/* (C) 2018 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
 *
 * Author: Stefan Sperling <ssperling@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 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 <strings.h>
#include <errno.h>
#include <stdbool.h>

#include <osmocom/bsc/debug.h>
#include <osmocom/bsc/acc_ramp.h>
#include <osmocom/bsc/gsm_data.h>

/*
 * Check if an ACC has been permanently barred for a BTS,
 * e.g. with the 'rach access-control-class' VTY command.
 */
static bool acc_is_enabled(struct gsm_bts *bts, unsigned int acc)
{
	OSMO_ASSERT(acc >= 0 && acc <= 9);
	if (acc == 8 || acc == 9)
		return (bts->si_common.rach_control.t2 & (1 << (acc - 8))) == 0;
	return (bts->si_common.rach_control.t3 & (1 << (acc))) == 0;
}

static void allow_one_acc(struct acc_ramp *acc_ramp, unsigned int acc)
{
	OSMO_ASSERT(acc >= 0 && acc <= 9);
	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: allowing Access Control Class %u\n", acc_ramp->bts->nr, acc);
	acc_ramp->barred_accs &= ~(1 << acc);
}

static void barr_one_acc(struct acc_ramp *acc_ramp, unsigned int acc)
{
	OSMO_ASSERT(acc >= 0 && acc <= 9);
	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: barring Access Control Class %u\n", acc_ramp->bts->nr, acc);
	acc_ramp->barred_accs |= (1 << acc);
}

static void barr_all_enabled_accs(struct acc_ramp *acc_ramp)
{
	unsigned int acc;
	for (acc = 0; acc < 10; acc++) {
		if (acc_is_enabled(acc_ramp->bts, acc))
			barr_one_acc(acc_ramp, acc);
	}
}

static void allow_all_enabled_accs(struct acc_ramp *acc_ramp)
{
	unsigned int acc;
	for (acc = 0; acc < 10; acc++) {
		if (acc_is_enabled(acc_ramp->bts, acc))
			allow_one_acc(acc_ramp, acc);
	}
}

static unsigned int get_next_step_interval(struct acc_ramp *acc_ramp)
{
	struct gsm_bts *bts = acc_ramp->bts;
	uint64_t load;

	if (acc_ramp->step_interval_is_fixed)
		return acc_ramp->step_interval_sec;

	/* Scale the step interval to current channel load average. */
	load = (bts->chan_load_avg << 8); /* convert to fixed-point */
	acc_ramp->step_interval_sec = ((load * ACC_RAMP_STEP_INTERVAL_MAX) / 100) >> 8;
	if (acc_ramp->step_interval_sec < ACC_RAMP_STEP_SIZE_MIN)
		acc_ramp->step_interval_sec = ACC_RAMP_STEP_INTERVAL_MIN;
	else if (acc_ramp->step_interval_sec > ACC_RAMP_STEP_INTERVAL_MAX)
		acc_ramp->step_interval_sec = ACC_RAMP_STEP_INTERVAL_MAX;

	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: step interval set to %u seconds based on %u%% channel load average\n",
	     bts->nr, acc_ramp->step_interval_sec, bts->chan_load_avg);
	return acc_ramp->step_interval_sec;
}

static void do_acc_ramping_step(void *data)
{
	struct acc_ramp *acc_ramp = data;
	int i;

	/* Shortcut in case we only do one ramping step. */
	if (acc_ramp->step_size == ACC_RAMP_STEP_SIZE_MAX) {
		allow_all_enabled_accs(acc_ramp);
		gsm_bts_set_system_infos(acc_ramp->bts);
		return;
	}

	/* Allow 'step_size' ACCs, starting from ACC0. ACC9 will be allowed last. */
	for (i = 0; i < acc_ramp->step_size; i++) {
		int idx = ffs(acc_ramp_get_barred_t3(acc_ramp));
		if (idx > 0) {
			/* One of ACC0-ACC7 is still bared. */
			unsigned int acc = idx - 1;
			if (acc_is_enabled(acc_ramp->bts, acc))
				allow_one_acc(acc_ramp, acc);
		} else {
			idx = ffs(acc_ramp_get_barred_t2(acc_ramp));
			if (idx == 1 || idx == 2) {
				/* ACC8 or ACC9 is still barred. */
				unsigned int acc = idx - 1 + 8;
				if (acc_is_enabled(acc_ramp->bts, acc))
					allow_one_acc(acc_ramp, acc);
			} else {
				/* All ACCs are now allowed. */
				break;
			}
		}
	}

	gsm_bts_set_system_infos(acc_ramp->bts);

