/*!
 *
 * 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    MqttClient.h
 * \author  (original)  Stephen Quong
 * \date    (original)  30-Jul-2026
 *
 */
#pragma once

#include <QByteArray>
#include <QHash>
#include <QObject>
#include <QSslConfiguration>
#include <QString>

class QMqttClient;

/*!
 * \brief   Publishes messages to the cloud over MQTT.
 * \details Wraps QtMqtt's QMqttClient for a QoS 1 publishing session.
 *
 *          The lifecycle is init() -> open() -> close(). init() only validates
 *          the configuration and builds the TLS configuration from it; the
 *          QMqttClient itself is created by open() and destroyed by close(),
 *          or by an unsolicited disconnect. A close()/open() pair is therefore
 *          a full reset, which is what allows the session to be reopened with
 *          rotated credentials.
 * \note    Connecting is asynchronous: open() only starts the attempt, and a
 *          true return does not mean the broker accepted the session.
 * \note    Must live on the thread that calls open(): the client's socket
 *          belongs to the thread that constructs it.
 * \note    The connection is always TLS. init() fails unless keyPath names a
 *          readable private key.
 */
class MqttClient : public QObject
{
    Q_OBJECT

public:
    /*!
     * \brief   Parameters for one MQTT session.
     */
    struct Config
    {
        QString endpoint;           // Broker FQDN or address; no scheme or trailing slash.
        quint16 port = 8883;        // Broker port; the session is always TLS.
        QString certPath;           // Client certificate for mTLS, PEM; optional.
        QString keyPath;            // Unencrypted private key matching certPath, PEM; required.
        QString caPath;             // CA bundle to verify the broker, PEM; optional, falls back
                                    // to the system CA set.
        QString clientId;           // Must equal the IoT Thing name; the device policy scopes iot:Connect to it.
        quint16 keepAliveSecs = 30; // MQTT keep-alive interval; PINGREQ is QMqttClient's job.
        bool cleanSession = true;   // No broker-side queue; durability is the device's job.
    };

    explicit MqttClient(QObject *parent = nullptr);
    ~MqttClient() override;

    bool init(const Config &config);

public Q_SLOTS:
    bool open();
    void close();
    bool publish(const QString &topic, const QByteArray &payload, qint64 messageId = -1);

private:
    void onStateChanged();
    void onMessageSent(qint32 id);
    void failPending();

    QMqttClient *_client = nullptr;
    Config _config;
    QSslConfiguration _sslConfig;
    QHash<qint32, qint64> _pending;
};