# frozen_string_literal: true

# The usage of the ReactiveCaching module is documented here:
# https://docs.gitlab.com/ee/development/reactive_caching.md
module ReactiveCaching
  extend ActiveSupport::Concern

  InvalidateReactiveCache = Class.new(StandardError)
  ExceededReactiveCacheLimit = Class.new(StandardError)

  WORK_TYPE = {
    no_dependency: ReactiveCachingWorker,
    external_dependency: ExternalServiceReactiveCachingWorker
  }.freeze

  included do
    extend ActiveModel::Naming

    class_attribute :reactive_cache_key
    class_attribute :reactive_cache_lease_timeout
    class_attribute :reactive_cache_refresh_interval
    class_attribute :reactive_cache_lifetime
    class_attribute :reactive_cache_hard_limit
    class_attribute :reactive_cache_work_type
    class_attribute :reactive_cache_worker_finder

    # defaults
    self.reactive_cache_key = -> (record) { [model_name.singular, record.id] }
    self.reactive_cache_lease_timeout = 2.minutes
    self.reactive_cache_refresh_interval = 1.minute
    self.reactive_cache_lifetime = 10.minutes
    self.reactive_cache_hard_limit = nil # this value should be set in megabytes. E.g: 1.megabyte
    self.reactive_cache_worker_finder = ->(id, *_args) do
      find_by(primary_key => id)
    end

    def calculate_reactive_cache(*args)
      raise NotImplementedError
    end

    def reactive_cache_updated(*args)
    end

    def with_reactive_cache(*args, &blk)
      unless within_reactive_cache_lifetime?(*args)
        refresh_reactive_cache!(*args)
        return
      end

      keep_alive_reactive_cache!(*args)

      begin
        data = Rails.cache.read(full_reactive_cache_key(*args))
        yield data unless data.nil?
      rescue InvalidateReactiveCache
        refresh_reactive_cache!(*args)
        nil
      end
    end

    def with_reactive_cache_set(resource, opts, &blk)
      data = with_reactive_cache(resource, opts, &blk)
      save_keys_in_set(resource, opts) if data

      data
    end

    # This method is used for debugging purposes and should not be used otherwise.
    def without_reactive_cache(*args, &blk)
      return with_reactive_cache(*args, &blk) unless Rails.env.development?

      data = self.class.reactive_cache_worker_finder.call(id, *args).calculate_reactive_cache(*args)
      yield data
    end

    def clear_reactive_cache!(*args)
      Rails.cache.delete(full_reactive_cache_key(*args))
      Rails.cache.delete(alive_reactive_cache_key(*args))
    end

    def clear_reactive_cache_set!(*args)
      cache_key = full_reactive_cache_key(args)

      reactive_set_cache.clear_cache!(cache_key)
    end

    def exclusively_update_reactive_cache!(*args)
      locking_reactive_cache(*args) do
        key = full_reactive_cache_key(*args)

        if within_reactive_cache_lifetime?(*args)
          enqueuing_update(*args) do
            new_value = calculate_reactive_cache(*args)
            check_exceeded_reactive_cache_limit!(new_value)

            old_value = Rails.cache.read(key)
            Rails.cache.write(key, new_value)
            reactive_cache_updated(*args) if new_value != old_value
          end
        else
          Rails.cache.delete(key)
        end
      end
    end

    private

    def save_keys_in_set(resource, opts)
      cache_key = full_reactive_cache_key(resource)

      reactive_set_cache.write(cache_key, "#{cache_key}:#{opts}")
    end

    def reactive_set_cache
      Gitlab::ReactiveCacheSetCache.new(expires_in: reactive_cache_lifetime)
    end

    def refresh_reactive_cache!(*args)
      clear_reactive_cache!(*args)
      keep_alive_reactive_cache!(*args)
      worker_class.perform_async(self.class, id, *args)
    end

    def keep_alive_reactive_cache!(*args)
      Rails.cache.write(alive_reactive_cache_key(*args), true, expires_in: self.class.reactive_cache_lifetime)
    end

    def full_reactive_cache_key(*qualifiers)
      prefix = self.class.reactive_cache_key
      prefix = prefix.call(self) if prefix.respond_to?(:call)

      ([prefix].flatten + qualifiers).join(':')
    end

    def alive_reactive_cache_key(*qualifiers)
      full_reactive_cache_key(*(qualifiers + ['alive']))
    end

    def locking_reactive_cache(*args)
      lease = Gitlab::ExclusiveLease.new(full_reactive_cache_key(*args), timeout: reactive_cache_lease_timeout)
      uuid = lease.try_obtain
      yield if uuid
    ensure
      Gitlab::ExclusiveLease.cancel(full_reactive_cache_key(*args), uuid)
    end

    def within_reactive_cache_lifetime?(*args)
      Rails.cache.exist?(alive_reactive_cache_key(*args))
    end

    def enqueuing_update(*args)
      yield

      worker_class.perform_in(self.class.reactive_cache_refresh_interval, self.class, id, *args)
    end

    def worker_class
      WORK_TYPE.fetch(self.class.reactive_cache_work_type.to_sym)
    end

    def reactive_cache_limit_enabled?
      !!self.reactive_cache_hard_limit
    end

    def check_exceeded_reactive_cache_limit!(data)
      return unless reactive_cache_limit_enabled?

      data_deep_size = Gitlab::Utils::DeepSize.new(data, max_size: self.class.reactive_cache_hard_limit)

      raise ExceededReactiveCacheLimit.new unless data_deep_size.valid?
    end
  end
end
