batch-mapper.rb

require "bundler/inline"

gemfile do
  source "https://rubygems.org"
  gem "ruby_event_store",
      github: "RailsEventStore/rails_event_store",
      ref: "45e685ecab7fe3f59e0fee07ac0630bbef00c840"
end

SomeEventWithPersonalInfo =
  Class.new(RubyEventStore::Event) do
    def self.encryption_schema
      { personal_info: ->(data) { data.fetch(:user_id) } }
    end
  end

class KeysRepository < RubyEventStore::Mappers::InMemoryEncryptionKeyRepository
  def fetch_keys(identifiers)
    # just created keys for the given identifiers if not exists
    # here shall be an API call to KMS storage
    identifiers.each do |identifier|
      create(identifier) unless key_of(identifier)
    end
  end
end

class CustomEncryptionMapper < RubyEventStore::Mappers::BatchMapper
  def initialize
    @keys_repository = KeysRepository.new
    super(
      RubyEventStore::Mappers::EncryptionMapper.new(
        @keys_repository,
        serializer: RubyEventStore::Serializers::YAML,
        forgotten_data: RubyEventStore::Mappers::ForgottenData.new
      )
    )
  end

  def records_to_events(records)
    # fetch keys identifiers from records metadata
    # simplified as in read code you need to assume not all records are encrypted
    identifiers =
      records
        .flat_map do |r|
          r.metadata[:encryption].values.map { |v| v[:identifier] }
        end
        .compact
    @keys_repository.fetch_keys(identifiers.uniq)
    super
  end

  def events_to_records(events)
    # fetch keys identifiers from events data
    # simplified - in real life it will be probably more complicated :)
    @keys_repository.fetch_keys(
      events.map { |e| e.data[:user_id] }.compact.uniq
    )
    super
  end
end

data = RubyEventStore::InMemoryRepository.new
res =
  RubyEventStore::Client.new(
    repository: data,
    mapper: CustomEncryptionMapper.new
  )

events =
  %w[sample@example.com another@example.com onemore@example.com].map do |email|
    SomeEventWithPersonalInfo.new(
      data: {
        personal_info: email,
        user_id: rand(1000)
      }
    )
  end

res.append(events)

puts "Stored data: #{data.send(:storage).values.map { |v| v.data }}"
puts "Read data:   #{res.read.map(&:data)}"