// async_client.cpp

/*******************************************************************************
 * Copyright (c) 2013-2022 Frank Pagliughi <fpagliughi@mindspring.com>
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v2.0
 * and Eclipse Distribution License v1.0 which accompany this distribution.
 *
 * The Eclipse Public License is available at
 *    http://www.eclipse.org/legal/epl-v20.html
 * and the Eclipse Distribution License is available at
 *   http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *    Frank Pagliughi - initial implementation and documentation
 *    Frank Pagliughi - MQTT v5 support
 *******************************************************************************/

#include "mqtt/async_client.h"

#include <chrono>
#include <condition_variable>
#include <cstdio>
#include <cstring>
#include <mutex>
#include <thread>

#include "mqtt/disconnect_options.h"
#include "mqtt/message.h"
#include "mqtt/response_options.h"
#include "mqtt/token.h"

namespace mqtt {

/////////////////////////////////////////////////////////////////////////////

void async_client::create()
{
    int rc = MQTTASYNC_SUCCESS;

    const auto& opts = createOpts_;
    mqttVersion_ = opts.mqtt_version();

    // The C client, when created for v5, can accommodate any version for
    // connections. This leaves the version solely to the connection.
    auto copts{opts.opts_};
    copts.MQTTVersion = MQTTVERSION_5;

    auto serverURI = opts.get_server_uri();
    auto clientId = opts.get_client_id();

    const auto userp{std::get_if<iclient_persistence*>(&opts.persistence_)};

    if (std::get_if<no_persistence>(&opts.persistence_) || (userp && !*userp)) {
        rc = MQTTAsync_createWithOptions(
            &cli_, serverURI.c_str(), clientId.c_str(), MQTTCLIENT_PERSISTENCE_NONE, nullptr,
            &copts
        );
    }
    else if (const auto dir{std::get_if<string>(&opts.persistence_)}; dir) {
        rc = MQTTAsync_createWithOptions(
            &cli_, serverURI.c_str(), clientId.c_str(), MQTTCLIENT_PERSISTENCE_DEFAULT,
            const_cast<char*>(dir->c_str()), &copts
        );
    }
    else {
        persist_.reset(new MQTTClient_persistence{
            *userp, &iclient_persistence::persistence_open,
            &iclient_persistence::persistence_close, &iclient_persistence::persistence_put,
            &iclient_persistence::persistence_get, &iclient_persistence::persistence_remove,
            &iclient_persistence::persistence_keys, &iclient_persistence::persistence_clear,
            &iclient_persistence::persistence_containskey
        });

        rc = MQTTAsync_createWithOptions(
            &cli_, serverURI.c_str(), clientId.c_str(), MQTTCLIENT_PERSISTENCE_USER,
            persist_.get(), &copts
        );
    }
    if (rc != MQTTASYNC_SUCCESS)
        throw exception(rc);
}

async_client::~async_client() { MQTTAsync_destroy(&cli_); }

// --------------------------------------------------------------------------
// Class static callbacks.
// These are the callbacks directly from the C-lib. In each case the
// 'context' should be the address of the async_client object that
// registered the callback.

// Callback for MQTTAsync_setConnected()
// This is installed with the normal callbacks and with a call to
// reconnect() to indicate that it succeeded. It signals the client's
// connect token then calls any registered callbacks.
void async_client::on_connected(void* context, char* cause)
{
    if (context) {
        async_client* cli = static_cast<async_client*>(context);
        string cause_str = cause ? string{cause} : string{};

        auto tok = cli->connTok_;
        if (tok)
            tok->on_success(nullptr);

        callback* cb = cli->userCallback_;
        if (cb)
            cb->connected(cause_str);

        auto& connHandler = cli->connHandler_;
        if (connHandler)
            connHandler(cause_str);
    }
}

