/* Paging helper and manager.... */
/* (C) 2009,2013 by Holger Hans Peter Freyther <zecke@selfish.org>
 * 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 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/>.
 *
 */

/*
 * Relevant specs:
 *     12.21:
 *       - 9.4.12 for CCCH Local Threshold
 *
 *     05.58:
 *       - 8.5.2 CCCH Load indication
 *       - 9.3.15 Paging Load
 *
 * Approach:
 *       - Send paging command to subscriber
 *       - On Channel Request we will remember the reason
 *       - After the ACK we will request the identity
 *	 - Then we will send assign the gsm_subscriber and
 *	 - and call a callback
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

#include <osmocom/core/talloc.h>
#include <osmocom/core/tdef.h>
#include <osmocom/gsm/gsm48.h>
#include <osmocom/gsm/gsm0502.h>

#include <osmocom/bsc/bsc_subscriber.h>
#include <osmocom/bsc/paging.h>
#include <osmocom/bsc/debug.h>
#include <osmocom/bsc/signal.h>
#include <osmocom/bsc/abis_rsl.h>
#include <osmocom/bsc/gsm_data.h>
#include <osmocom/bsc/chan_alloc.h>
#include <osmocom/bsc/gsm_08_08.h>
#include <osmocom/bsc/gsm_04_08_rr.h>
#include <osmocom/bsc/bsc_subscr_conn_fsm.h>

void *tall_paging_ctx = NULL;

#define PAGING_TIMER 0, 500000

/*
 * TODO MSCSPLIT: the paging in libbsc is closely tied to MSC land in that the
 * MSC realm callback functions used to be invoked from the BSC/BTS level. So
 * this entire file needs to be rewired for use with an A interface.
 */

/*
 * Kill one paging request update the internal list...
 */
static void paging_remove_request(struct gsm_bts_paging_state *paging_bts,
				  struct gsm_paging_request *to_be_deleted)
{
	osmo_timer_del(&to_be_deleted->T3113);
	llist_del(&to_be_deleted->entry);
	bsc_subscr_put(to_be_deleted->bsub);
	talloc_free(to_be_deleted);
}

static void page_ms(struct gsm_paging_request *request)
{
	uint8_t mi[128];
	unsigned int mi_len;
	unsigned int page_group;
	struct gsm_bts *bts = request->bts;

	log_set_context(LOG_CTX_BSC_SUBSCR, request->bsub);

	LOG_BTS(bts, DPAG, LOGL_INFO, "Going to send paging commands: imsi: %s tmsi: "
		"0x%08x for ch. type %d (attempt %d)\n", request->bsub->imsi,
		request->bsub->tmsi, request->chan_type, request->attempts);

	if (request->bsub->tmsi == GSM_RESERVED_TMSI)
		mi_len = gsm48_generate_mid_from_imsi(mi, request->bsub->imsi);
	else
		mi_len = gsm48_generate_mid_from_tmsi(mi, request->bsub->tmsi);

	page_group = gsm0502_calc_paging_group(&bts->si_common.chan_desc,
					       str_to_imsi(request->bsub->imsi));
	rsl_paging_cmd(bts, page_group, mi_len, mi, request->chan_type, false);
	log_set_context(LOG_CTX_BSC_SUBSCR, NULL);
}

static void paging_schedule_if_needed(struct gsm_bts_paging_state *paging_bts)
{
	if (llist_empty(&paging_bts->pending_requests))
		return;

	if (!osmo_timer_pending(&paging_bts->work_timer))
		osmo_timer_schedule(&paging_bts->work_timer, PAGING_TIMER);
}


static void paging_handle_pending_requests(struct gsm_bts_paging_state *paging_bts);
static void paging_give_credit(void *data)
{
	struct gsm_bts_paging_state *paging_bts = data;

	LOG_BTS(paging_bts->bts, DPAG, LOGL_NOTICE, "No PCH LOAD IND, adding 20 slots)\n");
	paging_bts->available_slots = 20;
	paging_handle_pending_requests(paging_bts);
}

/*! count the number of free channels for given RSL channel type required
 * \param[in] BTS on which we shall count
 * \param[in] rsl_type the RSL channel needed type
 * \returns number of free channels matching \a rsl_type in \a bts */
static int can_send_pag_req(struct gsm_bts *bts, int rsl_type)
{
	struct pchan_load pl;
	int count;

	memset(&pl, 0, sizeof(pl));
	bts_chan_load(&pl, bts);

	switch (rsl_type) {
	case RSL_CHANNEED_TCH_F:
	case RSL_CHANNEED_TCH_ForH:
		goto count_tch;
		break;
	case RSL_CHANNEED_SDCCH:
		goto count_sdcch;
		break;
	case RSL_CHANNEED_ANY:
	default:
		if (bts->network->pag_any_tch)
			goto count_tch;
		else
			goto count_sdcch;
		break;
	}

	return 0;

