require 'dm-core'
 
# An item is identified by a name, for example, Bread
class Item
  include DataMapper::Resource
 
  property      :name,                  String, :key => true, :length => 100
  has n,        :stacks
 
  # recipes which produce this item
  has n,        :producing_recipes,     :model => 'Recipe',
                                        :child_key => [:product_name]
 
  # recipes which use this item as an ingredient
  def consuming_recipes
    Recipe.all.select do |recipe|
      recipe.ingredients.any? do |ingredient|
        ingredient == self
      end
    end
  end
 
  # items which are products of consuming_recipes
  def derivatives
    consuming_recipes.map(&:product)
  end
 
  # items which are ingredients in producing_recipes
  def materials
    producing_recipes.inject do |items, recipe|
      items + recipe.ingredients
    end
  end
end
 
 
# A stack contains a number of the same item
class Stack
  include DataMapper::Resource
  property      :id,                    Serial
  property      :quantity,              Integer
  belongs_to    :item
  belongs_to    :bag
end
 
# A bag contains a number of stacks
class Bag
  include DataMapper::Resource
  property      :id,                    Serial
  property      :type,                  Discriminator
  has n,        :stacks
  has n,        :items,                 :through => :stacks
 
  # retrieve the quantity of the given item in the bag, when 0 returns default
  def [](item, default=0)
    if stack = stacks.first('item.name' => item.name)
      stack.quantity
    else
      default
    end
  end
 
  # set the quantity of the given item in the bag
  def []=(item, quantity)
    if stack = stacks.first('item.name' => item.name)
      stack.quantity = quantity
    else
      stacks << Stack.new(:item_name => item.name, :quantity => quantity)
    end
  end
 
  # return a hash of item => quantity
  def quantities
    ret = {}
    stacks.each {|stack| ret[stack.item] = stack.quantity}
  end
end
 
# A recipe has one product item, and a few ingredient items each with a
# quantity, for example, Bread = 2 Flour + 1 Yeast + 1 Water
class Recipe < Bag
#  include DataMapper::Resource
  belongs_to    :product,               :model => 'Item',
                                        :child_key => [:product_name]
  alias_method  :ingredients,           :items
end
 
# An identity is identified by an url, and has an inventory
class Identity
  include DataMapper::Resource
 
  property      :url,                   String, :key => true, :length => 100
  has 1,        :inventory
  has n,        :items,                 :through => :inventory
end
 
# An inventory has a number of different items, and belongs to an identity
class Inventory < Bag
#  include DataMapper::Resource
  belongs_to    :identity
end