README

Formula date manager for Sacred Harp singings

http://stevebrett.nfshost.com/shcalendar/

Annual Sacred Harp singings are organised using date formulae, usually relating to the day's position in the month (e.g. second Sunday), or a special date (e.g. Palm Sunday).

This tool allows for human input of what could be a quite complex recurrence rule by finding all likely formulae for a specific date. The user can then choose their singing formula from a list of options, and then generate future dates.

The current formula uses an array format that extends the RFC 5545 format used by rlanvin/php-rrule.

• OFFSET : string The offset of the event from the reference day, using the same format as BYDAY.
• STARTOFFSET : int For multi-day events, how many days the start of the event is before the end.
• SPECIAL : string The key of an array of special events.

Examples

The Saturday before the second Sunday in May

['BYMONTH' => 5,
   'BYDAY' => '2SU',
  'OFFSET' => '-1SA']

The second Saturday in February

['BYMONTH' => 2,
   'BYDAY' => '2SA']

The third Sunday in September and the Saturday before

[   'BYMONTH' => 9,
      'BYDAY' => '3SU',
'STARTOFFSET' => -1]

The Saturday after the Whitsun bank holiday

['SPECIAL' => 'whitsun',
  'OFFSET' => '1SA']

The Saturday before the first fifth Sunday after the 4th July (yes, this is a real singing!)

['SPECIAL' => '5SU47',
  'OFFSET' => '-1SA']