% -*- mode: Noweb; noweb-code-mode: c-mode -*-
\section{Using file modification dates}

\date{October 31, 1996}

This \texttt{noweb} filter 
sets the date to the modification date of the file being woven.
It relies on the convention that 
\begin{quote}
\verb+\date{+\emph{mumble}\verb+}+
\end{quote}
appears on a line by itself.  \emph{Mumble} stands for any string.
The filter replaces \emph{Mumble} with the modifcation date and time
of the file as announced by \verb+@file+.

The filter uses POSIX functions, and it uses the \texttt{noweb} input
stuff, so it has to be linked with 
\texttt{getline.o} \texttt{columns.o}, and \texttt{errors.o} from the
\texttt{noweb} distribution.
<<moddate.c*>>=
<<includes>>
<<local procs>>
main() {
  char *s;
  char *file = NULL;
  while (s = getline(stdin)) 
    if (match("@file ", s)) {
      printf("%s", s);
      file = get_file_name(s);
    } else if (matches_date(s) && file != NULL) 
      print_modification_time(file);
    else
      printf("%s", s);
}
@ 
Matching ideas are stolen from Icon.
<<local procs>>=
match(char *pattern, char *s) {
  return !strncmp(pattern, s, strlen(pattern));
}
<<local procs>>=
matches_date(char *s) {
  return match("@text \\date{", s) && s[strlen(s)-2] == '}';
}
@ 
Allocate space for a file name and strip the trailing newline.
<<local procs>>=
char *get_file_name(char *s) {
  char *p = (char *)malloc(strlen(s));  /* wastes some characters */
  assert(p);
  strcpy(p, s + strlen("@file "));
  p[strlen(p)-1] = 0;  /* trim newline */
  return p;
}
@ 
To get a nicer format for the time, I would replace the call to
[[asctime]] with something else.
<<local procs>>=  
void print_modification_time(char *file) {
  struct stat buf;
  int n = stat(file, &buf);
  char *time;
  if (n) {fprintf(stderr, "could not stat %s\n", file); exit(1); }
  time = asctime(localtime(&buf.st_mtime));
  if (time[strlen(time)-1] == '\n') 
    time[strlen(time)-1] = 0;
  printf("@text \\date{%s}\\def\\today{%s}\n", time, time);
}
@ 
<<includes>>=
#include <time.h>
#include <stdlib.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <stdio.h>
#include "getline.h"