	/* could available SDCCH */
count_sdcch:
	count = 0;
	count += pl.pchan[GSM_PCHAN_SDCCH8_SACCH8C].total
			- pl.pchan[GSM_PCHAN_SDCCH8_SACCH8C].used;
	count += pl.pchan[GSM_PCHAN_CCCH_SDCCH4].total
			- pl.pchan[GSM_PCHAN_CCCH_SDCCH4].used;
	return bts->paging.free_chans_need > count;

count_tch:
	count = 0;
	count += pl.pchan[GSM_PCHAN_TCH_F].total
			- pl.pchan[GSM_PCHAN_TCH_F].used;
	if (bts->network->neci)
		count += pl.pchan[GSM_PCHAN_TCH_H].total
				- pl.pchan[GSM_PCHAN_TCH_H].used;
	return bts->paging.free_chans_need > count;
}

/*
 * This is kicked by the periodic PAGING LOAD Indicator
 * coming from abis_rsl.c
 *
 * We attempt to iterate once over the list of items but
 * only upto available_slots.
 */
static void paging_handle_pending_requests(struct gsm_bts_paging_state *paging_bts)
{
	struct gsm_paging_request *request = NULL;

	/*
	 * Determine if the pending_requests list is empty and
	 * return then.
	 */
	if (llist_empty(&paging_bts->pending_requests)) {
		/* since the list is empty, no need to reschedule the timer */
		return;
	}

	/*
	 * In case the BTS does not provide us with load indication and we
	 * ran out of slots, call an autofill routine. It might be that the
	 * BTS did not like our paging messages and then we have counted down
	 * to zero and we do not get any messages.
	 */
	if (paging_bts->available_slots == 0) {
		osmo_timer_setup(&paging_bts->credit_timer, paging_give_credit,
				 paging_bts);
		osmo_timer_schedule(&paging_bts->credit_timer, 5, 0);
		return;
	}

	request = llist_entry(paging_bts->pending_requests.next,
			      struct gsm_paging_request, entry);

	/* we need to determine the number of free channels */
	if (paging_bts->free_chans_need != -1) {
		if (can_send_pag_req(request->bts, request->chan_type) != 0)
			goto skip_paging;
	}

	/* Skip paging if the bts is down. */
	if (!request->bts->oml_link)
		goto skip_paging;

	/* handle the paging request now */
	page_ms(request);
	paging_bts->available_slots--;
	request->attempts++;

	/* take the current and add it to the back */
	llist_del(&request->entry);
	llist_add_tail(&request->entry, &paging_bts->pending_requests);

skip_paging:
	osmo_timer_schedule(&paging_bts->work_timer, PAGING_TIMER);
}

static void paging_worker(void *data)
{
	struct gsm_bts_paging_state *paging_bts = data;

	paging_handle_pending_requests(paging_bts);
}

/*! initialize the bts paging state, if it hasn't been initialized yet */
static void paging_init_if_needed(struct gsm_bts *bts)
{
	if (bts->paging.bts)
		return;

	bts->paging.bts = bts;

	/* This should be initialized only once. There is currently no code that sets bts->paging.bts
	 * back to NULL, so let's just assert this one instead of graceful handling. */
	OSMO_ASSERT(llist_empty(&bts->paging.pending_requests));

	osmo_timer_setup(&bts->paging.work_timer, paging_worker,
			 &bts->paging);

	/* Large number, until we get a proper message */
	bts->paging.available_slots = 20;
}

/*! do we have any pending paging requests for given subscriber? */
static int paging_pending_request(struct gsm_bts_paging_state *bts,
				  struct bsc_subscr *bsub)
{
	struct gsm_paging_request *req;

	llist_for_each_entry(req, &bts->pending_requests, entry) {
		if (bsub == req->bsub)
			return 1;
	}

	return 0;
}

/*! Call-back once T3113 (paging timeout) expires for given paging_request */
static void paging_T3113_expired(void *data)
{
	struct gsm_paging_request *req = (struct gsm_paging_request *)data;

	log_set_context(LOG_CTX_BSC_SUBSCR, req->bsub);

	LOGP(DPAG, LOGL_INFO, "T3113 expired for request %p (%s)\n",
	     req, bsc_subscr_name(req->bsub));

