# encoding: utf-8

module Policy

  # Interface for the class that follows policies
  module Follower

    # Methods to be added to the follower class
    module ClassMethods

      # Declares a policy to be followed
      #
      # Mutates the object by adding an item to its {#policies}.
      #
      # @param [Symbol] name
      #
      # @return [:follows_policy] the name of the method
      def follows_policy(name)
        policies.add name

        :follows_policy
      end

      # Declares policies to be followed
      #
      # Mutates the object by adding items to its {#policies}.
      #
      # @param [Symbol, Array<Symbol>] names
      #
      # @return [:follows_policies] the name of the method
      def follows_policies(*names)
        names.each(&method(:follows_policy))

        :follows_policies
      end

      # @!attribute [r] policies
      # The collection of followed policies
      #
      # @return [Policy::Follower::Policies]
      def policies
        @policies ||= Policies.new(self)
      end

    end

    # Checks whether an object follows all its policies or subset of policies
    #
    # @overload follow_policies?()
    #   Checks whether an object follows all registered policies
    #
    # @overload follow_policies?(names)
    #   Checks whether an object follows given policies
    #
    #   @param [#to_sym, Array<#to_sym>] names
    #
    #   @raise [Policy::Follower::NameError]
    #     if the policy is not registered by name
    #
    # @raise [NoMethodError]
    #   if the name not implemented as follower's instance method
    # @raise [ViolationError]
    #   if the policy is violated by the follower
    #
    # @return [true] if no exception being raised
    def follow_policies?(*names)
      __policies__
        .subset(names)                       # raises NameError
        .map(&method(:__send__))             # raises NoMethodError
        .each(&method(:__validate_policy__)) # raises ViolationError
      true
    end

    # Checks whether an object follows given policy
    #
    # @param [#to_sym] name
    #   the name of the policy to follow
    #
    # @raise  (see #follow_policies?)
    #
    # @return (see #follow_policies?)
    def follow_policy?(name)
      follow_policies? name
    end

    # @private
    def self.included(klass)
      klass.instance_eval { extend ClassMethods }
    end

    private

    def __validate_policy__(policy)
      fail ViolationError.new(self, policy) unless policy.valid?
    end

    def __policies__
      self.class.policies
    end

  end # module Follower

end # module Policy