/* LAPV5-DL as per Section 10.1 of ITU-T G.964 */

/* (C) 2021 by Harald Welte <laforge@gnumonks.org>
 *
 * All Rights Reserved
 *
 * SPDX-License-Identifier: GPL-2.0+
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 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 General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 */

#include "v5x_internal.h"
#include "v5x_protocol.h"
#include "lapv5.h"

#include <stdio.h>
#include <string.h>
#include <errno.h>

#include <osmocom/core/linuxlist.h>
#include <osmocom/core/logging.h>
#include <osmocom/core/talloc.h>
#include <osmocom/core/msgb.h>
#include <osmocom/core/timer.h>
#include <osmocom/abis/lapd.h>
#include <osmocom/abis/lapd_pcap.h>

#define LAPD_ADDR2(sapi, cr) ((((sapi) & 0x3f) << 2) | (((cr) & 0x1) << 1))
#define LAPD_ADDR3(tei) ((((tei) & 0x7f) << 1) | 0x1)

#define LAPD_ADDR_SAPI(addr) ((addr) >> 2)
#define LAPD_ADDR_CR(addr) (((addr) >> 1) & 0x1)
#define LAPD_ADDR_EA(addr) ((addr) & 0x1)
#define LAPD_ADDR_TEI(addr) ((addr) >> 1)

#define LAPD_CTRL_I4(ns) (((ns) & 0x7f) << 1)
#define LAPD_CTRL_I5(nr, p) ((((nr) & 0x7f) << 1) | ((p) & 0x1))
#define LAPD_CTRL_S4(s) ((((s) & 0x3) << 2) | 0x1)
#define LAPD_CTRL_S5(nr, p) ((((nr) & 0x7f) << 1) | ((p) & 0x1))
#define LAPD_CTRL_U4(u, p) ((((u) & 0x1c) << (5-2)) | (((p) & 0x1) << 4) | (((u) & 0x3) << 2) | 0x3)

#define LAPD_CTRL_is_I(ctrl)	(((ctrl) & 0x1) == 0)
#define LAPD_CTRL_is_S(ctrl)	(((ctrl) & 0x3) == 1)
#define LAPD_CTRL_is_U(ctrl)	(((ctrl) & 0x3) == 3)

#define LAPD_CTRL_U_BITS(ctrl)	((((ctrl) & 0xC) >> 2) | ((ctrl) & 0xE0) >> 3)
#define LAPD_CTRL_U_PF(ctrl)	(((ctrl) >> 4) & 0x1)

#define LAPD_CTRL_S_BITS(ctrl)	(((ctrl) & 0xC) >> 2)
#define LAPD_CTRL_S_PF(ctrl)	(ctrl & 0x1)

#define LAPD_CTRL_I_Ns(ctrl)	(((ctrl) & 0xFE) >> 1)
#define LAPD_CTRL_I_P(ctrl)	(ctrl & 0x1)
#define LAPD_CTRL_Nr(ctrl)	(((ctrl) & 0xFE) >> 1)

#define LAPD_LEN(len)	((len << 2) | 0x1)
#define LAPD_EL	0x1

#define LAPD_SET_K(n, o)  {n,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}

#define LOGLI(li, level, fmt, args ...) \
	LOGP(DLLAPD, level, "(%s): " fmt, (li)->name, ## args)

#define LOGSAP(sap, level, fmt, args ...) \
	LOGP(DLLAPD, level, "(%s): " fmt, (sap)->dl.name, ## args)

#define DLSAP_MSGB_SIZE		128
#define DLSAP_MSGB_HEADROOM	56

const struct lapd_profile lapd_profile_lapv5dl = {
	.k		= LAPD_SET_K(7,7),
	.n200		= 3,
	.n201		= 260,
	.n202		= 3,
	.t200_sec	= 1,	.t200_usec	= 0,
	.t203_sec	= 10,	.t203_usec	= 0,
	.short_address	= 0
};


/* Structure representing a SAP within a TEI. It includes exactly one datalink
 * instance. */
struct lapv5_sap {
	struct llist_head list;		/* list of SAP within instance */
	struct lapv5_instance *li;	/* back-pointer */
	uint16_t dladdr;		/* V5-Data Link Address */

	struct lapd_datalink dl;	/* the actual data link */
};

