require 'thread'

module ActiveRecord
  # = Active Record Reflection
  module Reflection # :nodoc:
    extend ActiveSupport::Concern

    included do
      class_attribute :reflections
      class_attribute :aggregate_reflections
      self.reflections = {}
      self.aggregate_reflections = {}
    end

    def self.create(macro, name, scope, options, ar)
      case macro
      when :has_many, :belongs_to, :has_one
        klass = options[:through] ? ThroughReflection : AssociationReflection
      when :composed_of
        klass = AggregateReflection
      end

      klass.new(macro, name, scope, options, ar)
    end

    def self.add_reflection(ar, name, reflection)
      ar.reflections = ar.reflections.merge(name.to_s => reflection)
    end

    def self.add_aggregate_reflection(ar, name, reflection)
      ar.aggregate_reflections = ar.aggregate_reflections.merge(name.to_s => reflection)
    end

    # \Reflection enables to interrogate Active Record classes and objects
    # about their associations and aggregations. This information can,
    # for example, be used in a form builder that takes an Active Record object
    # and creates input fields for all of the attributes depending on their type
    # and displays the associations to other objects.
    #
    # MacroReflection class has info for AggregateReflection and AssociationReflection
    # classes.
    module ClassMethods
      # Returns an array of AggregateReflection objects for all the aggregations in the class.
      def reflect_on_all_aggregations
        aggregate_reflections.values
      end

      # Returns the AggregateReflection object for the named +aggregation+ (use the symbol).
      #
      #   Account.reflect_on_aggregation(:balance) # => the balance AggregateReflection
      #
      def reflect_on_aggregation(aggregation)
        aggregate_reflections[aggregation.to_s]
      end

      # Returns an array of AssociationReflection objects for all the
      # associations in the class. If you only want to reflect on a certain
      # association type, pass in the symbol (<tt>:has_many</tt>, <tt>:has_one</tt>,
      # <tt>:belongs_to</tt>) as the first parameter.
      #
      # Example:
      #
      #   Account.reflect_on_all_associations             # returns an array of all associations
      #   Account.reflect_on_all_associations(:has_many)  # returns an array of all has_many associations
      #
      def reflect_on_all_associations(macro = nil)
        association_reflections = reflections.values
        macro ? association_reflections.select { |reflection| reflection.macro == macro } : association_reflections
      end

      # Returns the AssociationReflection object for the +association+ (use the symbol).
      #
      #   Account.reflect_on_association(:owner)             # returns the owner AssociationReflection
      #   Invoice.reflect_on_association(:line_items).macro  # returns :has_many
      #
      def reflect_on_association(association)
        reflections[association.to_s]
      end

      # Returns an array of AssociationReflection objects for all associations which have <tt>:autosave</tt> enabled.
      def reflect_on_all_autosave_associations
        reflections.values.select { |reflection| reflection.options[:autosave] }
      end
    end

    # Base class for AggregateReflection and AssociationReflection. Objects of
    # AggregateReflection and AssociationReflection are returned by the Reflection::ClassMethods.
    #
    #   MacroReflection
    #     AggregateReflection
    #     AssociationReflection
    #       ThroughReflection
    class MacroReflection
      # Returns the name of the macro.
      #
      # <tt>composed_of :balance, class_name: 'Money'</tt> returns <tt>:balance</tt>
      # <tt>has_many :clients</tt> returns <tt>:clients</tt>
      attr_reader :name

      # Returns the macro type.
      #
      # <tt>composed_of :balance, class_name: 'Money'</tt> returns <tt>:composed_of</tt>
      # <tt>has_many :clients</tt> returns <tt>:has_many</tt>
      attr_reader :macro

      attr_reader :scope

      # Returns the hash of options used for the macro.
      #
      # <tt>composed_of :balance, class_name: 'Money'</tt> returns <tt>{ class_name: "Money" }</tt>
      # <tt>has_many :clients</tt> returns <tt>{}</tt>
      attr_reader :options

      attr_reader :active_record

      attr_reader :plural_name # :nodoc:

      def initialize(macro, name, scope, options, active_record)
        @macro         = macro
        @name          = name
        @scope         = scope
        @options       = options
        @active_record = active_record
        @klass         = options[:class]
        @plural_name   = active_record.pluralize_table_names ?
                            name.to_s.pluralize : name.to_s
      end

      def autosave=(autosave)
        @automatic_inverse_of = false
        @options[:autosave] = autosave
      end

