ledger.Transaction.Payee()

src/ledger/transaction.go

@@ -39,6 +39,35 @@ func (deltas Deltas) Transactions() Transactions {
 	return result
 }
 
+func (transaction Transaction) Payee() string {
+	balances := Deltas(transaction).Balances()
+
+	candidates := []string{}
+
+	for name, balance := range balances {
+		everyoneElse := balances.NotLike(`^` + name + `$`).Group(`^`)[""]
+		matches := true
+		for currency, value := range balance {
+			matches = matches && everyoneElse[currency]*-1 == value
+		}
+		if matches {
+			candidates = append(candidates, name)
+		}
+	}
+	slices.Sort(candidates)
+
+	if len(candidates) == 0 {
+		panic(balances)
+	}
+
+	for _, candidate := range candidates {
+		if strings.HasPrefix(candidate, "Withdrawal") {
+			return candidate
+		}
+	}
+	return candidates[len(candidates)-1]
+}
+
 type transaction struct {
 	date        string
 	description string