/* Find a SAP within a given TEI */
static struct lapv5_sap *lapv5_sap_find(struct lapv5_instance *li, uint16_t dladdr)
{
	struct lapv5_sap *sap;

	llist_for_each_entry(sap, &li->sap_list, list) {
		if (sap->dladdr == dladdr)
			return sap;
	}

	return NULL;
}

static int send_ph_data_req(struct lapd_msg_ctx *lctx, struct msgb *msg);
static int send_dlsap(struct osmo_dlsap_prim *dp, struct lapd_msg_ctx *lctx);

/* Allocate a new SAP within a given instance */
static struct lapv5_sap *lapv5_sap_alloc(struct lapv5_instance *li, uint16_t v5dladdr)
{
	struct lapv5_sap *sap;
	struct lapd_datalink *dl;
	struct lapd_profile *profile;
	char name[256];
	int k;

	snprintf(name, sizeof(name), "%s-%u", li->name, v5dladdr);

	sap = talloc_zero(li, struct lapv5_sap);
	if (!sap)
		return NULL;

	LOGP(DLLAPD, LOGL_NOTICE, "(%s): LAPV5 Allocating SAP for V5_DLADDR=%u (dl=%p, sap=%p)\n",
	     name, v5dladdr, &sap->dl, sap);

	sap->dladdr = v5dladdr;
	dl = &sap->dl;
	profile = &li->profile;

	k = profile->k[0];
	LOGP(DLLAPD, LOGL_NOTICE, "(%s): k=%d N200=%d N201=%d T200=%d.%d T203=%d.%d\n",
		name, k, profile->n200, profile->n201, profile->t200_sec,
		profile->t200_usec, profile->t203_sec, profile->t203_usec);
	lapd_dl_init2(dl, k, 128, profile->n201, name);
	dl->use_sabme = 1; /* use SABME instead of SABM (GSM) */
	dl->send_ph_data_req = send_ph_data_req;
	dl->send_dlsap = send_dlsap;
	dl->n200 = profile->n200;
	dl->n200_est_rel = profile->n200;
	dl->t200_sec = profile->t200_sec; dl->t200_usec = profile->t200_usec;
	dl->t203_sec = profile->t203_sec; dl->t203_usec = profile->t203_usec;
	dl->lctx.dl = &sap->dl;
	dl->lctx.sapi = v5dladdr & 0xff;
	dl->lctx.tei = v5dladdr >> 8;
	dl->lctx.n201 = profile->n201;

	lapd_set_mode(&sap->dl, (li->network_side) ? LAPD_MODE_NETWORK : LAPD_MODE_USER);

	llist_add(&sap->list, &li->sap_list);

	return sap;
}

/* Free SAP instance, including the datalink */
static void lapv5_sap_free(struct lapv5_sap *sap)
{
	LOGSAP(sap, LOGL_NOTICE, "LAPV5 Freeing SAP for DLADDR=%u (dl=%p, sap=%p)\n", sap->dladdr, &sap->dl, sap);

	/* free datalink structures and timers */
	lapd_dl_exit(&sap->dl);

	llist_del(&sap->list);
	talloc_free(sap);
}

/* General input function for any data received for this LAPV5 instance */
int lapv5_receive(struct lapv5_instance *li, struct msgb *msg, int *error)
{
	struct lapd_msg_ctx lctx;
	struct lapv5_sap *sap;
	uint16_t dladdr;
	bool is_isdn;
	int i;

	/* write to PCAP file, if enabled. */
	osmo_pcap_lapd_write(li->pcap_fd, OSMO_LAPD_PCAP_INPUT, msg);

	LOGLI(li, LOGL_DEBUG, "RX: %s\n", osmo_hexdump(msg->data, msg->len));
	if (msg->len < 2) {
		LOGLI(li, LOGL_ERROR, "LAPV5 frame receive len %d < 2, ignoring\n", msg->len);
		*error = LAPD_ERR_BAD_LEN;
		return -EINVAL;
	};
	msg->l2h = msg->data;

	memset(&lctx, 0, sizeof(lctx));

	i = 0;
	/* adress field */
	dladdr = v51_l3_addr_dec(msg->l2h[0] << 8 | msg->l2h[1], &is_isdn);
	if (!is_isdn) {
		LOGLI(li, LOGL_ERROR, "LAPV5 frame with single-octet addr not permitted\n");
		*error = LAPD_ERR_BAD_LEN;
		return -EINVAL;
	};
	lctx.lpd = 0;
	lctx.tei = dladdr >> 8;
	lctx.sapi = dladdr & 0xff;
	lctx.cr = LAPD_ADDR_CR(msg->l2h[0]);
	i += 2;

