/* MSC subscriber connection implementation */

/*
 * (C) 2016 by sysmocom s.m.f.c. <info@sysmocom.de>
 * All Rights Reserved
 *
 * Author: Neels Hofmeyr
 *
 * 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 <osmocom/core/logging.h>
#include <osmocom/core/fsm.h>
#include <osmocom/core/signal.h>

#include <osmocom/msc/osmo_msc.h>
#include <osmocom/msc/vlr.h>
#include <osmocom/msc/debug.h>
#include <osmocom/msc/transaction.h>
#include <osmocom/msc/signal.h>
#include <osmocom/msc/a_iface.h>
#include <osmocom/msc/iucs.h>

#include "../../bscconfig.h"
#ifdef BUILD_IU
#include <osmocom/ranap/iu_client.h>
#else
#include <osmocom/msc/iu_dummy.h>
#endif

#define SUBSCR_CONN_TIMEOUT 5 /* seconds */

static const struct value_string subscr_conn_fsm_event_names[] = {
	OSMO_VALUE_STRING(SUBSCR_CONN_E_INVALID),
	OSMO_VALUE_STRING(SUBSCR_CONN_E_COMPLETE_LAYER_3),
	OSMO_VALUE_STRING(SUBSCR_CONN_E_ACCEPTED),
	OSMO_VALUE_STRING(SUBSCR_CONN_E_COMMUNICATING),
	OSMO_VALUE_STRING(SUBSCR_CONN_E_RELEASE_WHEN_UNUSED),
	OSMO_VALUE_STRING(SUBSCR_CONN_E_MO_CLOSE),
	OSMO_VALUE_STRING(SUBSCR_CONN_E_CN_CLOSE),
	OSMO_VALUE_STRING(SUBSCR_CONN_E_UNUSED),
	{ 0, NULL }
};

static void update_counters(struct osmo_fsm_inst *fi, bool conn_accepted)
{
	struct gsm_subscriber_connection *conn = fi->priv;
	switch (conn->complete_layer3_type) {
	case COMPLETE_LAYER3_LU:
		rate_ctr_inc(&conn->network->msc_ctrs->ctr[
				conn_accepted ? MSC_CTR_LOC_UPDATE_COMPLETED
					      : MSC_CTR_LOC_UPDATE_FAILED]);
		break;
	case COMPLETE_LAYER3_CM_SERVICE_REQ:
		rate_ctr_inc(&conn->network->msc_ctrs->ctr[
				conn_accepted ? MSC_CTR_CM_SERVICE_REQUEST_ACCEPTED
					      : MSC_CTR_CM_SERVICE_REQUEST_REJECTED]);
		break;
	case COMPLETE_LAYER3_PAGING_RESP:
		rate_ctr_inc(&conn->network->msc_ctrs->ctr[
				conn_accepted ? MSC_CTR_PAGING_RESP_ACCEPTED
					      : MSC_CTR_PAGING_RESP_REJECTED]);
		break;
	default:
		break;
	}
}

static void evaluate_acceptance_outcome(struct osmo_fsm_inst *fi, bool conn_accepted)
{
	struct gsm_subscriber_connection *conn = fi->priv;

	update_counters(fi, conn_accepted);

	/* Trigger transactions that we paged for */
	if (conn->complete_layer3_type == COMPLETE_LAYER3_PAGING_RESP) {
		subscr_paging_dispatch(GSM_HOOK_RR_PAGING,
				       conn_accepted ? GSM_PAGING_SUCCEEDED : GSM_PAGING_EXPIRED,
				       NULL, conn, conn->vsub);
	}

	if (conn->complete_layer3_type == COMPLETE_LAYER3_CM_SERVICE_REQ
	    && conn_accepted) {
		conn->received_cm_service_request = true;
		msc_subscr_conn_get(conn, MSC_CONN_USE_CM_SERVICE);
	}

