require 'product_in_checkout.rb'

class Checkout
  class InvalidItem < StandardError; end

  def initialize(shop:)
    @shop = shop
    @items = []
  end

  def add(product_id:, quantity: 1)
    product = @shop.product_by_id(product_id)

    raise InvalidItem unless product

    new_or_existing_product_in_checkout(product).add_quantity(quantity)
  end

  def remove(product_id:, quantity: 1)
    product = @shop.product_by_id(product_id)

    raise InvalidItem unless product

    product_in_checkout = existing_product_in_checkout(product)

    return false unless product_in_checkout

    product_in_checkout.remove_quantity(quantity)

    trim_empty_items
  end

  def items
    @items
  end

  def item_quantities
    @items.map { |item| [item.product_id, item.quantity] }.to_h
  end

  def clear
    @items = []
  end

  def total
    @items.reduce(0.00) { |running_total, item| running_total + item.total }
  end

  private

  def existing_product_in_checkout(product)
    @items.find { |item| item.product_id == product.id }
  end

  def new_or_existing_product_in_checkout(product)
    product_in_checkout = existing_product_in_checkout(product)
    unless product_in_checkout
      product_in_checkout = ProductInCheckout.new(product: product)
      @items.push(product_in_checkout)
    end

    product_in_checkout
  end

  def trim_empty_items
    @items = @items.filter { |item| item.quantity > 0 }
  end
end