base_event.rb

module Event
  class BaseEvent
    attr_reader :id
    attr_reader :stream_id
    attr_reader :event_id
    attr_reader :payload
    attr_reader :metadata

    def initialize(id: nil, stream_id: nil, event_id: SecureRandom.uuid, payload: {}, metadata: {})
      @id = id
      @stream_id = stream_id
      @event_id = event_id
      @payload = payload
      @metadata = metadata
      @metadata[:timestamp] ||= Time.current

      validate
    end

    def to_hash
      {
        stream_id: stream_id,
        event_id: event_id,
        event_type: self.class.name,
        payload: payload,
        metadata: metadata
      }
    end

    def validate
      raise ArgumentError, 'BaseEvent: missing stream_id' if stream_id.nil?

      # The event_id attribute gets initialized to a RFC 4122 random UUID,
      # which has a hex-grouped-with-hyphens representation like:
      #
      #    example: 2d931510-d99f-494a-8c67-87feb05e1594
      #    counts:  12345678 1234 1234 1234 123456789012

      uuid = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/

      raise ArgumentError, 'BaseEvent: invalid stream_id' unless stream_id =~ uuid

      raise ArgumentError, 'BaseEvent: invalid event_id' unless event_id =~ uuid

      begin
        DateTime.parse(timestamp) unless timestamp.is_a?(Time)
      rescue ArgumentError
        raise ArgumentError, 'BaseEvent: invalid timestamp'
      end
    end
  end
end