From 1d18cb50c5b9b8558e64677f14093b2a595ec476 Mon Sep 17 00:00:00 2001
From: bel <bel@bel.bel>
Date: Sat, 20 Jul 2024 20:10:35 -0600
Subject: [PATCH] ledger.Transaction.Payee()

---
 src/ledger/balances.go         |  6 +++---
 src/ledger/transaction.go      | 29 +++++++++++++++++++++++++++++
 src/ledger/transaction_test.go | 13 +++++++++++++
 3 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/src/ledger/balances.go b/src/ledger/balances.go
index 89ca093..7d6d519 100644
--- a/src/ledger/balances.go
+++ b/src/ledger/balances.go
@@ -37,9 +37,9 @@ func (balances Balances) Group(pattern string) Balances {
 	result := make(Balances)
 	p := regexp.MustCompile(pattern)
 	for k, v := range balances {
-		k2 := p.FindString(k)
-		if k2 == "" {
-			k2 = k
+		k2 := k
+		if p.MatchString(k) {
+			k2 = p.FindString(k)
 		}
 
 		was := result[k2]
diff --git a/src/ledger/transaction.go b/src/ledger/transaction.go
index 0d67d38..6b382f4 100644
--- a/src/ledger/transaction.go
+++ b/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
diff --git a/src/ledger/transaction_test.go b/src/ledger/transaction_test.go
index 6ba09ed..69b86c3 100644
--- a/src/ledger/transaction_test.go
+++ b/src/ledger/transaction_test.go
@@ -8,6 +8,19 @@ import (
 	"testing"
 )
 
+func TestTransactionPayee(t *testing.T) {
+	given := Transaction{
+		Delta{Name: "x", Transaction: "a", Value: 1},
+		Delta{Name: "y", Transaction: "a", Value: 2},
+		Delta{Name: "Withdrawal:z", Transaction: "a", Value: -3},
+	}
+
+	got := given.Payee()
+	if got != "Withdrawal:z" {
+		t.Error(got)
+	}
+}
+
 func TestDeltasTransactions(t *testing.T) {
 	given := Deltas{
 		Delta{Date: "2", Name: "x", Transaction: "a"},