	if (conn_accepted)
		osmo_signal_dispatch(SS_SUBSCR, S_SUBSCR_ATTACHED, conn->vsub);
}

static void log_close_event(struct osmo_fsm_inst *fi, uint32_t event, void *data)
{
	if (data)
		LOGPFSML(fi, LOGL_DEBUG, "Close event, cause %u\n", *(uint32_t*)data);
}

static void subscr_conn_fsm_new(struct osmo_fsm_inst *fi, uint32_t event, void *data)
{
	switch (event) {
	case SUBSCR_CONN_E_COMPLETE_LAYER_3:
		osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_AUTH_CIPH, SUBSCR_CONN_TIMEOUT, 0);
		return;

	case SUBSCR_CONN_E_ACCEPTED:
		evaluate_acceptance_outcome(fi, true);
		osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_ACCEPTED, SUBSCR_CONN_TIMEOUT, 0);
		return;

	case SUBSCR_CONN_E_MO_CLOSE:
	case SUBSCR_CONN_E_CN_CLOSE:
		log_close_event(fi, event, data);
		evaluate_acceptance_outcome(fi, false);
		/* fall through */
	case SUBSCR_CONN_E_UNUSED:
		osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_RELEASING, SUBSCR_CONN_TIMEOUT, 0);
		return;

	default:
		OSMO_ASSERT(false);
	}
}

void subscr_conn_fsm_auth_ciph(struct osmo_fsm_inst *fi, uint32_t event, void *data)
{
	/* If accepted, transition the state, all other cases mean failure. */
	switch (event) {
	case SUBSCR_CONN_E_ACCEPTED:
		evaluate_acceptance_outcome(fi, true);
		osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_ACCEPTED, SUBSCR_CONN_TIMEOUT, 0);
		return;

	case SUBSCR_CONN_E_UNUSED:
		LOGPFSML(fi, LOGL_DEBUG, "Awaiting results for Auth+Ciph, overruling event %s\n",
			 osmo_fsm_event_name(fi->fsm, event));
		return;

	case SUBSCR_CONN_E_MO_CLOSE:
	case SUBSCR_CONN_E_CN_CLOSE:
		log_close_event(fi, event, data);
		evaluate_acceptance_outcome(fi, false);
		osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_RELEASING, SUBSCR_CONN_TIMEOUT, 0);
		return;


	default:
		OSMO_ASSERT(false);
	}
}

static bool subscr_conn_fsm_has_active_transactions(struct osmo_fsm_inst *fi)
{
	struct gsm_subscriber_connection *conn = fi->priv;
	struct gsm_trans *trans;

	if (conn->silent_call) {
		LOGPFSML(fi, LOGL_DEBUG, "%s: silent call still active\n", __func__);
		return true;
	}

	if (conn->received_cm_service_request) {
		LOGPFSML(fi, LOGL_DEBUG, "%s: still awaiting first request after a CM Service Request\n",
			 __func__);
		return true;
	}

	if (conn->vsub && !llist_empty(&conn->vsub->cs.requests)) {
		struct subscr_request *sr;
		if (!log_check_level(fi->fsm->log_subsys, LOGL_DEBUG)) {
			llist_for_each_entry(sr, &conn->vsub->cs.requests, entry) {
				LOGPFSML(fi, LOGL_DEBUG, "%s: still active: %s\n",
					 __func__, sr->label);
			}
		}
		return true;
	}

	if ((trans = trans_has_conn(conn))) {
		LOGPFSML(fi, LOGL_DEBUG,
			 "%s: connection still has active transaction: %s\n",
			 __func__, gsm48_pdisc_name(trans->protocol));
		return true;
	}

	return false;
}

static void subscr_conn_fsm_accepted_enter(struct osmo_fsm_inst *fi, uint32_t prev_state)
{
	if (!subscr_conn_fsm_has_active_transactions(fi))
		osmo_fsm_inst_dispatch(fi, SUBSCR_CONN_E_UNUSED, NULL);
}

