#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/types.h>
#include <string.h>
#include <assert.h>
#include <ctype.h>

void usage (char * progname)
{
	fprintf (stderr, "usage: %s [ -c | -a | -s ] file format\n", progname);
	exit (1);
}

int ncol;
int * fieldwidth;
int recordwidth;

int readformat (char * f)
{
	int i, j;
	ncol = 1;
	for (i=0; f[i]; i++)
		if (f[i] == ':')
			ncol++;
	recordwidth = 0;
	fieldwidth = malloc (ncol * sizeof (int));
	assert (fieldwidth);
	j = 0;
	while (1) {
		if (sscanf (f, "%d", &fieldwidth[j] ) != 1)
			return 0;
		recordwidth += fieldwidth[j];
		j++;
		while (isdigit ((int)*f))
			f++;
		if (*f == 0)
			break;
		if (*f != ':') 
			return 0;
		f++;
	}
	if (j != ncol)
		return 0;
	return 1;
}

void create (char * file)
{
	char * buf, * record;
	int i, len, offset;
	int fd;
	buf = malloc ((recordwidth+1)*sizeof (char));
	record = malloc ((recordwidth+1)*sizeof (char));
	assert (buf); assert (record);
	offset = 0;
	i = 0;
	while (i < ncol) {
		printf ("Beschreibung %d. Feld (maximal %d Zeichen: ",
			i+1, fieldwidth[i]); 
		fgets (buf, recordwidth+1, stdin);
		len = strlen (buf);
		if (buf[len-1] == '\n') {
			buf[len-1] = 0;
			len--;
		}
		if (len > fieldwidth[i]) {
			fprintf (stderr, "Beschreibung zu lang\n");
			continue;
		}
		strncpy (record+offset, buf, fieldwidth[i]);
		offset += fieldwidth[i];
		i++;
	}
	free (buf);
	fd = open (file, O_WRONLY | O_CREAT | O_EXCL, 0666);
	if (fd < 0) {
		perror ("open");
		exit (1);
	}
	if (write (fd, record, recordwidth) < 0) {
		perror ("write");
		exit (1);
	}
	if (close (fd) < 0) {
		perror ("close");
		exit (1);
	}
	free (record);
	printf ("OK. Datenbank mit dem Namen %s erzeugt\n", file);
}

void show (char * file)
{
	int i, fd, ret, offset;
	char * buf;
	char * buf2;
	fd = open (file, O_RDONLY);
	if (fd < 0) {
		perror ("open");
		exit (1);
	}
	buf = malloc (recordwidth * sizeof (char));
	buf2 = malloc ((recordwidth+1)* sizeof (char));
	assert (buf);
	while (1) {
		ret = read (fd, buf, recordwidth);
		if (ret < 0) {
			perror ("read");
		}
		if (ret == 0)
			break;
		if (ret != recordwidth) {
			fprintf (stderr, "Datenbank kaputt\n");
			exit (1);
		}
		offset = 0;
		for (i=0; i<ncol; ++i) {
			strncpy (buf2, buf+offset, fieldwidth[i]);
			buf2[fieldwidth[i]] = 0;
			printf ("%-*s ", fieldwidth[i], buf2);
			offset += fieldwidth[i];
		}
		printf ("\n");
	}
	free (buf);
	free (buf2);
	close (fd);
}

void append (char * file)
{
	char * buf, * record;
	char * desc, * desc2;
	int i, len, offset;
	int fd, ret;
	buf = malloc ((recordwidth+1)*sizeof (char));
	record = malloc ((recordwidth+1)*sizeof (char));
	desc = malloc ((recordwidth+1)*sizeof (char));
	desc2 = malloc ((recordwidth+1)*sizeof (char));
	assert (buf); assert (record); assert (desc); assert (desc2);
	fd = open (file, O_RDONLY);
	if (fd < 0) {
		perror ("open (read)");
		exit (1);
	}
	ret = read (fd, desc, recordwidth);
	if (ret < 0) {
		perror ("read");
		exit (1);
	}
	if (ret != recordwidth) {
		fprintf (stderr, "Datenbank kaputt\n");
		exit (1);
	}
	close (fd);
	offset = 0;
	i = 0;
	while (i < ncol) {
		strncpy (desc2, desc+offset, fieldwidth[i]);
		desc2[fieldwidth[i]] = 0;
		printf ("%s: ", desc2);
		fgets (buf, recordwidth+1, stdin);
		len = strlen (buf);
		if (buf[len-1] == '\n') {
			buf[len-1] = 0;
			len--;
		}
		if (len > fieldwidth[i]) {
			fprintf (stderr, "Text zu lang\n");
			continue;
		}
		strncpy (record+offset, buf, fieldwidth[i]);
		offset += fieldwidth[i];
		i++;
	}
	free (desc);
	free (desc2);
	free (buf);
	fd = open (file, O_WRONLY | O_APPEND);
	if (fd < 0) {
		perror ("open");
		exit (1);
	}
	if (write (fd, record, recordwidth) < 0) {
		perror ("write");
		exit (1);
	}
	if (close (fd) < 0) {
		perror ("close");
		exit (1);
	}
	free (record);
	printf ("OK. Datensatz zu %s hinzugefuegt\n", file);
}

int main (int argc, char *argv[])
{
	if (argc != 4)
		usage (argv[0]);
	if (argv[1][0] != '-')
		usage (argv[0]);
	if (!argv[1][1] || argv[1][2])
		usage (argv[0]);
	if (!readformat (argv[3]))
		usage (argv[0]);
	switch (argv[1][1]) {
	case 'c':
		create (argv[2]);
		break;
	case 's':
		show (argv[2]);
		break;
	case 'a':
		append (argv[2]);
		break;
	default:
		usage (argv[0]);
	}
	return 0;
}