/*
 * (C) 2023 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
 * Author: Vadim Yanitskiy <vyanitskiy@sysmocom.de>
 *
 * All Rights Reserved
 *
 * 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 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 <stdint.h>
#include <errno.h>

#include <osmocom/core/bits.h>
#include <osmocom/core/utils.h>
#include <osmocom/gsm/gsm44021.h>
#include <osmocom/gsm/gsm_utils.h>
#include <osmocom/gsm/protocol/gsm_04_08.h>
#include <osmocom/isdn/v110.h>

#include <osmo-bts/csd_v110.h>
#include <osmo-bts/lchan.h>

/* key is enum gsm48_chan_mode, so assuming a value in range 0..255 */
const struct csd_v110_lchan_desc csd_v110_lchan_desc[256] = {
#if 0
	[GSM48_CMODE_DATA_14k5] = {
		/* TCH/F14.4: 290 bits every 20 ms (14.5 kbit/s) */
		.fr = { .num_blocks = 1, .num_bits = 290 },
	},
#endif
	[GSM48_CMODE_DATA_12k0] = {
		/* TCH/F9.6: 4 * 60 bits every 20 ms (12.0 kbit/s) */
		.fr = { .num_blocks = 4, .num_bits = 60 },
	},
	[GSM48_CMODE_DATA_6k0] = {
		/* TCH/F4.8: 2 * 60 bits every 20 ms (6.0 kbit/s) */
		.fr = { .num_blocks = 2, .num_bits = 60 },
		/* TCH/H4.8: 4 * 60 bits every 40 ms (6.0 kbit/s) */
		.hr = { .num_blocks = 4, .num_bits = 60 },
	},
	[GSM48_CMODE_DATA_3k6] = {
		/* TCH/F2.4: 2 * 36 bits every 20 ms (3.6 kbit/s) */
		.fr = { .num_blocks = 2, .num_bits = 36 },
		/* TCH/H2.4: 4 * 36 bits every 40 ms (3.6 kbit/s) */
		.hr = { .num_blocks = 4, .num_bits = 36 },
	},
};

int csd_v110_rtp_encode(const struct gsm_lchan *lchan, uint8_t *rtp,
			const uint8_t *data, size_t data_len)
{
	const struct csd_v110_frame_desc *desc;
	ubit_t ra_bits[80 * 4];

	OSMO_ASSERT(lchan->tch_mode < ARRAY_SIZE(csd_v110_lchan_desc));
	if (lchan->type == GSM_LCHAN_TCH_F)
		desc = &csd_v110_lchan_desc[lchan->tch_mode].fr;
	else
		desc = &csd_v110_lchan_desc[lchan->tch_mode].hr;
	if (OSMO_UNLIKELY(desc->num_blocks == 0))
		return -ENOTSUP;

	/* handle empty/incomplete frames gracefully */
	if (OSMO_UNLIKELY(data_len < (desc->num_blocks * desc->num_bits)))
		return -ENODATA;

	/* RA1'/RA1: convert to an intermediate data rate */
	for (unsigned int i = 0; i < desc->num_blocks; i++) {
		struct osmo_v110_decoded_frame df;

		/* convert modified V.110 frames to normal V.110 frames */
		if (desc->num_bits == 60)
			osmo_csd_12k_6k_decode_frame(&df, &data[i * 60], 60);
		else /* desc->num_bits == 36 */
			osmo_csd_3k6_decode_frame(&df, &data[i * 36], 36);

		/* FIXME: E1 .. E3 must be set by out-of-band knowledge! */
		memset(&df.e_bits[0], 0, 3);

		osmo_v110_encode_frame(&ra_bits[i * 80], 80, &df);
	}

	/* RA1/RA2: convert from an intermediate rate to 64 kbit/s */
	if (desc->num_blocks == 4) {
		/* 4 * 80 bits (16 kbit/s) => 2 bits per octet */
		for (unsigned int i = 0, j = 0; i < RFC4040_RTP_PLEN; i++) {
			rtp[i]  = (0xff >> 2);
			rtp[i] |= (ra_bits[j++] << 7);
			rtp[i] |= (ra_bits[j++] << 6);
		}
	} else {
		/* 2 * 80 bits (8 kbit/s) => 1 bit per octet */
		for (unsigned int i = 0; i < RFC4040_RTP_PLEN; i++) {
			rtp[i]  = (0xff >> 1);
			rtp[i] |= (ra_bits[i] << 7);
		}
	}

	return RFC4040_RTP_PLEN;
}

int csd_v110_rtp_decode(const struct gsm_lchan *lchan, uint8_t *data,
			const uint8_t *rtp, size_t rtp_len)
{
	const struct csd_v110_frame_desc *desc;
	ubit_t ra_bits[80 * 4];

	OSMO_ASSERT(lchan->tch_mode < ARRAY_SIZE(csd_v110_lchan_desc));
	if (lchan->type == GSM_LCHAN_TCH_F)
		desc = &csd_v110_lchan_desc[lchan->tch_mode].fr;
	else
		desc = &csd_v110_lchan_desc[lchan->tch_mode].hr;
	if (OSMO_UNLIKELY(desc->num_blocks == 0))
		return -ENOTSUP;

	if (OSMO_UNLIKELY(rtp_len != RFC4040_RTP_PLEN))
		return -EINVAL;

	/* RA1/RA2: convert from 64 kbit/s to an intermediate rate */
	if (desc->num_blocks == 4) {
		/* 4 * 80 bits (16 kbit/s) => 2 bits per octet */
		for (unsigned int i = 0, j = 0; i < RFC4040_RTP_PLEN; i++) {
			ra_bits[j++] = (rtp[i] >> 7);
			ra_bits[j++] = (rtp[i] >> 6) & 0x01;
		}
	} else {
		/* 2 * 80 bits (8 kbit/s) => 1 bit per octet */
		for (unsigned int i = 0; i < RFC4040_RTP_PLEN; i++)
			ra_bits[i] = (rtp[i] >> 7);
	}

	/* RA1'/RA1: convert to an intermediate data rate */
	for (unsigned int i = 0; i < desc->num_blocks; i++) {
		struct osmo_v110_decoded_frame df;

		/* convert modified V.110 frames to normal V.110 frames */
		osmo_v110_decode_frame(&df, &ra_bits[i * 80], 80);
		if (desc->num_bits == 60)
			osmo_csd_12k_6k_encode_frame(&data[i * 60], 60, &df);
		else /* desc->num_bits == 36 */
			osmo_csd_3k6_encode_frame(&data[i * 36], 36, &df);
	}

	return desc->num_blocks * desc->num_bits;
}