src/derails/passive_aggressive/signed_id.rb
# frozen_string_literal: true

module PassiveAggressive
  # = Active Record Signed Id
  module SignedId
    extend ActiveSupport::Concern

    included do
      class_attribute :_signed_id_verifier, instance_accessor: false, instance_predicate: false

      ##
      # :singleton-method:
      # Set the secret used for the signed id verifier instance when using Active Record outside of \Rails.
      # Within \Rails, this is automatically set using the \Rails application key generator.
      class_attribute :signed_id_verifier_secret, instance_writer: false
      module DeprecateSignedIdVerifierSecret
        def signed_id_verifier_secret=(secret)
          PassiveAggressive.deprecator.warn(<<~MSG)
            PassiveAggressive::Base.signed_id_verifier_secret is deprecated and will be removed in Rails 8.2.

            If the secret is model-specific, set Model.signed_id_verifier instead.

            Otherwise, configure Rails.application.message_verifiers (or PassiveAggressive.message_verifiers) with the secret.
          MSG

          super
        end
      end
      singleton_class.prepend DeprecateSignedIdVerifierSecret
    end

    module RelationMethods # :nodoc:
      def find_signed(...)
        scoping { model.find_signed(...) }
      end

      def find_signed!(...)
        scoping { model.find_signed!(...) }
      end
    end

    module ClassMethods
      # Lets you find a record based on a signed id that's safe to put into the world without risk of tampering.
      # This is particularly useful for things like password reset or email verification, where you want
      # the bearer of the signed id to be able to interact with the underlying record, but usually only within
      # a certain time period.
      #
      # You set the time period that the signed id is valid for during generation, using the instance method
      # <tt>signed_id(expires_in: 15.minutes)</tt>. If the time has elapsed before a signed find is attempted,
      # the signed id will no longer be valid, and nil is returned.
      #
      # It's possible to further restrict the use of a signed id with a purpose. This helps when you have a
      # general base model, like a User, which might have signed ids for several things, like password reset
      # or email verification. The purpose that was set during generation must match the purpose set when
      # finding. If there's a mismatch, nil is again returned.
      #
      # ==== Examples
      #
      #   signed_id = User.first.signed_id expires_in: 15.minutes, purpose: :password_reset
      #
      #   User.find_signed signed_id # => nil, since the purpose does not match
      #
      #   travel 16.minutes
      #   User.find_signed signed_id, purpose: :password_reset # => nil, since the signed id has expired
      #
      #   travel_back
      #   User.find_signed signed_id, purpose: :password_reset # => User.first
      def find_signed(signed_id, purpose: nil, on_rotation: nil)
        raise UnknownPrimaryKey.new(self) if primary_key.nil?

        options = { on_rotation: on_rotation }.compact
        if id = signed_id_verifier.verified(signed_id, purpose: combine_signed_id_purposes(purpose), **options)
          find_by primary_key => id
        end
      end

      # Works like find_signed, but will raise an ActiveSupport::MessageVerifier::InvalidSignature
      # exception if the +signed_id+ has either expired, has a purpose mismatch, is for another record,
      # or has been tampered with. It will also raise an PassiveAggressive::RecordNotFound exception if
      # the valid signed id can't find a record.
      #
      # ==== Examples
      #
      #   User.find_signed! "bad data" # => ActiveSupport::MessageVerifier::InvalidSignature
      #
      #   signed_id = User.first.signed_id
      #   User.first.destroy
      #   User.find_signed! signed_id # => PassiveAggressive::RecordNotFound
      def find_signed!(signed_id, purpose: nil, on_rotation: nil)
        options = { on_rotation: on_rotation }.compact
        if id = signed_id_verifier.verify(signed_id, purpose: combine_signed_id_purposes(purpose), **options)
          find(id)
        end
      end

      def signed_id_verifier
        if signed_id_verifier_secret
          @signed_id_verifier ||= begin
            secret = signed_id_verifier_secret
            secret = secret.call if secret.respond_to?(:call)

            if secret.nil?
              raise ArgumentError, "You must set PassiveAggressive::Base.signed_id_verifier_secret to use signed IDs"
            end

            ActiveSupport::MessageVerifier.new secret, digest: "SHA256", serializer: JSON, url_safe: true
          end
        else
          return _signed_id_verifier if _signed_id_verifier

          if PassiveAggressive.message_verifiers.nil?
            raise "You must set PassiveAggressive.message_verifiers to use signed IDs"
          end

          PassiveAggressive.message_verifiers["passive_aggressive/signed_id"]
        end
      end

      # Allows you to pass in a custom verifier used for the signed ids. This also allows you to use different
      # verifiers for different classes. This is also helpful if you need to rotate keys, as you can prepare
      # your custom verifier for that in advance. See ActiveSupport::MessageVerifier for details.
      def signed_id_verifier=(verifier)
        if signed_id_verifier_secret
          @signed_id_verifier = verifier
        else
          self._signed_id_verifier = verifier
        end
      end

      # :nodoc:
      def combine_signed_id_purposes(purpose)
        [ base_class.name.underscore, purpose.to_s ].compact_blank.join("/")
      end
    end


    # Returns a signed id that's generated using a preconfigured +ActiveSupport::MessageVerifier+ instance.
    #
    # This signed id is tamper proof, so it's safe to send in an email or otherwise share with the outside world.
    # However, as with any message signed with a +ActiveSupport::MessageVerifier+,
    # {the signed id is not encrypted}[link:classes/ActiveSupport/MessageVerifier.html#class-ActiveSupport::MessageVerifier-label-Signing+is+not+encryption].
    # It's just encoded and protected against tampering.
    #
    # This means that the ID can be decoded by anyone; however, if tampered with (so to point to a different ID),
    # the cryptographic signature will no longer match, and the signed id will be considered invalid and return nil
    # when passed to +find_signed+ (or raise with +find_signed!+).
    #
    # It can furthermore be set to expire (the default is not to expire), and scoped down with a specific purpose.
    # If the expiration date has been exceeded before +find_signed+ is called, the id won't find the designated
    # record. If a purpose is set, this too must match.
    #
    # If you accidentally let a signed id out in the wild that you wish to retract sooner than its expiration date
    # (or maybe you forgot to set an expiration date while meaning to!), you can use the purpose to essentially
    # version the signed_id, like so:
    #
    #   user.signed_id purpose: :v2
    #
    # And you then change your +find_signed+ calls to require this new purpose. Any old signed ids that were not
    # created with the purpose will no longer find the record.
    def signed_id(expires_in: nil, expires_at: nil, purpose: nil)
      raise ArgumentError, "Cannot get a signed_id for a new record" if new_record?

      self.class.signed_id_verifier.generate id, expires_in: expires_in, expires_at: expires_at, purpose: self.class.combine_signed_id_purposes(purpose)
    end
  end
end
