skill-assessment-app/app/workers/candidate_reminder.rb

# frozen_string_literal: true
class CandidateReminder
  def initialize
    @collection = reminder_collection
  end

  def count
    @collection.count
  end
  alias size count

  def candidates
    Candidate.includes(:recruiter).where(id: @collection.map { |row| row['id'] })
  end

  def send_all
    candidates.each do |candidate|
      CandidateMailer.reminder(candidate).deliver_now
      flag_as_reminded candidate.id
    end
  end

  private

    def reminder_collection
      sql = "select c.id, c.test_hash, c.name, c.email, max(a.updated_at) last_updated
             from candidates c
               inner join answers a on a.candidate_id = c.id
             where completed = false and reminded = false
             group by c.id
             having MAX(a.updated_at) < DATE_SUB(NOW(), INTERVAL 24 HOUR);"
      ActiveRecord::Base.connection.exec_query(sql)
    end

    def flag_as_reminded candidate_id
      Candidate.find(candidate_id).update(reminded: true)
    end
end