static void subscr_conn_fsm_accepted(struct osmo_fsm_inst *fi, uint32_t event, void *data)
{
	switch (event) {
	case SUBSCR_CONN_E_COMMUNICATING:
		osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_COMMUNICATING, 0, 0);
		return;

	case SUBSCR_CONN_E_MO_CLOSE:
	case SUBSCR_CONN_E_CN_CLOSE:
		log_close_event(fi, event, data);
		/* fall through */
	case SUBSCR_CONN_E_UNUSED:
		osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_RELEASING, SUBSCR_CONN_TIMEOUT, 0);
		return;

	default:
		OSMO_ASSERT(false);
	}
}

static void subscr_conn_fsm_communicating(struct osmo_fsm_inst *fi, uint32_t event, void *data)
{
	switch (event) {
	case SUBSCR_CONN_E_COMMUNICATING:
		/* no-op */
		return;

	case SUBSCR_CONN_E_MO_CLOSE:
	case SUBSCR_CONN_E_CN_CLOSE:
		log_close_event(fi, event, data);
		/* fall through */
	case SUBSCR_CONN_E_UNUSED:
		osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_RELEASING, SUBSCR_CONN_TIMEOUT, 0);
		return;

	default:
		OSMO_ASSERT(false);
	}
}

static int subscr_conn_fsm_timeout(struct osmo_fsm_inst *fi)
{
	struct gsm_subscriber_connection *conn = fi->priv;
	if (msc_subscr_conn_in_release(conn)) {
		LOGPFSML(fi, LOGL_ERROR, "Timeout while releasing, discarding right now\n");
		osmo_fsm_inst_term(fi, OSMO_FSM_TERM_TIMEOUT, NULL);
	} else {
		uint32_t cause = GSM_CAUSE_NET_FAIL;
		osmo_fsm_inst_dispatch(fi, SUBSCR_CONN_E_CN_CLOSE, &cause);
	}
	return 0;
}

static void subscr_conn_fsm_releasing_onenter(struct osmo_fsm_inst *fi, uint32_t prev_state)
{
	struct gsm_subscriber_connection *conn = fi->priv;

	/* While we're still checking on release, prevent a last use count decrement from deallocating */
	msc_subscr_conn_get(conn, MSC_CONN_USE_RELEASE);

	/* Cancel pending CM Service Requests */
	if (conn->received_cm_service_request) {
		conn->received_cm_service_request = false;
		msc_subscr_conn_put(conn, MSC_CONN_USE_CM_SERVICE);
	}

	/* Cancel all VLR FSMs, if any */
	vlr_subscr_conn_timeout(conn->vsub);

	/* If we're closing in a middle of a trans, we need to clean up */
	trans_conn_closed(conn);

	switch (conn->via_ran) {
	case RAN_GERAN_A:
		a_iface_tx_clear_cmd(conn);
		break;
	case RAN_UTRAN_IU:
		ranap_iu_tx_release(conn->iu.ue_ctx, NULL);
		break;
	default:
		LOGP(DMM, LOGL_ERROR, "%s: Unknown RAN type, cannot tx release/clear\n",
		     vlr_subscr_name(conn->vsub));
		break;
	}

	/* FIXME: keep the conn until the Iu Release Outcome is
	 * received from the UE, or a timeout expires. For now, the log
	 * says "unknown UE" for each release outcome. */
	msc_subscr_conn_put(conn, MSC_CONN_USE_RELEASE);
}

static void subscr_conn_fsm_releasing(struct osmo_fsm_inst *fi, uint32_t event, void *data)
{
	OSMO_ASSERT(event == SUBSCR_CONN_E_UNUSED);
	osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_RELEASED, 0, 0);
}

static void subscr_conn_fsm_released(struct osmo_fsm_inst *fi, uint32_t prev_state)
{
	/* Terminate, deallocate and also deallocate the gsm_subscriber_connection, which is allocated as
	 * a talloc child of fi. Also calls the cleanup function. */
	osmo_fsm_inst_term(fi, OSMO_FSM_TERM_REGULAR, NULL);
}

