# frozen_string_literal: true

class ShoppingCart
  module Item
    module Contract
      cannot_be_nan = ->(val) { val.respond_to?(:nan?) and val.nan? and '%p cannot be nan' }
      cannot_be_inf = ->(val) { val.respond_to?(:infinite?) and val.infinite? and '%p cannot be infinite' }
      must_be_positive = ->(label) { ->(val) { val.positive? or "#{label} (%p) must be positive" } }

      PricePerUnit = ::BCDD::Contract[::Numeric] & cannot_be_nan & cannot_be_inf & must_be_positive['price per unit']
      Quantity     = ::BCDD::Contract[::Integer] & must_be_positive['quantity']
      Name         = ::BCDD::Contract[::String]  & ->(val) { val.empty? and 'item name must be filled' }

      NameAndData = ::BCDD::Contract.pairs(Name => { quantity: Quantity, price_per_unit: PricePerUnit })
    end
  end

  module Items
    module Contract
      extend ::BCDD::Contract[::Hash] & ->(items, errors) do
        return if items.empty?

        Item::Contract::NameAndData[items].then { |it| it.valid? or errors.concat(it.errors) }
      end
    end
  end

  def initialize(items = {})
    @items = +Items::Contract[items]
  end

  def add_item(item_name, quantity, price_per_unit)
    Items::Contract.invariant(@items) do |items|
      item_name = +Item::Contract::Name[item_name]

      item = items[item_name] ||= { quantity: 0, price_per_unit: 0 }

      item[:price_per_unit] = +Item::Contract::PricePerUnit[price_per_unit]
      item[:quantity]      += +Item::Contract::Quantity[quantity]
    end
  end

  def remove_item(item_name, quantity)
    Items::Contract.invariant(@items) do |items|
      item_name = +Item::Contract::Name[item_name]
      quantity  = +Item::Contract::Quantity[quantity]

      item = items[item_name]

      ::BCDD::Contract.assert!(item_name, 'item (%p) not found')
      ::BCDD::Contract.refute!(item_name, 'item (%p) not enough quantity to remove') { quantity > item[:quantity] }

      item[:quantity] -= quantity

      item[:quantity].tap { |number| items.delete(item_name) if number.zero? }
    end
  end

  def total_price
    (+Items::Contract[@items]).sum { |_name, data| data[:quantity] * data[:price_per_unit] }
  end
end