/*
 *  parallel.c - run commands in parallel until you run out of commands
 *
 *  Copyright © 2008  Tollef Fog Heen <tfheen@err.no>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  version 2 as published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 * USA
 *
 */

#define _GNU_SOURCE
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <sys/time.h>
#include <time.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/select.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#ifdef __sun
# include <sys/loadavg.h> /* getloadavg() */
#endif

#if !defined(WEXITED)
#define WEXITED 0
#endif

void usage() {
	printf("parallel [OPTIONS] command -- arguments\n\tfor each argument, "
	       "run command with argument, in parallel\n");
	printf("parallel [OPTIONS] -- commands\n\trun specified commands in parallel\n");
	exit(1);
}

void exec_child(char **command, char **arguments, int replace_cb, int nargs) {
	if (fork() != 0) {
		return;
	}

	if (command[0]) {
		char **argv;
		int argc = 0;
		int i;
		char *s;

		while (command[argc] != 0) {
			argc++;
		}
		if (! replace_cb)
			argc++;
		argv = calloc(sizeof(char*), argc + nargs);

		for (i = 0; i < argc; i++) {
			while (replace_cb && (s=strstr(command[i], "{}"))) {
				char *buf=malloc(strlen(command[i]) + strlen(arguments[0]));
				s[0]='\0';
				sprintf(buf, "%s%s%s", command[i], arguments[0], s+2);
				command[i]=buf;
			}
			argv[i] = command[i];
		}
		if (! replace_cb)
			memcpy(argv + i - 1, arguments, nargs * sizeof(char *));
		execvp(argv[0], argv);
		exit(1);
	}
	else {
		int ret=system(arguments[0]);
		if (WIFEXITED(ret)) {
			exit(WEXITSTATUS(ret));
		}
		else {
			exit(1);
		}
	}
	return;
}

int wait_for_child(int options) {
	id_t id_ignored = 0;
	siginfo_t infop;

	infop.si_pid = 0;
	waitid(P_ALL, id_ignored, &infop, WEXITED | options);
	if (infop.si_pid == 0) {
		return -1; /* Nothing to wait for */
	}
	if (infop.si_code == CLD_EXITED) {
		return infop.si_status;
	}
	return 1;
}

int main(int argc, char **argv) {
	int maxjobs = -1;
	int curjobs = 0;
	double maxload = -1;
	int argsatonce = 1;
	int opt;
	char **command = calloc(sizeof(char*), argc);
	char **arguments = NULL;
	int argidx = 0;
	int arglen = 0;
	int cidx = 0;
	int returncode = 0;
	int replace_cb = 0;
	char *t;

	while ((argv[optind] && strcmp(argv[optind], "--") != 0) &&
	       (opt = getopt(argc, argv, "+hij:l:n:")) != -1) {
		switch (opt) {
		case 'h':
			usage();
			break;
		case 'i':
			replace_cb = 1;
			break;
		case 'j':
			errno = 0;
			maxjobs = strtoul(optarg, &t, 0);
			if (errno != 0 || (t-optarg) != strlen(optarg)) {
				fprintf(stderr, "option '%s' is not a number\n",
					optarg);
				exit(2);
			}
			break;
		case 'l':
			errno = 0;
			maxload = strtod(optarg, &t);
			if (errno != 0 || (t-optarg) != strlen(optarg)) {
				fprintf(stderr, "option '%s' is not a number\n",
					optarg);
				exit(2);
			}
			break;
		case 'n':
			errno = 0;
			argsatonce = strtoul(optarg, &t, 0);
			if (errno != 0 || argsatonce < 1 || (t-optarg) != strlen(optarg)) {
				fprintf(stderr, "option '%s' is not a positive number\n",
					optarg);
				exit(2);
			}
			break;
		default: /* ’?’ */
			usage();
			break;
		}
	}
	
	if (replace_cb && argsatonce > 1) {
		fprintf(stderr, "options -i and -n are incomaptible\n");
		exit(2);
	}

	if (maxjobs < 0) {
#ifdef _SC_NPROCESSORS_ONLN
		maxjobs = sysconf(_SC_NPROCESSORS_ONLN);
#else
#warning Cannot autodetect number of CPUS on this system: _SC_NPROCESSORS_ONLN not defined.
		maxjobs = 1;
#endif
	}
	
	while (optind < argc) {
		if (strcmp(argv[optind], "--") == 0) {
			int i;

			optind++;
			arglen = argc - optind;
			arguments = calloc(sizeof(char *), arglen);
			if (! arguments) {
				exit(1);
			}

			for (i = 0; i < arglen; i++) {
				arguments[i] = strdup(argv[optind + i]);
			}
			optind += i;
		}
		else {
			command[cidx] = strdup(argv[optind]);
			cidx++;
		}
		optind++;
	}

	if (argsatonce > 1 && ! command[0]) {
		fprintf(stderr, "option -n cannot be used without a command\n");
		exit(2);
	}

	while (argidx < arglen) {
		double load;

		getloadavg(&load, 1);

		if ((maxjobs == 0 || curjobs < maxjobs) &&
		    (maxload < 0 || load < maxload)) {

			if (argsatonce > arglen - argidx)
				argsatonce = arglen - argidx;
			exec_child(command, arguments + argidx,
				   replace_cb, argsatonce);
			argidx += argsatonce;
			curjobs++;
		}
		
		if (maxjobs == 0 || curjobs == maxjobs) {
			returncode |= wait_for_child(0);
			curjobs--;
		}

		if (maxload > 0 && load >= maxload) {
			int r;
			sleep(1); /* XXX We should have a better
				   * heurestic than this */
			r = wait_for_child(WNOHANG);
			if (r > 0)
				returncode |= r;
			if (r != -1)
				curjobs--;
		}
	}
	while (curjobs > 0) {
		returncode |= wait_for_child(0);
		curjobs--;
	}

	return returncode;
}