      # Returns the class for the macro.
      #
      # <tt>composed_of :balance, class_name: 'Money'</tt> returns the Money class
      # <tt>has_many :clients</tt> returns the Client class
      def klass
        @klass ||= class_name.constantize
      end

      # Returns the class name for the macro.
      #
      # <tt>composed_of :balance, class_name: 'Money'</tt> returns <tt>'Money'</tt>
      # <tt>has_many :clients</tt> returns <tt>'Client'</tt>
      def class_name
        @class_name ||= (options[:class_name] || derive_class_name).to_s
      end

      # Returns +true+ if +self+ and +other_aggregation+ have the same +name+ attribute, +active_record+ attribute,
      # and +other_aggregation+ has an options hash assigned to it.
      def ==(other_aggregation)
        super ||
          other_aggregation.kind_of?(self.class) &&
          name == other_aggregation.name &&
          !other_aggregation.options.nil? &&
          active_record == other_aggregation.active_record
      end

      private
        def derive_class_name
          name.to_s.camelize
        end
    end


    # Holds all the meta-data about an aggregation as it was specified in the
    # Active Record class.
    class AggregateReflection < MacroReflection #:nodoc:
      def mapping
        mapping = options[:mapping] || [name, name]
        mapping.first.is_a?(Array) ? mapping : [mapping]
      end
    end

    # Holds all the meta-data about an association as it was specified in the
    # Active Record class.
    class AssociationReflection < MacroReflection #:nodoc:
      # Returns the target association's class.
      #
      #   class Author < ActiveRecord::Base
      #     has_many :books
      #   end
      #
      #   Author.reflect_on_association(:books).klass
      #   # => Book
      #
      # <b>Note:</b> Do not call +klass.new+ or +klass.create+ to instantiate
      # a new association object. Use +build_association+ or +create_association+
      # instead. This allows plugins to hook into association object creation.
      def klass
        @klass ||= active_record.send(:compute_type, class_name)
      end

      attr_reader :type, :foreign_type

      def initialize(macro, name, scope, options, active_record)
        super
        @collection = :has_many == macro
        @automatic_inverse_of = nil
        @type         = options[:as] && "#{options[:as]}_type"
        @foreign_type = options[:foreign_type] || "#{name}_type"
        @constructable = calculate_constructable(macro, options)
        @association_scope_cache = {}
        @scope_lock = Mutex.new
      end

      def association_scope_cache(conn, owner)
        key = conn.prepared_statements
        if options[:polymorphic]
          key = [key, owner.read_attribute(@foreign_type)]
        end
        @association_scope_cache[key] ||= @scope_lock.synchronize {
          @association_scope_cache[key] ||= yield
        }
      end

      # Returns a new, unsaved instance of the associated class. +attributes+ will
      # be passed to the class's constructor.
      def build_association(attributes, &block)
        klass.new(attributes, &block)
      end

      def constructable? # :nodoc:
        @constructable
      end

      def table_name
        klass.table_name
      end

      def quoted_table_name
        klass.quoted_table_name
      end

      def join_table
        @join_table ||= options[:join_table] || derive_join_table
      end

      def foreign_key
        @foreign_key ||= options[:foreign_key] || derive_foreign_key
      end

      def primary_key_column
        klass.columns_hash[klass.primary_key]
      end

      def association_foreign_key
        @association_foreign_key ||= options[:association_foreign_key] || class_name.foreign_key
      end

      # klass option is necessary to support loading polymorphic associations
      def association_primary_key(klass = nil)
        options[:primary_key] || primary_key(klass || self.klass)
      end

      def active_record_primary_key
        @active_record_primary_key ||= options[:primary_key] || primary_key(active_record)
      end

      def counter_cache_column
        if options[:counter_cache] == true
          "#{active_record.name.demodulize.underscore.pluralize}_count"
        elsif options[:counter_cache]
          options[:counter_cache].to_s
        end
      end

      def check_validity!
        check_validity_of_inverse!
      end

      def check_validity_of_inverse!
        unless options[:polymorphic]
          if has_inverse? && inverse_of.nil?
            raise InverseOfAssociationNotFoundError.new(self)
          end
        end
      end

      def check_preloadable!
        return unless scope

        if scope.arity > 0
          ActiveSupport::Deprecation.warn <<-WARNING
The association scope '#{name}' is instance dependent (the scope block takes an argument).
Preloading happens before the individual instances are created. This means that there is no instance
being passed to the association scope. This will most likely result in broken or incorrect behavior.
Joining, Preloading and eager loading of these associations is deprecated and will be removed in the future.
          WARNING
        end
      end
      alias :check_eager_loadable! :check_preloadable!

