#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

#include <osmocom/gsm/apn.h>

#define APN_OI_GPRS_FMT	"mnc%03u.mcc%03u.gprs"
#define APN_GPRS_FMT	"%s.mnc%03u.mcc%03u.gprs"

static char apn_strbuf[APN_MAXLEN+1];

char *osmo_apn_qualify(unsigned int mcc, unsigned int mnc, const char *ni)
{
	snprintf(apn_strbuf, sizeof(apn_strbuf)-1, APN_GPRS_FMT,
		ni, mnc, mcc);
	apn_strbuf[sizeof(apn_strbuf)-1] = '\0';

	return apn_strbuf;
}

char *osmo_apn_qualify_from_imsi(const char *imsi,
				 const char *ni, int have_3dig_mnc)
{
	char cbuf[3+1], nbuf[3+1];

	strncpy(cbuf, imsi, 3);
	cbuf[3] = '\0';

	if (have_3dig_mnc) {
		strncpy(nbuf, imsi+3, 3);
		nbuf[3] = '\0';
	} else {
		strncpy(nbuf, imsi+3, 2);
		nbuf[2] = '\0';
	}
	return osmo_apn_qualify(atoi(cbuf), atoi(nbuf), ni);
}

/**
 * Convert an encoded APN into a dot-separated string.
 *
 * \param out_str      the destination buffer (size must be >= max(app_enc_len,1))
 * \param apn_enc      the encoded APN
 * \param apn_enc_len  the length of the encoded APN
 *
 * \returns out_str on success and NULL otherwise
 */
char * osmo_apn_to_str(char *out_str, const uint8_t *apn_enc, size_t apn_enc_len)
{
	char *str = out_str;
	size_t rest_chars = apn_enc_len;

	while (rest_chars > 0 && apn_enc[0]) {
		size_t label_size = apn_enc[0];
		if (label_size + 1 > rest_chars)
			return NULL;

		memmove(str, apn_enc + 1, label_size);
		str += label_size;
		rest_chars -= label_size + 1;
		apn_enc += label_size + 1;

		if (rest_chars)
			*(str++) = '.';
	}
	str[0] = '\0';

	return out_str;
}

/**
 * Convert a dot-separated string into an encoded APN.
 *
 * \param apn_enc          the encoded APN
 * \param max_apn_enc_len  the size of the apn_enc buffer
 * \param str              the source string
 *
 * \returns out_str on success and NULL otherwise
 */
int osmo_apn_from_str(uint8_t *apn_enc, size_t max_apn_enc_len, const char *str)
{
	uint8_t *last_len_field;
	int len;

	/* Can we even write the length field to the output? */
	if (max_apn_enc_len == 0)
		return -1;

	/* Remember where we need to put the length once we know it */
	last_len_field = apn_enc;
	len = 1;
	apn_enc += 1;

	while (str[0]) {
		if (len >= max_apn_enc_len)
			return -1;

		if (str[0] == '.') {
			*last_len_field = (apn_enc - last_len_field) - 1;
			last_len_field = apn_enc;
		} else {
			*apn_enc = str[0];
		}
		apn_enc += 1;
		str += 1;
		len += 1;
	}

	*last_len_field = (apn_enc - last_len_field) - 1;

	return len;
}