boom

app/models/digital.rb

@@ -0,0 +1,10 @@
+class Digital < ActiveRecord::Base
+
+  belongs_to :variant
+  has_many :digital_links, :dependent => :destroy
+
+  has_attached_file :attachment, :path => ":rails_root/private/digitals/:id/:basename.:extension"
+
+  # TODO: Limit the attachment to one single file. Paperclip supports many by default :/
+    
+end

app/models/digital_link.rb

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+class DigitalLink < ActiveRecord::Base
+  
+  belongs_to :digital
+  belongs_to :line_item
+
+  before_validation :set_defaults, :on => :create
+  
+  # Can this link stil be used? It is valid if it's less than 24 hours old and was not accessed more than 3 times
+  def authorizable?
+    self.created_at > 1.day.ago and self.access_counter < 3
+  end
+  
+  # This method should be called when a download is initiated.
+  # It returns +true+ or +false+ depending on whether the authorization is granted.
+  def authorize!
+    authorizable? && increment!(:access_counter) ? true : false
+  end
+  
+  private
+  
+  # Populating the secret automatically and zero'ing the access_counter (otherwise it might turn out to be NULL)
+  def set_defaults
+    self.secret = SecureRandom.hex(15)
+    self.access_counter = 0
+  end
+
+end

app/models/line_item_decorator.rb

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+LineItem.class_eval do
+  
+  has_many :digital_links
+  
+  after_save :create_digital_links, :if => :digital?
+  
+  # Is this item digital?
+  def digital?
+    variant.digital?
+  end
+  
+  private
+  
+  # Create the download link for this item if it is digital.
+  def create_digital_links
+    digital_links.delete_all
+    self.quantity.times do
+      digital_links.create!(:digital => variant.digital)
+    end
+  end
+  
+end

app/models/order_decorator.rb

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+Order.class_eval do
+  
+  # Are all products/variants of this Order to be downloaded by the customer?
+  def digital?
+    line_items.map { |item| return false unless item.digital? }
+    true
+  end
+  
+  # Determine which method to use for shipping of digital products.
+  def digital_shipping_method
+    rates = rate_hash
+    # If there is a shipping method has "Download" in its name then we take that one.
+    rates.each { |rate| return rate if rate[:name].downcase.include?('download') }
+    # Other than that, we take the first one that we find that doesn't cost anything.
+    rates.each { |rate| return rate if rate[:cost] == 0 }
+    # Well, at this point we have a problem. No shipping method is cost-free or called "download".
+    nil
+  end
+
+end

app/models/variant_decorator.rb

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+Variant.class_eval do
+  
+  has_one :digital, :dependent => :destroy
+  after_save :destroy_digital, :if => :deleted?
+  
+  # Is this variant to be downloaded by the customer?
+  def digital?
+    digital.present?
+  end
+  
+  private
+  
+  # Spree never deleted Digitals, that's why ":dependent => :destroy" won't work on Digital.
+  # We need to delete the Digital manually here as soon as the Variant is nullified.
+  # Otherwise you'll have orphan Digitals (and their attached files!) associated with unused Variants. 
+  def destroy_digital
+    digital.destroy
+  end
+
+end