Prerequisite: Lua Task 7 - Wikibase client. This task requires a lot of research and independent learning and is considerably more difficult than the introductory seven tasks. You should have successfully and comfortably completed all of the introductory tasks before attempting any of the advanced ones. It is not suitable for beginners to programming, although students new to Lua with previous experience in other programming languages should be able to produce acceptable solutions. Read through the entire task before starting work on it.

On the English Wikipedia, we find 5 types of allowed date formats:

• "dmy" – e.g. 31 August 2013
• "mdy" – e.g. August 31, 2013
• "iso"-style – e.g. 2013-08-27
• year – e.g. 2013
• month and year – e.g. August 2013

Wikipedia always gives month names in full (i.e. December, not Dec) and only uses all-numeric dates in special cases. Text that is imported from outside of Wikipedia may be in any of large number of formats, or sometimes malformed but understandable. There is often a need to take a piece of text and extract a date from it, displaying it in the required format. This is a common sort of task in natural language processing.

Examine the table below:

Notes:

• The first column has examples of text that may contain dates.
• The second column contains the requested formats (from a parameter like |format=mdy). If there is no format parameter given, then the date output attempts to match the format of the text supplied.
• The third column shows the expected output. Certain words, e.g. "around", "uncertain" indicate that the date is approximate; we normally add "circa" before approximate dates.

This task requires you to create your own function which can take text such as may be found in the first column and an optional format parameter. It will output a date either in the requested format or in a format matching that of the text supplied. You should test your function against all of the text shown in the table above, at least. Copy the table into your sandbox and change the entries in the last column to make calls to your function by supplying the value in the first column and the format in the second. See how close you can get to reproducing the table above.

To complete this task you will need to make use of the techniques you learned in the first six tasks, as well as doing further research on string-handling functions and patterns, and possibly making use of other libraries.

You must work in a fresh module sandbox and user sandbox. If I were doing the task, I would use Module:Sandbox/RexxS/Dates and User:RexxS/Sandbox/Dates.

Meeting the requirement to add "circa" may prove to be difficult, so get a function working without it to start with, and consider adding it in later if time permits. If you can get a function working without it, that is the minimum needed to successfully complete the task if you have no more time, but please try to accomplish the entire task if time permits.