	/* must be destroyed before calling cbfn, to prevent double free */
	rate_ctr_inc(&req->bts->bts_ctrs->ctr[BTS_CTR_PAGING_EXPIRED]);

	/* destroy it now. Do not access req afterwards */
	paging_remove_request(&req->bts->paging, req);

	log_set_context(LOG_CTX_BSC_SUBSCR, NULL);
}

#define GSM_FRAME_DURATION_us	4615
#define GSM51_MFRAME_DURATION_us (51 * GSM_FRAME_DURATION_us) /* 235365 us */
static unsigned int calculate_timer_3113(struct gsm_bts *bts)
{
	unsigned int to_us, to;
	struct osmo_tdef *d = osmo_tdef_get_entry(bts->network->T_defs, 3113);

	/* Note: d should always contain a valid pointer since all timers,
	 * including 3113 are statically pre-defined in
	 * struct osmo_tdef gsm_network_T_defs. */
	OSMO_ASSERT(d);

	if (!bts->T3113_dynamic)
		return d->val;

	/* TODO: take into account load of paging group for req->bsub */

	/* MFRMS defines repeat interval of paging messages for MSs that belong
	 * to same paging group across multiple 51 frame multiframes.
	 * MAXTRANS defines maximum number of RACH retransmissions.
	 */
	to_us = GSM51_MFRAME_DURATION_us * (bts->si_common.chan_desc.bs_pa_mfrms + 2) *
		bts->si_common.rach_control.max_trans;

	/* ceiling in seconds + extra time */
	to = (to_us + 999999) / 1000000 + d->val;
	LOG_BTS(bts, DPAG, LOGL_DEBUG, "Paging request: T3113 expires in %u seconds\n", to);
	return to;
}

/*! Start paging + paging timer for given subscriber on given BTS
 * \param bts BTS on which to page
 * \param[in] bsub subscriber we want to page
 * \param[in] type type of radio channel we're requirign
 * \param[in] msc MSC which has issue this paging
 * \returns 0 on success, negative on error */
static int _paging_request(struct gsm_bts *bts, struct bsc_subscr *bsub, int type,
			   struct bsc_msc_data *msc)
{
	struct gsm_bts_paging_state *bts_entry = &bts->paging;
	struct gsm_paging_request *req;
	unsigned int t3113_timeout_s;

	rate_ctr_inc(&bts->bts_ctrs->ctr[BTS_CTR_PAGING_ATTEMPTED]);

	if (paging_pending_request(bts_entry, bsub)) {
		LOG_BTS(bts, DPAG, LOGL_INFO, "Paging request already pending for %s\n",
			bsc_subscr_name(bsub));
		rate_ctr_inc(&bts->bts_ctrs->ctr[BTS_CTR_PAGING_ALREADY]);
		return -EEXIST;
	}

	LOG_BTS(bts, DPAG, LOGL_DEBUG, "Start paging of subscriber %s\n", bsc_subscr_name(bsub));
	req = talloc_zero(tall_paging_ctx, struct gsm_paging_request);
	OSMO_ASSERT(req);
	req->bsub = bsc_subscr_get(bsub);
	req->bts = bts;
	req->chan_type = type;
	req->msc = msc;
	osmo_timer_setup(&req->T3113, paging_T3113_expired, req);
	t3113_timeout_s = calculate_timer_3113(bts);
	osmo_timer_schedule(&req->T3113, t3113_timeout_s, 0);
	llist_add_tail(&req->entry, &bts_entry->pending_requests);
	paging_schedule_if_needed(bts_entry);

	return 0;
}

/*! Handle PAGING request from MSC for one (matching) BTS
 * \param bts BTS on which to page
 * \param[in] bsub subscriber we want to page
 * \param[in] type type of radio channel we're requirign
 * \param[in] msc MSC which has issue this paging
 * returns 1 on success; 0 in case of error (e.g. TRX down) */
int paging_request_bts(struct gsm_bts *bts, struct bsc_subscr *bsub, int type,
			struct bsc_msc_data *msc)
{
	int rc;

	/* skip all currently inactive TRX */
	if (!trx_is_usable(bts->c0))
		return 0;

	/* maybe it is the first time we use it */
	paging_init_if_needed(bts);

	/* Trigger paging, pass any error to the caller */
	rc = _paging_request(bts, bsub, type, msc);
	if (rc < 0)
		return 0;
	return 1;
}

