购物车商品服务费计算规则 算法购物车

购物车商品服务费计算规则：
总服务费 ＝ order_items明细费用加和 ＋ order服务费用
order服务费用（Bank Charge，Shipping Fee）
order_items服务费（Handling Fee，Global Shipping，Frontend QC，HNMR 等）
order服务费用由当前选中cart_item按kg数量转换统计重量，选取区间价格写入order_servers
order_items服务费，遍历cart_item的服务费写入order_servers

需要注意的是：
1，服务费没有记录到数据库之前，实际运算为准，记录到数据库后，以数据库中数值为准。（防止算法的改变影响历史数据）
2，购物车多件数费用＝ （单件成本＋ 单件服务费）＊ 件数 － （单件成本 ＊ 件数） － 实际服务费
3，多件数的实际服务费，例如算国际运费的时候，服务费是总重量重新计算的服务费。
4, 前台购物车是，总服务费不可编辑，所以展示的时候和create的时候都要单独调init_with_default_serves去算费用（不能在前台有可编辑的地方）；后台则需要可编辑费用，编辑后存储，取存储值，没编辑前取算法默认值。



路径：app/controllers/my_ichemical/orders_controller.rb 
action：new
订单创建时初始化：
@order.migrate_from_cart_items


路径：app/models/orders/order.rb

 def migrate_from_cart_items(cart_item_ids: nil)
    cart_items = user.cart_items.checked.default_where(myself: self.myself)
    cart_items.each do |cart_item|
      self.order_items.build cart_item_id: cart_item.id, good_type: cart_item.good_type, good_id: cart_item.good_id, quantity: cart_item.quantity
    end
    init_with_default_serves
  end

  def init_with_default_serves(cart_item_ids: nil)
    summary = CartItem.checked_items(user_id: self.user_id, myself: self.myself, extra: self.extra)
    summary.promote_charges.each do |promote_charge|
      self.order_promotes.build(promote_charge_id: promote_charge.id, promote_id: promote_charge.promote_id, amount: promote_charge.subtotal)
    end
    # 总订单的服务费根据重量算在总单子上
    summary.serve_charges.each do |serve_charge|
      self.order_serves.build(serve_charge_id: serve_charge.id, serve_id: serve_charge.serve_id, amount: serve_charge.subtotal)
    end
    compute_sum
  end

路径：app/models/cart_item.rb

def self.checked_items(user_id: nil, buyer_id: nil, session_id: nil, myself: nil, extra: {})
    if user_id
      @checked_items = CartItem.default_where(user_id: user_id, myself: myself).pending.checked
      buyer_id = User.find(user_id).buyer_id
      puts "-----> Checked User: #{user_id}"
    elsif buyer_id
      @checked_items = CartItem.default_where(buyer_id: buyer_id, myself: myself).pending.checked
      puts "-----> Checked Buyer: #{buyer_id}"
    elsif session_id
      @checked_items = CartItem.default_where(session_id: session_id, myself: myself).pending.checked
      puts "-----> Checked Session: #{session_id}"
    else
      @checked_items = CartItem.none
      puts "-----> Checked None!"
    end
    SummaryService.new(@checked_items, buyer_id: buyer_id, extra: extra)
  end

路径：app/models/concerns/summary_service.rb

def compute_serve
    @serve_charges = []

    QuantityServe.total.overall.each do |serve|
      charge = serve.compute_price(total_quantity, extra)
      @serve_charges << charge
    end

    @serve_price = checked_items.sum { |cart_item| cart_item.serve_price }
    @total_serve_price = serve_charges.sum { |i| i.subtotal }
end

路径：app/models/serve.rb

def compute_price(amount, extra_hash = {})
    extra_hash.stringify_keys!

    if self.contain_max
      range = { 'min-lte': amount.to_d, 'max-gte': amount.to_d }
    else
      range = { 'min-lte': amount.to_d, 'max-gt': amount.to_d }
    end
    
    query = range.merge(extra_hash.slice(*extra))
    charge = self.charges.default_where(query).first
    if charge && !(amount.to_d == 0 && self.id == 5)
      charge.subtotal = charge.final_price(amount)
      charge.default_subtotal = charge.subtotal
    else
      charge = self.charges.build
      charge.subtotal = 0
    end
    charge
  end


路径：app/models/orders/order_item.rb

# 子订单服务费在order_items创建时回调
cart_item.serve_charges.each do |serve_charge|
    op = self.order_serves.build(serve_charge_id: serve_charge.id, serve_id: serve_charge.serve_id, amount: serve_charge.subtotal)
    op.order = self.order
end