module Ecom
  module Core
    class MeasurementUnit < ApplicationRecord
      METRIC = 'Metric'.freeze
      IMPERIAL = 'Imperial'.freeze
      SYSTEM_OF_MEASURMENT = [METRIC, IMPERIAL].freeze

      # commonly used physical quantities in construction
      LENGTH = 'Length'.freeze
      MASS = 'Mass'.freeze
      TIME = 'Time'.freeze
      CURRENT = 'Current'.freeze
      TEMPRATURE = 'Temprature'.freeze

      AREA = 'Area'.freeze
      VOLUME = 'Volume'.freeze
      ENERGY = 'Energy'.freeze
      DENSITY = 'DENSITY'.freeze

      PHYSICAL_QUANTITIES = [LENGTH, MASS, TIME, CURRENT, TEMPRATURE, AREA, VOLUME, ENERGY, DENSITY].freeze

      validates :name, :abbrivation, :physical_quantity,
                :conversion_factor, :system_of_measurement, presence: true

      validates :is_si_unit, inclusion: { in: [true, false] }

      validates :system_of_measurement, inclusion: SYSTEM_OF_MEASURMENT
      validates :physical_quantity, inclusion: PHYSICAL_QUANTITIES

      validate :si_unit_with_conversion_factor
      validate :si_unit_system_of_measurement_and_physical_quantity

      def si_unit_with_conversion_factor
        if is_si_unit && conversion_factor != 1
          errors.add(:base, 'Conversion factor for an SI unit has to be 1')
        elsif !is_si_unit && conversion_factor == 1
          errors.add(:base, 'Only SI units can have a conversion factor 1')
        end
      end

      # scope si unit with system of measurement and physical quantity
      def si_unit_system_of_measurement_and_physical_quantity
        return if system_of_measurement.nil? || physical_quantity.nil?

        existing_record = MeasurementUnit
                          .where(system_of_measurement: system_of_measurement,
                                 physical_quantity: physical_quantity, is_si_unit: true).first
        return unless (new_record? && existing_record.present?) || (persisted? && existing_record != self)

        errors.add(:is_si_unit,
                   'There exist an si unit of measurement for the given physical quantity and system of measurement')
      end
    end
  end
end