/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2013, Digium, Inc.
 *
 * Mark Michelson <mmichelson@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*** MODULEINFO
	<depend>pjproject</depend>
	<depend>res_pjsip</depend>
	<depend>res_pjsip_pubsub</depend>
	<support_level>core</support_level>
 ***/

#include "asterisk.h"

#include <pjsip.h>
#include <pjsip_simple.h>
#include <pjlib.h>

#include "asterisk/res_pjsip.h"
#include "asterisk/res_pjsip_pubsub.h"
#include "asterisk/res_pjsip_body_generator_types.h"
#include "asterisk/module.h"
#include "asterisk/logger.h"
#include "asterisk/astobj2.h"
#include "asterisk/sorcery.h"
#include "asterisk/stasis.h"
#include "asterisk/app.h"

struct mwi_subscription;
AO2_GLOBAL_OBJ_STATIC(unsolicited_mwi);

#define STASIS_BUCKETS 13
#define MWI_BUCKETS 53

#define MWI_TYPE "application"
#define MWI_SUBTYPE "simple-message-summary"

#define MWI_DATASTORE "MWI datastore"

static void mwi_subscription_shutdown(struct ast_sip_subscription *sub);
static void mwi_to_ami(struct ast_sip_subscription *sub, struct ast_str **buf);
static int mwi_new_subscribe(struct ast_sip_endpoint *endpoint,
		const char *resource);
static int mwi_subscription_established(struct ast_sip_subscription *sub);
static void *mwi_get_notify_data(struct ast_sip_subscription *sub);

static struct ast_sip_notifier mwi_notifier = {
	.default_accept = MWI_TYPE"/"MWI_SUBTYPE,
	.new_subscribe = mwi_new_subscribe,
	.subscription_established = mwi_subscription_established,
	.get_notify_data = mwi_get_notify_data,
};

static struct ast_sip_subscription_handler mwi_handler = {
	.event_name = "message-summary",
	.body_type = AST_SIP_MESSAGE_ACCUMULATOR,
	.accept = { MWI_TYPE"/"MWI_SUBTYPE, },
	.subscription_shutdown = mwi_subscription_shutdown,
	.to_ami = mwi_to_ami,
	.notifier = &mwi_notifier,
};

/*!
 * \brief Wrapper for stasis subscription
 *
 * An MWI subscription has a container of these. This
 * represents a stasis subscription for MWI state.
 */
struct mwi_stasis_subscription {
	/*! The MWI stasis subscription */
	struct stasis_subscription *stasis_sub;
	/*! The mailbox corresponding with the MWI subscription. Used as a hash key */
	char mailbox[1];
};

/*!
 * \brief A subscription for MWI
 *
 * This subscription is the basis for MWI for an endpoint. Each
 * endpoint that uses MWI will have a corresponding mwi_subscription.
 *
 * This structure acts as the owner for the underlying SIP subscription.
 * When the mwi_subscription is destroyed, the SIP subscription dies, too.
 * The mwi_subscription's lifetime is governed by its underlying stasis
 * subscriptions. When all stasis subscriptions are destroyed, the
 * mwi_subscription is destroyed as well.
 */
struct mwi_subscription {
	/*! Container of \ref mwi_stasis_subscription structures.
	 * A single MWI subscription may be fore multiple mailboxes, thus
	 * requiring multiple stasis subscriptions
	 */
	struct ao2_container *stasis_subs;
	/*! The SIP subscription. Unsolicited MWI does not use this */
	struct ast_sip_subscription *sip_sub;
	/*! Is the MWI solicited (i.e. Initiated with an external SUBSCRIBE) ? */
	unsigned int is_solicited;
	/*! Identifier for the subscription.
	 * The identifier is the same as the corresponding endpoint's stasis ID.
	 * Used as a hash key
	 */
	char id[1];
};

static void mwi_stasis_cb(void *userdata, struct stasis_subscription *sub,
		struct stasis_message *msg);

static struct mwi_stasis_subscription *mwi_stasis_subscription_alloc(const char *mailbox, struct mwi_subscription *mwi_sub)
{
	struct mwi_stasis_subscription *mwi_stasis_sub;
	struct stasis_topic *topic;

	if (!mwi_sub) {
		return NULL;
	}

	mwi_stasis_sub = ao2_alloc(sizeof(*mwi_stasis_sub) + strlen(mailbox), NULL);
	if (!mwi_stasis_sub) {
		return NULL;
	}

	topic = ast_mwi_topic(mailbox);

