scrobblerlog: implemented append mode

backends/scrobblerlog/scrobblerlog.go

@@ -22,6 +22,7 @@ THE SOFTWARE.
 package scrobblerlog
 
 import (
+	"bufio"
 	"os"
 	"sort"
 	"time"
@@ -33,6 +34,7 @@ import (
 type ScrobblerLogBackend struct {
 	filePath       string
 	includeSkipped bool
+	append         bool
 	file           *os.File
 	log            ScrobblerLog
 }
@@ -42,26 +44,57 @@ func (b *ScrobblerLogBackend) Name() string { return "scrobbler-log" }
 func (b *ScrobblerLogBackend) FromConfig(config *viper.Viper) models.Backend {
 	b.filePath = config.GetString("file-path")
 	b.includeSkipped = config.GetBool("include-skipped")
-	return b
-}
-
-func (b *ScrobblerLogBackend) StartImport() error {
-	file, err := os.Create(b.filePath)
-	if err != nil {
-		return err
+	b.append = true
+	if config.IsSet("append") {
+		b.append = config.GetBool("append")
 	}
-
 	b.log = ScrobblerLog{
 		Timezone: "UNKNOWN",
 		Client:   "Rockbox unknown $Revision$",
 	}
+	return b
+}
 
-	err = WriteHeader(file, &b.log)
+func (b *ScrobblerLogBackend) StartImport() error {
+	flags := os.O_RDWR | os.O_CREATE
+	if !b.append {
+		flags |= os.O_TRUNC
+	}
+	file, err := os.OpenFile(b.filePath, flags, 0666)
 	if err != nil {
-		file.Close()
 		return err
 	}
 
+	if b.append {
+		stat, err := file.Stat()
+		if err != nil {
+			file.Close()
+			return err
+		}
+
+		if stat.Size() == 0 {
+			// Zero length file, treat as a new file
+			b.append = false
+		} else {
+			// Verify existing file is a scrobbler log
+			reader := bufio.NewReader(file)
+			err = ReadHeader(reader, &b.log)
+			if err != nil {
+				file.Close()
+				return err
+			}
+			file.Seek(0, 2)
+		}
+	}
+
+	if !b.append {
+		err = WriteHeader(file, &b.log)
+		if err != nil {
+			file.Close()
+			return err
+		}
+	}
+
 	b.file = file
 	return nil
 }