// Callback for when the connection is lost.
// This is called from the MQTTAsync_connectionLost registered via
// MQTTAsync_setCallbacks().
// It calls the registered handlers then, if there's a consumer queue, it
// places a null pointer in the queue to alert the consumer to a closed
// connection.
void async_client::on_connection_lost(void* context, char* cause)
{
    if (context) {
        async_client* cli = static_cast<async_client*>(context);
        string cause_str = cause ? string(cause) : string();

        callback* cb = cli->userCallback_;
        if (cb)
            cb->connection_lost(cause_str);

        auto& connLostHandler = cli->connLostHandler_;
        if (connLostHandler)
            connLostHandler(cause_str);

        consumer_queue_type& que = cli->que_;
        if (que)
            que->put(const_message_ptr{});
    }
}

// Callback from the C lib for when a disconnect packet is received from
// the server.
void async_client::on_disconnected(
    void* context, MQTTProperties* cprops, MQTTReasonCodes reasonCode
)
{
    if (context) {
        async_client* cli = static_cast<async_client*>(context);

        auto& disconnectedHandler = cli->disconnectedHandler_;
        if (disconnectedHandler) {
            properties props(*cprops);
            disconnectedHandler(props, ReasonCode(reasonCode));
        }

        consumer_queue_type& que = cli->que_;
        if (que)
            que->put(const_message_ptr{});
    }
}

// Callback for when a subscribed message arrives.
// This is called from the MQTTAsync_messageArrived registered via
// MQTTAsync_setCallbacks().
int async_client::on_message_arrived(
    void* context, char* topicName, int topicLen, MQTTAsync_message* msg
)
{
    if (context) {
        async_client* cli = static_cast<async_client*>(context);
        callback* cb = cli->userCallback_;
        consumer_queue_type& que = cli->que_;
        message_handler& msgHandler = cli->msgHandler_;

        if (cb || que || msgHandler) {
            size_t len = (topicLen == 0) ? strlen(topicName) : size_t(topicLen);

            string topic{topicName, len};
            auto m = message::create(std::move(topic), *msg);

            if (msgHandler)
                msgHandler(m);

            if (cb)
                cb->message_arrived(m);

            if (que)
                que->put(m);
        }
    }

    MQTTAsync_freeMessage(&msg);
    MQTTAsync_free(topicName);

    // TODO: Should the user code determine the return value?
    // The Java version does doesn't seem to...
    return to_int(true);
}

// Callback from the C lib for when a registered updateConnectOptions
// needs to be called.
int async_client::on_update_connection(void* context, MQTTAsync_connectData* cdata)
{
    if (context) {
        async_client* cli = static_cast<async_client*>(context);
        auto& updateConnection = cli->updateConnectionHandler_;

        if (updateConnection) {
            connect_data data(*cdata);
            if (updateConnection(data)) {
                // Copy username and password into newly allocated buffers.
                // The C lib will take ownership of the memory
                auto n = data.get_user_name().length();
                if (n > 0) {
                    char* username = static_cast<char*>(MQTTAsync_malloc(n + 1));
                    strncpy(username, data.get_user_name().c_str(), n + 1);
                    username[n] = '\0';
                    cdata->username = username;
                }
                else
                    cdata->username = nullptr;

                n = data.get_password().length();
                if (n > 0) {
                    char* passwd = static_cast<char*>(MQTTAsync_malloc(n));
                    memcpy(passwd, data.get_password().data(), n);
                    cdata->binarypwd.data = passwd;
                }
                else
                    cdata->binarypwd.data = nullptr;
                cdata->binarypwd.len = int(n);

                return to_int(true);
            }
        }
    }
    return 0;  // false
}

// --------------------------------------------------------------------------
// Private methods

void async_client::add_token(token_ptr tok)
{
    if (tok) {
        guard g(lock_);
        pendingTokens_.push_back(tok);
    }
}

void async_client::add_token(delivery_token_ptr tok)
{
    if (tok) {
        guard g(lock_);
        pendingDeliveryTokens_.push_back(tok);
    }
}

// Note that we uniquely identify a token by the address of its raw pointer,
// since the message ID is not unique.