#define S(x)	(1 << (x))

static const struct osmo_fsm_state subscr_conn_fsm_states[] = {
	[SUBSCR_CONN_S_NEW] = {
		.name = OSMO_STRINGIFY(SUBSCR_CONN_S_NEW),
		.in_event_mask = S(SUBSCR_CONN_E_COMPLETE_LAYER_3) |
				 S(SUBSCR_CONN_E_ACCEPTED) |
				 S(SUBSCR_CONN_E_MO_CLOSE) |
				 S(SUBSCR_CONN_E_CN_CLOSE) |
				 S(SUBSCR_CONN_E_UNUSED),
		.out_state_mask = S(SUBSCR_CONN_S_AUTH_CIPH) |
				  S(SUBSCR_CONN_S_ACCEPTED) |
				  S(SUBSCR_CONN_S_RELEASING),
		.action = subscr_conn_fsm_new,
	},
	[SUBSCR_CONN_S_AUTH_CIPH] = {
		.name = OSMO_STRINGIFY(SUBSCR_CONN_S_AUTH_CIPH),
		.in_event_mask = S(SUBSCR_CONN_E_ACCEPTED) |
				 S(SUBSCR_CONN_E_MO_CLOSE) |
				 S(SUBSCR_CONN_E_CN_CLOSE) |
				 S(SUBSCR_CONN_E_UNUSED),
		.out_state_mask = S(SUBSCR_CONN_S_ACCEPTED) |
				  S(SUBSCR_CONN_S_RELEASING),
		.action = subscr_conn_fsm_auth_ciph,
	},
	[SUBSCR_CONN_S_ACCEPTED] = {
		.name = OSMO_STRINGIFY(SUBSCR_CONN_S_ACCEPTED),
		/* allow everything to release for any odd behavior */
		.in_event_mask = S(SUBSCR_CONN_E_COMMUNICATING) |
		                 S(SUBSCR_CONN_E_RELEASE_WHEN_UNUSED) |
				 S(SUBSCR_CONN_E_ACCEPTED) |
				 S(SUBSCR_CONN_E_MO_CLOSE) |
				 S(SUBSCR_CONN_E_CN_CLOSE) |
				 S(SUBSCR_CONN_E_UNUSED),
		.out_state_mask = S(SUBSCR_CONN_S_RELEASING) |
				  S(SUBSCR_CONN_S_COMMUNICATING),
		.onenter = subscr_conn_fsm_accepted_enter,
		.action = subscr_conn_fsm_accepted,
	},
	[SUBSCR_CONN_S_COMMUNICATING] = {
		.name = OSMO_STRINGIFY(SUBSCR_CONN_S_COMMUNICATING),
		/* allow everything to release for any odd behavior */
		.in_event_mask = S(SUBSCR_CONN_E_RELEASE_WHEN_UNUSED) |
				 S(SUBSCR_CONN_E_ACCEPTED) |
				 S(SUBSCR_CONN_E_COMMUNICATING) |
				 S(SUBSCR_CONN_E_MO_CLOSE) |
				 S(SUBSCR_CONN_E_CN_CLOSE) |
				 S(SUBSCR_CONN_E_UNUSED),
		.out_state_mask = S(SUBSCR_CONN_S_RELEASING),
		.action = subscr_conn_fsm_communicating,
	},
	[SUBSCR_CONN_S_RELEASING] = {
		.name = OSMO_STRINGIFY(SUBSCR_CONN_S_RELEASING),
		.in_event_mask = S(SUBSCR_CONN_E_UNUSED),
		.out_state_mask = S(SUBSCR_CONN_S_RELEASED),
		.onenter = subscr_conn_fsm_releasing_onenter,
		.action = subscr_conn_fsm_releasing,
	},
	[SUBSCR_CONN_S_RELEASED] = {
		.name = OSMO_STRINGIFY(SUBSCR_CONN_S_RELEASED),
		.onenter = subscr_conn_fsm_released,
	},
};

