package ride

import "time"

const MovingTimeAlgorithmVersion = "v1"

// movingTimeMinSpeedMps is the minimum implied speed between two consecutive
// track points for the interval to count as moving (1 km/h).
const movingTimeMinSpeedMps = 1.0 / 3.6

// Baseline backtest (356 rides, `-backtest`): mean err 3.9% (stderr 0.4),
// p50 1.6, p75 4.6, p90 8.4, p95 12.1, p99 44.9.
// Worst offenders overcount stationary GPS jitter (lunch stops) and
// undercount trainer rides with little GPS movement. Tuned in future commits.
func MovingTime(r Ride) time.Duration {
	var moving time.Duration
	for i := 1; i < r.Len(); i++ {
		dt := r.Timestamp(i).Sub(r.Timestamp(i - 1))
		if dt <= 0 {
			continue
		}
		dd := r.DistanceM(i) - r.DistanceM(i - 1)
		if dd/dt.Seconds() > movingTimeMinSpeedMps {
			moving += dt
		}
	}
	return moving
}