Parse and create ISO 8601 Date and time intervals, like PT15M in PHP

Question

A library and webservice I am using communicates time-intervals in ISO 8601 format: PnYnMnDTnHnMnS. I want to convert such formats to seconds. And vice versa. Seconds are a

Answer 1

It looks like PHP 5.3's DateInterval supports this.

If you can't use 5.3, I suppose any such conversion function would know how many seconds are in a year, a month, a day, an hour, and a minute. Then, when converting from seconds, it would divide in that order, each time taking the modulo of the previous operation, until only <60 seconds are left. When converting from an ISO 8601 interval representation it should be trivial to parse the string and multiply each found element accordingly.