/**
 * @file FrameDecoder.h
 * @brief Per-element timestamp reconstruction for UDPS frames.
 *
 * The C client's udps_frame_element_time() is explicitly an arrival-anchored
 * estimate. It is not sufficient: the kernel frequently delivers several queued
 * datagrams in one burst, so two packets are processed microseconds apart even
 * though each represents ~10 ms of signal, and arrival-time interpolation then
 * crams a packet's samples into that tiny gap — the trace renders as a sawtooth.
 * Source/Applications/StreamHub/UDPSourceSession.cpp documents this failure and
 * solves it; these are the same rules, computed from udps_frame_t's own fields.
 *
 * One rule deliberately differs. StreamHub anchors every accumulated-scalar
 * burst on the packet's own hrt, converted with the LOCAL MARTe
 * HighResolutionTimer frequency — correct only because StreamHub runs on the
 * producer's host. A bench scope attaches over the network and has no access to
 * that frequency; it can only regress hrt against arrival time, which is
 * exactly what the bursty delivery above corrupts. So when a SamplingRate is
 * declared this decoder chains bursts instead, using the packet counter to
 * account for loss and arrival time only as a backstop. The consequence is that
 * a declared rate measured against the producer's crystal rather than ours makes
 * the reconstructed timeline drift, and drift that only arrival time can
 * observe must be corrected against arrival time — see rule 3.
 */
#pragma once

#include "TimeBase.h"
#include "Types.h"

#include <vector>

namespace udpscope {

class FrameDecoder {
public:
    /** Installs the signal table. Clears all per-signal timing history. */
    void setSignals(const std::vector<SignalMeta>& signals);

    const std::vector<SignalMeta>& signals() const { return signals_; }

    /** Call once per frame, before any timestamps() call for that frame. */
    void beginFrame(const FrameView& f);

    /**
     * @brief Timestamps for every value of signal @p idx in this frame.
     * @return false when the signal produced nothing usable — an empty slot, or
     *         the first PACKET burst after connect, which has no previous
     *         arrival to span from and would otherwise poison the ring with
     *         wrongly spaced timestamps.
     */
    bool timestamps(const FrameView& f, uint32_t idx, std::vector<double>& tsOut);

    /** Forgets all timing history; call on reconnect. */
    void reset();

private:
    bool packetBurst(uint32_t idx, uint32_t nElems, double wallNow,
                     std::vector<double>& tsOut);

    struct SigState {
        ClockOffset offset;
        double      lastPacketWall  = 0.0;
        bool        lastPacketValid = false;
        /** Raw ticks, not seconds — see the comment in the samplingRate == 0
         *  branch for why a tick difference is the only safe way to measure a
         *  producer-side interval while the rate is still being re-estimated. */
        uint64_t    lastAccHrt      = 0u;
        /** Producer seconds since this signal's first usable packet, built by
         *  SUMMING short tick deltas. Never recomputed from an absolute tick
         *  count; see the samplingRate == 0 branch. */
        double      accProdSec      = 0.0;
        bool        lastAccValid    = false;
        uint32_t    prevAccCount    = 0;
        /** For accumulated scalars with a declared sampling rate: end timestamp
         *  of the most recently emitted burst, and the packet counter it came
         *  from. The next burst is chained onto that end, with the counter gap
         *  reinstating the exact duration of any lost datagrams. */
        double      lastEmittedEnd   = 0.0;
        uint32_t    lastCounter      = 0u;
        bool        lastEmittedValid = false;
    };

    std::vector<SignalMeta> signals_;
    std::vector<SigState>   state_;
    HrtRateFit              hrtFit_;
};

} /* namespace udpscope */