#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>

#define USAGE "usage: %s file [...]\n", name
#define d(...) do { if (dflag > 0) \
	fprintf(stderr, __VA_ARGS__); } while (0);
#define dd(...) do { if (dflag > 1) \
	fprintf(stderr, __VA_ARGS__); } while (0);
#define ddd(...) do { if (dflag > 2) \
	fprintf(stderr, __VA_ARGS__); } while (0);

#define MAXBUF 1024
#define MAXCMDS 32
#define MAXCMD 1024
#define MAXDEP 1024
#define MAXTGT 64

extern char *optarg;
extern int optind;

void cleandep(char **);
void cleantgt(char **);
char *nextdep(char **);

int
main(int argc, char *argv[])
{
	char *b, buf[MAXBUF], *cmd[MAXCMDS], *d, *dep, *name, *tgt;
	FILE *fp;
	int c, dflag, fflag, i, icmd, j, s;
	struct stat sb, ssb;

	/* allocate memory */
	for (i = 0; i < MAXCMDS; i++) {
		cmd[i] = malloc(MAXCMD*sizeof(char));
		if (!cmd[i]) err(1, "malloc");
	}
	dep = malloc(MAXDEP*sizeof(char));
	if (!dep) err(1, "malloc");
	tgt = malloc(MAXTGT*sizeof(char));
	if (!tgt) err(1, "malloc");

	tgt[0] = dep[0] = 0;

	/* process arguments */
	name = argv[0];
	dflag = fflag = 0;
	while ((c = getopt(argc, argv, "df")) != -1)
		switch (c) {
		case 'd':
			dflag++;
			break;
		case 'f':
			fflag = 1;
			break;
		default:
			fprintf(stderr, USAGE);
			return 1;
		}
	argc -= optind;
	argv += optind;
	if (argc == 0) {
		fprintf(stderr, USAGE);
		return 1;
	}

	/* process each file */
	for (i = icmd = 0; i < argc; i++, icmd = 0) {
		fp = fopen(argv[i], "r");
		if (!fp) err(1, "fopen");

		/* read line by line */
		for (j = 0; j < 20 && fgets(buf, MAXBUF, fp); j++) {
			buf[strcspn(buf, "\n")] = 0;

			/* parse line */
			b = buf;
			for (; *b; b++) {
				/* command line */
				if (strncmp(b, "	$ ", 3) == 0
				 || strncmp(b, " $ ", 3) == 0) {
					strncpy(cmd[icmd++], b+3, MAXBUF-1);

					/* find target */
					for (b = b+3; *b; b++) {
						if (!(*b+1)) continue;
						if (*b != '>') continue;
						strncpy(tgt, b+1, MAXTGT-1);

					}

					ddd("%s: command line    '%s'\n",
						argv[i], buf);
					continue;
				}

				/* dependency line */
				if (strncmp(b, "	% ", 3) == 0
				 || strncmp(b, " % ", 3) == 0) {
					strncpy(dep, b+3, MAXDEP-1);
					ddd("%s: dependency line '%s'\n",
						argv[i], buf);
					continue;
				}
			}
		}

		if (!icmd) {
			fprintf(stderr, "%s: no command line found\n", argv[i]);
			goto next;
		}

		if (fflag || !*tgt)
			goto build;

		/* compare source > target */
		cleantgt(&tgt);
		dd("%s: target '%s'\n", argv[i], tgt);
		if (stat(argv[i], &sb))
			err(1, argv[i]);
		if (stat(tgt, &ssb)) {
			if (errno == ENOENT)
				goto build;
			err(1, tgt);
		}
		if (sb.st_mtime > ssb.st_mtime) {
			d("%s: %s is modified, building\n",
				argv[i], argv[i]);
			goto build;
		}

		if (!*dep)
			goto uptodate;

		/* compare dependencies > target */
		cleandep(&dep);
		while (d = nextdep(&dep)) {
			dd("%s: depend '%s'\n",
				argv[i], d);

			if (stat(d, &sb)) {
				if (errno != ENOENT)
					err(1, d);
				fprintf(stderr, "%s: dependency %s does not "
					"exist\n", argv[i], d);
				continue;
			}
			if (sb.st_mtime > ssb.st_mtime) {
				d("%s: %s is modified, building\n",
					argv[i], d);
				free(d);
				goto build;
			}
			free(d);
		}

uptodate:
		fprintf(stderr, "%s: already up-to-date\n", argv[i]);
		goto next;

build:
		/* run commands */
		buf[0] = 0;
		strcat(buf, "set -ex\n");
		for (j = 0; j < icmd; j++) {
			strncat(buf, cmd[j], MAXBUF-1);
			strncat(buf, "\n", MAXBUF-1);
		}
		s = system(buf);
		if (s == 0)
			goto next;

		if (WIFEXITED(s)) {
			fprintf(stderr, "%s: exited with %d\n",
				argv[i], WEXITSTATUS(s));
			exit(WEXITSTATUS(s));
		} else if (WIFSIGNALED(s)) {
			fprintf(stderr, "%s: terminated by signal %d\n",
				argv[i], WTERMSIG(s));
			exit(1);
		}

next:
		fclose(fp);
	}
}

void
cleandep(char **dep)
{
	for (; **dep; (*dep)++)
		if (!isspace(**dep)) break;
}

void
cleantgt(char **tgt)
{
	char *t;

	for (; **tgt; (*tgt)++)
		if (!isspace(**tgt)) break;

	for (t = *tgt; *t; t++)
		if (isspace(*t)
		 || *t == '|'
		 || *t == '&'
		 || *t == ';'
		 || *t == ')') {
			*t = 0; break;
		}
}

char *
nextdep(char **dep)
{
	char *d;
	int i;

	for (i = 0; (*dep)[i]; i++) {
		if (isspace((*dep)[i]) || (*dep)[i+1] == 0) {
			d = strdup(*dep);
			d[i+((*dep)[i+1]==0)] = 0;

			for (; (*dep)[i]; i++)
				if (!isspace((*dep)[i])) break;

			(*dep) += i + ((*dep)[i+1]==0);
			break;
		}
	}

	return d;
}