void async_client::remove_token(token* tok)
{
    if (!tok)
        return;

    guard g(lock_);
    for (auto p = pendingDeliveryTokens_.begin(); p != pendingDeliveryTokens_.end(); ++p) {
        if (p->get() == tok) {
            delivery_token_ptr dtok = *p;
            pendingDeliveryTokens_.erase(p);

            // If there's a user callback registered, we can now call
            // delivery_complete()

            if (userCallback_) {
                const_message_ptr msg = dtok->get_message();
                if (msg && msg->get_qos() > 0) {
                    callback* cb = userCallback_;
                    g.unlock();
                    cb->delivery_complete(dtok);
                }
            }
            return;
        }
    }
    for (auto p = pendingTokens_.begin(); p != pendingTokens_.end(); ++p) {
        if (p->get() == tok) {
            pendingTokens_.erase(p);
            return;
        }
    }
}

// --------------------------------------------------------------------------
// Callback management

void async_client::set_callback(callback& cb)
{
    guard g(lock_);
    userCallback_ = &cb;

    int rc = MQTTAsync_setConnected(cli_, this, &async_client::on_connected);

    if (rc == MQTTASYNC_SUCCESS) {
        rc = MQTTAsync_setCallbacks(
            cli_, this, &async_client::on_connection_lost, &async_client::on_message_arrived,
            nullptr /*&async_client::on_delivery_complete*/
        );
    }
    else
        MQTTAsync_setConnected(cli_, nullptr, nullptr);

    if (rc != MQTTASYNC_SUCCESS) {
        userCallback_ = nullptr;
        throw exception(rc);
    }
}

void async_client::disable_callbacks()
{
    // TODO: It would be nice to disable callbacks at the C library level,
    // but the setCallback function currently does not accept a nullptr for
    // the "message arrived" parameter. So, for now we send it an empty
    // lambda function.
    int rc = MQTTAsync_setCallbacks(
        cli_, this, nullptr,
        [](void*, char*, int, MQTTAsync_message*) -> int { return to_int(true); }, nullptr
    );

    if (rc != MQTTASYNC_SUCCESS)
        throw exception(rc);
}

void async_client::set_connected_handler(connection_handler cb)
{
    connHandler_ = cb;
    check_ret(::MQTTAsync_setConnected(cli_, this, &async_client::on_connected));
}

void async_client::set_connection_lost_handler(connection_handler cb)
{
    connLostHandler_ = cb;
    check_ret(
        ::MQTTAsync_setConnectionLostCallback(cli_, this, &async_client::on_connection_lost)
    );
}

void async_client::set_disconnected_handler(disconnected_handler cb)
{
    disconnectedHandler_ = cb;
    check_ret(::MQTTAsync_setDisconnected(cli_, this, &async_client::on_disconnected));
}

void async_client::set_message_callback(message_handler cb)
{
    msgHandler_ = cb;
    check_ret(
        ::MQTTAsync_setMessageArrivedCallback(cli_, this, &async_client::on_message_arrived)
    );
}

void async_client::set_update_connection_handler(update_connection_handler cb)
{
    updateConnectionHandler_ = cb;
    check_ret(
        ::MQTTAsync_setUpdateConnectOptions(cli_, this, &async_client::on_update_connection)
    );
}

// --------------------------------------------------------------------------
// Connect

token_ptr async_client::connect() { return connect(connect_options{}); }

token_ptr async_client::connect(connect_options opts)
{
    // TODO: We should update the MQTT version from the response
    //  	(when the server confirms the requested version)
    mqttVersion_ = opts.opts_.MQTTVersion;

    // The C lib is very picky about version and clean start/session
    if (opts.opts_.MQTTVersion < 5)
        opts.opts_.cleanstart = 0;
    else
        opts.opts_.cleansession = 0;

    // TODO: If connTok_ is non-null, there could be a pending connect
    // which might complete after creating/assigning a new one. If that
    // happened, the callback would have the context address of the previous
    // token which was destroyed. So for now, keep the old one alive within
    // this function, and check the behavior of the C library...
    auto tmpTok = connTok_;
    connTok_ = token::create(token::Type::CONNECT, *this);
    add_token(connTok_);

    opts.set_token(connTok_);

