module TemporalTables
  # This is mixed into all History classes.
  module TemporalClass
    def self.included(base)
      base.class_eval do
        base.extend ClassMethods

        self.table_name += "_h"

        cattr_accessor :visited_associations
        @@visited_associations = []

        # The at_value field stores the time from the query that yielded
        # this record.
        attr_accessor :at_value

        class << self
          prepend STIWithHistory

          delegate :at, to: :all
        end

        # Iterates all associations, makes sure their history classes are
        # created and initialized, and modifies the associations to point
        # to the target classes' history classes.
        def self.temporalize_associations!
          reflect_on_all_associations.dup.each do |association|
            unless @@visited_associations.include?(association.name) || association.options[:polymorphic]
              @@visited_associations << association.name

              # Calling .history here will ensure that the history class
              # for this association is created and initialized
              clazz = association.class_name.constantize.history

              # Recreate the association, updating it to point at the
              # history class.  The foreign key is explicitly set since it's
              # inferred from the class_name, but shouldn't be in this case.
              send(association.macro, association.name,
                association.options.merge(
                  class_name:  clazz.name,
                  foreign_key: association.foreign_key,
                  primary_key: clazz.orig_class.primary_key
                )
              )
            end
          end
        end
      end
    end

    module STIWithHistory
      def sti_name
        super.sub /History$/, ""
      end

      def find_sti_class(type_name)
        type_name += "History" unless type_name =~ /History\Z/

        begin
          super
        rescue ActiveRecord::SubclassNotFound
          superclass.send(:find_sti_class, type_name)
        end
      end
    end

    module ClassMethods
      def orig_class
        name.sub(/History$/, "").constantize
      end

      def descends_from_active_record?
        superclass.descends_from_active_record?
      end

      def build_temporal_constraint(at_value)
        arel_table[:eff_to].gteq(at_value).and(
          arel_table[:eff_from].lteq(at_value)
        )
      end
    end

    def orig_class
      self.class.orig_class
    end

    def orig_id
      attributes[orig_class.primary_key]
    end

    def orig_obj
      @orig_obj ||= orig_class.find_by_id orig_id
    end

    def prev
      @prev ||= history.where(self.class.arel_table[:eff_from].lt(eff_from)).last
    end

    def next
      @next ||= history.where(self.class.arel_table[:eff_from].gt(eff_from)).first
    end
  end
end