// DragonX Wallet - ImGui Edition
// Copyright 2024-2026 The Hush Developers
// Released under the GPLv3
//
// A tiny, pure block-sync rate estimator for the status-bar / peers-card ETA. Pure (no ImGui, no App):
// App owns one instance, feeds it the current height + a monotonic clock once per frame while syncing,
// and resets it on connect / disconnect / rescan / restart so a height drop never produces a stale or
// absurd ("412h") ETA.
#pragma once

#include <cstddef>
#include <cstdio>

namespace dragonx {
namespace util {

class SyncRateEstimator {
public:
    void reset() { prevBlocks_ = -1; prevTime_ = 0.0; rate_ = 0.0; }

    // Call once per frame while syncing. `now` is monotonic seconds (e.g. ImGui::GetTime()).
    void update(int blocks, double now) {
        // First sample, a rescan/restart height drop, or a clock reset → re-baseline, don't compute.
        if (prevBlocks_ < 0 || blocks < prevBlocks_ || now < prevTime_) {
            prevBlocks_ = blocks; prevTime_ = now; rate_ = 0.0; return;
        }
        const double dt = now - prevTime_;
        if (blocks > prevBlocks_) {
            if (dt > 0.5) {
                const double raw = (blocks - prevBlocks_) / dt;
                rate_ = rate_ > 0.0 ? rate_ * 0.7 + raw * 0.3 : raw;   // smooth (same alpha as the old code)
                prevBlocks_ = blocks; prevTime_ = now;
            }
        } else if (dt > 10.0) {            // stalled: decay and re-baseline the clock
            rate_ *= 0.5; prevTime_ = now;
            if (rate_ < 0.1) rate_ = 0.0;
        }
    }

    double rate() const { return rate_; }   // blocks/sec, 0 when unknown

    // <= 0 when unknown. Capped at ~1 year so a tiny rate can't overflow.
    long long etaSeconds(int blocksLeft) const {
        if (rate_ <= 0.1 || blocksLeft <= 0) return -1;
        const double s = blocksLeft / rate_;
        return s > 3.15e7 ? 31500000LL : static_cast<long long>(s);
    }

private:
    int    prevBlocks_ = -1;   // -1 = unset (distinct from a legitimate height 0)
    double prevTime_   = 0.0;
    double rate_       = 0.0;
};

// Human ETA with days, e.g. "3d 4h", "5h 12m", "7m 9s", "42s". English unit letters (as the old code).
inline void formatEta(long long s, char* out, std::size_t n) {
    if (s >= 86400)      std::snprintf(out, n, "%lldd %lldh", s / 86400, (s % 86400) / 3600);
    else if (s >= 3600)  std::snprintf(out, n, "%lldh %lldm", s / 3600, (s % 3600) / 60);
    else if (s >= 60)    std::snprintf(out, n, "%lldm %llds", s / 60, s % 60);
    else                 std::snprintf(out, n, "%llds", s);
}

} // namespace util
} // namespace dragonx