package engine

// Profile is an ordered chain of propagators executed sequentially. Each
// propagator picks up where the previous one finished.
type Profile struct {
	// Stages are run in order. For Direction=Reverse they are still
	// iterated from index 0 onwards but each propagator integrates with
	// negative dt.
	Stages []*Propagator

	// Direction controls the sign of dt across the profile.
	Direction Direction

	// Globals are constraints evaluated alongside each stage's local
	// Constraints. Useful for profile-wide bounds like "stop after N hours".
	Globals []Constraint
}

// Run executes the profile from the given launch point. Returns one
// Result per executed stage, including any Fallback chains that were
// activated. The supplied EventSink is shared across stages and aggregates
// non-fatal observations.
//
// events may be nil; pass NewEventSink() to capture observations.
func (p *Profile) Run(t0 float64, launch State, events *EventSink) []Result {
	if p.Direction == 0 {
		p.Direction = Forward
	}

	results := make([]Result, 0, len(p.Stages))
	t, s := t0, launch

	for i := 0; i < len(p.Stages); i++ {
		stage := p.Stages[i]
		ctx := StageContext{
			ProfileStart:    t0,
			PropagatorStart: t,
			Launch:          launch,
			PropagatorState: s,
			Direction:       p.Direction,
		}
		res := stage.run(ctx, t, s, p.Globals, events)
		results = append(results, res)

		last := res.Points[len(res.Points)-1]
		t = last.Time
		s = State{Lat: last.Lat, Lng: last.Lng, Altitude: last.Altitude}

		// Follow Fallback chains until none remains.
		for res.Outcome == OutcomeFallback && stage.Fallback != nil {
			stage = stage.Fallback
			ctx = StageContext{
				ProfileStart:    t0,
				PropagatorStart: t,
				Launch:          launch,
				PropagatorState: s,
				Direction:       p.Direction,
			}
			res = stage.run(ctx, t, s, p.Globals, events)
			results = append(results, res)
			last = res.Points[len(res.Points)-1]
			t = last.Time
			s = State{Lat: last.Lat, Lng: last.Lng, Altitude: last.Altitude}
		}
	}

	return results
}