      def join_id_for(owner) #:nodoc:
        key = (source_macro == :belongs_to) ? foreign_key : active_record_primary_key
        owner[key]
      end

      def through_reflection
        nil
      end

      def source_reflection
        self
      end

      # A chain of reflections from this one back to the owner. For more see the explanation in
      # ThroughReflection.
      def chain
        [self]
      end

      def nested?
        false
      end

      # An array of arrays of scopes. Each item in the outside array corresponds to a reflection
      # in the #chain.
      def scope_chain
        scope ? [[scope]] : [[]]
      end

      alias :source_macro :macro

      def has_inverse?
        inverse_name
      end

      def inverse_of
        return unless inverse_name

        @inverse_of ||= klass.reflect_on_association inverse_name
      end

      def polymorphic_inverse_of(associated_class)
        if has_inverse?
          if inverse_relationship = associated_class.reflect_on_association(options[:inverse_of])
            inverse_relationship
          else
            raise InverseOfAssociationNotFoundError.new(self, associated_class)
          end
        end
      end

      # Returns whether or not this association reflection is for a collection
      # association. Returns +true+ if the +macro+ is either +has_many+ or
      # +has_and_belongs_to_many+, +false+ otherwise.
      def collection?
        @collection
      end

      # Returns whether or not the association should be validated as part of
      # the parent's validation.
      #
      # Unless you explicitly disable validation with
      # <tt>validate: false</tt>, validation will take place when:
      #
      # * you explicitly enable validation; <tt>validate: true</tt>
      # * you use autosave; <tt>autosave: true</tt>
      # * the association is a +has_many+ association
      def validate?
        !options[:validate].nil? ? options[:validate] : (options[:autosave] == true || macro == :has_many)
      end

      # Returns +true+ if +self+ is a +belongs_to+ reflection.
      def belongs_to?
        macro == :belongs_to
      end

      def association_class
        case macro
        when :belongs_to
          if options[:polymorphic]
            Associations::BelongsToPolymorphicAssociation
          else
            Associations::BelongsToAssociation
          end
        when :has_many
          if options[:through]
            Associations::HasManyThroughAssociation
          else
            Associations::HasManyAssociation
          end
        when :has_one
          if options[:through]
            Associations::HasOneThroughAssociation
          else
            Associations::HasOneAssociation
          end
        end
      end

      def polymorphic?
        options.key? :polymorphic
      end

      VALID_AUTOMATIC_INVERSE_MACROS = [:has_many, :has_one, :belongs_to]
      INVALID_AUTOMATIC_INVERSE_OPTIONS = [:conditions, :through, :polymorphic, :foreign_key]

      protected

        def actual_source_reflection # FIXME: this is a horrible name
          self
        end

      private

        def calculate_constructable(macro, options)
          case macro
          when :belongs_to
            !options[:polymorphic]
          when :has_one
            !options[:through]
          else
            true
          end
        end

        # Attempts to find the inverse association name automatically.
        # If it cannot find a suitable inverse association name, it returns
        # nil.
        def inverse_name
          options.fetch(:inverse_of) do
            if @automatic_inverse_of == false
              nil
            else
              @automatic_inverse_of ||= automatic_inverse_of
            end
          end
        end

        # returns either nil or the inverse association name that it finds.
        def automatic_inverse_of
          if can_find_inverse_of_automatically?(self)
            inverse_name = ActiveSupport::Inflector.underscore(active_record.name).to_sym

            begin
              reflection = klass.reflect_on_association(inverse_name)
            rescue NameError
              # Give up: we couldn't compute the klass type so we won't be able
              # to find any associations either.
              reflection = false
            end

            if valid_inverse_reflection?(reflection)
              return inverse_name
            end
          end

          false
        end

        # Checks if the inverse reflection that is returned from the
        # +automatic_inverse_of+ method is a valid reflection. We must
        # make sure that the reflection's active_record name matches up
        # with the current reflection's klass name.
        #
        # Note: klass will always be valid because when there's a NameError
        # from calling +klass+, +reflection+ will already be set to false.
        def valid_inverse_reflection?(reflection)
          reflection &&
            klass.name == reflection.active_record.name &&
            can_find_inverse_of_automatically?(reflection)
        end