	/* Safe strcpy */
	strcpy(mwi_stasis_sub->mailbox, mailbox);
	ao2_ref(mwi_sub, +1);
	ast_debug(3, "Creating stasis MWI subscription to mailbox %s for endpoint %s\n", mailbox, mwi_sub->id);
	mwi_stasis_sub->stasis_sub = stasis_subscribe_pool(topic, mwi_stasis_cb, mwi_sub);
	return mwi_stasis_sub;
}

static int stasis_sub_hash(const void *obj, const int flags)
{
	const struct mwi_stasis_subscription *object;
	const char *key;

	switch (flags & OBJ_SEARCH_MASK) {
	case OBJ_SEARCH_KEY:
		key = obj;
		break;
	case OBJ_SEARCH_OBJECT:
		object = obj;
		key = object->mailbox;
		break;
	default:
		ast_assert(0);
		return 0;
	}
	return ast_str_hash(key);
}

static int stasis_sub_cmp(void *obj, void *arg, int flags)
{
	const struct mwi_stasis_subscription *sub_left = obj;
	const struct mwi_stasis_subscription *sub_right = arg;
	const char *right_key = arg;
	int cmp;

	switch (flags & OBJ_SEARCH_MASK) {
	case OBJ_SEARCH_OBJECT:
		right_key = sub_right->mailbox;
		/* Fall through */
	case OBJ_SEARCH_KEY:
		cmp = strcmp(sub_left->mailbox, right_key);
		break;
	case OBJ_SEARCH_PARTIAL_KEY:
		cmp = strncmp(sub_left->mailbox, right_key, strlen(right_key));
		break;
	default:
		cmp = 0;
		break;
	}
	if (cmp) {
		return 0;
	}
	return CMP_MATCH;
}

static void mwi_subscription_destructor(void *obj)
{
	struct mwi_subscription *sub = obj;

	ast_debug(3, "Destroying MWI subscription for endpoint %s\n", sub->id);
	ao2_cleanup(sub->sip_sub);
	ao2_cleanup(sub->stasis_subs);
}

static struct mwi_subscription *mwi_subscription_alloc(struct ast_sip_endpoint *endpoint,
		unsigned int is_solicited, struct ast_sip_subscription *sip_sub)
{
	struct mwi_subscription *sub;
	const char *endpoint_id = ast_sorcery_object_get_id(endpoint);

	sub = ao2_alloc(sizeof(*sub) + strlen(endpoint_id),
			mwi_subscription_destructor);

	if (!sub) {
		return NULL;
	}

	/* Safe strcpy */
	strcpy(sub->id, endpoint_id);

	/* Unsolicited MWI doesn't actually result in a SIP subscription being
	 * created. This is because a SIP subscription associates with a dialog.
	 * Most devices expect unsolicited MWI NOTIFYs to appear out of dialog. If
	 * they receive an in-dialog MWI NOTIFY (i.e. with a to-tag), then they
	 * will reject the NOTIFY with a 481, thus resulting in message-waiting
	 * state not being updated on the device
	 */
	if (is_solicited) {
		sub->sip_sub = ao2_bump(sip_sub);
	}

	sub->stasis_subs = ao2_container_alloc(STASIS_BUCKETS, stasis_sub_hash, stasis_sub_cmp);
	if (!sub->stasis_subs) {
		ao2_cleanup(sub);
		return NULL;
	}
	sub->is_solicited = is_solicited;

	ast_debug(3, "Created %s MWI subscription for endpoint %s\n", is_solicited ? "solicited" : "unsolicited", sub->id);

	return sub;
}

static int mwi_sub_hash(const void *obj, const int flags)
{
	const struct mwi_subscription *object;
	const char *key;

