module MongoModel
  module DocumentExtensions
    module Validations
      module ClassMethods
        # Validates whether the value of the specified attributes are unique across the system. Useful for making sure that only one user
        # can be named "davidhh".
        #
        #   class Person < MongoModel::Document
        #     validates_uniqueness_of :user_name, :scope => :account_id
        #   end
        #
        # It can also validate whether the value of the specified attributes are unique based on multiple scope parameters. For example,
        # making sure that a teacher can only be on the schedule once per semester for a particular class.
        #
        #   class TeacherSchedule < MongoModel::Document
        #     validates_uniqueness_of :teacher_id, :scope => [:semester_id, :class_id]
        #   end
        #
        # When the document is created, a check is performed to make sure that no document exists in the database with the given value for the specified
        # attribute (that maps to a property). When the document is updated, the same check is made but disregarding the document itself.
        #
        # Configuration options:
        # * <tt>:message</tt> - Specifies a custom error message (default is: "has already been taken").
        # * <tt>:scope</tt> - One or more properties by which to limit the scope of the uniqueness constraint.
        # * <tt>:case_sensitive</tt> - Looks for an exact match. Ignored by non-text columns (+true+ by default).
        # * <tt>:allow_nil</tt> - If set to true, skips this validation if the attribute is +nil+ (default is +false+).
        # * <tt>:allow_blank</tt> - If set to true, skips this validation if the attribute is blank (default is +false+).
        # * <tt>:if</tt> - Specifies a method, proc or string to call to determine if the validation should
        #   occur (e.g. <tt>:if => :allow_validation</tt>, or <tt>:if => Proc.new { |user| user.signup_step > 2 }</tt>). The
        #   method, proc or string should return or evaluate to a true or false value.
        # * <tt>:unless</tt> - Specifies a method, proc or string to call to determine if the validation should
        #   not occur (e.g. <tt>:unless => :skip_validation</tt>, or <tt>:unless => Proc.new { |user| user.signup_step <= 2 }</tt>). The
        #   method, proc or string should return or evaluate to a true or false value.
        #
        # === Concurrency and integrity
        #
        # Note that this validation method does not have the same race condition suffered by ActiveRecord and other ORMs.
        # A unique index is added to the collection to ensure that the collection never ends up in an invalid state.
        def validates_uniqueness_of(*attr_names)
          configuration = { :case_sensitive => true }
          configuration.update(attr_names.extract_options!)
          
          # Enable safety checks on save
          self.save_safely = true
          
          # Create unique indexes to deal with race condition
          attr_names.each do |attr_name|
            if configuration[:case_sensitive]
              index *[attr_name] + Array(configuration[:scope]) << { :unique => true }
            else
              lowercase_key = "_lowercase_#{attr_name}"
              before_save { attributes[lowercase_key] = send(attr_name).downcase }
              index *[lowercase_key] + Array(configuration[:scope]) << { :unique => true }
            end
          end
          
          validates_each(attr_names, configuration) do |record, attr_name, value|
            unique_scope = scoped
            
            if configuration[:case_sensitive] || !value.is_a?(String)
              unique_scope = unique_scope.where(attr_name => value)
            else
              unique_scope = unique_scope.where("_lowercase_#{attr_name}" => value.downcase)
            end
            
            Array(configuration[:scope]).each do |scope|
              unique_scope = unique_scope.where(scope => record.send(scope))
            end
            
            unique_scope = unique_scope.where(:id.ne => record.id) unless record.new_record?
            
            if unique_scope.any?
              record.errors.add(attr_name, :taken, :default => configuration[:message], :value => value)
            end
          end
        end
      end
    end
  end
end