        # Checks to see if the reflection doesn't have any options that prevent
        # us from being able to guess the inverse automatically. First, the
        # <tt>inverse_of</tt> option cannot be set to false. Second, we must
        # have <tt>has_many</tt>, <tt>has_one</tt>, <tt>belongs_to</tt> associations.
        # Third, we must not have options such as <tt>:polymorphic</tt> or
        # <tt>:foreign_key</tt> which prevent us from correctly guessing the
        # inverse association.
        #
        # Anything with a scope can additionally ruin our attempt at finding an
        # inverse, so we exclude reflections with scopes.
        def can_find_inverse_of_automatically?(reflection)
          reflection.options[:inverse_of] != false &&
            VALID_AUTOMATIC_INVERSE_MACROS.include?(reflection.macro) &&
            !INVALID_AUTOMATIC_INVERSE_OPTIONS.any? { |opt| reflection.options[opt] } &&
            !reflection.scope
        end

        def derive_class_name
          class_name = name.to_s
          class_name = class_name.singularize if collection?
          class_name.camelize
        end

        def derive_foreign_key
          if belongs_to?
            "#{name}_id"
          elsif options[:as]
            "#{options[:as]}_id"
          else
            active_record.name.foreign_key
          end
        end

        def derive_join_table
          [active_record.table_name, klass.table_name].sort.join("\0").gsub(/^(.*_)(.+)\0\1(.+)/, '\1\2_\3').gsub("\0", "_")
        end

        def primary_key(klass)
          klass.primary_key || raise(UnknownPrimaryKey.new(klass))
        end
    end

    # Holds all the meta-data about a :through association as it was specified
    # in the Active Record class.
    class ThroughReflection < AssociationReflection #:nodoc:
      delegate :foreign_key, :foreign_type, :association_foreign_key,
               :active_record_primary_key, :type, :to => :source_reflection

      def initialize(macro, name, scope, options, active_record)
        super
        @source_reflection_name = options[:source]
      end

      # Returns the source of the through reflection. It checks both a singularized
      # and pluralized form for <tt>:belongs_to</tt> or <tt>:has_many</tt>.
      #
      #   class Post < ActiveRecord::Base
      #     has_many :taggings
      #     has_many :tags, through: :taggings
      #   end
      #
      #   class Tagging < ActiveRecord::Base
      #     belongs_to :post
      #     belongs_to :tag
      #   end
      #
      #   tags_reflection = Post.reflect_on_association(:tags)
      #   tags_reflection.source_reflection
      #   # => <ActiveRecord::Reflection::AssociationReflection: @macro=:belongs_to, @name=:tag, @active_record=Tagging, @plural_name="tags">
      #
      def source_reflection
        through_reflection.klass.reflect_on_association(source_reflection_name)
      end

      # Returns the AssociationReflection object specified in the <tt>:through</tt> option
      # of a HasManyThrough or HasOneThrough association.
      #
      #   class Post < ActiveRecord::Base
      #     has_many :taggings
      #     has_many :tags, through: :taggings
      #   end
      #
      #   tags_reflection = Post.reflect_on_association(:tags)
      #   tags_reflection.through_reflection
      #   # => <ActiveRecord::Reflection::AssociationReflection: @macro=:has_many, @name=:taggings, @active_record=Post, @plural_name="taggings">
      #
      def through_reflection
        active_record.reflect_on_association(options[:through])
      end

      # Returns an array of reflections which are involved in this association. Each item in the
      # array corresponds to a table which will be part of the query for this association.
      #
      # The chain is built by recursively calling #chain on the source reflection and the through
      # reflection. The base case for the recursion is a normal association, which just returns
      # [self] as its #chain.
      #
      #   class Post < ActiveRecord::Base
      #     has_many :taggings
      #     has_many :tags, through: :taggings
      #   end
      #
      #   tags_reflection = Post.reflect_on_association(:tags)
      #   tags_reflection.chain
      #   # => [<ActiveRecord::Reflection::ThroughReflection: @macro=:has_many, @name=:tags, @options={:through=>:taggings}, @active_record=Post>,
      #         <ActiveRecord::Reflection::AssociationReflection: @macro=:has_many, @name=:taggings, @options={}, @active_record=Post>]
      #
      def chain
        @chain ||= begin
          a = source_reflection.chain
          b = through_reflection.chain
          chain = a + b
          chain[0] = self # Use self so we don't lose the information from :source_type
          chain
        end
      end

