bpi growth is also just compounding interest but ignore for now

ledger/register.go

@@ -0,0 +1,43 @@
+package ledger
+
+import (
+	"slices"
+	"time"
+)
+
+type Register map[string]Balances
+
+func (register Register) Names() []string {
+	names := map[string]int{}
+	for _, v := range register {
+		for name := range v {
+			names[name] = 1
+		}
+	}
+
+	result := make([]string, 0, len(register))
+	for k := range names {
+		result = append(result, k)
+	}
+	slices.Sort(result)
+	return result
+}
+
+func (register Register) Dates() []string {
+	result := make([]string, 0, len(register))
+	for k := range register {
+		result = append(result, k)
+	}
+	slices.Sort(result)
+	return result
+}
+
+func (register Register) Times() []time.Time {
+	dates := register.Dates()
+	result := make([]time.Time, len(dates))
+	for i := range dates {
+		v, _ := dateToTime(dates[i])
+		result[i] = v
+	}
+	return result
+}