#
# The ActiveFacts Runtime API Concept class
# Copyright (c) 2008 Clifford Heath. Read the LICENSE file.
#
module ActiveFacts
  module API
    module Vocabulary; end

    # Concept contains methods that are added as class methods to all Value and Entity classes.
    module Concept
      # What vocabulary (Ruby module) does this concept belong to?
      def vocabulary
        modspace        # The module that contains this concept.
      end

      # Each Concept maintains a list of the Roles it plays:
      def roles(name = nil)
        unless instance_variable_defined? "@roles"
          @roles = RoleCollection.new     # Initialize and extend without warnings.
        end
        case name
        when nil
          @roles
        when Symbol, String
          # Search this class then all supertypes:
          unless role = @roles[name.to_sym]
            role = nil
            supertypes.each do |supertype|
                r = supertype.roles(name) rescue nil
                next unless r
                role = r
                break
              end
          end
          raise "Role #{basename}.#{name} is not defined" unless role
          # Bind the role if possible, but don't require it:
          role.resolve_player(vocabulary) rescue nil unless Class === role.player
          role
        else
          nil
        end
      end

      # Define a unary fact type attached to this concept; in essence, a boolean attribute.
      #
      # Example: maybe :is_ceo
      def maybe(role_name)
        realise_role(roles[role_name] = Role.new(TrueClass, nil, role_name))
      end

      # Define a binary fact type relating this concept to another,
      # with a uniqueness constraint only on this concept's role.
      # This method creates two accessor methods, one in this concept and one in the other concept.
      # Parameters after the role_name may be omitted if not required:
      # * role_name - a Symbol for the name of the role (this end of the relationship).
      # * other_player - A class name, Symbol or String naming a class, required if it doesn't match the role_name. Use a symbol or string if the class isn't defined yet, and the methods will be created later, when the class is first defined.
      # * :mandatory - if this role may not be NULL in a valid fact population. Mandatory constraints are only enforced during validation (e.g. before saving).
      # * :other_role_name - use if the role at the other end should have a name other than the default :all_<concept> or :all_<concept>_by_<role_name>
      def has_one(*args)
        role_name, related, mandatory, related_role_name = extract_binary_params(false, args)
        define_binary_fact_type(false, role_name, related, mandatory, related_role_name)
      end

      # Define a binary fact type joining this concept to another,
      # with uniqueness constraints in both directions, i.e. a one-to-one relationship
      # This method creates two accessor methods, one in this concept and one in the other concept.
      # Parameters after the role_name may be omitted if not required:
      # * role_name - a Symbol for the name of the role (this end of the relationship)
      # * other_player - A class name, Symbol or String naming a class, required if it doesn't match the role_name. Use a symbol or string if the class isn't defined yet, and the methods will be created later, when the class is first defined
      # * :mandatory - if this role may not be NULL in a valid fact population. Mandatory constraints are only enforced during validation (e.g. before saving)
      # * :other_role_name - use if the role at the other end should have a name other than the default :<concept> or :<concept>_by_<role_name>
      def one_to_one(*args)
        role_name, related, mandatory, related_role_name =
          extract_binary_params(true, args)
        define_binary_fact_type(true, role_name, related, mandatory, related_role_name)
      end

      # Access supertypes or add new supertypes; multiple inheritance.
      # With parameters (Class objects), it adds new supertypes to this class. Instances of this class will then have role methods for any new superclasses (transitively). Superclasses must be Ruby classes which are existing Concepts.
      # Without parameters, it returns the array of Concept supertypes (one by Ruby inheritance, any others as defined using this method)
      def supertypes(*concepts)
        class_eval do
          @supertypes ||= []
          all_supertypes = supertypes_transitive
          concepts.each do |concept|
            next if all_supertypes.include? concept
            case concept
            when Class
              @supertypes << concept
            when Symbol
              # No late binding here:
              @supertypes << (concept = vocabulary.const_get(concept.to_s.camelcase))
            else
              raise "Illegal supertype #{concept.inspect} for #{self.class.basename}"
            end

            # Realise the roles (create accessors) of this supertype.
            # REVISIT: The existing accessors at the other end will need to allow this class as role player
            # REVISIT: Need to check all superclass roles recursively, unless we hit a common supertype
            #puts "Realising concept #{concept.name} in #{basename}"
            realise_supertypes(concept, all_supertypes)
          end
          [(superclass.vocabulary && superclass rescue nil), *@supertypes].compact
        end
      end

