# A relation defines a type of {Tie} between two {Actor Actors}. From social literature, 
# {Relation Relations} can be affective (friendship, liking, respect), formal or biological
# (authority, kinship), transfer of material resources (transactions, lending and borrowing),
# messages or conversations, physical connection and affiliation to same organizations.
#
# = Relation types defined in {SocialStream Social Stream}
#
# All the above cases could be supported in {SocialStream Social Stream}.
# Nevertheless, the following {Relation Relations} are defined. All of them inherit from the
# {Relation} class:
#
# {Relation::Custom}:: user-defined {Relation}. Every {SocialStream::Models::Subject Subject}
#                      is able to define their own {Relation::Custom Custom relation},
#                      giving them a custom name 
#                      (for instance: friend, colleague, partner, buddy) and {Permission Permissions}.
# {Relation::Public}:: default {Relation} for ocassional {Tie Ties}.
# {Relation::Reject}:: the {SocialStream::Models::Subject Subject} does not want to add the other
#                      as a contact. A new {Tie} is created using this {Relation}
#
# You can define new {Relation Relations} in your application. Just create a new class and
# inherit from {Relation}. This class already supports
# {http://api.rubyonrails.org/classes/ActiveRecord/Base.html#label-Single+table+inheritance Single Table Inheritance (STI)}.
#
# = Relations and link building
#
# When a {SocialStream::Models::Subject Subject} creates a new link to other
# {SocialStream::Models::Subject Subject}, she must specify one or serveral {Relation Relations}
# for that link. (friend, colleague, {Relation::Public} or {Relation::Reject}.
# A new {Tie} will be created for each {Relation}
#
# = Permissions
#
# {SocialStream::Models::Subject Subjects} assign {Permission permissions} to {Relation Relations}.
# This way, when establishing {Tie ties}, they are granting permissions to their contacts.
#
# See the documentation of {Permission} for more details on permission definition.
#
# = {Activity Activities} and {Relation Relations}
#
# Each {Activity} can be attached to one or more {Relation relations}.
# It sets the {Audience} that has access to it, and the {Permission Permissions} that rule that access.
#
class Relation < ActiveRecord::Base
  Positive = %w{ custom public }
  Negative = %w{ reject }

  belongs_to :actor

  has_many :relation_permissions, :dependent => :destroy
  has_many :permissions, :through => :relation_permissions

  has_many :ties, :dependent => :destroy
  has_many :contacts, :through => :ties

  has_many :audiences, :dependent => :destroy
  has_many :activities, :through => :audiences

  validates_presence_of :actor_id

  scope :actor, lambda { |a|
    where(:actor_id => Actor.normalize_id(a))
  }

  scope :mode, lambda { |st, rt|
    where(:sender_type => st, :receiver_type => rt)
  }

  before_create :initialize_sender_type

  class << self
    # Get relation from object, if possible
    #
    # Options::
    # sender:: The sender of the tie
    def normalize(r, options = {})
      case r
      when Relation
        r
      when String
        if options[:sender]
          options[:sender].relation_custom(r)
        else
          raise "Must provide a sender when looking up relations from name: #{ options[:sender] }"
        end
      when Integer
        Relation.find r
      when Array
        r.map{ |e| Relation.normalize(e, options) }
      else
        raise "Unable to normalize relation #{ r.class }: #{ r.inspect }"
      end
    end

    def normalize_id(r, options = {})
      case r
      when Integer
        r
      when Array
        r.map{ |e| Relation.normalize_id(e, options) }
      else
        normalize(r, options).id
      end
    end

    # Positive relation names: [ 'Relation::Custom', 'Relation::Public' ]
    def positive_names
      Positive.map{ |r| "Relation::#{ r.classify }" }
    end

    # Negative relations: [ 'Relation::Reject' ]
    def negative_names
      Negative.map{ |r| "Relation::#{ r.classify }" }
    end

    # All the relations that allow subject to perform action
    #
    # Options:
    #   in:: Limit possible relations to a set
    #   public_relations:: include also {Relation::Public} whose activities can always be read
    def allow(subject, action, object, options = {})
      q = 
        select("DISTINCT relations.*").
        joins(:contacts).
        joins(:permissions)

      conds =
        Permission.arel_table[:action].eq(action).and(Permission.arel_table[:object].eq(object))

      # Relation::Public permissions cannot be customized yet
      if action == 'read' && object == 'activity' && (options[:public].nil? || options[:public])
        conds = conds.or(Relation.arel_table[:type].eq('Relation::Public'))
      end

      # Add in condition
      if ! options[:in].nil?
        conds = conds.and(Relation.arel_table[:id].in(Relation.normalize_id(Array(options[:in]))))
      end

      # subject conditions
      conds = conds.and(Contact.arel_table[:receiver_id].eq(Actor.normalize_id(subject)))

      q.where(conds)
    end

    def allow?(*args)
      allow(*args).to_a.any?
    end
  end

  # Relation class scoped in the same mode that this relation
  def mode
    Relation.mode(sender_type, receiver_type)
  end

  # Is this {Relation} a Positive one?
  def positive?
    self.class.positive_names.include?(self.class.to_s)
  end

  private

  # Before create callback
  def initialize_sender_type
    return if actor.blank?

    self.sender_type = actor.subject_type
  end
end