	switch (flags & OBJ_SEARCH_MASK) {
	case OBJ_SEARCH_KEY:
		key = obj;
		break;
	case OBJ_SEARCH_OBJECT:
		object = obj;
		key = object->id;
		break;
	default:
		ast_assert(0);
		return 0;
	}
	return ast_str_hash(key);
}

static int mwi_sub_cmp(void *obj, void *arg, int flags)
{
	const struct mwi_subscription *sub_left = obj;
	const struct mwi_subscription *sub_right = arg;
	const char *right_key = arg;
	int cmp;

	switch (flags & OBJ_SEARCH_MASK) {
	case OBJ_SEARCH_OBJECT:
		right_key = sub_right->id;
		/* Fall through */
	case OBJ_SEARCH_KEY:
		cmp = strcmp(sub_left->id, right_key);
		break;
	case OBJ_SEARCH_PARTIAL_KEY:
		cmp = strncmp(sub_left->id, right_key, strlen(right_key));
		break;
	default:
		cmp = 0;
		break;
	}
	if (cmp) {
		return 0;
	}
	return CMP_MATCH;
}

static int get_message_count(void *obj, void *arg, int flags)
{
	RAII_VAR(struct stasis_message *, msg, NULL, ao2_cleanup);
	struct mwi_stasis_subscription *mwi_stasis = obj;
	struct ast_sip_message_accumulator *counter = arg;
	struct ast_mwi_state *mwi_state;

	msg = stasis_cache_get(ast_mwi_state_cache(), ast_mwi_state_type(), mwi_stasis->mailbox);
	if (!msg) {
		return 0;
	}

	mwi_state = stasis_message_data(msg);
	counter->old_msgs += mwi_state->old_msgs;
	counter->new_msgs += mwi_state->new_msgs;
	return 0;
}

struct unsolicited_mwi_data {
	struct mwi_subscription *sub;
	struct ast_sip_endpoint *endpoint;
	pjsip_evsub_state state;
	const struct ast_sip_body *body;
};

static int send_unsolicited_mwi_notify_to_contact(void *obj, void *arg, int flags)
{
	struct unsolicited_mwi_data *mwi_data = arg;
	struct mwi_subscription *sub = mwi_data->sub;
	struct ast_sip_endpoint *endpoint = mwi_data->endpoint;
	pjsip_evsub_state state = mwi_data->state;
	const struct ast_sip_body *body = mwi_data->body;
	struct ast_sip_contact *contact = obj;
	const char *state_name;
	pjsip_tx_data *tdata;
	pjsip_sub_state_hdr *sub_state;
	pjsip_event_hdr *event;
	const pjsip_hdr *allow_events = pjsip_evsub_get_allow_events_hdr(NULL);

	if (ast_sip_create_request("NOTIFY", NULL, endpoint, NULL, contact, &tdata)) {
		ast_log(LOG_WARNING, "Unable to create unsolicited NOTIFY request to endpoint %s URI %s\n", sub->id, contact->uri);
		return 0;
	}

	if (!ast_strlen_zero(endpoint->subscription.mwi.fromuser)) {
		pjsip_fromto_hdr *from = pjsip_msg_find_hdr(tdata->msg, PJSIP_H_FROM, NULL);
		pjsip_name_addr *from_name_addr = (pjsip_name_addr *) from->uri;
		pjsip_sip_uri *from_uri = pjsip_uri_get_uri(from_name_addr->uri);

		pj_strdup2(tdata->pool, &from_uri->user, endpoint->subscription.mwi.fromuser);
	}

	switch (state) {
	case PJSIP_EVSUB_STATE_ACTIVE:
		state_name = "active";
		break;
	case PJSIP_EVSUB_STATE_TERMINATED:
	default:
		state_name = "terminated";
		break;
	}

	sub_state = pjsip_sub_state_hdr_create(tdata->pool);
	pj_cstr(&sub_state->sub_state, state_name);
	pjsip_msg_add_hdr(tdata->msg, (pjsip_hdr *) sub_state);

	event = pjsip_event_hdr_create(tdata->pool);
	pj_cstr(&event->event_type, "message-summary");
	pjsip_msg_add_hdr(tdata->msg, (pjsip_hdr *) event);

