step one

internal/engine/profile.go

@@ -0,0 +1,55 @@
+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 whole profile.
+	Direction Direction
+
+	// Globals are constraints evaluated alongside each stage's local Constraints.
+	// Useful for profile-wide bounds like "stop after N hours total".
+	Globals []Constraint
+}
+
+// Run executes the profile from the given launch point. Returns one Result
+// per executed stage, including any Fallback chains that were activated.
+func (p *Profile) Run(t0 float64, launch State) []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]
+		res := stage.run(t, s, p.Direction, p.Globals)
+		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. Each fallback consumes
+		// from the same point the previous stage stopped at.
+		for res.Outcome == OutcomeFallback && stage.Fallback != nil {
+			stage = stage.Fallback
+			res = stage.run(t, s, p.Direction, p.Globals)
+			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}
+		}
+
+		// If a propagator's stop fired (not a fallback), end the profile.
+		if res.Outcome == OutcomeStopped {
+			continue
+		}
+	}
+
+	return results
+}