	/* If we have not allowed all ACCs yet, schedule another ramping step. */
	if (acc_ramp_get_barred_t2(acc_ramp) != 0x00 ||
	    acc_ramp_get_barred_t3(acc_ramp) != 0x00)
		osmo_timer_schedule(&acc_ramp->step_timer, get_next_step_interval(acc_ramp), 0);
}

/*!
 * Initialize an acc_ramp data structure.
 * Storage for this structure must be provided by the caller.
 *
 * If ACC ramping is enabled, all ACCs are denied by default.
 * A subsequent call to acc_ramp_start() will begin the ramping process.
 * If ACC ramping is disabled, all ACCs will be allowed by default,
 * and there is no need to do anything else.
 *
 * \param[in] acc_ramp Pointer to acc_ramp structure to be initialized.
 * \param[in] enable Indicates whether ACC ramping should be enabled or disabled.
 * \param[in] bts BTS which uses this ACC ramp data structure.
 */
void acc_ramp_init(struct acc_ramp *acc_ramp, bool enable, struct gsm_bts *bts)
{
	acc_ramp->bts = bts;
	acc_ramp->acc_ramping_enabled = enable;
	acc_ramp->step_size = ACC_RAMP_STEP_SIZE_DEFAULT;
	acc_ramp->step_interval_sec = ACC_RAMP_STEP_INTERVAL_MIN;
	acc_ramp->step_interval_is_fixed = false;
	osmo_timer_setup(&acc_ramp->step_timer, do_acc_ramping_step, acc_ramp);

	if (acc_ramp->acc_ramping_enabled)
		barr_all_enabled_accs(acc_ramp);
	else
		allow_all_enabled_accs(acc_ramp);
}

/*!
 * Change the ramping step size which controls how many ACCs will be allowed per ramping step.
 * Returns negative on error (step_size out of range), else zero.
 * \param[in] acc_ramp Pointer to acc_ramp structure.
 * \param[in] step_size The new step size value.
 */
int acc_ramp_set_step_size(struct acc_ramp *acc_ramp, unsigned int step_size)
{
	if (step_size < ACC_RAMP_STEP_SIZE_MIN || step_size > ACC_RAMP_STEP_SIZE_MAX)
		return -ERANGE;

	acc_ramp->step_size = step_size;
	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: ramping step size set to %u\n", acc_ramp->bts->nr, step_size);
	return 0;
}

/*!
 * Change the ramping step interval to a fixed value. Unless this function is called,
 * the interval is automatically scaled to the BTS channel load average.
 * \param[in] acc_ramp Pointer to acc_ramp structure.
 * \param[in] step_interval The new fixed step interval in seconds.
 */
int acc_ramp_set_step_interval(struct acc_ramp *acc_ramp, unsigned int step_interval)
{
	if (step_interval < ACC_RAMP_STEP_INTERVAL_MIN || step_interval > ACC_RAMP_STEP_INTERVAL_MAX)
		return -ERANGE;

	acc_ramp->step_interval_sec = step_interval;
	acc_ramp->step_interval_is_fixed = true;
	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: ramping step interval set to %u seconds\n",
	     acc_ramp->bts->nr, step_interval);
	return 0;
}

/*!
 * Clear a previously set fixed ramping step interval, so that the interval
 * is again automatically scaled to the BTS channel load average.
 * \param[in] acc_ramp Pointer to acc_ramp structure.
 */
void acc_ramp_set_step_interval_dynamic(struct acc_ramp *acc_ramp)
{
	acc_ramp->step_interval_is_fixed = false;
	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: ramping step interval set to 'dynamic'\n",
	     acc_ramp->bts->nr);
}

/*!
 * Begin the ramping process. Perform at least one ramping step to allow 'step_size' ACCs.
 * If 'step_size' is ACC_RAMP_STEP_SIZE_MAX, all ACCs will be allowed immediately.
 * \param[in] acc_ramp Pointer to acc_ramp structure.
 */
void acc_ramp_start(struct acc_ramp *acc_ramp)
{
	/* Abort any previously running ramping process. */
	acc_ramp_abort(acc_ramp);

	/* Set all availble ACCs to barred and start ramping up. */
	barr_all_enabled_accs(acc_ramp);
	do_acc_ramping_step(acc_ramp);
}

/*!
 * Abort the ramping process. If ramping is disabled or has already finished,
 * then this function has no effect.
 * \param[in] acc_ramp Pointer to acc_ramp structure.
 */
void acc_ramp_abort(struct acc_ramp *acc_ramp)
{
	if (osmo_timer_pending(&acc_ramp->step_timer))
		osmo_timer_del(&acc_ramp->step_timer);
}