      # Consider the following example:
      #
      #   class Person
      #     has_many :articles
      #     has_many :comment_tags, through: :articles
      #   end
      #
      #   class Article
      #     has_many :comments
      #     has_many :comment_tags, through: :comments, source: :tags
      #   end
      #
      #   class Comment
      #     has_many :tags
      #   end
      #
      # There may be scopes on Person.comment_tags, Article.comment_tags and/or Comment.tags,
      # but only Comment.tags will be represented in the #chain. So this method creates an array
      # of scopes corresponding to the chain.
      def scope_chain
        @scope_chain ||= begin
          scope_chain = source_reflection.scope_chain.map(&:dup)

          # Add to it the scope from this reflection (if any)
          scope_chain.first << scope if scope

          through_scope_chain = through_reflection.scope_chain.map(&:dup)

          if options[:source_type]
            through_scope_chain.first <<
              through_reflection.klass.where(foreign_type => options[:source_type])
          end

          # Recursively fill out the rest of the array from the through reflection
          scope_chain + through_scope_chain
        end
      end

      # The macro used by the source association
      def source_macro
        source_reflection.source_macro
      end

      # A through association is nested if there would be more than one join table
      def nested?
        chain.length > 2
      end

      # We want to use the klass from this reflection, rather than just delegate straight to
      # the source_reflection, because the source_reflection may be polymorphic. We still
      # need to respect the source_reflection's :primary_key option, though.
      def association_primary_key(klass = nil)
        # Get the "actual" source reflection if the immediate source reflection has a
        # source reflection itself
        actual_source_reflection.options[:primary_key] || primary_key(klass || self.klass)
      end

      # Gets an array of possible <tt>:through</tt> source reflection names in both singular and plural form.
      #
      #   class Post < ActiveRecord::Base
      #     has_many :taggings
      #     has_many :tags, through: :taggings
      #   end
      #
      #   tags_reflection = Post.reflect_on_association(:tags)
      #   tags_reflection.source_reflection_names
      #   # => [:tag, :tags]
      #
      def source_reflection_names
        options[:source] ? [options[:source]] : [name.to_s.singularize, name].uniq
      end

      def source_reflection_name # :nodoc:
        return @source_reflection_name if @source_reflection_name

        names = [name.to_s.singularize, name].collect { |n| n.to_sym }.uniq
        names = names.find_all { |n|
          through_reflection.klass.reflect_on_association(n)
        }

        if names.length > 1
          example_options = options.dup
          example_options[:source] = source_reflection_names.first
          ActiveSupport::Deprecation.warn <<-eowarn
Ambiguous source reflection for through association.  Please specify a :source
directive on your declaration like:

  class #{active_record.name} < ActiveRecord::Base
    #{macro} :#{name}, #{example_options}
  end

          eowarn
        end

        @source_reflection_name = names.first
      end

      def source_options
        source_reflection.options
      end

      def through_options
        through_reflection.options
      end

      def check_validity!
        if through_reflection.nil?
          raise HasManyThroughAssociationNotFoundError.new(active_record.name, self)
        end

        if through_reflection.options[:polymorphic]
          raise HasManyThroughAssociationPolymorphicThroughError.new(active_record.name, self)
        end

        if source_reflection.nil?
          raise HasManyThroughSourceAssociationNotFoundError.new(self)
        end

        if options[:source_type] && source_reflection.options[:polymorphic].nil?
          raise HasManyThroughAssociationPointlessSourceTypeError.new(active_record.name, self, source_reflection)
        end

        if source_reflection.options[:polymorphic] && options[:source_type].nil?
          raise HasManyThroughAssociationPolymorphicSourceError.new(active_record.name, self, source_reflection)
        end

        if macro == :has_one && through_reflection.collection?
          raise HasOneThroughCantAssociateThroughCollection.new(active_record.name, self, through_reflection)
        end

        check_validity_of_inverse!
      end

      protected

      def actual_source_reflection # FIXME: this is a horrible name
        source_reflection.actual_source_reflection
      end

      private
        def derive_class_name
          # get the class_name of the belongs_to association of the through reflection
          options[:source_type] || source_reflection.class_name
        end
    end
  end
end