How to create counters that display and increment dates in ConTeXt?

Question

I need to create a document that has section titles named "October 1, 2012", "October 2, 2012", etc., like this:

\section{October 1, 2012}
    This is text for the first day.
\section{October 2, 2012}
    This is text for the second day.

Is there a simple way to create a counter, set to the initial date, and then to increment it? E.g.:

 \section{\insertdate\incrementdate}
     This is text for the first day.
 \section{\insertdate\incrementdate}
     This is text for the second day.

• This would need to know about leap years.
• When displayed in the table of contents, this should match the sections.

In some situations, I may need to query the current value of year, month, and day, e.g.:

This is month \month and year \year.

This would display:

This is month 10 and year 2012.

In other situations, I may need to use the current value of year, month, and day, in a conditional, e.g.:

IF day IS 1, THEN:
    "This is the start of a new month."
ELSE:
    "It is not the start of a new month."

How can such a counter be created in ConTeXt?

Answer 1

Here is a simple implementation. The command \setupdate sets the current date (its syntax is same as \date command); the command \incrementdate increments the date; and the command \getdate typesets the current date.

You can access the current day, month, and year using \getdate[...], which accepts the same specification as \date. So \getdate[month] gives the name of the month (in the current language), \getdate[m] gives the number of the current month, \getdate[weekday] gives the day of the week, etc.

\unprotect

\newcount\daycounter
\newcount\monthcounter
\newcount\yearcounter

\unexpanded\def\setupdate
  {\dosingleargument\setup_date_aux}

\def\setup_date_aux[#1]%
  {\letdummyparameter\c!d\normalday
   \letdummyparameter\c!m\normalmonth
   \letdummyparameter\c!y\normalyear
   \getdummyparameters[#1]%
   \daycounter  \directdummyparameter\c!d\relax
   \monthcounter\directdummyparameter\c!m\relax
   \yearcounter \directdummyparameter\c!y\relax
  }

\unexpanded\def\incrementdate
  {\getdayspermonth\yearcounter\monthcounter
   \doifelse\numberofdays{\the\daycounter}
      {\daycounter\plusone
       \doifelse\!!twelve{\the\monthcounter}
          {\monthcounter\plusone
           \advance\yearcounter\plusone}
          {\advance\monthcounter\plusone}}
      {\advance\daycounter\plusone}}

\def\getdate
    {\date[d=\the\daycounter, m=\the\monthcounter, y=\the\yearcounter]}

\protect

\setupdate[d={25},m={12},y={2011}]

\starttext
\placecontent
\dorecurse{200}
{\expanded{\section{\getdate}}
 The current month is \getdate[month] \getdate[weekday]
 \incrementdate}
\stoptext

As can be seen from the output of the above example, this implementation correctly handles leap years and works in section titles (provided you use \expanded).