English-Friendly Interval Calculation

I am working on a small program to digest and store RSS feeds (in part using Ray Camden's nice RSS.cfc). One thing I ran into is that I want to be able to specify how frequently feeds should get updated. It seems obvious that I should have an argument for this in the init() method of my CFC. What I don't want, however, is to either limit myself to one interval (days, for example) or to have multiple arguments just for the interval.

Moreover, I really want to be able to specify the interval in a human-readable format. So, I created a UDF (implemented as a method in my CFC) to make date calculations based on a readable string indicating the interval.

Here are some examples of intervals that it will calculate:

• daily
• annually
• every day
• every other minute
• every 3rd quarter
• every fourth year
• every other Saturday
• 4th Saturday
• three weeks
• 2 months, 2 days, 11 minutes
• - every second Sunday

Most of these should be pretty obvious, but the last two might require a touch of explanation. The UDF will accept a comma delimited list, in which case it will apply all of the intervals to the date given.

If the interval starts with a "-" then it will subtract the interval given. The subtraction will only apply to the entire interval, not to single items in the list.

[More]