static void subscr_conn_fsm_cleanup(struct osmo_fsm_inst *fi, enum osmo_fsm_term_cause cause);

static struct osmo_fsm subscr_conn_fsm = {
	.name = "Subscr_Conn",
	.states = subscr_conn_fsm_states,
	.num_states = ARRAY_SIZE(subscr_conn_fsm_states),
	.allstate_event_mask = 0,
	.allstate_action = NULL,
	.log_subsys = DMM,
	.event_names = subscr_conn_fsm_event_names,
	.cleanup = subscr_conn_fsm_cleanup,
	.timer_cb = subscr_conn_fsm_timeout,
};

char *msc_subscr_conn_get_conn_id(struct gsm_subscriber_connection *conn)
{
	char *id;

	switch (conn->via_ran) {
	case RAN_GERAN_A:
		id = talloc_asprintf(conn, "GERAN_A-%08x", conn->a.conn_id);
		break;
	case RAN_UTRAN_IU:
		id = talloc_asprintf(conn, "UTRAN_IU-%08x", iu_get_conn_id(conn->iu.ue_ctx));
		break;
	default:
		LOGP(DMM, LOGL_ERROR, "RAN of conn %p unknown!\n", conn);
		return NULL;
	}

	return id;
}

/* Tidy up before the FSM deallocates */
static void subscr_conn_fsm_cleanup(struct osmo_fsm_inst *fi, enum osmo_fsm_term_cause cause)
{
	struct gsm_subscriber_connection *conn = fi->priv;

	if (subscr_conn_fsm_has_active_transactions(fi))
		LOGPFSML(fi, LOGL_ERROR, "Deallocating despite active transactions\n");

	if (!conn) {
		LOGP(DRLL, LOGL_ERROR, "Freeing NULL subscriber connection\n");
		return;
	}

	if (conn->vsub) {
		DEBUGP(DRLL, "%s: Freeing subscriber connection\n", vlr_subscr_name(conn->vsub));
		conn->vsub->lu_fsm = NULL;
		conn->vsub->msc_conn_ref = NULL;
		vlr_subscr_put(conn->vsub);
		conn->vsub = NULL;
	} else
		DEBUGP(DRLL, "Freeing subscriber connection with NULL subscriber\n");

	llist_del(&conn->entry);
}

/* Signal success of Complete Layer 3. Allow to keep the conn open for Auth and Ciph. */
void msc_subscr_conn_complete_layer_3(struct gsm_subscriber_connection *conn)
{
	if (!conn)
		return;
	osmo_fsm_inst_dispatch(conn->fi, SUBSCR_CONN_E_COMPLETE_LAYER_3, NULL);
}

void subscr_conn_release_when_unused(struct gsm_subscriber_connection *conn)
{
	if (!conn)
		return;
	if (msc_subscr_conn_in_release(conn)) {
		DEBUGP(DMM, "%s: %s: conn already in release (%s)\n",
		       vlr_subscr_name(conn->vsub), __func__,
		       osmo_fsm_inst_state_name(conn->fi));
		return;
	}
	if (conn->fi->state == SUBSCR_CONN_S_NEW) {
		DEBUGP(DMM, "%s: %s: conn still being established (%s)\n",
		       vlr_subscr_name(conn->vsub), __func__,
		       osmo_fsm_inst_state_name(conn->fi));
		return;
	}
	osmo_fsm_inst_dispatch(conn->fi, SUBSCR_CONN_E_RELEASE_WHEN_UNUSED, NULL);
}

