udpscope/src/condition.cpp

// SPDX-License-Identifier: MIT
// SPDX-FileCopyrightText: 2026 Martino Ferrari

#include "condition.hpp"

#include <cmath>

namespace udpscope {

void EventDetector::configure(const EventCondition& c, double dt) noexcept {
  if (c == cond_ && dt == dt_) return;
  cond_ = c;
  dt_ = dt;
  // a = 1 - exp(-2*pi*fc*dt), clamped just under Nyquist so a never exceeds 1.
  // fc == 0 leaves a == 1, which is a pass-through.
  pole_a_ = 1.0;
  if (cond_.hf_fc > 0.0 && dt > 0.0) {
    const double nyquist = 0.5 / dt;
    const double fc = cond_.hf_fc < nyquist * 0.99 ? cond_.hf_fc : nyquist * 0.99;
    pole_a_ = 1.0 - std::exp(-2.0 * 3.14159265358979323846 * fc * dt);
  }
  reset();
}

void EventDetector::reset() noexcept {
  have_prev_ = false;
  prev_ = 0.0;
  in_pulse_ = false;
  pulse_up_ = false;
  pulse_start_s_ = 0.0;
  inside_ = false;
  last_cross_s_ = 0.0;
  dropped_ = false;
  pole_y_ = 0.0;
  pole_have_ = false;
  side_ = 0;
}

double EventDetector::filter(double v) noexcept {
  // A NaN must stay a NaN and must not poison the state: a dropout is a real
  // reading here, not an error.
  if (!std::isfinite(v)) return v;
  if (!pole_have_) {
    pole_y_ = v;
    pole_have_ = true;
    return pole_y_;
  }
  pole_y_ += pole_a_ * (v - pole_y_);
  return pole_y_;
}

void EventDetector::decide(double v, bool& up, bool& down) noexcept {
  up = false;
  down = false;
  if (cond_.noise_band <= 0.0) {
    up = crossed_up(v);
    down = crossed_down(v);
    return;
  }
  // A Schmitt trigger: a sample inside the band decides nothing, and a crossing
  // is a change between two *decided* sides. Seeding from the undecided side
  // would fire on a signal that starts inside the band and leaves it without
  // ever reaching `level`.
  const int was = side_;
  if (v >= cond_.level + cond_.noise_band) side_ = 1;
  else if (v <= cond_.level - cond_.noise_band) side_ = -1;
  up = was == -1 && side_ == 1;
  down = was == 1 && side_ == -1;
}

double EventDetector::feed(double value, double t) noexcept {
  value = filter(value);
  if (!have_prev_) {
    prev_ = value;
    have_prev_ = true;
    // The window condition needs a side to change *from*, and the dropout a last-seen time
    // to count from; neither can be derived from a crossing that has not happened. Seeding
    // them here is what lets both handlers run without a "have we started" guard.
    const double lo = cond_.level < cond_.level2 ? cond_.level : cond_.level2;
    const double hi = cond_.level < cond_.level2 ? cond_.level2 : cond_.level;
    inside_ = value >= lo && value <= hi;
    last_cross_s_ = t;
    dropped_ = false;
    return kNoEvent;
  }
  double event = kNoEvent;
  switch (cond_.type) {
    case TriggerType::Edge:
      event = feed_edge(value, t);
      break;
    case TriggerType::PulseWidth:
      event = feed_pulse(value, t);
      break;
    case TriggerType::Window:
      event = feed_window(value, t);
      break;
    case TriggerType::Dropout:
      event = feed_dropout(value, t);
      break;
  }
  // After the handler: every crossing test above reads `prev_` as the previous sample.
  prev_ = value;
  return event;
}

double EventDetector::feed_edge(double value, double t) noexcept {
  bool up = false;
  bool down = false;
  decide(value, up, down);
  const bool fired = (cond_.edge == TriggerEdge::Rising && up) ||
                     (cond_.edge == TriggerEdge::Falling && down) ||
                     (cond_.edge == TriggerEdge::Both && (up || down));
  return fired ? t : kNoEvent;
}