/*! Stop paging a given subscriber on a given BTS.
 *  If \a conn is non-NULL, we also call the paging call-back function
 *  to notify the paging originator that paging has completed.
 * \param[in] bts BTS on which we shall stop paging
 * \param[in] bsub subscriber which we shall stop paging
 * \param[in] conn connection to the subscriber (if any)
 * \param[in] msg message received from subscrbier (if any)
 * \returns 0 if an active paging request was stopped, an error code otherwise. */
/* we consciously ignore the type of the request here */
static int _paging_request_stop(struct gsm_bts *bts, struct bsc_subscr *bsub,
				struct gsm_subscriber_connection *conn,
				struct msgb *msg)
{
	struct gsm_bts_paging_state *bts_entry = &bts->paging;
	struct gsm_paging_request *req, *req2;

	paging_init_if_needed(bts);

	llist_for_each_entry_safe(req, req2, &bts_entry->pending_requests,
				  entry) {
		if (req->bsub == bsub) {
			/* now give up the data structure */
			paging_remove_request(&bts->paging, req);
			LOG_BTS(bts, DPAG, LOGL_DEBUG, "Stop paging %s\n", bsc_subscr_name(bsub));
			return 0;
		}
	}

	return -ENOENT;
}

/*! Stop paging on all other bts'
 * \param[in] bts_list list of BTSs to iterate
 * \param[in] _bts BTS which has received a paging response
 * \param[in] bsub subscriber
 * \param[in] msgb L3 message that we have received from \a bsub on \a _bts */
void paging_request_stop(struct llist_head *bts_list,
			 struct gsm_bts *_bts, struct bsc_subscr *bsub,
			 struct gsm_subscriber_connection *conn,
			 struct msgb *msg)
{
	struct gsm_bts *bts;

	log_set_context(LOG_CTX_BSC_SUBSCR, bsub);
	conn->bsub = bsc_subscr_get(bsub);
	gscon_update_id(conn);

	/* Stop this first and dispatch the request */
	if (_bts) {
		if (_paging_request_stop(_bts, bsub, conn, msg) == 0) {
			rate_ctr_inc(&_bts->bts_ctrs->ctr[BTS_CTR_PAGING_RESPONDED]);
			rate_ctr_inc(&_bts->network->bsc_ctrs->ctr[BSC_CTR_PAGING_RESPONDED]);
		}
	}

	/* Make sure to cancel this everywhere else */
	llist_for_each_entry(bts, bts_list, list) {
		/* Sort of an optimization. */
		if (bts == _bts)
			continue;
		_paging_request_stop(bts, bsub, NULL, NULL);
	}
	log_set_context(LOG_CTX_BSC_SUBSCR, NULL);
}


/*! Update the BTS paging buffer slots on given BTS */
void paging_update_buffer_space(struct gsm_bts *bts, uint16_t free_slots)
{
	paging_init_if_needed(bts);

	osmo_timer_del(&bts->paging.credit_timer);
	bts->paging.available_slots = free_slots;
	paging_schedule_if_needed(&bts->paging);
}

/*! Count the number of pending paging requests on given BTS */
unsigned int paging_pending_requests_nr(struct gsm_bts *bts)
{
	unsigned int requests = 0;
	struct gsm_paging_request *req;

	paging_init_if_needed(bts);

	llist_for_each_entry(req, &bts->paging.pending_requests, entry)
		++requests;

	return requests;
}

/*! Find any paging data for the given subscriber at the given BTS. */
struct bsc_msc_data *paging_get_msc(struct gsm_bts *bts, struct bsc_subscr *bsub)
{
	struct gsm_paging_request *req;

	llist_for_each_entry(req, &bts->paging.pending_requests, entry)
		if (req->bsub == bsub)
			return req->msc;

	return NULL;
}

/*! Flush all paging requests at a given BTS for a given MSC (or NULL if all MSC should be flushed). */
void paging_flush_bts(struct gsm_bts *bts, struct bsc_msc_data *msc)
{
	struct gsm_paging_request *req, *req2;

	paging_init_if_needed(bts);

	llist_for_each_entry_safe(req, req2, &bts->paging.pending_requests, entry) {
		if (msc && req->msc != msc)
			continue;
		/* now give up the data structure */
		LOG_BTS(bts, DPAG, LOGL_DEBUG, "Stop paging %s (flush)\n", bsc_subscr_name(req->bsub));
		paging_remove_request(&bts->paging, req);
	}
}

/*! Flush all paging requests issued by \a msc on any BTS in \a net */
void paging_flush_network(struct gsm_network *net, struct bsc_msc_data *msc)
{
	struct gsm_bts *bts;

	llist_for_each_entry(bts, &net->bts_list, list)
		paging_flush_bts(bts, msc);
}