/*!
 *
 * Copyright (c) 2024-2026 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    CloudConnectFrame.h
 * \author  (original)  Stephen Quong
 * \date    (original)  24-May-2026
 *
 */
#pragma once

#include <QByteArray>

/*!
 * \brief   CloudConnect frame for communicating between client and CloudConnect.
 *
 *          Frame layout — header only (payload_length == 0):
 *
 *          Byte:  0    1    2    3    4    5    6-9         10   11
 *                 ┌─────────┬────────┬────────┬───────────┬────────┐
 *                 │ AA  55  │ topic  │ seq_num│ pay_length│hdr_crc │
 *                 │  sync   │ uint16 │ uint16 │  uint32   │ uint16 │
 *                 └─────────┴────────┴────────┴───────────┴────────┘
 *
 *          Frame layout — with payload (payload_length > 0):
 *
 *          ┌── 12-byte header ──┬── N bytes payload ──┬── pay_crc (4 B) ──┐
 *          │     header         │      uint8[]        │  CRC-32/ISO-HDLC  │
 *          └────────────────────┴─────────────────────┴───────────────────┘
 *
 *          Header CRC: CRC-16/CCITT (poly 0x1021, init 0xFFFF, no reflection).
 *          Payload CRC: CRC-32/ISO-HDLC (IEEE 802.3, reflected poly 0xEDB88320).
 */
class CloudConnectFrame
{
public:
    /*!
     * \brief   MQTT topic identifier carried in every frame header
     */
    enum class Topic : quint16 {
        HighPriority        = 0x0001,
        NormalPriority      = 0x0002,
        DeviceLogFile       = 0x0003,
        TreatmentLogFile    = 0x0004,
        CloudSyncLogFile    = 0x0005,
    };

    /*!
     * \brief   Result returned by read() after processing each byte chunk
     */
    enum class ReadState {
        Incomplete,
        Complete,
        HeaderError,
        PayloadError,
    };

    static QByteArray build(Topic topic, quint16 sequence, const QByteArray &payload = {});
    ReadState read(QByteArray &bytes);

    Topic topic() const;
    quint16 sequence() const;
    QByteArray payload() const;

    void reset();

private:
    static constexpr int SYNC_SIZE = 2;
    static constexpr quint8 SYNC[SYNC_SIZE] = {0xAA, 0x55};
    static constexpr int HEADER_SIZE = 12;
    static constexpr int TOPIC_SIZE = 2;
    static constexpr int SEQUENCE_SIZE = 2;
    static constexpr int HEADER_CRC_SIZE = 2;
    static constexpr int PAYLOAD_CRC_SIZE = 4;
    static constexpr quint32 MAX_PAYLOAD_LEN = 64 * 1024;

    static quint16 crc16ccitt(const quint8 *data, int len);
    static quint32 crc32isohdlc(const quint8 *data, int len);

    QByteArray _headerBuf;
    Topic _rxTopic = Topic::NormalPriority;
    quint16 _rxSequence = 0;
    quint32 _rxPayloadLen = 0;
    QByteArray _rxPayload;
};