openfoodnetwork/app/services/orders/fetch_adjustments_service.rb

# frozen_string_literal: true

# This service allows orders with eager-loaded adjustment objects to calculate various adjustment
# types without triggering additional queries.
#
# For example; `order.adjustments.shipping.sum(:amount)` would normally trigger a new query
# regardless of whether or not adjustments have been preloaded, as `#shipping` is an adjustment
# scope, eg; `scope :shipping, where(originator_type: 'Spree::ShippingMethod')`.
#
# Here the adjustment scopes are moved to a shared module, and `adjustments.loaded?` is used to
# check if the objects have already been fetched and initialized. If they have, `order.adjustments`
# will be an Array, and we can select the required objects without hitting the database. If not, it
# will fetch the adjustments via their scopes as normal.

module Orders
  class FetchAdjustmentsService
    include AdjustmentScopes

    def initialize(order)
      @order = order
    end

    def admin_and_handling_total
      admin_and_handling_fees.map(&:amount).sum
    end

    def payment_fee
      sum_adjustments "payment_fee"
    end

    def ship_total
      sum_adjustments "shipping"
    end

    private

    attr_reader :order

    def adjustments
      order.all_adjustments
    end

    def adjustments_eager_loaded?
      adjustments.loaded?
    end

    def sum_adjustments(scope)
      collect_adjustments(scope).map(&:amount).sum
    end

    def collect_adjustments(scope)
      if adjustments_eager_loaded?
        adjustment_scope = public_send("#{scope}_scope")

        # Adjustments are already loaded here, this block is using `Array#select`
        adjustments.select do |adjustment|
          match_by_scope(adjustment, adjustment_scope) && match_by_scope(adjustment, eligible_scope)
        end
      else
        adjustments.where(nil).eligible.public_send scope
      end
    end

    def admin_and_handling_fees
      if adjustments_eager_loaded?
        adjustments.select do |adjustment|
          match_by_scope(adjustment, eligible_scope) &&
            adjustment.originator_type == 'EnterpriseFee' &&
            adjustment.adjustable_type != 'Spree::LineItem'
        end
      else
        adjustments.eligible.
          where("originator_type = ? AND adjustable_type != ?", 'EnterpriseFee', 'Spree::LineItem')
      end
    end

    def match_by_scope(adjustment, scope)
      adjustment.public_send(scope.keys.first) == scope.values.first
    end
  end
end