aromajoin/jp-shipping-rate

# frozen_string_literal: true

# external modules
require 'singleton'
require 'yaml'

require_relative 'jp_shipping_rate/version'

#
# This is a singleton class provides interface API calculate EMS shipping rate
# from Japan.
# There are several basic functions such as look-up international shipping rate,
# domestic shipping rate, look-up region of a country,
# Japan's area of a prefecture.
#
# Usage:
# shipping_rate = JPShippingRate.instance
# shipping_rate.international(1500, "US")
# => 8500
# or
#
# Note: Just support domestic from Kyoto for now.
# shipping_rate.domestic(140, "okinawa")
# => 3200
#
class JPShippingRate
  include Singleton

  def initialize
    @rates = load_shipping_rates
    @regions = load_regions
    @jp_areas = load_domestic_areas
  end

  # For internaltion shipping (EMS):
  # 1. How much weight of the parcel?
  # 2. Identify country region from country code of destination
  # 3. Look up the shipping rate for weight and region
  # 4. plus base extra charges for internaltional shipping and insurrance charge?
  def international(weight, to_country_code)
    region = region_of_country(to_country_code)
    rate = 0
    rate += international_rate(weight, region) if weight > 0
    rate + international_extra_charges
  end

  # For domestic shipping:
  # 1. default size = 120 for now, parcel size is total of length, width and height
  # 2. state of destination is in lowercase format, e.g. kyoto, tokyo, osaka
  # 3. calculate cost with given size and state
  # 4. plus extra charges for domestic shipping and insurrance charge?
  def domestic(size = 120, to_state)
    area = area_of_prefecture(to_state)
    rate = 0
    rate += domestic_rate(size, area) if size > 0
    rate + domestic_extra_charges
  end

  # Find region of the country
  # with given country code from the order info.
  def region_of_country(country_code = 'JP')
    result = @regions['asia'].to_s
    @regions.each do |region, countries|
      countries.each do |country|
        return result = region.to_s unless country[country_code].nil?
      end
    end
  rescue NoMethodError
    return 'asia'
  end

  # Find domestic area of Japan's states
  # Such as: Hokkaido, Kanto, Okinawa, ...
  def area_of_prefecture(state_name = 'kyoto')
    result = 'okinawa'
    @jp_areas.each do |area, states|
      states.each do |state|
        return result = area.to_s unless state[state_name].nil?
      end
    end
  rescue NoMethodError
    return 'hokkaido'
  end

  # Calculate an extra charge for internation EMS
  # with a base extra charge and insurrance condition?
  def international_extra_charges(base = 3_500, insurrance = false)
    extra = base
    extra += 3_000 if insurrance
    extra
  end

  # Calculate an extra charge for domestic shipping
  # with a base extra charge and insurrance condition?
  def domestic_extra_charges(base = 850, insurrance = false)
    extra = base
    extra += 1_000 if insurrance
    extra
  end

  # Calculate EMS rate with given params
  # @param: weight::Integer - Weight of the parcel.
  # @param: region::String - Regions that is defined by Japan Post service
  def international_rate(weight, region)
    rate = 0
    @rates['international_ems'].each do |w, r|
      next if w.to_i < weight
      r.each do |r_rate|
        return rate = r_rate[region] unless r_rate[region].nil?
      end
    end
    rate
  end

  # Calculate domestic shipping rate with given params
  # @param size::Integer - size of total of length, width and height
  # @param area::String - Areas of Japan (Okinawa, Hokkaido, Kanto,...)
  def domestic_rate(size = 100, area = 'okinawa')
    rate = 0
    @rates['domestic_parcel'].each do |w, r|
      next if w.to_i < size
      r.each do |r_rate|
        return rate = r_rate[area] unless r_rate[area].nil?
      end
    end
    rate
  end

  private

  def root_path
    File.expand_path '../..', __FILE__
  end

  # Load data of EMS shipping rates
  def load_shipping_rates
    YAML.load_file("#{root_path}/config/rates.yml")
  end

  # Load data of region of countries
  def load_regions
    YAML.load_file("#{root_path}/config/countries.yml")
  end

  # Load Japan areas
  def load_domestic_areas
    YAML.load_file("#{root_path}/config/japan_areas.yml")
  end
end