	/* control field */
	if (LAPD_CTRL_is_I(msg->l2h[i])) {
		lctx.format = LAPD_FORM_I;
		lctx.n_send = LAPD_CTRL_I_Ns(msg->l2h[i]);
		i++;
		if (msg->len < 4) {
			LOGLI(li, LOGL_ERROR, "LAPV5 I frame receive len %d < 4, ignoring\n", msg->len);
			*error = LAPD_ERR_BAD_LEN;
			return -EINVAL;
		}
		lctx.n_recv = LAPD_CTRL_Nr(msg->l2h[i]);
		lctx.p_f = LAPD_CTRL_I_P(msg->l2h[i]);
	} else if (LAPD_CTRL_is_S(msg->l2h[i])) {
		lctx.format = LAPD_FORM_S;
		lctx.s_u = LAPD_CTRL_S_BITS(msg->l2h[i]);
		i++;
		if (msg->len < 4 && i == 3) {
			LOGLI(li, LOGL_ERROR, "LAPV5 S frame receive len %d < 4, ignoring\n", msg->len);
			*error = LAPD_ERR_BAD_LEN;
			return -EINVAL;
		}
		lctx.n_recv = LAPD_CTRL_Nr(msg->l2h[i]);
		lctx.p_f = LAPD_CTRL_S_PF(msg->l2h[i]);
	} else if (LAPD_CTRL_is_U(msg->l2h[i])) {
		lctx.format = LAPD_FORM_U;
		lctx.s_u = LAPD_CTRL_U_BITS(msg->l2h[i]);
		lctx.p_f = LAPD_CTRL_U_PF(msg->l2h[i]);
	} else
		lctx.format = LAPD_FORM_UKN;
	i++;
	/* length */
	msg->l3h = msg->l2h + i;
	msgb_pull(msg, i);
	lctx.length = msg->len;

	sap = lapv5_sap_find(li, dladdr);
	if (!sap) {
		LOGLI(li, LOGL_INFO, "LAPV5 No SAP for DLADDR=%u, allocating\n", dladdr);
		sap = lapv5_sap_alloc(li, dladdr);
		if (!sap) {
			*error = LAPD_ERR_NO_MEM;
			msgb_free(msg);
			return -ENOMEM;
		}
	}
	lctx.dl = &sap->dl;
	lctx.n201 = lctx.dl->maxf;

	if (msg->len > lctx.n201) {
		LOGSAP(sap, LOGL_ERROR, "message len %d > N201(%d) (discarding)\n", msg->len, lctx.n201);
		msgb_free(msg);
		*error = LAPD_ERR_BAD_LEN;
		return -EINVAL;
	}

	/* send to LAPD */
	return lapd_ph_data_ind(msg, &lctx);
}

/* Start a (user-side) SAP for the specified TEI/SAPI on the LAPD instance */
int lapv5_sap_start(struct lapv5_instance *li, uint16_t dladdr)
{
	struct lapv5_sap *sap;
	struct osmo_dlsap_prim dp;
	struct msgb *msg;

	sap = lapv5_sap_find(li, dladdr);
	if (sap)
		return -EEXIST;

	sap = lapv5_sap_alloc(li, dladdr);
	if (!sap)
		return -ENOMEM;

	LOGSAP(sap, LOGL_NOTICE, "LAPV5 DL-ESTABLISH request DLADDR=%u\n", dladdr);

	/* prepare prim */
	msg = msgb_alloc_headroom(DLSAP_MSGB_SIZE, DLSAP_MSGB_HEADROOM, "DL EST");
	msg->l3h = msg->data;
        osmo_prim_init(&dp.oph, 0, PRIM_DL_EST, PRIM_OP_REQUEST, msg);

        /* send to L2 */
        return lapd_recv_dlsap(&dp, &sap->dl.lctx);
}

/* Stop a (user-side) SAP for the specified TEI/SAPI on the LAPD instance */
int lapv5_sap_stop(struct lapv5_instance *li, uint16_t dladdr)
{
	struct lapv5_sap *sap;
	struct osmo_dlsap_prim dp;
	struct msgb *msg;

	sap = lapv5_sap_find(li, dladdr);
	if (!sap)
		return -ENODEV;