void msc_subscr_conn_close(struct gsm_subscriber_connection *conn, uint32_t cause)
{
	if (!conn) {
		LOGP(DMM, LOGL_ERROR, "Cannot release NULL connection\n");
		return;
	}
	if (msc_subscr_conn_in_release(conn)) {
		DEBUGP(DMM, "%s(vsub=%s, cause=%u): already in release, ignore.\n",
		       __func__, vlr_subscr_name(conn->vsub), cause);
		return;
	}
	osmo_fsm_inst_dispatch(conn->fi, SUBSCR_CONN_E_CN_CLOSE, &cause);
}

bool msc_subscr_conn_in_release(struct gsm_subscriber_connection *conn)
{
	if (conn->fi->state == SUBSCR_CONN_S_RELEASING)
		return true;
	if (conn->fi->state == SUBSCR_CONN_S_RELEASED)
		return true;
	return false;
}

bool msc_subscr_conn_is_accepted(const struct gsm_subscriber_connection *conn)
{
	if (!conn)
		return false;
	if (!conn->vsub)
		return false;
	if (!(conn->fi->state == SUBSCR_CONN_S_ACCEPTED
	      || conn->fi->state == SUBSCR_CONN_S_COMMUNICATING))
		return false;
	return true;
}

/* Indicate that *some* communication is happening with the phone. */
void msc_subscr_conn_communicating(struct gsm_subscriber_connection *conn)
{
	osmo_fsm_inst_dispatch(conn->fi, SUBSCR_CONN_E_COMMUNICATING, NULL);
}

void msc_subscr_conn_init(void)
{
	osmo_fsm_register(&subscr_conn_fsm);
}

/* Allocate a new subscriber conn and FSM.
 * Deallocation is by msc_subscr_conn_put(): when the use count reaches zero, the
 * SUBSCR_CONN_E_RELEASE_COMPLETE event is dispatched, the FSM terminates and deallocates both FSM and
 * conn. As long as the FSM is waiting for responses from the subscriber, it will itself hold a use count
 * on the conn. */
struct gsm_subscriber_connection *msc_subscr_conn_alloc(struct gsm_network *network,
							enum ran_type via_ran, uint16_t lac)
{
	struct gsm_subscriber_connection *conn;
	struct osmo_fsm_inst *fi;

	fi = osmo_fsm_inst_alloc(&subscr_conn_fsm, network, NULL, LOGL_DEBUG, NULL);
	if (!fi) {
		LOGP(DMM, LOGL_ERROR, "Failed to allocate conn FSM\n");
		return NULL;
	}

	conn = talloc_zero(fi, struct gsm_subscriber_connection);
	if (!conn) {
		osmo_fsm_inst_free(fi);
		return NULL;
	}

	*conn = (struct gsm_subscriber_connection){
		.network = network,
		.via_ran = via_ran,
		.lac = lac,
		.fi = fi,
	};

	fi->priv = conn;
	llist_add_tail(&conn->entry, &network->subscr_conns);
	return conn;
}

bool msc_subscr_conn_is_establishing_auth_ciph(const struct gsm_subscriber_connection *conn)
{
	if (!conn)
		return false;
	return conn->fi->state == SUBSCR_CONN_S_AUTH_CIPH;
}

const struct value_string complete_layer3_type_names[] = {
	{ COMPLETE_LAYER3_NONE, "NONE" },
	{ COMPLETE_LAYER3_LU, "LU" },
	{ COMPLETE_LAYER3_CM_SERVICE_REQ, "CM_SERVICE_REQ" },
	{ COMPLETE_LAYER3_PAGING_RESP, "PAGING_RESP" },
	{ 0, NULL }
};

void msc_subscr_conn_update_id(struct gsm_subscriber_connection *conn,
			       enum complete_layer3_type from, const char *id)
{
       conn->complete_layer3_type = from;
       osmo_fsm_inst_update_id(conn->fi, id);
       LOGPFSML(conn->fi, LOGL_DEBUG, "Updated ID from %s\n", complete_layer3_type_name(from));
}