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

#include <QByteArray>

/*!
 * \brief   LeahiRt to Connectivity Agent message framing
 * \details Transport-agnostic binary framing. build() makes a wire-ready frame;
 *          feed() parses inbound bytes (see FeedResult). On Complete, read
 *          msgId()/sequence()/payload(), then reset().
 *
 *          Frame layout — header only (payload_length == 0):
 *
 *          Byte:  0    1    2    3    4    5    6-9         10   11
 *                 ┌─────────┬────────┬────────┬───────────┬────────┐
 *                 │ AA  55  │ msg_id │ seq_num│ pay_length│hdr_crc │
 *                 │  sync   │uint16BE│uint16BE│ uint32 BE │uint16BE│
 *                 └─────────┴────────┴────────┴───────────┴────────┘
 *
 *          Frame layout — with payload (payload_length > 0):
 *
 *          ┌── 12-byte header ──┬── N bytes payload ──┬── pay_crc (4 B) ──┐
 *          │     (see above)    │      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 AgentMessage
{
public:
    /*!
     * \brief   MQTT topic identifier carried in every frame header
     * \details The Connectivity Agent uses this value to determine the MQTT topic.
     */
    enum class MsgId : quint16 {
        ClinicalData = 0x0001,
        Diagnostic = 0x0002,
        Ack = 0x0003,
        Alarms = 0x0004,
        Audit = 0x0005,
        DeviceLogFile = 0x0006,
        TreatmentLogFile = 0x0007,
        CloudSyncLogFile = 0x0008,
    };

    /*!
     * \brief   Result returned by feed() after processing each byte chunk
     */
    enum class FeedResult {
        Incomplete,   ///< More bytes needed — continue feeding.
        Complete,     ///< Full valid frame assembled — read accessors, then call reset().
        HeaderError,  ///< Header CRC mismatch — frame dropped, state reset automatically.
        PayloadError, ///< Payload CRC mismatch or oversized payload — frame dropped, state reset automatically.
    };

    static QByteArray build(MsgId msgId, quint16 sequence, const QByteArray &payload = {});
    FeedResult feed(QByteArray &bytes);

    /*!
     * \brief   AgentMessage::msgId
     * \details Message identifier of the last complete frame.
     *          Valid only after feed() returns FeedResult::Complete.
     * \return  MsgId of the last complete frame
     */
    MsgId msgId() const { return _rxMsgId; }

    /*!
     * \brief   AgentMessage::sequence
     * \details Sequence number of the last complete frame.
     *          Valid only after feed() returns FeedResult::Complete.
     * \return  sequence number of the last complete frame
     */
    quint16 sequence() const { return _rxSequence; }

    /*!
     * \brief   AgentMessage::payload
     * \details Payload bytes of the last complete frame. Empty for zero-length frames.
     *          Valid only after feed() returns FeedResult::Complete.
     * \return  payload of the last complete frame
     */
    QByteArray payload() const { return _rxPayload; }

    void reset();

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

    static constexpr int SYNC_SIZE = 2;
    static constexpr quint8 SYNC[SYNC_SIZE] = {0xAA, 0x55};
    static constexpr int HEADER_SIZE = 12;
    static constexpr int MSGID_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;

    QByteArray _headerBuf;
    MsgId _rxMsgId = MsgId::ClinicalData;
    quint16 _rxSequence = 0;
    quint32 _rxPayloadLen = 0;
    QByteArray _rxPayload;
};