      # Return the array of all Concept supertypes, transitively.
      def supertypes_transitive
        class_eval do
          supertypes = []
          supertypes << superclass if Module === (superclass.vocabulary rescue nil)
          supertypes += (@supertypes ||= [])
          supertypes.inject([]) {|a, t|
              next if a.include?(t)
              a += [t]
              a += t.supertypes_transitive rescue []
            }.uniq
        end
      end

      # Every new role added or inherited comes through here:
      def realise_role(role) #:nodoc:
        #puts "Realising role #{role.player.basename rescue role.player}.#{role.name} in #{basename}"

        if (!role.counterpart)
          # Unary role
          define_unary_role_accessor(role)
        elsif (role.unique)
          define_single_role_accessor(role, role.counterpart.unique)
        else
          define_array_role_accessor(role)
        end
      end

      # REVISIT: Use method_missing to catch all_some_role_by_other_role_and_third_role, to sort_by those roles?

      private

      def realise_supertypes(concept, all_supertypes = nil)
        all_supertypes ||= supertypes_transitive
        s = concept.supertypes
        #puts "realising #{concept.basename} supertypes #{s.inspect} of #{basename}"
        s.each {|t|
            next if all_supertypes.include? t
            realise_supertypes(t, all_supertypes)
            all_supertypes << t
          }
        #puts "Realising roles of #{concept.basename} in #{basename}"
        realise_roles(concept)
      end

      # Realise all the roles of a concept on this concept, used when a supertype is added:
      def realise_roles(concept)
        concept.roles.each do |role_name, role|
          realise_role(role)
        end
      end

      # Shared code for both kinds of binary fact type (has_one and one_to_one)
      def define_binary_fact_type(one_to_one, role_name, related, mandatory, related_role_name)
        # puts "#{self}.#{role_name} is to #{related.inspect}, #{mandatory ? :mandatory : :optional}, related role is #{related_role_name}"

        roles[role_name] = role = Role.new(related, nil, role_name, mandatory)

        # There may be a forward reference here where role_name is a Symbol,
        # and the block runs later when that Symbol is bound to the concept.
        when_bound(related, self, role_name, related_role_name) do |target, definer, role_name, related_role_name|
          if (one_to_one)
            target.roles[related_role_name] = role.counterpart = Role.new(definer, role, related_role_name, false)
          else
            target.roles[related_role_name] = role.counterpart = Role.new(definer, role, related_role_name, false, false)
          end
          #puts "Realising role pair #{definer.basename}.#{role_name} <-> #{target.basename}.#{related_role_name}"
          realise_role(role)
          target.realise_role(role.counterpart)
        end
      end

      def define_unary_role_accessor(role)
        # puts "Defining #{basename}.#{role_name} as unary"
        class_eval do
          define_method "#{role.name}=" do |value|
            #puts "Setting #{self.class.name} #{object_id}.@#{role.name} to #{(value ? true : nil).inspect}"
            instance_variable_set("@#{role.name}", value ? true : nil)
            # REVISIT: Provide a way to find all instances playing/not playing this role
            # Analogous to true.all_thing_by_role_name...
          end
        end
        define_single_role_getter(role)
      end

      def define_single_role_getter(role)
        class_eval do
          define_method role.name do
            instance_variable_get("@#{role.name}") rescue nil
          end
        end
      end

      # REVISIT: Add __add_to(constellation) and __remove(constellation) here?
      def define_single_role_accessor(role, one_to_one)
        # puts "Defining #{basename}.#{role.name} to #{role.player.basename} (#{one_to_one ? "assigning" : "populating"} #{role.counterpart.name})"
        define_single_role_getter(role)

        if (one_to_one)
          # This gets called to assign nil to the related role in the old correspondent:
          # value is included here so we can check that the correct value is being nullified, if necessary
          nullify_reference = lambda{|from, role_name, value| from.send("#{role_name}=".to_sym, nil) }

          # This gets called to replace an old single value for a new one in the related role of a new correspondent
          assign_reference = lambda{|from, role_name, old_value, value| from.send("#{role_name}=".to_sym, value) }

          define_single_role_setter(role, nullify_reference, assign_reference)
        else
          # This gets called to delete this object from the role value array in the old correspondent
          delete_reference = lambda{|from, role_name, value| from.send(role_name).__delete(value) }

          # This gets called to replace an old value by a new one in the related role value array of a new correspondent
          replace_reference = lambda{|from, role_name, old_value, value| 
              array = from.send(role_name)
              array.__replace(array - [old_value].compact + [value])
            }

          define_single_role_setter(role, delete_reference, replace_reference)
        end
      end

      def define_single_role_setter(role, deassign_old, assign_new)
        class_eval do
          define_method "#{role.name}=" do |value|
            role_var = "@#{role.name}"