	pjsip_msg_add_hdr(tdata->msg, pjsip_hdr_shallow_clone(tdata->pool, allow_events));
	ast_sip_add_body(tdata, body);
	ast_sip_send_request(tdata, NULL, endpoint, NULL, NULL);

	return 0;
}

static void send_unsolicited_mwi_notify(struct mwi_subscription *sub,
		struct ast_sip_message_accumulator *counter)
{
	RAII_VAR(struct ast_sip_endpoint *, endpoint, ast_sorcery_retrieve_by_id(ast_sip_get_sorcery(),
				"endpoint", sub->id), ao2_cleanup);
	char *endpoint_aors;
	char *aor_name;
	struct ast_sip_body body;
	struct ast_str *body_text;
	struct ast_sip_body_data body_data = {
		.body_type = AST_SIP_MESSAGE_ACCUMULATOR,
		.body_data = counter,
	};

	if (!endpoint) {
		ast_log(LOG_WARNING, "Unable to send unsolicited MWI to %s because endpoint does not exist\n",
				sub->id);
		return;
	}
	if (ast_strlen_zero(endpoint->aors)) {
		ast_log(LOG_WARNING, "Unable to send unsolicited MWI to %s because the endpoint has no"
				" configured AORs\n", sub->id);
		return;
	}

	body.type = MWI_TYPE;
	body.subtype = MWI_SUBTYPE;

	body_text = ast_str_create(64);

	if (!body_text) {
		return;
	}

	if (ast_sip_pubsub_generate_body_content(body.type, body.subtype, &body_data, &body_text)) {
		ast_log(LOG_WARNING, "Unable to generate SIP MWI NOTIFY body.\n");
		ast_free(body_text);
		return;
	}

	body.body_text = ast_str_buffer(body_text);

	endpoint_aors = ast_strdupa(endpoint->aors);

	ast_debug(5, "Sending unsolicited MWI NOTIFY to endpoint %s, new messages: %d, old messages: %d\n",
			sub->id, counter->new_msgs, counter->old_msgs);

	while ((aor_name = strsep(&endpoint_aors, ","))) {
		RAII_VAR(struct ast_sip_aor *, aor, ast_sip_location_retrieve_aor(aor_name), ao2_cleanup);
		RAII_VAR(struct ao2_container *, contacts, NULL, ao2_cleanup);
		struct unsolicited_mwi_data mwi_data = {
			.sub = sub,
			.endpoint = endpoint,
			.body = &body,
		};

		if (!aor) {
			ast_log(LOG_WARNING, "Unable to locate AOR %s for unsolicited MWI\n", aor_name);
			continue;
		}

		contacts = ast_sip_location_retrieve_aor_contacts(aor);
		if (!contacts || (ao2_container_count(contacts) == 0)) {
			ast_log(LOG_NOTICE, "No contacts bound to AOR %s. Cannot send unsolicited MWI until a contact registers.\n", aor_name);
			continue;
		}

		ao2_callback(contacts, OBJ_NODATA, send_unsolicited_mwi_notify_to_contact, &mwi_data);
	}

	ast_free(body_text);
}

static void send_mwi_notify(struct mwi_subscription *sub)
{
	struct ast_sip_message_accumulator counter = {
		.old_msgs = 0,
		.new_msgs = 0,
	};
	struct ast_sip_body_data data = {
		.body_type = AST_SIP_MESSAGE_ACCUMULATOR,
		.body_data = &counter,
	};

	ao2_callback(sub->stasis_subs, OBJ_NODATA, get_message_count, &counter);

	if (sub->is_solicited) {
		ast_sip_subscription_notify(sub->sip_sub, &data, 0);
		return;
	}

	send_unsolicited_mwi_notify(sub, &counter);
}

static int unsubscribe_stasis(void *obj, void *arg, int flags)
{
	struct mwi_stasis_subscription *mwi_stasis = obj;
	if (mwi_stasis->stasis_sub) {
		ast_debug(3, "Removing stasis subscription to mailbox %s\n", mwi_stasis->mailbox);
		mwi_stasis->stasis_sub = stasis_unsubscribe(mwi_stasis->stasis_sub);
	}
	return CMP_MATCH;
}