    // TODO: Lock!
    connOpts_ = std::move(opts);
    int rc = MQTTAsync_connect(cli_, &connOpts_.opts_);

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(connTok_);
        connTok_.reset();
        throw exception(rc);
    }

    return connTok_;
}

token_ptr async_client::connect(connect_options opts, void* userContext, iaction_listener& cb)
{
    // If the options specified a new MQTT protocol version, we should
    // use it, otherwise default to the version requested when the client
    // was created.
    if (opts.opts_.MQTTVersion == 0 && mqttVersion_ >= 5)
        opts.opts_.MQTTVersion = mqttVersion_;
    else
        mqttVersion_ = opts.opts_.MQTTVersion;

    // The C lib is very picky about version and clean start/session
    if (opts.opts_.MQTTVersion >= 5)
        opts.opts_.cleansession = 0;
    else
        opts.opts_.cleanstart = 0;

    auto tmpTok = connTok_;
    connTok_ = token::create(token::Type::CONNECT, *this, userContext, cb);
    add_token(connTok_);

    opts.set_token(connTok_);

    connOpts_ = std::move(opts);
    int rc = MQTTAsync_connect(cli_, &connOpts_.opts_);

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(connTok_);
        connTok_.reset();
        throw exception(rc);
    }

    return connTok_;
}

// --------------------------------------------------------------------------
// Re-connect

token_ptr async_client::reconnect()
{
    auto tok = connTok_;

    if (!tok)
        throw exception(MQTTASYNC_FAILURE, "Can't reconnect before a successful connect");

    tok->reset();
    add_token(tok);

    int rc = MQTTAsync_setConnected(cli_, this, &async_client::on_connected);

    if (rc == MQTTASYNC_SUCCESS)
        rc = MQTTAsync_reconnect(cli_);

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

// --------------------------------------------------------------------------
// Disconnect

token_ptr async_client::disconnect(disconnect_options opts)
{
    auto tok = token::create(token::Type::DISCONNECT, *this);
    add_token(tok);

    opts.set_token(tok, mqttVersion_);

    int rc = MQTTAsync_disconnect(cli_, &opts.opts_);

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

token_ptr async_client::disconnect(int timeout, void* userContext, iaction_listener& cb)
{
    auto tok = token::create(token::Type::DISCONNECT, *this, userContext, cb);
    add_token(tok);

    disconnect_options opts(timeout);
    opts.set_token(tok, mqttVersion_);

    int rc = MQTTAsync_disconnect(cli_, &opts.opts_);

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

// --------------------------------------------------------------------------
// Queries

delivery_token_ptr async_client::get_pending_delivery_token(int msgID) const
{
    // Messages with QOS=1 or QOS=2 that require a response/acknowledge should
    // have a non-zero 16-bit message ID. The library keeps the token objects
    // for all of these messages that are in flight. When the acknowledge comes
    // back from the broker, the C++ library can look up the token from the
    // msgID and signal it, indicating completion.

    if (msgID > 0) {
        guard g(lock_);
        for (const auto& t : pendingDeliveryTokens_) {
            if (t->get_message_id() == msgID)
                return t;
        }
    }
    return delivery_token_ptr();
}

std::vector<delivery_token_ptr> async_client::get_pending_delivery_tokens() const
{
    std::vector<delivery_token_ptr> toks;
    guard g(lock_);
    for (const auto& t : pendingDeliveryTokens_) {
        if (t->get_message_id() > 0) {
            toks.push_back(t);
        }
    }
    return toks;
}

