/*!
 *
 * Copyright (c) 2026 Diality Inc. - All Rights Reserved.
 * \copyright
 * THIS CODE MAY NOT BE COPIED OR REPRODUCED IN ANY FORM, IN PART OR IN
 * WHOLE, WITHOUT THE EXPLICIT PERMISSION OF THE COPYRIGHT OWNER.
 *
 * \file    MqttTransport.h
 * \author  (original)  Stephen Quong
 * \date    (original)  30-Jul-2026
 *
 */
#pragma once

#include <QByteArray>
#include <QString>

#include <functional>

/*!
 * \brief   Transport between MqttPublisher and a concrete MQTT client.
 */
class MqttTransport
{
public:
    /*!
     * \brief   Parameters for one MQTT-over-mTLS session.
     */
    struct Config
    {
        QString endpoint;             ///< ATS endpoint FQDN; no scheme, port or trailing slash.
        quint16 port = 8883;          ///< Port 443 additionally requires ALPN "x-amzn-mqtt-ca".
        QString certPath;             ///< Client certificate, PEM.
        QString keyPath;              ///< Unencrypted private key matching certPath, PEM.
        QString caPath;               ///< Root CA bundle used to verify the broker.
        QString clientId;             ///< Must equal the IoT Thing name; the device policy scopes iot:Connect to it.
        quint16 keepAliveSecs = 30;   ///< MQTT keep-alive interval.
        bool cleanSession = true;     ///< No broker-side queue; durability is the device's job.
    };

    /// Reports a connection state transition, on the client library's thread.
    using StateCallback = std::function<void(bool connected)>;

    /// Reports one publish outcome; messageId echoes the value publish() was given.
    using AckCallback = std::function<void(qint64 messageId, bool success)>;

    virtual ~MqttTransport() = default;

    /// Begins connecting. False means the attempt could not be started; success arrives via StateCallback.
    virtual bool open(const Config &config) = 0;

    /// Closes the connection. The transition is reported through StateCallback.
    virtual void close() = 0;

    /// True while the session is established.
    virtual bool isConnected() const = 0;

    /// Sends one QoS 1 publish. True means handed to the client, not delivered; delivery is the AckCallback.
    virtual bool publish(const QString &topic, const QByteArray &payload, qint64 messageId) = 0;

    /// Installs the callbacks. Must be called before open().
    virtual void setCallbacks(StateCallback onState, AckCallback onAck) = 0;

    /// Removes the callbacks and waits for any still running to finish.
    virtual void clearCallbacks() = 0;
};