bool EventDetector::qualifies(double width_s) const noexcept {
  const double a = cond_.width_s < cond_.width2_s ? cond_.width_s : cond_.width2_s;
  const double b = cond_.width_s < cond_.width2_s ? cond_.width2_s : cond_.width_s;
  switch (cond_.cmp) {
    case WidthCmp::Less:
      return width_s < cond_.width_s;
    case WidthCmp::Greater:
      return width_s > cond_.width_s;
    case WidthCmp::Within:
      return width_s >= a && width_s <= b;
    case WidthCmp::Outside:
      return width_s < a || width_s > b;
  }
  return false;
}

double EventDetector::feed_pulse(double value, double t) noexcept {
  const bool up = crossed_up(value);
  const bool down = crossed_down(value);
  if (!in_pulse_) {
    // Which crossing opens a pulse is what `edge` selects: Rising measures the time spent
    // above the level, Falling the time below, Both every excursion either way.
    const bool opens = (cond_.edge == TriggerEdge::Rising && up) ||
                       (cond_.edge == TriggerEdge::Falling && down) ||
                       (cond_.edge == TriggerEdge::Both && (up || down));
    if (opens) {
      in_pulse_ = true;
      pulse_up_ = up;
      pulse_start_s_ = t;
    }
    return kNoEvent;
  }
  const bool closes = pulse_up_ ? down : up;
  if (!closes) return kNoEvent;
  const double width = t - pulse_start_s_;
  if (cond_.edge == TriggerEdge::Both) {
    // The closing edge of one excursion is the opening edge of the next, so a square wave
    // measures *every* half-period. Dropping the state here instead would measure every
    // other one, and the hits would come out half as dense as the waveform.
    pulse_up_ = !pulse_up_;
    pulse_start_s_ = t;
  } else {
    in_pulse_ = false;
  }
  return qualifies(width) ? t : kNoEvent;
}

double EventDetector::feed_window(double value, double t) noexcept {
  const double lo = cond_.level < cond_.level2 ? cond_.level : cond_.level2;
  const double hi = cond_.level < cond_.level2 ? cond_.level2 : cond_.level;
  // The band is applied on the edge the signal must *leave*, and clamped to just
  // under half the window so `lo + band` can never pass `hi - band`.
  double band = cond_.noise_band > 0.0 ? cond_.noise_band : 0.0;
  const double room = 0.49 * (hi - lo);
  if (band > room) band = room;
  const bool inside = inside_ ? (value >= lo - band && value <= hi + band)
                              : (value >= lo + band && value <= hi - band);
  if (inside == inside_) return kNoEvent;
  inside_ = inside;
  // The event is the *change of side*, so `Rising` reads as "into the band" and `Falling`
  // as "out of it". A band of zero width is not a band: `inside` reduces to an exact
  // float-equality test against the level, so the condition fires on none of an ordinary
  // signal's samples and on every transition of one that sits exactly at the level -- a
  // +/-1 square against a band of [1, 1] fired 19 times in a standalone check. Neither
  // answer is a band, so the panel refuses one.
  const bool fired = (cond_.edge == TriggerEdge::Rising && inside) ||
                     (cond_.edge == TriggerEdge::Falling && !inside) ||
                     cond_.edge == TriggerEdge::Both;
  return fired ? t : kNoEvent;
}

double EventDetector::feed_dropout(double value, double t) noexcept {
  const bool up = crossed_up(value);
  const bool down = crossed_down(value);
  const bool crossed = (cond_.edge == TriggerEdge::Rising && up) ||
                       (cond_.edge == TriggerEdge::Falling && down) ||
                       (cond_.edge == TriggerEdge::Both && (up || down));
  if (crossed) {
    last_cross_s_ = t;
    dropped_ = false;
    return kNoEvent;
  }
  // One event per silence, not one per sample of it: without the latch a dead signal would
  // report an event on every sample after the timeout and fill the search's hit list with
  // one answer repeated.
  if (dropped_) return kNoEvent;
  if (t - last_cross_s_ <= cond_.timeout_s) return kNoEvent;
  dropped_ = true;
  return t;
}

}  // namespace udpscope