impl updating ledger file batch and single by idx

ledger.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"io/ioutil"
 	"os"
+	"path"
 )
 
 type Ledger struct {
@@ -23,6 +24,34 @@ func NewLedger(path string) (Ledger, error) {
 	}, err
 }
 
+func (ledger Ledger) SetTransaction(i int, transaction Transaction) error {
+	transactions, err := ledger.Transactions()
+	if err != nil {
+		return err
+	}
+	if i >= len(transactions) {
+		return errors.New("i too high")
+	}
+	transactions[i] = transaction
+	return ledger.SetTransactions(transactions)
+}
+
+func (ledger Ledger) SetTransactions(transactions []Transaction) error {
+	f, err := ioutil.TempFile(os.TempDir(), path.Base(ledger.path)+".*")
+	if err != nil {
+		return err
+	}
+	for _, transaction := range transactions {
+		if _, err := fmt.Fprintf(f, "%s\n", transaction.Marshal()); err != nil {
+			return err
+		}
+	}
+	if err := f.Close(); err != nil {
+		return err
+	}
+	return os.Rename(f.Name(), ledger.path)
+}
+
 func (ledger Ledger) Transactions() ([]Transaction, error) {
 	f, err := ledger.open()
 	if err != nil {

ledger_test.go

@@ -1,6 +1,14 @@
 package main
 
-import "testing"
+import (
+	"fmt"
+	"io"
+	"os"
+	"path"
+	"testing"
+
+	"github.com/google/uuid"
+)
 
 func TestLedgerTransactions(t *testing.T) {
 	ledger, err := NewLedger("./testdata/ledger.dat")
@@ -36,3 +44,56 @@ func TestLedgerTransactions(t *testing.T) {
 		t.Logf("%+v => \n%s", transactions[i], transactions[i].Marshal())
 	}
 }
+
+func TestLedgerSetTransaction(t *testing.T) {
+	aTransaction := func() Transaction {
+		return Transaction{
+			Date:        "2021-07-20",
+			Description: uuid.New().String(),
+			Payee:       "payee",
+			Payer:       "payer",
+			Amount:      1.23,
+		}
+	}
+	path := path.Join(t.TempDir(), "ledger.dat")
+	a, err := os.Open("./testdata/ledger.dat")
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, err := os.Create(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := io.Copy(b, a); err != nil {
+		t.Fatal(err)
+	}
+	a.Close()
+	b.Close()
+
+	ledger, err := NewLedger(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	transactions, err := ledger.Transactions()
+	if err != nil {
+		t.Fatal(err)
+	}
+	was := fmt.Sprintf("%+v", transactions)
+	transactions[0] = aTransaction()
+	want := fmt.Sprintf("%+v", transactions)
+	if err := ledger.SetTransaction(0, transactions[0]); err != nil {
+		t.Fatal(err)
+	}
+	transactions, err = ledger.Transactions()
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := fmt.Sprintf("%+v", transactions)
+	if got == was {
+		t.Fatal(got)
+	}
+	if got != want {
+		t.Fatal(want, got)
+	}
+}