/*******************************************************************************
*
* timepreserve.c
*       
* AUTHOR:
*   Dan Harkless                                                    <opensource@
*   http://harkless.org/dan/software/                              harkless.org>
* 
* COPYRIGHT:
*   This file is Copyright (C) 2002 by Dan Harkless, and is released under the
*   GNU General Public License <http://www.gnu.org/copyleft/gpl.html>.
*
* USAGE:  
*   % timepreserve <wrapped_commandline> <file_1> [<file_2>...]
*
* EXAMPLES:
*   % timepreserve "touch *" *  # a no-op
*   % timepreserve "exifedit -b -t r *.jpg" *.jpg
*   % timepreserve "wrjpgcom -comment 'a cow' cow.jpg > X; mv X cow.jpg" cow.jpg
*                                                                            
* DESCRIPTION:                                                               
*   Preserves the access and modification timestamps of one or more files across
*   the execution of a commandline that would otherwise modify them.
*   <wrapped_commandline> must be passed as a single parameter (so quote it),
*   and is given to /bin/sh for interpretation so you can do things like I/O
*   redirection, as illustrated above.  The exit status returned by the wrapped
*   commandline will be returned by timepreserve, unless one of our system calls
*   fail, in which case we return EXIT_FAILURE (1).
*
*   If we fail to read the timestamps from any of the specified files, we'll
*   abort before running the commandline, but if writing a timestamp back to one
*   of those files after running the commandline fails, we'll output a
*   descriptive error including the timestamp we were trying to write back (so
*   that info doesn't get lost) and continue with the rest of the files.
*
* DATE        MODIFICATION
* ==========  ==================================================================
* 2002-11-28  D'oh!  Subtracted 2 from argc when allocating timestamp_array but
*             forgot to subtract 2 when indexing into it.  Program worked, but
*             on Linux would seg fault in libc function chunk_free() after
*             exiting (this didn't show up on Solaris).
* 2002-03-17  Upgraded to work with more than one file.
* 2002-03-16  Original.
*
*******************************************************************************/


#include <sys/types.h>  /* supposed to precede <sys/stat.h> and <utime.h> */

#include <errno.h>      /* for errno */
#include <stdio.h>      /* for fprintf(), etc. */
#include <stdlib.h>     /* for EXIT_FAILURE and EXIT_SUCCESS */
#include <string.h>     /* for strerror() and strrchr() */
#include <sys/stat.h>   /* for stat() and struct stat */
#include <sys/wait.h>   /* for waitpid(), etc. */
#include <unistd.h>     /* for execl(), etc. */
#include <utime.h>      /* for struct utimbuf and utime() */


int  main(int  argc, char**  argv) {
    char*            last_slash = strrchr(argv[0], '/');
    char*            our_program_name;
    int              child_pid, exit_status = EXIT_SUCCESS, i,
                     packed_exit_status;
    struct stat      file_stat;
    struct utimbuf*  timestamp_array;

    if (last_slash == NULL)
	our_program_name = argv[0];
    else
	our_program_name = last_slash + 1;
    
    if (argc < 3) {
        fprintf(stderr,
		"Usage: %s <wrapped_commandline> <file_1> [<file_2>...]\n",
		our_program_name);
        return EXIT_FAILURE;
    }

    timestamp_array = malloc((argc - 2) * sizeof(struct utimbuf));

    for (i = 2; i < argc; i++) {
	if (stat(argv[i], &file_stat) < 0) {
	    fprintf(stderr, "%s: \"%s\": %s. Aborting.\n",
		    our_program_name, argv[i], strerror(errno));
	    return EXIT_FAILURE;
	}
    
	timestamp_array[i - 2].actime = file_stat.st_atime;
	timestamp_array[i - 2].modtime = file_stat.st_mtime;
    }
    
    child_pid = fork();
    
    if (child_pid < 0) {
	/* fork() failed. */
	fprintf(stderr, "%s: fork(): %s.\n",
		our_program_name, strerror(errno));
	return EXIT_FAILURE;
    }
    else if (child_pid == 0) {
	/* We are the child. */
	execl("/bin/sh", "/bin/sh", "-c", argv[1], NULL);
	/* If we get here, execl() failed. */
	fprintf(stderr, "%s: execl(): %s.\n",
		our_program_name, strerror(errno));
	return EXIT_FAILURE;
    }
    else
	/* We are the parent.  Reap the child and decode exit status. */
	if (waitpid(child_pid, &packed_exit_status, 0) < 0) {
	    fprintf(stderr, "%s: waitpid(): %s.\n",
		    our_program_name, strerror(errno));
	    exit_status = EXIT_FAILURE;
	}
	else {
	    if (WIFEXITED(packed_exit_status))
		exit_status = WEXITSTATUS(packed_exit_status);
	    else if (WIFSIGNALED(packed_exit_status))
		exit_status = WTERMSIG(packed_exit_status);
	    else
		exit_status = EXIT_FAILURE;
	}
    
    for (i = 2; i < argc; i++)
	if (utime(argv[i], &timestamp_array[i - 2]) < 0) {
	    fprintf(stderr,
		    "%s: Failed to set \"%s\" to ac=%lu, mod=%lu: %s.\n",
		    our_program_name, argv[i], timestamp_array[i - 2].actime,
		    timestamp_array[i - 2].modtime, strerror(errno));
	    exit_status = EXIT_FAILURE;
	}
    
    return exit_status;
}