we did it bois and it is FRAGILE

cmd/clitest/main.go

@@ -88,6 +88,11 @@ func main() {
 					if err != nil {
 						panic(err)
 					}
+					for _, name := range register.Names() {
+						for _, d := range register.Dates() {
+							log.Printf("%s | %s | %+v", name, d, register[d][name])
+						}
+					}
 				}
 				for _, nameRate := range r.URL.Query()["predictCompoundingInterest"] {
 					name := strings.Split(nameRate, "=")[0]

ledger/predict.go

@@ -22,13 +22,20 @@ func RegisterWithContributionPrediction(reg Register, window time.Duration) (Reg
 }
 
 func registerWithContributionPredictionForName(reg Register, window time.Duration, name string) error {
-	currencies := make(map[Currency]int)
+	latest := make(Balance)
-	for d := range reg {
+	for _, d := range reg.Dates() {
-		for c := range reg[d][name] {
+		if _, ok := reg[d][name]; ok {
-			currencies[c] = 1
+			latest = reg[d][name]
 		}
 	}
-	for c := range currencies {
+	for _, predictionTime := range predictionTimes(window) {
+		k := predictionTime.Format("2006-01")
+		if _, ok := reg[k]; !ok {
+			reg[k] = make(Balances)
+		}
+		reg[k][name] = maps.Clone(latest)
+	}
+	for c := range latest {
 		err := registerWithContributionPredictionForNameForCurrency(reg, window, name, c)
 		if err != nil {
 			return err
@@ -48,17 +55,17 @@ func registerWithContributionPredictionForNameForCurrency(reg Register, window t
 		if err != nil {
 			return err
 		}
-		if time.Since(t) > time.Hour*24*180 {
+		if time.Since(t) > time.Hour*24*180 || time.Now().Before(t) { // only include -6months..now
 			continue
 		}
-		if v, ok := reg[d][name][currency]; ok {
+		if v, ok := reg[d][name][currency]; ok && (len(contributions) == 0 || contributions[len(contributions)-1].v != v) {
 			contributions = append(contributions, contribution{t: t, v: v})
 		}
 	}
 	sort.Slice(contributions, func(i, j int) bool {
 		return contributions[i].t.Before(contributions[j].t)
 	})
-	if len(contributions) < 3 {
+	if len(contributions) < 5 {
 		return nil
 	}
 
@@ -78,7 +85,7 @@ func registerWithContributionPredictionForNameForCurrency(reg Register, window t
 		slices.Sort(lapses)
 		return lapses[len(lapses)/2]
 	}
-	contributsSlice := func(percent float64) []contribution {
+	contributionsSlice := func(percent float64) []contribution {
 		wouldBe := int(percent * float64(len(contributions)))
 		if wouldBe == 0 {
 			wouldBe = 2
@@ -86,9 +93,9 @@ func registerWithContributionPredictionForNameForCurrency(reg Register, window t
 		return contributions[len(contributions)-1-wouldBe:]
 	}
 
-	eighth := contributsSlice(7.0 / 8.0)
+	eighth := contributionsSlice(7.0 / 8.0)
-	quarter := contributsSlice(3.0 / 4.0)
+	quarter := contributionsSlice(3.0 / 4.0)
-	half := contributsSlice(1.0 / 2.0)
+	half := contributionsSlice(1.0 / 2.0)
 	medianValueDelta := func() float64 {
 		medians := []float64{
 			getMedianValueDelta(eighth),
@@ -108,23 +115,10 @@ func registerWithContributionPredictionForNameForCurrency(reg Register, window t
 		return medians[1]
 	}()
 
-	latest := func() float64 {
-		last := 0.0
-		for _, d := range reg.Dates() {
-			last = reg[d][name][currency]
-		}
-		return last
-	}()
 	for _, predictionTime := range predictionTimes(window) {
 		k := predictionTime.Format("2006-01")
-		if _, ok := reg[k]; !ok {
-			reg[k] = make(Balances)
-		}
-		if _, ok := reg[k][name]; !ok {
-			reg[k][name] = make(Balance)
-		}
 		expectedDelta := float64(predictionTime.Sub(time.Now())) * medianValueDelta / float64(medianLapse)
-		reg[k][name][currency] = latest + expectedDelta
+		reg[k][name][currency] += expectedDelta
 	}
 	return nil
 }

ledger/predict_test.go

@@ -23,6 +23,9 @@ func TestRegisterPrediction(t *testing.T) {
 		for _, date := range got.Dates() {
 			for _, name := range got.Names() {
 				t.Logf("%s | %s = %+v", date, name, got[date][name])
+				if ti, _ := dateToTime(date); ti.After(time.Now().Add(time.Hour*24*60)) && got[date][name]["XYZ"] == 0 {
+					t.Error("predicting future contributions lost unmodified currency", got[date][name])
+				}
 			}
 		}
 	})
@@ -90,6 +93,6 @@ func newTestRegister() map[string]Balances {
 		s(lastYear.Add(day * 184)): Balances{"X": Balance{USD: 8}},
 		s(lastYear.Add(day * 214)): Balances{"X": Balance{USD: 10}},
 		s(lastYear.Add(day * 244)): Balances{"X": Balance{USD: 12}},
-		s(lastYear.Add(day * 274)): Balances{"X": Balance{USD: 16}},
+		s(lastYear.Add(day * 274)): Balances{"X": Balance{USD: 16, "XYZ": 1}},
 	}
 }