class Date

If no config.beginning_of_week was specified, returns :monday.
If Date.beginning_of_week has not been set for the current request, returns the week start specified in config.beginning_of_week.
Returns the week start (e.g. :monday) for the current request, if this has been set (via Date.beginning_of_week=).

def beginning_of_week
  Thread.current[:beginning_of_week] || beginning_of_week_default || :monday
end