#include <stdio.h>
#include <sys/file.h>
#include <fcntl.h>

/** publishnews.c - read items from a FIFO publish to a file **/
/**     usage: publishnews fifoname reportname               **/
/**      note: uses an array of arrays and copies them down  **/
/**            Need to change to a circular list             **/

#define	LINES	10
#define	LINELEN	512
#define  oops(m,x)  { perror(m); exit(x); }

char	report[LINES][LINELEN];

main(int ac, char *av[])
{
	FILE	*fp_report, *fp_fifo;
	int	fd_report;
	int	line;

	if ( ac != 3 ){
		fprintf(stderr,"usage: publishnews fifo output\n");
		exit(1);
	}
	if ((fp_fifo = fopen(av[1], "r")) == NULL )
		oops(av[1],2);

	if ( (fd_report = open(av[2],O_CREAT|O_TRUNC|O_RDWR,0644)) == -1 )
		oops(av[2],3);

	while( 1 ){

		/** read next line from fifo */

		if ( fgets(report[0],LINELEN,fp_fifo) == NULL ){
			fclose(fp_fifo);
			fp_fifo = fopen(av[1],"r");
			continue;
		}

		/** update report */

		lock_operation(fd_report, F_WRLCK);

		   fp_report = fopen(av[2],"w"); 
		   if ( fp_report == NULL )
			oops(av[2],4);

		   for(line = 0 ; line<LINES; line++ )
			fputs(report[line],fp_report);
		   fclose(fp_report);

		lock_operation(fd_report, F_UNLCK);

		for( line = LINES-1; line > 0 ; line-- )    /* push down */
			strcpy(report[line], report[line-1]);
	}
}

lock_operation(int fd, int op)
{
	struct flock lock;

	lock.l_whence = SEEK_SET;
	lock.l_start = lock.l_len = 0;
	lock.l_pid = getpid();
	lock.l_type = op;

	if ( fcntl(fd, F_SETLKW, &lock) == -1 )
		oops("lock operation", 6);
}