rename based on plans

ana/legacy_interest.go

@@ -0,0 +1,60 @@
+package ana
+
+import (
+	"maps"
+	"math"
+	"regexp"
+	"time"
+
+	"gogs.inhome.blapointe.com/ana-ledger/ledger"
+)
+
+func RegisterWithCompoundingInterestPrediction(reg ledger.Register, window time.Duration, pattern string, apy float64) (ledger.Register, error) {
+	lastBalances := make(ledger.Balances)
+	p := regexp.MustCompile(pattern)
+	for _, d := range reg.Dates() {
+		if t, _ := dateToTime(d); time.Now().Before(t) {
+			continue
+		}
+		for name := range reg[d] {
+			if p.MatchString(name) {
+				lastBalances[name] = reg[d][name]
+			}
+		}
+	}
+
+	predictedTimes := predictionTimes(window)
+	result := maps.Clone(reg)
+	for _, predictionTime := range predictedTimes {
+		k := predictionTime.Format("2006-01")
+		if _, ok := result[k]; !ok {
+			result[k] = make(ledger.Balances)
+		}
+		for k2, v2 := range lastBalances {
+			if _, ok := result[k][k2]; !ok {
+				result[k][k2] = maps.Clone(v2)
+			}
+		}
+	}
+
+	addedSoFar := make(ledger.Balances)
+	for _, predictionTime := range predictedTimes {
+		k := predictionTime.Format("2006-01")
+		for name := range lastBalances {
+			if _, ok := addedSoFar[name]; !ok {
+				addedSoFar[name] = make(ledger.Balance)
+			}
+			for currency := range result[k][name] {
+				// A = P(1 + r/n)**nt
+				p := result[k][name][currency] + addedSoFar[name][currency]
+				r := apy
+				n := 12.0
+				t := 1.0 / 12.0
+				result[k][name][currency] = p * math.Pow(1.0+(r/n), n*t)
+				addedSoFar[name][currency] += (result[k][name][currency] - p)
+			}
+		}
+	}
+
+	return result, nil
+}