clean tdd

ledger/file.go

@@ -1,6 +1,12 @@
 package ledger
 
-import "io"
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+var filesAppendDelim = "\t"
 
 type Files []string
 
@@ -11,7 +17,42 @@ func NewFiles(p string, q ...string) (Files, error) {
 }
 
 func (files Files) Add(payee string, delta Delta) error {
-	//   TODO
+	currencyValue := fmt.Sprintf("%s%.2f", delta.Currency, delta.Value)
+	if delta.Currency != USD {
+		currencyValue = fmt.Sprintf("%.2f %s", delta.Value, delta.Currency)
+	}
+	return files.append(fmt.Sprintf("%s   %s\n%s%s%s%s\n%s%s",
+		delta.Date, delta.Description,
+		filesAppendDelim, delta.Name, filesAppendDelim+filesAppendDelim+filesAppendDelim, currencyValue,
+		filesAppendDelim, payee,
+	))
+}
+
+func (files Files) append(s string) error {
+	if err := files.trimTrainlingWhitespace(); err != nil {
+		return err
+	}
+
+	f, err := os.OpenFile(string(files[0]), os.O_APPEND|os.O_CREATE|os.O_WRONLY, os.ModePerm)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	fmt.Fprintf(f, "\n%s", s)
+	return f.Close()
+}
+
+func (files Files) trimTrainlingWhitespace() error {
+	f, err := os.Open(string(files[0]))
+	if os.IsNotExist(err) {
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
 	return io.EOF
 }