An elegant base presenter to help build json and caching solution using redis and marshalling & parsing json using Oj gem

base_presenter.rb

class BasePresenter
  CACHE_TTL = 600

  def initialize(resource, includes, flag)
    @resource = resource
    @includes = includes
    @flag = flag
  end

  private

  def pr_cache_key
    "pr:#{resource.id}:#{flag}:#{resource.class.name}:#{includes.join(":")}"
  end

  def cached_hash
    hash = $redis_reader.get(pr_cache_key)
    return unless hash.present?

    Oj.load(hash)
  end

  def set_cache(hash, ttl = CACHE_TTL)
    return unless hash.present?

    $redis_writer.setex(pr_cache_key, ttl, Oj.dump(hash, mode: :compat))
  end

  def del_cache
    $redis_writer.del(pr_cache_key)
  end
end

user_presenter.rb

class UserPresenter < BasePresenter
  def initialize(user, includes: [], flag: nil)
    super(user, includes, flag)
  end

  def as_json
    return cached_hash if cached_hash.present?

    hash = { id: @resource.id,
      username: @resource.username,
      email: @resource.email,
      first_name: @resource.first_name,
      last_name: @resource.last_name }
      
    set_cache(hash)
    hash
  end
end