  module Navigator
    def self.included(base)
      base.extend ClassMethods
    end

    module ClassMethods
      def navigate(options = {})
        @navigator_options = options
      end

      def navigator_scope_option
        (@navigator_options[:scope] || :unscoped)
      end

      def navigator_field
        @navigator_options[:field]
      end

      def navigator_order_clause
        @navigator_options[:order] || navigator_field
      end
    end

    def next
      return @next unless @next.nil?
      @next = if self == last_next_item
                nil
              else
                future_posts.reject { |p| p == self }.last
              end
    end

    def prev
      return @prev unless @prev.nil?
      @prev = if self == last_prev_item
                nil
              else
                past_posts.reject { |p| p == self }.first
              end
    end

    private
    def last_next_item
      future_posts.first
    end

    def last_prev_item
      past_posts.last
    end

    def future_posts
      @future_posts ||= posts('>=')
    end

    def past_posts
      @past_posts ||= posts('<=')
    end

    def posts(operator)
      self.class.send(navigator_scope_option)
                .order(navigator_order_clause)
                .where("#{navigator_field.to_s} #{operator} ?",
                        send(navigator_field))
    end

    def navigator_field
      self.class.navigator_field
    end

    def navigator_scope_option
      self.class.navigator_scope_option
    end

    def navigator_order_clause
      self.class.navigator_order_clause
    end
  end
end