static void mwi_subscription_shutdown(struct ast_sip_subscription *sub)
{
	struct mwi_subscription *mwi_sub;
	RAII_VAR(struct ast_datastore *, mwi_datastore,
			ast_sip_subscription_get_datastore(sub, MWI_DATASTORE), ao2_cleanup);

	if (!mwi_datastore) {
		return;
	}

	mwi_sub = mwi_datastore->data;
	ao2_callback(mwi_sub->stasis_subs, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, unsubscribe_stasis, NULL);
}

static struct ast_datastore_info mwi_ds_info = { };

static int add_mwi_datastore(struct mwi_subscription *sub)
{
	RAII_VAR(struct ast_datastore *, mwi_datastore, NULL, ao2_cleanup);

	mwi_datastore = ast_sip_subscription_alloc_datastore(&mwi_ds_info, MWI_DATASTORE);
	if (!mwi_datastore) {
		return -1;
	}
	mwi_datastore->data = sub;

	ast_sip_subscription_add_datastore(sub->sip_sub, mwi_datastore);
	return 0;
}

/*!
 * \brief Determines if an endpoint is receiving unsolicited MWI for a particular mailbox.
 *
 * \param endpoint The endpoint to check
 * \param mailbox The candidate mailbox
 * \retval 0 The endpoint does not receive unsolicited MWI for this mailbox
 * \retval 1 The endpoint receives unsolicited MWI for this mailbox
 */
static int endpoint_receives_unsolicited_mwi_for_mailbox(struct ast_sip_endpoint *endpoint,
		const char *mailbox)
{
	struct ao2_container *unsolicited = ao2_global_obj_ref(unsolicited_mwi);
	struct ao2_iterator *mwi_subs;
	struct mwi_subscription *mwi_sub;
	const char *endpoint_id = ast_sorcery_object_get_id(endpoint);
	int ret = 0;

	if (!unsolicited) {
		return 0;
	}

	mwi_subs = ao2_find(unsolicited, endpoint_id, OBJ_SEARCH_KEY | OBJ_MULTIPLE);
	ao2_cleanup(unsolicited);

	if (!mwi_subs) {
		return 0;
	}

	for (; (mwi_sub = ao2_iterator_next(mwi_subs)) && !ret; ao2_cleanup(mwi_sub)) {
		struct mwi_stasis_subscription *mwi_stasis;

		mwi_stasis = ao2_find(mwi_sub->stasis_subs, mailbox, OBJ_SEARCH_KEY);
		if (mwi_stasis) {
			ret = 1;
			ao2_cleanup(mwi_stasis);
		}
	}

	ao2_iterator_destroy(mwi_subs);
	return ret;
}

/*!
 * \brief Determine if an endpoint is a candidate to be able to subscribe for MWI
 *
 * Currently, this just makes sure that the endpoint is not already receiving unsolicted
 * MWI for any of an AOR's configured mailboxes.
 *
 * \param obj The AOR to which the endpoint is subscribing.
 * \param arg The endpoint that is attempting to subscribe.
 * \param flags Unused.
 * \retval 0 Endpoint is a candidate to subscribe to MWI on the AOR.
 * \retval -1 The endpoint cannot subscribe to MWI on the AOR.
 */
static int mwi_validate_for_aor(void *obj, void *arg, int flags)
{
	struct ast_sip_aor *aor = obj;
	struct ast_sip_endpoint *endpoint = arg;
	char *mailboxes;
	char *mailbox;

	if (ast_strlen_zero(aor->mailboxes)) {
		return 0;
	}

	mailboxes = ast_strdupa(aor->mailboxes);
	while ((mailbox = strsep(&mailboxes, ","))) {
		if (endpoint_receives_unsolicited_mwi_for_mailbox(endpoint, mailbox)) {
			ast_log(LOG_NOTICE, "Endpoint '%s' already configured for unsolicited MWI for mailbox '%s'. "
					"Denying MWI subscription to %s\n", ast_sorcery_object_get_id(endpoint), mailbox,
					ast_sorcery_object_get_id(aor));
			return -1;
		}
	}

