First draft of a KHumanDateTimeParser class

[Denis Steckelmacher]

Hi,

Two or three days ago, I asked on this mailing list if there was any
implementation of a human-entered date-time parser in the KDE libraries 
or
elsewhere.

I received very interesting responses, for instance one that confirmed 
that there
isn't any parser like that in kdelibs, and another one that pointed me 
to the
Date::Manip Perl module.

During the week-end, I played with Date::Manip and thought about a C++
implementation that could be extensible yet simple to implement and to 
localize.

After two days of coding, here is my first draft :

     https://github.com/steckdenis/khumandatetime

It is a simple parser that reads rules from a XML file. The README.md 
file in
the repository explains how to write rules, I hope it is not too 
difficult, and
that my English doesn't hurt you too much.

In its current state, this parser is able to understand things like 
"two days
ago", "in 3 months", "next Monday at 3.00 pm" or even "16 May 2009" (a 
bug in
the English rules, that I just see now, makes parsing "16th of May 
2009"
impossible, I have forgotten the "of").

One thing it can't properly parse is complex relations like "next 
Tuesday".
Currently, the parser adds one week to the current date, and then sets 
its day
of week to "Tuesday". It works if the current day of week is already 
Tuesday or
a later day, but if we are a Monday, next Tuesday is tomorrow, not in 
one week.

The same problem is present for dates like "Last Monday". If the Monday 
of the
current week already passed, the parser will erroneously return the 
Monday of
last week, not the Monday of this week.

Fixing this problem may really complicate the parser, as it would 
require the
parsing rules to have "if" conditions. Another solution may to 
hard-code such
logic in C++.

When I was implementing this parser, I realized that every western 
language
will have nearly the same rules, and that duplicating them for every 
language
will be a waste of time. What about considering this parser an 
experiment
and hard-coding the most useful rules in KCalendarSystem, using i18n() 
calls
to translate everything ? With a bit of code, it could be possible to
implement any rule, even the "last Monday" ones. I thought of 
implementing
them in KCalendarSystem because the rules seem to be more
calendar-system-specific than language-specific.

Happy testing,
Denis Steckelmacher.