// --------------------------------------------------------------------------
// Publish

delivery_token_ptr async_client::publish(
    string_ref topic, const void* payload, size_t n, int qos, bool retained
)
{
    auto msg = message::create(std::move(topic), payload, n, qos, retained);
    return publish(std::move(msg));
}

delivery_token_ptr async_client::publish(
    string_ref topic, binary_ref payload, int qos, bool retained
)
{
    auto msg = message::create(std::move(topic), std::move(payload), qos, retained);
    return publish(std::move(msg));
}

delivery_token_ptr async_client::publish(
    string_ref topic, const void* payload, size_t n, int qos, bool retained,
    void* userContext, iaction_listener& cb
)
{
    auto msg = message::create(std::move(topic), payload, n, qos, retained);
    return publish(std::move(msg), userContext, cb);
}

delivery_token_ptr async_client::publish(const_message_ptr msg)
{
    auto tok = delivery_token::create(*this, msg);
    add_token(tok);

    delivery_response_options rspOpts(tok, mqttVersion_);

    int rc =
        MQTTAsync_sendMessage(cli_, msg->get_topic().c_str(), &(msg->msg_), &rspOpts.opts_);

    if (rc == MQTTASYNC_SUCCESS) {
        tok->set_message_id(rspOpts.opts_.token);
    }
    else {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

delivery_token_ptr async_client::publish(
    const_message_ptr msg, void* userContext, iaction_listener& cb
)
{
    delivery_token_ptr tok = delivery_token::create(*this, msg, userContext, cb);
    add_token(tok);

    delivery_response_options rspOpts(tok, mqttVersion_);

    int rc =
        MQTTAsync_sendMessage(cli_, msg->get_topic().c_str(), &(msg->msg_), &rspOpts.opts_);

    if (rc == MQTTASYNC_SUCCESS) {
        tok->set_message_id(rspOpts.opts_.token);
    }
    else {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

// --------------------------------------------------------------------------
// Subscribe

token_ptr async_client::subscribe(
    const string& topicFilter, int qos,
    const subscribe_options& opts /*=subscribe_options()*/,
    const properties& props /*=properties()*/
)
{
    auto tok = token::create(token::Type::SUBSCRIBE, *this, topicFilter);
    tok->set_num_expected(0);  // Indicates non-array response for single val
    add_token(tok);

    auto rspOpts = response_options_builder(mqttVersion_)
                       .token(tok)
                       .subscribe_opts(opts)
                       .properties(props)
                       .finalize();

    int rc = MQTTAsync_subscribe(cli_, topicFilter.c_str(), qos, &rspOpts.opts_);

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

token_ptr async_client::subscribe(
    const string& topicFilter, int qos, void* userContext, iaction_listener& cb,
    const subscribe_options& opts /*=subscribe_options()*/,
    const properties& props /*=properties()*/
)
{
    auto tok = token::create(token::Type::SUBSCRIBE, *this, topicFilter, userContext, cb);
    tok->set_num_expected(0);
    add_token(tok);

    auto rspOpts = response_options_builder(mqttVersion_)
                       .token(tok)
                       .subscribe_opts(opts)
                       .properties(props)
                       .finalize();

    int rc = MQTTAsync_subscribe(cli_, topicFilter.c_str(), qos, &rspOpts.opts_);

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

token_ptr async_client::subscribe(
    const_string_collection_ptr topicFilters, const qos_collection& qos,
    const std::vector<subscribe_options>& opts
    /*=std::vector<subscribe_options>()*/,
    const properties& props /*=properties()*/
)
{
    size_t n = topicFilters->size();

    if (n != qos.size())
        throw std::invalid_argument("Collection sizes don't match");

    auto tok = token::create(token::Type::SUBSCRIBE, *this, topicFilters);
    tok->set_num_expected(n);
    add_token(tok);

    auto rspOpts = response_options_builder(mqttVersion_)
                       .token(tok)
                       .subscribe_opts(opts)
                       .properties(props)
                       .finalize();

    int rc = MQTTAsync_subscribeMany(
        cli_, int(n), topicFilters->c_arr(), const_cast<int*>(qos.data()), &rspOpts.opts_
    );

