Provides Redis distributed lock api

temporary_lock.rb

# frozen_string_literal: true

# @example provides Redis distributed lock api
#
# $ TemporaryLock.create!(:example, 'c22a0420-51c8-4e47-843c-92a37e8d2eba')
#   => #<TemporaryLock:0x000055b43e328410 @key="temporary_lock:example:c22a0420-51c8-4e47-843c-92a37e8d2eba">
#
# @example raises `TemporaryLock::StaleObjectError` when `id` already registered
#
# $ TemporaryLock.create!(:example, 'c22a0420-51c8-4e47-843c-92a37e8d2eba')
#   => TemporaryLock::StaleObjectError: Attempted to update a stale object: temporary_lock:example:c22a0420-51c8-4e47-843c-92a37e8d2eba
#   => from /app/app/models/temporary_lock.rb:21:in `create!'

class TemporaryLock
  class EmptyIdError < StandardError; end
  class StaleObjectError < StandardError; end

  EXPIRE = 14.days.to_i

  attr_reader :key
  private_class_method :new

  def initialize(name, id)
    @key = redis_key!(name, id)
  end

  def self.create!(name, id)
    lock = new(name, id)

    return lock if lock.persist

    raise StaleObjectError.new(
      "Attempted to update a stale object: #{lock.key}"
    )
  end

  def persist
    redis_client.set(
      key,
      serialize(true),
      ex: EXPIRE,
      nx: true
    )
  end

  private

  def serialize(data)
    Oj.dump(data)
  end

  def redis_key!(name, id)
    raise EmptyIdError.new('Tried lock with empty `id`') unless id.presence

    [:temporary_lock, name, id].join(':')
  end

  def redis_client
    Redis::Namespace.new(
      'mejuri-redis-lock',
      redis: Redis.new(
        host: ENV['REDIS_HOST'],
        port: ENV['REDIS_PORT'],
        db: ENV['REDIS_DB'].to_i
      )
    )
  end
end