/* 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>

#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_START),
	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),
	{ 0, NULL }
};

const struct value_string complete_layer3_type_names[] = {
	OSMO_VALUE_STRING(SUBSCR_CONN_FROM_INVALID),
	OSMO_VALUE_STRING(SUBSCR_CONN_FROM_LU),
	OSMO_VALUE_STRING(SUBSCR_CONN_FROM_CM_SERVICE_REQ),
	OSMO_VALUE_STRING(SUBSCR_CONN_FROM_PAGING_RESP),
	{ 0, NULL }
};

static void paging_event(struct gsm_subscriber_connection *conn,
			 enum gsm_paging_event pe)
{
	subscr_paging_dispatch(GSM_HOOK_RR_PAGING, pe, NULL, conn, conn->vsub);
}

void subscr_conn_fsm_init(struct osmo_fsm_inst *fi, uint32_t event, void *data)
{
	OSMO_ASSERT(event == SUBSCR_CONN_E_START);
	osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_NEW,
				SUBSCR_CONN_TIMEOUT, 0);
}

void subscr_conn_fsm_new(struct osmo_fsm_inst *fi, uint32_t event, void *data)
{
	struct gsm_subscriber_connection *conn = fi->priv;
	enum complete_layer3_type from = SUBSCR_CONN_FROM_INVALID;
	bool success;

	if (data) {
		from = *(enum complete_layer3_type*)data;
		LOGPFSM(fi, "%s\n", complete_layer3_type_name(from));
	}

	/* If accepted, transition the state, all other cases mean failure. */
	switch (event) {
	case SUBSCR_CONN_E_ACCEPTED:
		osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_ACCEPTED,
					SUBSCR_CONN_TIMEOUT, 0);
		break;

	case SUBSCR_CONN_E_MO_CLOSE:
	case SUBSCR_CONN_E_CN_CLOSE:
		if (data)
			LOGPFSM(fi, "Close event, cause %u\n",
				*(uint32_t*)data);
		/* will release further below, see
		 * 'if (fi->state != SUBSCR_CONN_S_ACCEPTED)' */
		break;

	default:
		LOGPFSML(fi, LOGL_ERROR,
			 "Unexpected event: %d %s\n", event,
			 osmo_fsm_event_name(fi->fsm, event));
		break;
	}

	success = (fi->state == SUBSCR_CONN_S_ACCEPTED);

	if (from == SUBSCR_CONN_FROM_LU)
		rate_ctr_inc(&conn->network->msc_ctrs->ctr[
		             	success ? MSC_CTR_LOC_UPDATE_COMPLETED
					: MSC_CTR_LOC_UPDATE_FAILED]);

	/* signal paging success or failure in case this was a paging */
	if (from == SUBSCR_CONN_FROM_PAGING_RESP)
		paging_event(conn,
			     success ? GSM_PAGING_SUCCEEDED
			     	     : GSM_PAGING_EXPIRED);

	/* FIXME rate counters */
	/*rate_ctr_inc(&conn->network->msc_ctrs->ctr[MSC_CTR_LOC_UPDATE_COMPLETED]);*/

	/* On failure, discard the conn */
	if (!success) {
		/* TODO: on MO_CLOSE or CN_CLOSE, first go to RELEASING and
		 * await BSC/RNC confirmation? */
		osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_RELEASED, 0, 0);
		return;
	}

	if (from == SUBSCR_CONN_FROM_CM_SERVICE_REQ) {
		conn->received_cm_service_request = true;
		LOGPFSML(fi, LOGL_DEBUG, "received_cm_service_request = true\n");
	}

	osmo_fsm_inst_dispatch(fi, SUBSCR_CONN_E_RELEASE_WHEN_UNUSED, data);
}

static void subscr_conn_fsm_release_when_unused(struct osmo_fsm_inst *fi, uint32_t event, void *data)
{
	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;
	}

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

	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;
	}

	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;
	}

	LOGPFSML(fi, LOGL_DEBUG, "%s: releasing conn\n", __func__);
	osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_RELEASED, 0, 0);
}

static void subscr_conn_fsm_accepted_enter(struct osmo_fsm_inst *fi, uint32_t prev_state)
{
	struct gsm_subscriber_connection *conn = fi->priv;
	osmo_signal_dispatch(SS_SUBSCR, S_SUBSCR_ATTACHED, conn->vsub);
}

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_RELEASE_WHEN_UNUSED:
		subscr_conn_fsm_release_when_unused(fi, event, data);
		return;

	default:
		break;
	}
	/* Whatever unexpected happens in the accepted state, it means release.
	 * Even if an unexpected event is passed, the safest thing to do is
	 * discard the conn. We don't expect another SUBSCR_CONN_E_ACCEPTED. */
	osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_RELEASED, 0, 0);
}