	LOGSAP(sap, LOGL_NOTICE, "LAPV5 DL-RELEASE request DLADDR=%u\n", dladdr);

	/* prepare prim */
	msg = msgb_alloc_headroom(DLSAP_MSGB_SIZE, DLSAP_MSGB_HEADROOM, "DL REL");
	msg->l3h = msg->data;
        osmo_prim_init(&dp.oph, 0, PRIM_DL_REL, PRIM_OP_REQUEST, msg);

        /* send to L2 */
        return lapd_recv_dlsap(&dp, &sap->dl.lctx);
}

/* Transmit Data (DL-DATA request) on the given LAPD Instance / DLADDR */
void lapv5_transmit(struct lapv5_instance *li, uint8_t dladdr, struct msgb *msg)
{
	struct lapv5_sap *sap;
	struct osmo_dlsap_prim dp;

	sap = lapv5_sap_find(li, dladdr);
	if (!sap) {
		LOGLI(li, LOGL_INFO, "LAPV5 Tx on unknown DLADDR=%u\n", dladdr);
		msgb_free(msg);
		return;
	}

	/* prepare prim */
	msg->l3h = msg->data;
        osmo_prim_init(&dp.oph, 0, PRIM_DL_DATA, PRIM_OP_REQUEST, msg);

        /* send to L2 */
        lapd_recv_dlsap(&dp, &sap->dl.lctx);
};

static int send_ph_data_req(struct lapd_msg_ctx *lctx, struct msgb *msg)
{
	struct lapd_datalink *dl = lctx->dl;
	struct lapv5_sap *sap = container_of(dl, struct lapv5_sap, dl);
	struct lapv5_instance *li = sap->li;
	int format = lctx->format;

	/* control field */
	switch (format) {
	case LAPD_FORM_I:
		msg->l2h = msgb_push(msg, 2);
		msg->l2h[0] = LAPD_CTRL_I4(lctx->n_send);
		msg->l2h[1] = LAPD_CTRL_I5(lctx->n_recv, lctx->p_f);
		break;
	case LAPD_FORM_S:
		msg->l2h = msgb_push(msg, 2);
		msg->l2h[0] = LAPD_CTRL_S4(lctx->s_u);
		msg->l2h[1] = LAPD_CTRL_S5(lctx->n_recv, lctx->p_f);
		break;
	case LAPD_FORM_U:
		msg->l2h = msgb_push(msg, 1);
		msg->l2h[0] = LAPD_CTRL_U4(lctx->s_u, lctx->p_f);
		break;
	default:
		msgb_free(msg);
		return -EINVAL;
	}
	/* address field */
	msg->l2h = msgb_push(msg, 2);
	msg->l2h[0] = LAPD_ADDR2(lctx->sapi, lctx->cr);
	msg->l2h[1] = LAPD_ADDR3(lctx->tei);

	/* write to PCAP file, if enabled. */
	osmo_pcap_lapd_write(li->pcap_fd, OSMO_LAPD_PCAP_OUTPUT, msg);

	/* forward frame to L1 */
	LOGDL(dl, LOGL_DEBUG, "TX: %s\n", osmo_hexdump(msg->data, msg->len));
	li->transmit_cb(msg, li->transmit_cbdata);

	return 0;
}

/* A DL-SAP message is received from datalink instance and forwarded to L3 */
static int send_dlsap(struct osmo_dlsap_prim *dp, struct lapd_msg_ctx *lctx)
{
	struct lapd_datalink *dl = lctx->dl;
	struct lapv5_sap *sap = container_of(dl, struct lapv5_sap, dl);
	struct lapv5_instance *li;
	const char *op = (dp->oph.operation == PRIM_OP_INDICATION) ? "indication" : "confirm";
	uint16_t dladdr;

	li = sap->li;

	dladdr = lctx->tei << 8 | lctx->sapi;

