1 files changed, 56 insertions, 0 deletions
diff --git a/vrsite/log.go b/vrsite/log.go
new file mode 100644
index 0000000..a0a4f3e
--- /dev/null
+++ b/vrsite/log.go
@@ -0,0 +1,56 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"sync"
+)
+
+// logStore is implemented by the production jj sidecar and by the file-backed
+// adapter used in tests. Append's callback makes session note numbering atomic
+// with the content update.
+type logStore interface {
+	Read() ([]byte, error)
+	Generation() (string, error)
+	Append(func(current []byte) ([]byte, error)) error
+	String() string
+}
+
+type fileLog struct {
+	path string
+	mu   sync.Mutex
+}
+
+func newFileLog(path string) *fileLog { return &fileLog{path: path} }
+
+func (l *fileLog) String() string { return l.path }
+
+func (l *fileLog) Read() ([]byte, error) { return os.ReadFile(l.path) }
+
+func (l *fileLog) Generation() (string, error) {
+	info, err := os.Stat(l.path)
+	if err != nil {
+		return "", err
+	}
+	return fmt.Sprintf("%d:%d", info.Size(), info.ModTime().UnixNano()), nil
+}
+
+func (l *fileLog) Append(makePayload func(current []byte) ([]byte, error)) error {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	current, err := os.ReadFile(l.path)
+	if err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	payload, err := makePayload(current)
+	if err != nil {
+		return err
+	}
+	f, err := os.OpenFile(l.path, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	_, err = f.Write(payload)
+	return err
+}