/// Running totals for the ride in progress.
///
/// Ported from `com.rippr.Accumulator`.
///
/// Distance and elevation both need consecutive-row differences, so they are folded in
/// here as points are written and persisted onto the `Trip` row once per flush. That
/// lets the recording screen show live numbers without rescanning the point table.
///
/// The values this produces are an *estimate*. They are overwritten by
/// [computeSummary] when the trip completes, which is also why this reuses
/// [ElevationAccumulator] rather than reimplementing hysteresis: a naive version
/// measured 1498 m of phantom climbing on a parked bike.
///
/// Not thread-safe — the writer loop owns it, under the recorder's write lock.
library;

import 'dart:math' as math;

import '../domain/models.dart';
import '../geo/geo.dart';
import '../stats/ride_statistics.dart';
import '../telemetry/telemetry.dart';

class Accumulator {
  /// The last point of the *previous* batch.
  ///
  /// Without this, distance restarts at every flush boundary and silently under-reports
  /// by roughly one inter-point hop per batch — a few percent, which nobody notices
  /// until they compare against an odometer.
  TrackPoint? _lastPoint;

  ElevationAccumulator _elevation = ElevationAccumulator();
  double _restoredElevationM = 0.0;

  double _distanceM = 0.0;
  int _movingMillis = 0;
  double _maxSpeedKmh = 0.0;
  int _pointCount = 0;

  double get distanceM => _distanceM;
  int get movingMillis => _movingMillis;
  double get maxSpeedKmh => _maxSpeedKmh;
  int get pointCount => _pointCount;

  void fold(List<TrackPoint> points) {
    for (final point in points) {
      _pointCount++;
      _maxSpeedKmh = math.max(_maxSpeedKmh, point.speedKmh);
      _elevation.add(point.altitudeM);

      final prev = _lastPoint;
      // Distance and moving time only accrue *within* a segment. Points either side of
      // a pause can be kilometres apart and that gap was never ridden.
      if (prev != null && prev.segmentId == point.segmentId) {
        _distanceM += haversineMeters(
          prev.latitude,
          prev.longitude,
          point.latitude,
          point.longitude,
        );
        final dt = point.timestamp - prev.timestamp;
        if (dt >= 1 &&
            dt <= maxSampleGapMillis &&
            point.speedKmh >= speedNoiseFloorKmh) {
          _movingMillis += dt;
        }
      }
      _lastPoint = point;
    }
  }

  /// Elevation gain including the run still in progress.
  ///
  /// Reads a snapshot rather than mutating, so it is safe to call on every flush while
  /// recording continues.
  double elevationGain() =>
      _restoredElevationM + _elevation.gainIncludingPending();

  /// Seeds from a trip already in progress after the process is restarted.
  void restore({
    required double distanceM,
    required int movingMillis,
    required double maxSpeedKmh,
    required double elevationGainM,
    required int pointCount,
    TrackPoint? lastPoint,
  }) {
    _distanceM = distanceM;
    _movingMillis = movingMillis;
    _maxSpeedKmh = maxSpeedKmh;
    _pointCount = pointCount;
    _lastPoint = lastPoint;
    // Elevation cannot be resumed mid-run from a scalar total, so the accumulator
    // restarts and only gain from here on is added to the persisted figure. The
    // authoritative recomputation at trip completion corrects any drift.
    _elevation = ElevationAccumulator();
    _restoredElevationM = elevationGainM;
  }

  void reset() {
    _lastPoint = null;
    _elevation = ElevationAccumulator();
    _distanceM = 0.0;
    _movingMillis = 0;
    _maxSpeedKmh = 0.0;
    _pointCount = 0;
    _restoredElevationM = 0.0;
  }

  /// Clears the cross-segment anchor so a resumed ride does not span the pause.
  void onSegmentChanged() {
    _lastPoint = null;
  }
}