/* An command-line interface to ftruncate
 *
 * Dylan Simon <https://dylex.net:9947/src/>
 */

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdbool.h>
#include <argp.h>

static const struct argp_option options[] = {
	{"size", 'l', "BYTES", 0, "set file size", 0},
	{"adjust", 'a', "BYTES", 0, "adjust file size", 0},
	{"interactive", 'i', 0, 0, "prompt before any loss", 0},
	{"force", 'f', 0, 0, "never prompt", 0},
	{} 
};
error_t parse(int, char *, struct argp_state *);

static const struct argp parser = {
	.options = options,
	.parser = &parse,
	.args_doc = "FILE ...",
	.doc = "Truncate a file to the specified size (or 0)."
};
	
off_t Len = 0;
long long Adj = 0;
bool Interactive = false;

error_t parse(int key, char *optarg, struct argp_state *state)
{
	char *e;
	int f = -1;

	switch (key) {
		case 'l':
			if (Adj)
				argp_error(state, "only one of -l or -a may be specified");
			Len = strtoull(optarg, &e, 0);
			if (*e || !*optarg)
				argp_error(state, "invalid file length: %s", optarg);
			break;

		case 'a':
			if (Len)
				argp_error(state, "only one of -l or -a may be specified");
			Adj = strtoll(optarg, &e, 0);
			if (*e || !*optarg)
				argp_error(state, "invalid file adjustment: %s", optarg);
			break;

		case 'i':
			Interactive = true;
			break;

		case 'f':
			Interactive = false;
			break;

		case ARGP_KEY_ARG:
			if ((f = open(optarg, O_WRONLY | O_CREAT, 0666)) < 0)
				argp_failure(state, 1, errno, "%s", optarg);
			struct stat s = {};
			if (Adj || Interactive)
				if (fstat(f, &s) < 0)
					argp_failure(state, 1, errno, "%s", optarg);
			if (Adj)
			{
				if (s.st_size + Adj < 0)
					Len = 0;
				else
					Len = s.st_size + Adj;
			}
			if (Interactive)
			{
				if (Len < s.st_size)
				{
					fprintf(stderr, "%s: remove %lu bytes of %s? ", state->name, s.st_size - Len, optarg);
					int yn = -1;
					int c;
					while ((c = getchar()) != EOF && c != '\n')
					{
						if (yn != -1);
						else if (c == 'y' || c == 'Y')
							yn = 1;
						else if (!isspace(c))
							yn = 0;
					}
					if (yn != 1)
						break;
				}
			}
			if (ftruncate(f, Len) < 0)
				argp_failure(state, 1, errno, "%s", optarg);
			break;

		case ARGP_KEY_NO_ARGS:
			argp_usage(state);
		default:
			return ARGP_ERR_UNKNOWN;
	}
	if (f != -1)
		close(f);
	return 0;
}


int main(int argc, char **argv)
{
	if ((errno = argp_parse(&parser, argc, argv, 0, 0, 0)))
	{
		fprintf(stderr, "%s: argp: %m\n", argv[0]);
		exit(1);
	}
	exit(0);
}