require 'active_support/core_ext/array'
require 'active_support/core_ext/hash/except'
require 'active_support/core_ext/kernel/singleton_class'

module ActiveRecord
  # = Active Record \Named \Scopes
  module Scoping
    module Named
      extend ActiveSupport::Concern

      module ClassMethods
        # Returns an <tt>ActiveRecord::Relation</tt> scope object.
        #
        #   posts = Post.all
        #   posts.size # Fires "select count(*) from  posts" and returns the count
        #   posts.each {|p| puts p.name } # Fires "select * from posts" and loads post objects
        #
        #   fruits = Fruit.all
        #   fruits = fruits.where(color: 'red') if options[:red_only]
        #   fruits = fruits.limit(10) if limited?
        #
        # You can define a scope that applies to all finders using
        # <tt>ActiveRecord::Base.default_scope</tt>.
        def all
          if current_scope
            current_scope.clone
          else
            scope = relation
            scope.default_scoped = true
            scope
          end
        end

        # Collects attributes from scopes that should be applied when creating
        # an AR instance for the particular class this is called on.
        def scope_attributes # :nodoc:
          if current_scope
            current_scope.scope_for_create
          else
            scope = relation
            scope.default_scoped = true
            scope.scope_for_create
          end
        end

        # Are there default attributes associated with this scope?
        def scope_attributes? # :nodoc:
          current_scope || default_scopes.any?
        end

        # Adds a class method for retrieving and querying objects. A \scope
        # represents a narrowing of a database query, such as
        # <tt>where(color: :red).select('shirts.*').includes(:washing_instructions)</tt>.
        #
        #   class Shirt < ActiveRecord::Base
        #     scope :red, -> { where(color: 'red') }
        #     scope :dry_clean_only, -> { joins(:washing_instructions).where('washing_instructions.dry_clean_only = ?', true) }
        #   end
        #
        # The above calls to +scope+ define class methods <tt>Shirt.red</tt> and
        # <tt>Shirt.dry_clean_only</tt>. <tt>Shirt.red</tt>, in effect,
        # represents the query <tt>Shirt.where(color: 'red')</tt>.
        #
        # You should always pass a callable object to the scopes defined
        # with +scope+. This ensures that the scope is re-evaluated each
        # time it is called.
        #
        # Note that this is simply 'syntactic sugar' for defining an actual
        # class method:
        #
        #   class Shirt < ActiveRecord::Base
        #     def self.red
        #       where(color: 'red')
        #     end
        #   end
        #
        # Unlike <tt>Shirt.find(...)</tt>, however, the object returned by
        # <tt>Shirt.red</tt> is not an Array; it resembles the association object
        # constructed by a +has_many+ declaration. For instance, you can invoke
        # <tt>Shirt.red.first</tt>, <tt>Shirt.red.count</tt>,
        # <tt>Shirt.red.where(size: 'small')</tt>. Also, just as with the
        # association objects, named \scopes act like an Array, implementing
        # Enumerable; <tt>Shirt.red.each(&block)</tt>, <tt>Shirt.red.first</tt>,
        # and <tt>Shirt.red.inject(memo, &block)</tt> all behave as if
        # <tt>Shirt.red</tt> really was an Array.
        #
        # These named \scopes are composable. For instance,
        # <tt>Shirt.red.dry_clean_only</tt> will produce all shirts that are
        # both red and dry clean only. Nested finds and calculations also work
        # with these compositions: <tt>Shirt.red.dry_clean_only.count</tt>
        # returns the number of garments for which these criteria obtain.
        # Similarly with <tt>Shirt.red.dry_clean_only.average(:thread_count)</tt>.
        #
        # All scopes are available as class methods on the ActiveRecord::Base
        # descendant upon which the \scopes were defined. But they are also
        # available to +has_many+ associations. If,
        #
        #   class Person < ActiveRecord::Base
        #     has_many :shirts
        #   end
        #
        # then <tt>elton.shirts.red.dry_clean_only</tt> will return all of
        # Elton's red, dry clean only shirts.
        #
        # \Named scopes can also have extensions, just as with +has_many+
        # declarations:
        #
        #   class Shirt < ActiveRecord::Base
        #     scope :red, -> { where(color: 'red') } do
        #       def dom_id
        #         'red_shirts'
        #       end
        #     end
        #   end
        #
        # Scopes can also be used while creating/building a record.
        #
        #   class Article < ActiveRecord::Base
        #     scope :published, -> { where(published: true) }
        #   end
        #
        #   Article.published.new.published    # => true
        #   Article.published.create.published # => true
        #
        # \Class methods on your model are automatically available
        # on scopes. Assuming the following setup:
        #
        #   class Article < ActiveRecord::Base
        #     scope :published, -> { where(published: true) }
        #     scope :featured, -> { where(featured: true) }
        #
        #     def self.latest_article
        #       order('published_at desc').first
        #     end
        #
        #     def self.titles
        #       map(&:title)
        #     end
        #
        #   end
        #
        # We are able to call the methods like this:
        #
        #   Article.published.featured.latest_article
        #   Article.featured.titles

        def scope(name, body, &block)
          extension = Module.new(&block) if block

          # Check body.is_a?(Relation) to prevent the relation actually being
          # loaded by respond_to?
          if body.is_a?(Relation) || !body.respond_to?(:call)
            ActiveSupport::Deprecation.warn(
              "Using #scope without passing a callable object is deprecated. For " \
              "example `scope :red, where(color: 'red')` should be changed to " \
              "`scope :red, -> { where(color: 'red') }`. There are numerous gotchas " \
              "in the former usage and it makes the implementation more complicated " \
              "and buggy. (If you prefer, you can just define a class method named " \
              "`self.red`.)"
            )
          end

          singleton_class.send(:define_method, name) do |*args|
            options  = body.respond_to?(:call) ? unscoped { body.call(*args) } : body
            relation = all.merge(options)

            extension ? relation.extending(extension) : relation
          end
        end
      end
    end
  end
end
