compute balances

balance.go

@@ -0,0 +1,9 @@
+package main
+
+type Balances map[string]float32
+
+func (balances Balances) Add(key string, v float32) {
+	was, _ := balances[key]
+	was += v
+	balances[key] = was
+}

ledger.go

@@ -52,6 +52,19 @@ func (ledger Ledger) SetTransactions(transactions []Transaction) error {
 	return os.Rename(f.Name(), ledger.path)
 }
 
+func (ledger Ledger) Balances() (Balances, error) {
+	transactions, err := ledger.Transactions()
+	if err != nil {
+		return nil, err
+	}
+	balances := make(Balances)
+	for _, transaction := range transactions {
+		balances.Add(transaction.Payee, transaction.Amount)
+		balances.Add(transaction.Payer, -1*transaction.Amount)
+	}
+	return balances, nil
+}
+
 func (ledger Ledger) Transactions() ([]Transaction, error) {
 	f, err := ledger.open()
 	if err != nil {

ledger_test.go

@@ -10,7 +10,7 @@ import (
 	"github.com/google/uuid"
 )
 
-func TestLedgerTransactions(t *testing.T) {
+func TestLedgerTransactionsBalances(t *testing.T) {
 	ledger, err := NewLedger("./testdata/ledger.dat")
 	if err != nil {
 		t.Fatal(err)
@@ -34,8 +34,8 @@ func TestLedgerTransactions(t *testing.T) {
 	if want := (Transaction{
 		Date:        "2021-07-30",
 		Description: "Testing detecting deposits via email alerts 5421705162",
-		Payer:       "AssetAccount:Cash:Uccu",
 		Payee:       "Debts:Credit:ChaseAarpChaseVisa",
+		Payer:       "AssetAccount:Cash:Uccu",
 		Amount:      100.00,
 	}); transactions[1] != want {
 		t.Fatalf("want \n\t%+v, got \n\t%+v", want, transactions[1])
@@ -43,6 +43,18 @@ func TestLedgerTransactions(t *testing.T) {
 	for i := range transactions {
 		t.Logf("%+v => \n%s", transactions[i], transactions[i].Marshal())
 	}
+	balances, err := ledger.Balances()
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantBalances := map[string]float32{
+		transactions[0].Payee: 37.86,
+		transactions[0].Payer: 62.14,
+		transactions[1].Payer: -100,
+	}
+	if fmt.Sprint(balances) != fmt.Sprint(wantBalances) {
+		t.Fatalf("want \n%+v, got \n%+v", wantBalances, balances)
+	}
 }
 
 func TestLedgerSetTransaction(t *testing.T) {