/*
 * Run a predicate command on data read from standard
 * input; print only the data for which the predicate
 * returns true.
 *
 * Dan Cross <net!gajendra!cross>
 */

#include <sys/types.h>
#include <sys/wait.h>

#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static void usage(char *progname);
static void process(FILE *in, int argc, char *argv[]);
static int  probe(char *filename, int argc, char *argv[]);

int seperator;

int
main(int argc, char *argv[])
{
	char **nargv;
	int ch, i;

	seperator = '\n';
	while ((ch = getopt(argc, argv, "0?")) != -1) {
		switch (ch) {
		case '0':
			seperator = '\0';
			break;
		case '?':
		default:
			usage(argv[0]);
			break;
		}
	}
	argc -= optind;
	argv += optind;
	nargv = malloc((argc + 2) * sizeof(char *));
	memset(nargv, 0, (argc + 2) * sizeof(char *));
	for (i = 0; i <= argc; i++)
		nargv[i] = argv[i];
	nargv[argc + 1] = NULL;
	process(stdin, argc + 1, nargv);

	return(EXIT_SUCCESS);
}

static void
process(FILE *in, int argc, char *argv[])
{
	char *s;
	char buffer[65536];
	int ch;

	memset(buffer, 0, sizeof(buffer));
	s = buffer;
	while ((ch = fgetc(in)) != EOF) {
		if ((s - buffer) >= sizeof(buffer)) {
			memset(buffer, 0, sizeof(buffer));
			while ((ch = fgetc(in)) != EOF && ch != seperator);
			continue;
		}
		if (ch == seperator) {
			*s = '\0';
			if (probe(buffer, argc, argv)) {
				write(STDOUT_FILENO, buffer, s - buffer);
				write(STDOUT_FILENO, &seperator, 1);
			}
			memset(buffer, 0, sizeof(buffer));
			s = buffer;
		} else
			*s++ = ch;
	}
	if (ferror(in))
		perror("read");
}

static int
probe(char *s, int argc, char *argv[])
{
	pid_t pid;
	int status;

	status = 0;
	argv[argc - 1] = s;
	pid = vfork();
	if (pid < 0) {
		perror("fork");
		exit(EXIT_FAILURE);
	} else if (pid == 0) {
		execvp(*argv, argv);
		perror("execvp");
		_exit(EXIT_FAILURE);
	} else {
		if (waitpid(pid, &status, 0) < 0)
			perror("waitpid");
	}

	return(status == 0);
}

static void
usage(char *progname)
{
	fprintf(stderr, "Usage: %s [ -0 ].\n", progname);
	exit(EXIT_FAILURE);
}