            # If role.player isn't bound to a class yet, bind it.
            role.resolve_player(self.class.vocabulary) unless Class === role.player

            # Get old value, and jump out early if it's unchanged:
            old = instance_variable_get(role_var) rescue nil
            return if old == value        # Occurs during one_to_one assignment, for example

            value = role.adapt(constellation, value) if value
            return if old == value        # Occurs when same value is assigned

            # DEBUG: puts "assign #{self.class.basename}.#{role.name} <-> #{value.inspect}.#{role.counterpart.name}#{old ? " (was #{old.inspect})" : ""}"

            # REVISIT: Defend against changing identifying roles, and decide what to do.

            # puts "Setting binary #{role_var} to #{value.verbalise}"
            instance_variable_set(role_var, value)

            # De-assign/remove "self" at the old other end too:
            deassign_old.call(old, role.counterpart.name, self) if old

            # Assign/add "self" at the other end too:
            assign_new.call(value, role.counterpart.name, old, self) if value
          end
        end
      end

      def define_array_role_accessor(role)
        class_eval do
          define_method "#{role.name}" do
            unless (r = instance_variable_get(role_var = "@#{role.name}") rescue nil)
              r = instance_variable_set(role_var, RoleValueArray.new)
            end
            # puts "fetching #{self.class.basename}.#{role.name} array, got #{r.class}, first is #{r[0] ? r[0].verbalise : "nil"}"
            r
          end
        end
      end

      # Extract the parameters to a role definition and massage them into the right shape.
      #
      # This function returns an array:
      # [ role_name,
      # related,
      # mandatory,
      # related_role_name ]
      #
      # Role naming rule:
      #   "all_" if there may be more than one (only ever on related end)
      #   Role Name:
      # If a role name is defined at this end:
      #   Role Name
      # else:
      #   Leading Adjective
      #   Role player name (not role name)
      #   Trailing Adjective
      # "_by_<other_role_name>" if other_role_name != this role player's name, and not other_player_this_player
      def extract_binary_params(one_to_one, args)
        # Params:
        #   role_name (Symbol)
        #   other player (Symbol or Class)
        #   mandatory (:mandatory)
        #   other end role name if any (Symbol),
        role_name = nil
        related = nil
        mandatory = false
        related_role_name = nil
        role_player = self.basename.snakecase

        # Get the role name first:
        case a = args.shift
        when Symbol, String
          role_name = a.to_sym
        when Class
          role_name = a.name.snakecase.to_sym
        else
          raise "Illegal first parameter to role: #{a.inspect}"
        end
        # puts "role_name = #{role_name.inspect}"

        # The related class might be forward-referenced, so handle a Symbol/String instead of a Class.
        case related_name = a = args.shift
        when Class
          related = a
          related_name = a.basename
        when :mandatory, Numeric
          args.unshift(a)       # Oops, undo.
          related_name =
          related = role_name
        when Symbol, String
          related = a
        else
          related = role_name
        end
        related_name ||= role_name
        related_name = related_name.to_s.snakecase

        # resolve the Symbol to a Class now if possible:
        resolved = vocabulary.concept(related) rescue nil
        related = resolved if resolved
        # puts "related = #{related.inspect}"

        if args[0] == :mandatory
          mandatory = true
          args.shift
        end

        if Symbol == args[0]
          related_role_name = args.shift
        end

        reading = args[0]

        # Avoid a confusing mismatch:
        # Note that if you have a role "supervisor" and a sub-class "Supervisor", this'll bitch.
        if (Class === related && (indicated = vocabulary.concept(role_name)) && indicated != related)
          raise "Role name #{role_name} indicates a different player #{indicated} than specified"
        end

        # puts "Calculating related method name for related_role_name=#{related_role_name.inspect}, related_name=#{related_name.inspect}, role_player=#{role_player.inspect}, role_name=#{role_name.inspect}:"

        related_role_name ||= (role_player || "")  # REVISIT: Add adjectives here
        unless one_to_one
          related_role_name = "all_#{role_player}" +
            if related_name == role_name.to_s || role_name.to_s == "#{role_player}_#{related_name}"
              ""
            else
              "_by_#{role_name}"
            end
        end

        [ role_name,
          related,
          mandatory,
          related_role_name.to_sym 
        ]
      end

      def when_bound(concept, *args, &block)
        case concept
        when Class
          block.call(concept, *args)    # Execute block in the context of the concept
        when Symbol
          vocabulary.__delay(concept.to_s.camelcase(true), args, &block)
        when String     # Arrange for this to happen later
          vocabulary.__delay(concept, args, &block)
        else
          raise "Delayed binding not possible for #{concept.inspect}"
        end
      end
    end
  end
end