CronoTrigger

gem 'crono_trigger'

class AddLockedByColumnToYourModel < ActiveRecord::Migration[5.2]
  def change
    add_column :your_models, :locked_by, :string
  end
end

class CreateMailNotifications < ActiveRecord::Migration
  def change
    create_table :mail_notifications do |t|

      # columns for CronoTrigger::Schedulable
      t.string    :cron
      t.datetime  :next_execute_at
      t.datetime  :last_executed_at
      t.integer   :execute_lock, limit: 8, default: 0, null: false
      t.datetime  :started_at
      t.datetime  :finished_at
      t.string    :last_error_name
      t.string    :last_error_reason
      t.datetime  :last_error_time
      t.integer   :retry_count, default: 0, null: false


      t.timestamps
    end
    add_index :mail_notifications, [:next_execute_at, :execute_lock, :started_at, :finished_at], name: "crono_trigger_index_on_mail_notifications"
  end
end

class MailNotification < ActiveRecord::Base
  include CronoTrigger::Schedulable

  self.crono_trigger_options = {
    retry_limit: 5,
    retry_interval: 10,
    exponential_backoff: true,
    execute_lock_timeout: 300,
  }

  # `execute`, `retry` callback is defined
  # can use `before_execute`, `after_execute`, `around_execute`
  # `before_retry`, `after_retry`, `around_retry`

  # If execute method raise Exception, worker retry task until reach `retry_limit`
  # If `retry_count` reaches `retry_limit`, task schedule is reset.
  # 
  # If record has cron value, reset process set next execution time by cron definition
  # If record has no cron value, reset process clear next execution time
  def execute
    send_mail

    throw :retry # break execution and retry task
    throw :abort # break execution
    throw :ok    # break execution and handle task as success
    throw :ok_without_reset    # break execution and handle task as success but without schedule reseting and unlocking
  end
end

# one time schedule
MailNotification.create.activate_schedule!(at: Time.current.since(5.minutes))

# cron schedule
MailNotification.create(cron: "0 12 * * *").activate_schedule!
# or
MailNotification.new(cron: "0 12 * * *").activate_schedule!.save

# if update cron column or timezone column
# update next_execute_at automatically by before_update callback
mail = MailNotification.create(cron: "0 12 * * *").activate_schedule!
mail.next_execute_at # => next 12:00 with Time.zone
mail.update(cron: "0 13 * * *")
mail.next_execute_at # => next 13:00 with Time.zone
mail.update(timezone: "Asia/Tokyo")
mail.next_execute_at # => next 13:00 with Asia/Japan

CronoTrigger.configure do |config|
  # These handlers are called when the execute method fails even after retries.
  config.error_handlers << proc do |exception, record|
    ActiveRecord::Base.logger.error("Failed to process #{record.class}##{record.id}: #{exception} (#{exception.class})")
  end

  # These handlers are called when an exception occurs outside of the execute method.
  config.global_error_handlers << proc do |exception|
    ActiveRecord::Base.logger.error("#{exception} (#{exception.class})\n#{exception.backtrace.join("\n")}")
  end

  # db_error_retriable_options are passed to `Retriable.retriable` used in the idempotent code that accesses the database
  # except for the code processing each record.
  # Here is the default value.
  config.db_error_retriable_options = {
    on: {
      ActiveRecord::ConnectionNotEstablished => nil,
    },
  }
end

CronoTrigger.configure do |config|
  config.db_error_retriable_options = {
    on: {
      ActiveRecord::ConnectionNotEstablished => nil,
      Mysql2::Error::ConnectionError => nil,
      ActiveRecord::StatementInvalid => /MySQL server is running with the --read-only option/,
    },
    on_retry: proc do |exception, try, elapsed_time, interval|
      ActiveRecord::Base.logger.info("#{try}th: Retry on #{exception.class}: #{exception}")
      next unless exception.is_a?(ActiveRecord::StatementInvalid)

      ActiveRecord::Base.logger.info("#{try}th: Reconnect to MySQL on #{exception.class}: #{exception}")
      # NOTE: The connection acquired here might be different from the one used in the code that raised the error,
      #   but we don't have a way to get the latter connection.
      ActiveRecord::Base.connection_pool.with_connection(&:reconnect!)
    end,
  }
end

# config/routes.rb
require "crono_trigger/web"
mount CronoTrigger::Web => '/crono_trigger'