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

#define USAGE "usage: %s file [...]\n", argv[0]

extern char *optarg;
extern int optind;

int
main(int argc, char *argv[])
{
	char *b, *bb, *bbb, buf[1024], *cmd[32], dep[1024], *t, *tt, tgt[64];
	FILE *fp;
	int c, dflag, i, icmd, j, max;
	struct stat sb, ssb;

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

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

	/* allocate memory */
	for (i = 0; i < 32; i++) {
		cmd[i] = malloc(1024*sizeof(char));
		if (!cmd[i]) err(1, "malloc");
	}

	/* 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, sizeof(buf), fp); j++) {
			buf[strcspn(buf, "\n")] = 0;

			/* parse line */
			b = buf;
			for (b++; *b; b++) {
				if (!(*(b+1) && *(b+2) && *(b+3))) continue;
				if (!(*b == ' ' || *b == '	')) continue;

				/* command line */
				if (*(b+1) == '$' && *(b+2) == ' ') {
					strncpy(cmd[icmd++],b+3,sizeof(buf)-1);

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

					}

					if (dflag < 3) continue;
					fprintf(stderr,
						"%s: command line '%s'\n",
						argv[i], buf);
					continue;
				}

				/* depends line */
				if (*(b+1) == '%' && *(b+2) == ' ') {
					strncpy(dep, b+3, sizeof(dep)-1);
					if (dflag < 3) continue;
					fprintf(stderr,
						"%s: depends line '%s'\n",
						argv[i], buf);
					continue;
				}
			}
		}

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

		if (!*tgt)
			goto build;

		/* compare source > target */
		for (t = tgt; *t; t++)
			if (!isspace(*t)) break;
		for (tt = tgt; *tt; tt++)
			if (isspace(*tt)) { *tt = 0; break; }
		if (stat(t, &ssb))
			err(1, t);
		if (stat(argv[i], &sb))
			err(1, argv[i]);
		if (sb.st_mtime > ssb.st_mtime) {
			if (dflag)
				fprintf(stderr, "%s: building because "
					"%s is modified\n", argv[i], argv[i]);
			goto build;
		}

		if (!*dep)
			goto uptodate;

		/* compare dependencies > target */
		for (t = dep; *t; t++)
			if (!isspace(*t)) break;
		for (j = 0; t[j]; j++) {
			if (isspace(t[j]) || t[j+1] == 0) {
				tt = strdup(t);
				tt[j+(t[j+1]==0)] = 0;

				if (dflag > 1)
					fprintf(stderr, "%s: depend '%s'\n",
						argv[i], tt);

				if (stat(tt, &sb))
					err(1, tt);
				free(tt);
				if (sb.st_mtime > ssb.st_mtime) {
					if (dflag)
						fprintf(stderr,
							"%s: building because "
							"%s is modified\n",
							argv[i], tt);
					goto build;
				}

				for (; t[j]; j++)
					if (!isspace(t[j])) break;
				t += j;
				j = 0;
			}
		}

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

build:
		/* run commands */
		for (j = 0; j < icmd; j++) {
			fprintf(stderr, "%s: %s\n", argv[i], cmd[j]);
			system(cmd[j]);
		}

done:
		fclose(fp);
	}
}