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

token_ptr async_client::subscribe(
    const_string_collection_ptr topicFilters, const qos_collection& qos, void* userContext,
    iaction_listener& cb,
    const std::vector<subscribe_options>& opts
    /*=std::vector<subscribe_options>()*/,
    const properties& props /*=properties()*/
)
{
    size_t n = topicFilters->size();

    if (n != qos.size())
        throw std::invalid_argument("Collection sizes don't match");

    auto tok = token::create(token::Type::SUBSCRIBE, *this, topicFilters, userContext, cb);
    tok->set_num_expected(n);
    add_token(tok);

    auto rspOpts = response_options_builder(mqttVersion_)
                       .token(tok)
                       .subscribe_opts(opts)
                       .properties(props)
                       .finalize();

    int rc = MQTTAsync_subscribeMany(
        cli_, int(n), topicFilters->c_arr(), const_cast<int*>(qos.data()), &rspOpts.opts_
    );

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

// --------------------------------------------------------------------------
// Unsubscribe

token_ptr async_client::
    unsubscribe(const string& topicFilter, const properties& props /*=properties()*/)
{
    auto tok = token::create(token::Type::UNSUBSCRIBE, *this, topicFilter);
    tok->set_num_expected(0);  // Indicates non-array response for single val
    add_token(tok);

    auto rspOpts =
        response_options_builder(mqttVersion_).token(tok).properties(props).finalize();

    int rc = MQTTAsync_unsubscribe(cli_, topicFilter.c_str(), &rspOpts.opts_);

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

token_ptr async_client::unsubscribe(
    const_string_collection_ptr topicFilters, const properties& props /*=properties()*/
)
{
    size_t n = topicFilters->size();

    auto tok = token::create(token::Type::UNSUBSCRIBE, *this, topicFilters);
    tok->set_num_expected(n);
    add_token(tok);

    auto rspOpts =
        response_options_builder(mqttVersion_).token(tok).properties(props).finalize();

    int rc = MQTTAsync_unsubscribeMany(cli_, int(n), topicFilters->c_arr(), &rspOpts.opts_);

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

token_ptr async_client::unsubscribe(
    const_string_collection_ptr topicFilters, void* userContext, iaction_listener& cb,
    const properties& props /*=properties()*/
)
{
    size_t n = topicFilters->size();

    auto tok = token::create(token::Type::UNSUBSCRIBE, *this, topicFilters, userContext, cb);
    tok->set_num_expected(n);
    add_token(tok);

    auto rspOpts =
        response_options_builder(mqttVersion_).token(tok).properties(props).finalize();

    int rc = MQTTAsync_unsubscribeMany(cli_, int(n), topicFilters->c_arr(), &rspOpts.opts_);

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

token_ptr async_client::unsubscribe(
    const string& topicFilter, void* userContext, iaction_listener& cb,
    const properties& props /*=properties()*/
)
{
    auto tok = token::create(token::Type::UNSUBSCRIBE, *this, topicFilter, userContext, cb);
    add_token(tok);

    auto rspOpts =
        response_options_builder(mqttVersion_).token(tok).properties(props).finalize();

    int rc = MQTTAsync_unsubscribe(cli_, topicFilter.c_str(), &rspOpts.opts_);

    if (rc != MQTTASYNC_SUCCESS) {
        remove_token(tok);
        throw exception(rc);
    }

    return tok;
}

// --------------------------------------------------------------------------

void async_client::start_consuming()
{
    // Make sure callbacks don't happen while we update the que, etc
    disable_callbacks();

    // TODO: Should we replace user callback?
    // userCallback_ = nullptr;

    que_.reset(new thread_queue<const_message_ptr>);

    int rc = MQTTAsync_setCallbacks(
        cli_, this, &async_client::on_connection_lost, &async_client::on_message_arrived,
        nullptr
    );

    if (rc != MQTTASYNC_SUCCESS)
        throw exception(rc);
}

void async_client::stop_consuming()
{
    try {
        disable_callbacks();
        que_.reset();
    }
    catch (...) {
        que_.reset();
        throw;
    }
}

/////////////////////////////////////////////////////////////////////////////
// end namespace mqtt
}  // namespace mqtt