	switch (dp->oph.primitive) {
	case PRIM_DL_EST:
		LOGDL(dl, LOGL_NOTICE, "LAPD DL-ESTABLISH %s DLADDR=%u\n", op, dladdr);
		break;
	case PRIM_DL_REL:
		LOGDL(dl, LOGL_NOTICE, "LAPD DL-RELEASE %s DLADDR=%u\n", op, dladdr);
		lapv5_sap_free(sap);
		/* note: sap and dl is now gone, don't use it anymore */
		break;
	default:
		;
	}

	li->receive_cb(dp, dladdr, li->receive_cbdata);

	return 0;
}

/* Allocate a new LAPV5 instance */
struct lapv5_instance *lapv5_instance_alloc(int network_side,
	void (*tx_cb)(struct msgb *msg, void *cbdata), void *tx_cbdata,
	void (*rx_cb)(struct osmo_dlsap_prim *odp, uint16_t dladdr, void *rx_cbdata), void *rx_cbdata,
	const struct lapd_profile *profile, const char *name)
{
	struct lapv5_instance *li;

	li = talloc_zero(NULL, struct lapv5_instance);
	if (!li)
		return NULL;

	li->network_side = network_side;
	li->transmit_cb = tx_cb;
	li->transmit_cbdata = tx_cbdata;
	li->receive_cb = rx_cb;
	li->receive_cbdata = rx_cbdata;
	li->pcap_fd = -1;
	li->name = talloc_strdup(li, name);
	memcpy(&li->profile, profile, sizeof(li->profile));

	INIT_LLIST_HEAD(&li->sap_list);

	return li;
}


/* Change lapd-profile on the fly (use with caution!) */
void lapv5_instance_set_profile(struct lapv5_instance *li, const struct lapd_profile *profile)
{
	memcpy(&li->profile, profile, sizeof(li->profile));
}

void lapv5_instance_free(struct lapv5_instance *li)
{
	struct lapv5_sap *sap, *sap2;

	/* Free all SAP instances */
	llist_for_each_entry_safe(sap, sap2, &li->sap_list, list) {
		lapv5_sap_free(sap);
	}

	talloc_free(li);
}

/***********************************************************************
 * LAPV5-EF (Encapsulation Function)
 ***********************************************************************/

/* The LAPV5-EF adds another layer around of the LAPD-style LAPV5-DL.  It consists of
 * a two-byte header in front of the normal data link header. Examples see Figure E.1/G.964 */


/* main entry point for receiving signaling frames from the AN. The assumption is that
 * the flag octets are removed and the msg->data points to the first octet of the EFaddr,
 * while the last octet (before msg->tail) points to the last FCS octet. */
int lapv5ef_rx(struct v5x_link *link, struct msgb *msg)
{
	struct lapd_datalink *dl;
	uint16_t efaddr, efaddr_enc;
	bool is_isdn;

	msg->l1h = msg->data;

	if (msgb_length(msg) < 2) {
		msgb_free(msg);
		return -EINVAL;
	}

	msg->l2h = msg->l1h + 2;
	efaddr_enc = msg->l1h[0] << 8 | msg->l1h[1];
	efaddr = v51_l3_addr_dec(efaddr_enc, &is_isdn);

	if (!is_isdn) {
		/* EFaddr are structured like isdn-type L3 Address */
		msgb_free(msg);
		return -EINVAL;
	}

	switch (efaddr) {
	case V51_DLADDR_PSTN:
		/* hand-over to LAPD-DL instance for PSTN */
		dl = &link->interface->pstn.dl;
		/* TODO */
		break;
	case V51_DLADDR_CTRL:
		/* hand-over to LAPD-DL instance for CTRL */
		/* TODO */
		dl = &link->interface->control.dl;
		break;
	case V52_DLADDR_BCC:
		dl = &link->interface->bcc.dl;
		/* TOOD: implement V5.2 */
		msgb_free(msg);
		break;
	case V52_DLADDR_PROTECTION:
		dl = &link->interface->protection[0].dl;
		/* TOOD: implement V5.2 */
		msgb_free(msg);
		break;
	case V52_DLADDR_LCP:
		dl = &link->interface->lcp.dl;
		/* TOOD: implement V5.2 */
		msgb_free(msg);
		break;
	default:
		if (efaddr >= 8176) {
			/* reserved as per Section 9.2.2.2 of G.964 */
			msgb_free(msg);
			return -EINVAL;
		}
		/* relay function for LAPD of user ports */
		/* TODO */
	}

	return 0;
}