Privilege # ensure that Privilege class is loaded

# This module provides access control behavior to ActiveRecord models.
# The class into which it is included must provide a '#client' method
# the result of which will be used as the context for authorization
# checks.
module AccessControl

  # Indicates if +an_account+ is allowed to know of the existence of this
  # object.
  def visible_to?(an_account)
    raise NotImplementedError
  end

  # Indicates if +an_account+ should allowed to create this object.
  # This should be called before calling +#save+ on a new model object
  # and the save should be performed only if true is returned.
  def creatable_by?(an_account)
    raise NotImplementedError
  end

  # Indicates if +an_account+ should be allowed to modify this object.
  # This should before performing any actions which result in the
  # database being updated.  Such action should only be performed if
  # true is returned.
  def modifiable_by?(an_account)
    raise NotImplementedError
  end

  def self.included(a_class)
    a_class.extend(ActiveRecordClassMethods)

    a_class.send(:visibility_privilege, "view_#{a_class.name.underscore}")
    a_class.send(:creation_privilege, "create_#{a_class.name.underscore}")
    a_class.send(:modification_privilege, "modify_#{a_class.name.underscore}")
  end

  module ActiveRecordClassMethods
    protected

    # Declares that object of the class on which this is called are
    # visible to users that have the specified privilege.
    def visibility_privilege(privilege_name)
      define_method(:visible_to?) do |an_account|
        an_account.has_privilege_at?(privilege_name, client)
      end
    end

    # Declares that objects of this class are creatable by accounts who
    # hold the +privilege+ at the client which owns this resource.
    def creation_privilege(privilege_name)
      define_method(:creatable_by?) do |an_account|
        an_account.has_privilege_at?(privilege_name, client)
      end
      (class << self; self; end).instance_eval do
        define_method(:creatable_by?) do |an_account|
          !an_account.clients_at_which_account_has(Privilege(privilege_name)).empty?
        end
      end
    end

    # Declares that objects of this class are modifiable by accounts
    # who hold the +privilege+ at the client which owns this resource.
    def modification_privilege(privilege_name)
      define_method(:modifiable_by?) do |an_account|
        an_account.has_privilege_at?(privilege_name, client)
      end
    end

    # Adds optional +:visible_to => an_account+ option to +#find(:all,
    # options)+.  This option will exclude any objects which are not
    # visible to the specified account from the returned collection.
    def find_every_with_visible_to_handling(options)
      if account = options[:visible_to]
        find_every_without_visible_to_handling(options).select {|rec| rec.visible_to?(account)}
      else
        find_every_without_visible_to_handling(options)
      end
    end

    # Validates that the options passed to +#find()+ are all valid
    # options
    def validate_find_options(options)
      options.assert_valid_keys((class << ::ActiveRecord::Base; self; end)::VALID_FIND_OPTIONS + [:visible_to])
    end

    def self.extended(ar_class)
      (class << ar_class; self; end).alias_method_chain :find_every, :visible_to_handling
    end
  end

end