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

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

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

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

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

		/* read line by line */
		while (fgets(buf, sizeof(buf), fp)) {
			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);

					}
					continue;
				}

				/* depend line */
				if (*(b+1) == '%' && *(b+2) == ' ') {
					strncpy(dep, b+3, sizeof(dep)-1);
					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)
			goto build;

		/* compare dependencies > target */
		if (*dep) {
			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 (stat(tt, &sb))
						err(1, tt);
					free(tt);
					if (sb.st_mtime > ssb.st_mtime)
						goto build;

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

		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);
	}
}