	return 0;
}

static int mwi_on_aor(void *obj, void *arg, int flags)
{
	struct ast_sip_aor *aor = obj;
	struct mwi_subscription *sub = arg;
	char *mailboxes;
	char *mailbox;

	if (ast_strlen_zero(aor->mailboxes)) {
		return 0;
	}

	mailboxes = ast_strdupa(aor->mailboxes);
	while ((mailbox = strsep(&mailboxes, ","))) {
		RAII_VAR(struct mwi_stasis_subscription *, mwi_stasis_sub,
				mwi_stasis_subscription_alloc(mailbox, sub), ao2_cleanup);
		if (mwi_stasis_sub) {
			ao2_link(sub->stasis_subs, mwi_stasis_sub);
		}
	}

	return 0;
}

static struct mwi_subscription *mwi_create_subscription(
	struct ast_sip_endpoint *endpoint, struct ast_sip_subscription *sip_sub)
{
	struct mwi_subscription *sub = mwi_subscription_alloc(endpoint, 1, sip_sub);

	if (!sub) {
		return NULL;
	}

	if (add_mwi_datastore(sub)) {
		ast_log(LOG_WARNING, "Unable to allocate datastore on MWI "
			"subscription from %s\n", sub->id);
		ao2_ref(sub, -1);
		return NULL;
	}

	return sub;
}

static struct mwi_subscription *mwi_subscribe_single(
	struct ast_sip_endpoint *endpoint, struct ast_sip_subscription *sip_sub, const char *name)
{
	RAII_VAR(struct ast_sip_aor *, aor,
		 ast_sip_location_retrieve_aor(name), ao2_cleanup);
	struct mwi_subscription *sub;

	if (!aor) {
		/*! I suppose it's possible for the AOR to disappear on us
		 * between accepting the subscription and sending the first
		 * NOTIFY...
		 */
		ast_log(LOG_WARNING, "Unable to locate aor %s. MWI "
			"subscription failed.\n", name);
		return NULL;
	}

	if (!(sub = mwi_create_subscription(endpoint, sip_sub))) {
		return NULL;
	}

	mwi_on_aor(aor, sub, 0);
	return sub;
}

static struct mwi_subscription *mwi_subscribe_all(
	struct ast_sip_endpoint *endpoint, struct ast_sip_subscription *sip_sub)
{
	struct mwi_subscription *sub;

	sub = mwi_create_subscription(endpoint, sip_sub);

	if (!sub) {
		return NULL;
	}

	ast_sip_for_each_aor(endpoint->aors, mwi_on_aor, sub);
	return sub;
}

static int mwi_new_subscribe(struct ast_sip_endpoint *endpoint,
		const char *resource)
{
	RAII_VAR(struct ast_sip_aor *, aor, NULL, ao2_cleanup);

	if (ast_strlen_zero(resource)) {
		if (ast_sip_for_each_aor(endpoint->aors, mwi_validate_for_aor, endpoint)) {
			return 500;
		}
		return 200;
	}

	aor = ast_sip_location_retrieve_aor(resource);

	if (!aor) {
		ast_log(LOG_WARNING, "Unable to locate aor %s. MWI "
			"subscription failed.\n", resource);
		return 404;
	}

	if (ast_strlen_zero(aor->mailboxes)) {
		ast_log(LOG_NOTICE, "AOR %s has no configured mailboxes. "
			"MWI subscription failed\n", resource);
		return 404;
	}

	if (mwi_validate_for_aor(aor, endpoint, 0)) {
		return 500;
	}

	return 200;
}

static int mwi_subscription_established(struct ast_sip_subscription *sip_sub)
{
	const char *resource = ast_sip_subscription_get_resource_name(sip_sub);
	struct mwi_subscription *sub;
	struct ast_sip_endpoint *endpoint = ast_sip_subscription_get_endpoint(sip_sub);