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_RELEASE_WHEN_UNUSED:
		subscr_conn_fsm_release_when_unused(fi, event, data);
		return;

	default:
		break;
	}
	/* Whatever unexpected happens in the accepted state, it means release.
	 * Even if an unexpected event is passed, the safest thing to do is
	 * discard the conn. We don't expect another SUBSCR_CONN_E_ACCEPTED. */
	osmo_fsm_inst_state_chg(fi, SUBSCR_CONN_S_RELEASED, 0, 0);
}

static void subscr_conn_fsm_cleanup(struct osmo_fsm_inst *fi,
				    enum osmo_fsm_term_cause cause)
{
	struct gsm_subscriber_connection *conn = fi->priv;
	fi->priv = NULL;

	if (!conn)
		return;
	conn->fi = NULL;
 	msc_subscr_conn_close(conn, cause);
	msc_subscr_conn_put(conn, MSC_CONN_USE_FSM);
}

int subscr_conn_fsm_timeout(struct osmo_fsm_inst *fi)
{
	struct gsm_subscriber_connection *conn = fi->priv;
	if (conn)
		vlr_subscr_conn_timeout(conn->vsub);
	else
		osmo_fsm_inst_dispatch(fi, SUBSCR_CONN_E_CN_CLOSE, NULL);
	return 0;
}

static void subscr_conn_fsm_release(struct osmo_fsm_inst *fi, uint32_t prev_state)
{
	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_INIT] = {
		.name = OSMO_STRINGIFY(SUBSCR_CONN_S_INIT),
		.in_event_mask = S(SUBSCR_CONN_E_START),
		.out_state_mask = S(SUBSCR_CONN_S_NEW),
		.action = subscr_conn_fsm_init,
	},
	[SUBSCR_CONN_S_NEW] = {
		.name = OSMO_STRINGIFY(SUBSCR_CONN_S_NEW),
		.in_event_mask = S(SUBSCR_CONN_E_ACCEPTED) |
				 S(SUBSCR_CONN_E_MO_CLOSE) |
				 S(SUBSCR_CONN_E_CN_CLOSE),
		.out_state_mask = S(SUBSCR_CONN_S_ACCEPTED) |
				  S(SUBSCR_CONN_S_RELEASED),
		.action = subscr_conn_fsm_new,
	},
	[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),
		.out_state_mask = S(SUBSCR_CONN_S_RELEASED) |
				  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),
		.out_state_mask = S(SUBSCR_CONN_S_RELEASED),
		.action = subscr_conn_fsm_communicating,
	},
	[SUBSCR_CONN_S_RELEASED] = {
		.name = OSMO_STRINGIFY(SUBSCR_CONN_S_RELEASED),
		.onenter = subscr_conn_fsm_release,
	},
};

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;
}

int msc_create_conn_fsm(struct gsm_subscriber_connection *conn, const char *id)
{
	struct osmo_fsm_inst *fi;
	OSMO_ASSERT(conn);

	if (conn->fi) {
		LOGP(DMM, LOGL_ERROR,
		     "%s: Error: connection already in use\n", id);
		return -EINVAL;
	}

	/* Allocate the FSM not with the subscr_conn. Semantically it would
	 * make sense, but in subscr_conn_fsm_cleanup(), we want to discard the
	 * subscriber connection. If the FSM is freed along with the subscriber
	 * connection, then in _osmo_fsm_inst_term() the osmo_fsm_inst_free()
	 * that follows the cleanup() call would run into a double free. */
	fi = osmo_fsm_inst_alloc(&subscr_conn_fsm, conn->network,
				 msc_subscr_conn_get(conn, MSC_CONN_USE_FSM),
				 LOGL_DEBUG, id);

	if (!fi) {
		LOGP(DMM, LOGL_ERROR,
		     "%s: Failed to allocate subscr conn master FSM\n", id);
		return -ENOMEM;
	}
	conn->fi = fi;
	osmo_fsm_inst_dispatch(conn->fi, SUBSCR_CONN_E_START, NULL);
	return 0;
}

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

void msc_subscr_conn_communicating(struct gsm_subscriber_connection *conn)
{
	OSMO_ASSERT(conn);
	/* This function is called to indicate that *some* communication is happening with the phone.
	 * Late in the process, that may be a Release Confirm and the FSM and conn are already in
	 * teardown. No need to signal SUBSCR_CONN_E_COMMUNICATING then. */
	if (conn->fi)
		osmo_fsm_inst_dispatch(conn->fi, SUBSCR_CONN_E_COMMUNICATING, NULL);
}

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