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

#pragma once

#include <limits>

namespace udpscope {

/// Which way through a level counts. Shared by every condition type: for `Window` it is
/// the direction through the *band* (into it, out of it, or either), and for `Dropout` it
/// selects which crossings count as the signal still being alive.
///
/// It lives here rather than in `trigger.hpp` because the buffer search needs the
/// evaluator without the engine's arming state.
enum class TriggerEdge { Rising, Falling, Both };

/// What shape in the signal counts as an event.
enum class TriggerType { Edge, PulseWidth, Window, Dropout };

/// How a measured pulse width is compared with the condition's bounds. `Less` is the
/// glitch trigger: "a pulse shorter than it should be".
enum class WidthCmp { Less, Greater, Within, Outside };

/// Everything that decides whether a sample is an event. No arming, no capture window:
/// those belong to `TriggerConfig`.
struct EventCondition {
  TriggerType type = TriggerType::Edge;
  double level = 0.0;
  double level2 = 0.0;               ///< Window: the band's other edge. Ignored otherwise.
  TriggerEdge edge = TriggerEdge::Rising;
  WidthCmp cmp = WidthCmp::Greater;  ///< PulseWidth only.
  double width_s = 1.0e-3;           ///< PulseWidth only.
  double width2_s = 2.0e-3;          ///< PulseWidth, Within/Outside only.
  double timeout_s = 1.0e-3;         ///< Dropout only.

  bool operator==(const EventCondition& o) const noexcept {
    return type == o.type && level == o.level && level2 == o.level2 && edge == o.edge &&
           cmp == o.cmp && width_s == o.width_s && width2_s == o.width2_s &&
           timeout_s == o.timeout_s;
  }
  bool operator!=(const EventCondition& o) const noexcept { return !(*this == o); }
};

/// The event condition's state machine: one sample in, an event time or nothing out.
///
/// It holds no arming state and no capture state -- that is `TriggerEngine`'s job -- which
/// is what lets the buffer search run the *same* evaluator over retained samples and get
/// the answers the live trigger would have given.
///
/// Every condition but `Edge` is sequential: a pulse's width is only known at its closing
/// edge, and a dropout is a measured absence. Callers must therefore feed it **every**
/// sample in stream order, including samples they intend to ignore; a gap is a pulse it can
/// never close.
class EventDetector {
 public:
  /// What `feed()` returns when the sample is not an event.
  static constexpr double kNoEvent = std::numeric_limits<double>::quiet_NaN();

  /// Re-applying the same condition is a no-op, deliberately: the producer calls this on
  /// every packet, and resetting there would restart the machine before any pulse could
  /// close. A genuinely different condition resets, because its state means nothing.
  void configure(const EventCondition& c) noexcept;
  void reset() noexcept;

  /// One sample, in stream order. Returns the event's own stream time, or `kNoEvent`.
  ///
  /// There is no finite-value check: a NaN sample is benign here (every comparison against
  /// it is false, so it cannot fire), and rejecting one would leave `prev_` at the last good
  /// value and let the sample *after* the NaN fire a crossing that today cannot happen.
  double feed(double value, double t) noexcept;

  double last_value() const noexcept { return prev_; }
  bool have_last() const noexcept { return have_prev_; }

 private:
  bool crossed_up(double v) const noexcept {
    return prev_ < cond_.level && v >= cond_.level;
  }
  bool crossed_down(double v) const noexcept {
    return prev_ > cond_.level && v <= cond_.level;
  }
  double feed_edge(double value, double t) noexcept;
  double feed_pulse(double value, double t) noexcept;
  double feed_window(double value, double t) noexcept;
  double feed_dropout(double value, double t) noexcept;
  /// Whether a measured width satisfies `cond_.cmp`. `Within`/`Outside` take their two
  /// bounds in either order, so a panel cannot make an empty band by typing the larger
  /// figure into the first spin.
  bool qualifies(double width_s) const noexcept;

  EventCondition cond_{};
  bool have_prev_ = false;
  double prev_ = 0.0;
  bool in_pulse_ = false;      ///< PulseWidth: an opening edge has been seen.
  bool pulse_up_ = false;      ///< PulseWidth: its polarity, so we know which edge closes it.
  double pulse_start_s_ = 0.0;
  bool inside_ = false;        ///< Window: which side of the band the previous sample was.
  double last_cross_s_ = 0.0;  ///< Dropout: when the signal was last seen crossing.
  bool dropped_ = false;       ///< Dropout: the timeout has already been reported.
};

}  // namespace udpscope