	/* no aor in uri? subscribe to all on endpoint */
	if (ast_strlen_zero(resource)) {
		sub = mwi_subscribe_all(endpoint, sip_sub);
	} else {
		sub = mwi_subscribe_single(endpoint, sip_sub, resource);
	}

	if (!sub) {
		ao2_cleanup(endpoint);
		return -1;
	}

	ao2_cleanup(sub);
	ao2_cleanup(endpoint);
	return 0;
}

static void *mwi_get_notify_data(struct ast_sip_subscription *sub)
{
	struct ast_sip_message_accumulator *counter;
	struct mwi_subscription *mwi_sub;
	struct ast_datastore *mwi_datastore;

	mwi_datastore = ast_sip_subscription_get_datastore(sub, MWI_DATASTORE);
	if (!mwi_datastore) {
		return NULL;
	}
	mwi_sub = mwi_datastore->data;

	counter = ao2_alloc(sizeof(*counter), NULL);
	if (!counter) {
		ao2_cleanup(mwi_datastore);
		return NULL;
	}

	ao2_callback(mwi_sub->stasis_subs, OBJ_NODATA, get_message_count, counter);
	ao2_cleanup(mwi_datastore);
	return counter;
}

static void mwi_subscription_mailboxes_str(struct ao2_container *stasis_subs,
					   struct ast_str **str)
{
	int num = ao2_container_count(stasis_subs);

	struct mwi_stasis_subscription *node;
	struct ao2_iterator i = ao2_iterator_init(stasis_subs, 0);

	while ((node = ao2_iterator_next(&i))) {
		if (--num) {
			ast_str_append(str, 0, "%s,", node->mailbox);
		} else {
			ast_str_append(str, 0, "%s", node->mailbox);
		}
		ao2_ref(node, -1);
	}
	ao2_iterator_destroy(&i);
}

static void mwi_to_ami(struct ast_sip_subscription *sub,
		       struct ast_str **buf)
{
	struct mwi_subscription *mwi_sub;
	RAII_VAR(struct ast_datastore *, mwi_datastore,
			ast_sip_subscription_get_datastore(sub, MWI_DATASTORE), ao2_cleanup);

	if (!mwi_datastore) {
		return;
	}

	mwi_sub = mwi_datastore->data;

	ast_str_append(buf, 0, "SubscriptionType: mwi\r\n");
	ast_str_append(buf, 0, "Mailboxes: ");
	mwi_subscription_mailboxes_str(mwi_sub->stasis_subs, buf);
	ast_str_append(buf, 0, "\r\n");
}

static int serialized_notify(void *userdata)
{
	struct mwi_subscription *mwi_sub = userdata;

	send_mwi_notify(mwi_sub);
	ao2_ref(mwi_sub, -1);
	return 0;
}

static int serialized_cleanup(void *userdata)
{
	struct mwi_subscription *mwi_sub = userdata;

	/* This is getting rid of the reference that was added
	 * just before this serialized task was pushed.
	 */
	ao2_cleanup(mwi_sub);
	/* This is getting rid of the reference held by the
	 * stasis subscription
	 */
	ao2_cleanup(mwi_sub);
	return 0;
}

static void mwi_stasis_cb(void *userdata, struct stasis_subscription *sub,
		struct stasis_message *msg)
{
	struct mwi_subscription *mwi_sub = userdata;

	if (stasis_subscription_final_message(sub, msg)) {
		ao2_ref(mwi_sub, +1);
		ast_sip_push_task(NULL, serialized_cleanup, mwi_sub);
		return;
	}

	if (ast_mwi_state_type() == stasis_message_type(msg)) {
		struct ast_taskprocessor *serializer = mwi_sub->is_solicited ? ast_sip_subscription_get_serializer(mwi_sub->sip_sub) : NULL;
		ao2_ref(mwi_sub, +1);
		ast_sip_push_task(serializer, serialized_notify, mwi_sub);
	}
}

static int create_mwi_subscriptions_for_endpoint(void *obj, void *arg, int flags)
{
	RAII_VAR(struct mwi_subscription *, aggregate_sub, NULL, ao2_cleanup);
	struct ast_sip_endpoint *endpoint = obj;
	struct ao2_container *mwi_subscriptions = arg;
	char *mailboxes;
	char *mailbox;

