module SidekiqScheduler::Utils

def self.calc_cron_run_time(cron, time)
  time = time.floor # remove sub seconds to prevent rounding errors.
  return time if cron.match?(time) # If the time is a perfect match then return it.
  next_t = cron.next_time(time).to_t
  previous_t = cron.previous_time(time).to_t
  # The `time` var is some point between `previous_t` and `next_t`.
  # Figure out how far off we are from each side in seconds.
  next_diff = next_t - time
  previous_diff = time - previous_t
  if next_diff == previous_diff
    # In the event `time` is exactly between `previous_t` and `next_t` the diff will not be equal to
    # `cron.rough_frequency`. In that case we round down.
    cron.rough_frequency == next_diff ? time : previous_t
  elsif next_diff > previous_diff
    # We are closer to the previous run time so return that.
    previous_t
  else
    # We are closer to the next run time so return that.
    next_t
  end
end