/* Osmocom CBC (Cell Broacast Centre) */

/* (C) 2019 by Harald Welte <laforge@gnumonks.org>
 * All Rights Reserved
 *
 * SPDX-License-Identifier: AGPL-3.0+
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#include <iconv.h>
#include <osmocom/gsm/gsm_utils.h>
#include <osmocom/core/utils.h>

#include <osmocom/cbc/charset.h>

/* pad the entire "remainder" of a buffer with repeated instances of the given pad character */
static void pad_with_septets(uint8_t *buf, size_t buf_len, int num_septets, char pad_char)
{
	unsigned int bit_offset;

	for (bit_offset = num_septets * 7; bit_offset + 7 <= buf_len * 8; bit_offset += 7) {
		unsigned int byte_offset = bit_offset / 8;
		unsigned int bits = bit_offset % 8;

		/* put one more septet */
		buf[byte_offset] |= ((pad_char << bits) & 0xff);
		if (bits > 1)
			buf[byte_offset+1] = (pad_char) >> (8-bits);
	}
}


/* return number of output bytes written */
int charset_utf8_to_gsm7(uint8_t *out, size_t out_len, const char *in, size_t in_len)
{
	int octets, num_septets, num_bits, num_bytes_used;

	/* FIXME: implement this for 'escape' characters outside 7bit alphabet */
	num_septets = gsm_7bit_encode_n(out, out_len, in, &octets);
	num_bits = num_septets * 7;

	/* we need to pad the entire remainder of the message with <CR> */
	pad_with_septets(out, out_len, num_septets, '\r');

	/* return actual number of output octets used, excluding any padding */
	num_bytes_used = num_bits/8;
	if (num_bits % 8)
		num_bytes_used++;
	return num_bytes_used;
}

/* return number of output bytes written */
int charset_gsm7_to_utf8(char *out, size_t out_len, const uint8_t *in, size_t in_len)
{
	/* FIXME: implement this for 'escape' characters outside 7bit alphabet */
	return gsm_7bit_decode_n_ussd(out, out_len, in, in_len);
}


static struct {
	iconv_t utf8_to_ucs2;
	iconv_t ucs2_to_utf8;
} g_iconv_state;

int charset_utf8_to_ucs2(uint8_t *out, size_t out_len, const char *in, size_t in_len)
{
	iconv_t ic = g_iconv_state.utf8_to_ucs2;
	int rc;

	/* reset the conversion state */
	rc = iconv(ic, NULL, NULL, NULL, NULL);
	if (rc < 0)
		return rc;

	return iconv(ic, (char **) &in, &in_len, (char **) &out, &out_len);
}

int charset_ucs2_to_utf8(char *out, size_t out_len, const uint8_t *in, size_t in_len)
{
	iconv_t ic = g_iconv_state.ucs2_to_utf8;
	int rc;

	/* reset the conversion state */
	rc = iconv(ic, NULL, NULL, NULL, NULL);
	if (rc < 0)
		return rc;

	return iconv(ic, (char **) &in, &in_len, &out, &out_len);
}

static void __attribute__ ((constructor)) charset_init(void)
{
	g_iconv_state.utf8_to_ucs2 = iconv_open("UCS2", "utf8");
	OSMO_ASSERT(g_iconv_state.utf8_to_ucs2 != (iconv_t) -1);

	g_iconv_state.ucs2_to_utf8 = iconv_open("utf8", "UCS2");
	OSMO_ASSERT(g_iconv_state.utf8_to_ucs2 != (iconv_t) -1);
}