	if (ast_strlen_zero(endpoint->subscription.mwi.mailboxes)) {
		return 0;
	}

	if (endpoint->subscription.mwi.aggregate) {
		aggregate_sub = mwi_subscription_alloc(endpoint, 0, NULL);
		if (!aggregate_sub) {
			return 0;
		}
	}

	mailboxes = ast_strdupa(endpoint->subscription.mwi.mailboxes);
	while ((mailbox = strsep(&mailboxes, ","))) {
		struct mwi_subscription *sub = aggregate_sub ?:
			mwi_subscription_alloc(endpoint, 0, NULL);
		RAII_VAR(struct mwi_stasis_subscription *, mwi_stasis_sub,
				mwi_stasis_subscription_alloc(mailbox, sub), ao2_cleanup);
		if (mwi_stasis_sub) {
			ao2_link(sub->stasis_subs, mwi_stasis_sub);
		}
		if (!aggregate_sub) {
			ao2_link(mwi_subscriptions, sub);
			ao2_cleanup(sub);
		}
	}
	if (aggregate_sub) {
		ao2_link(mwi_subscriptions, aggregate_sub);
	}
	return 0;
}

static int unsubscribe(void *obj, void *arg, int flags)
{
	struct mwi_subscription *mwi_sub = obj;

	ao2_callback(mwi_sub->stasis_subs, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, unsubscribe_stasis, NULL);
	return CMP_MATCH;
}

static void create_mwi_subscriptions(void)
{
	struct ao2_container *mwi_subscriptions = ao2_container_alloc(MWI_BUCKETS, mwi_sub_hash, mwi_sub_cmp);
	RAII_VAR(struct ao2_container *, old_mwi_subscriptions, ao2_global_obj_ref(unsolicited_mwi), ao2_cleanup);
	RAII_VAR(struct ao2_container *, endpoints, ast_sorcery_retrieve_by_fields(
				ast_sip_get_sorcery(), "endpoint", AST_RETRIEVE_FLAG_MULTIPLE | AST_RETRIEVE_FLAG_ALL, NULL),
			ao2_cleanup);

	if (!mwi_subscriptions) {
		return;
	}

	/* We remove all the old stasis subscriptions first before applying the new configuration. This
	 * prevents a situation where there might be multiple overlapping stasis subscriptions for an
	 * endpoint for mailboxes. Though there may be mailbox changes during the gap between unsubscribing
	 * and resubscribing, up-to-date mailbox state will be sent out to the endpoint when the
	 * new stasis subscription is established
	 */
	if (old_mwi_subscriptions) {
		ao2_callback(old_mwi_subscriptions, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, unsubscribe, NULL);
	}
	ao2_callback(endpoints, OBJ_NODATA, create_mwi_subscriptions_for_endpoint, mwi_subscriptions);
	ao2_global_obj_replace_unref(unsolicited_mwi, mwi_subscriptions);
	ao2_ref(mwi_subscriptions, -1);
}

static int reload(void)
{
	create_mwi_subscriptions();
	return 0;
}

static int load_module(void)
{
	CHECK_PJSIP_MODULE_LOADED();

	if (ast_sip_register_subscription_handler(&mwi_handler)) {
		return AST_MODULE_LOAD_DECLINE;
	}
	create_mwi_subscriptions();
	return AST_MODULE_LOAD_SUCCESS;
}

static int unload_module(void)
{
	RAII_VAR(struct ao2_container *, mwi_subscriptions, ao2_global_obj_ref(unsolicited_mwi), ao2_cleanup);
	if (mwi_subscriptions) {
		ao2_callback(mwi_subscriptions, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, unsubscribe, NULL);
		ao2_global_obj_release(unsolicited_mwi);
	}
	ast_sip_unregister_subscription_handler(&mwi_handler);
	return 0;
}

AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_LOAD_ORDER, "PJSIP MWI resource",
		.support_level = AST_MODULE_SUPPORT_CORE,
		.load = load_module,
		.unload = unload_module,
		.reload = reload,
		.load_pri = AST_MODPRI_CHANNEL_DEPEND,
);