1 files changed, 78 insertions, 0 deletions
diff --git a/util/lamport/persisted_lamport.go b/util/lamport/persisted_lamport.go
new file mode 100644
index 00000000..4f12dd1b
--- /dev/null
+++ b/util/lamport/persisted_lamport.go
@@ -0,0 +1,78 @@
+package lamport
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+type Persisted struct {
+	Clock
+	filePath string
+}
+
+func NewPersisted(filePath string) *Persisted {
+	clock := &Persisted{
+		Clock:    NewClock(),
+		filePath: filePath,
+	}
+	return clock
+}
+
+func LoadPersisted(filePath string) (*Persisted, error) {
+	clock := &Persisted{
+		filePath: filePath,
+	}
+
+	err := clock.read()
+	if err != nil {
+		return nil, err
+	}
+
+	return clock, nil
+}
+
+func (c *Persisted) Increment() (Time, error) {
+	time := c.Clock.Increment()
+	return time, c.Write()
+}
+
+func (c *Persisted) Witness(time Time) error {
+	// TODO: rework so that we write only when the clock was actually updated
+	c.Clock.Witness(time)
+	return c.Write()
+}
+
+func (c *Persisted) read() error {
+	content, err := ioutil.ReadFile(c.filePath)
+	if err != nil {
+		return err
+	}
+
+	var value uint64
+	n, err := fmt.Sscanf(string(content), "%d", &value)
+
+	if err != nil {
+		return err
+	}
+
+	if n != 1 {
+		return fmt.Errorf("could not read the clock")
+	}
+
+	c.Clock = NewClockWithTime(value)
+
+	return nil
+}
+
+func (c *Persisted) Write() error {
+	dir := filepath.Dir(c.filePath)
+	err := os.MkdirAll(dir, 0777)
+	if err != nil {
+		return err
+	}
+
+	data := []byte(fmt.Sprintf("%d", c.counter))
+	return ioutil.WriteFile(c.filePath, data, 0644)
+}