moving ledger predictions to /ana

ana/bpi.go

@@ -0,0 +1,42 @@
+package ana
+
+import (
+	"maps"
+	"regexp"
+	"time"
+
+	"gogs.inhome.blapointe.com/ana-ledger/ledger"
+)
+
+func BPIsWithFixedGrowthPrediction(bpis ledger.BPIs, window time.Duration, pattern string, apy float64) (ledger.BPIs, error) {
+	last := map[ledger.Currency]struct {
+		t string
+		v float64
+	}{}
+	for currency, bpi := range bpis {
+		for date, value := range bpi {
+			if date > last[currency].t {
+				was := last[currency]
+				was.t = date
+				was.v = value
+				last[currency] = was
+			}
+		}
+	}
+
+	result := make(ledger.BPIs)
+	p := regexp.MustCompile(pattern)
+	for currency, v := range bpis {
+		result[currency] = maps.Clone(v)
+		if p.MatchString(string(currency)) {
+			for _, predictionTime := range predictionTimes(window) {
+				k2 := predictionTime.Format("2006-01")
+				was := last[currency]
+				was.v *= 1.0 + (apy / 12.0)
+				result[currency][k2] = was.v
+				last[currency] = was
+			}
+		}
+	}
+	return result, nil
+}

ana/bpi_test.go

@@ -0,0 +1,35 @@
+package ana
+
+import (
+	"slices"
+	"testing"
+	"time"
+
+	"gogs.inhome.blapointe.com/ana-ledger/ledger"
+)
+
+func TestBPIPrediction(t *testing.T) {
+	t.Run("fixed growth", func(t *testing.T) {
+		bpis := ledger.BPIs{
+			ledger.USD: ledger.BPI{
+				"2001-01": -1000,
+				"2001-02": 100,
+			},
+		}
+
+		got, err := BPIsWithFixedGrowthPrediction(bpis, time.Hour*24*365, string(ledger.USD), 0.06)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		dates := []string{}
+		for d := range got[ledger.USD] {
+			dates = append(dates, d)
+		}
+		slices.Sort(dates)
+
+		for _, d := range dates {
+			t.Logf("%s | %s %.2f", ledger.USD, d, got[ledger.USD][d])
+		}
+	})
+}

ana/window.go

@@ -0,0 +1,13 @@
+package ana
+
+import "time"
+
+func predictionTimes(window time.Duration) []time.Time {
+	result := []time.Time{}
+	last := time.Now()
+	for last.Before(time.Now().Add(window)) {
+		last = last.Add(-1 * time.Hour * 24 * time.Duration(last.Day())).Add(time.Hour * 24 * 33)
+		result = append(result, last)
+	}
+	return result
+}