Refactoring Tickets

- Tickets now independent from registration
- Implemented money gem
#419

app/models/ticket.rb

@@ -0,0 +1,59 @@
+class Ticket < ActiveRecord::Base
+  belongs_to :conference
+  has_many :ticket_purchases
+  has_many :buyers, -> { distinct }, through: :ticket_purchases, source: :user
+
+  attr_accessible :conference, :title, :url, :description, :conference_id, :price_cents, :price_currency, :price
+  monetize :price_cents, with_model_currency: :price_currency
+
+  # This validation is for the sake of simplicity.
+  # If we would allow different currencies per conference we also have to handle convertions between currencies!
+  validate :tickets_of_conference_have_same_currency
+
+  validates :price_cents, :price_currency, :title, presence: true
+
+  validates_numericality_of :price_cents, greater_than: 0
+
+  def bought?(user)
+    buyers.include?(user)
+  end
+
+  def paid?(user)
+    ticket_purchases.where(user_id: user.id, paid: false).count == 0
+  end
+
+  def quantity_bought_by(user)
+    result = ticket_purchases.where(user_id: user.id).first
+    result ? result.quantity : 0
+  end
+
+  def total_price(user)
+    quantity_bought_by(user) * price
+  end
+
+  def self.total_price(conference, user)
+    tickets = Ticket.where(conference_id: conference.id)
+    result = nil
+    begin
+      tickets.each do |ticket|
+        price = ticket.total_price(user)
+        if result
+          result +=  price unless price.zero?
+        else
+          result = price
+        end
+      end
+    rescue Money::Bank::UnknownRate
+      result = Money.new(-1, 'USD')
+    end
+    result ? result : Money.new(0, 'USD')
+  end
+
+  private
+
+  def tickets_of_conference_have_same_currency
+    unless Ticket.where(conference_id: conference_id).all?{|t| t.price_currency == self.price_currency }
+      errors.add(:price_currency, 'Currency is different from the exist ticktes of this conference.')
+    end
+  end
+end