package lamport
import (
"fmt"
"io/ioutil"
"os"
"path/filepath"
)
type Persisted struct {
Clock
filePath string
}
// NewPersisted create a new persisted Lamport clock
func NewPersisted(filePath string) (*Persisted, error) {
clock := &Persisted{
Clock: NewClock(),
filePath: filePath,
}
dir := filepath.Dir(filePath)
err := os.MkdirAll(dir, 0777)
if err != nil {
return nil, err
}
return clock, nil
}
// LoadPersisted load a persisted Lamport clock from a file
func LoadPersisted(filePath string) (*Persisted, error) {
clock := &Persisted{
filePath: filePath,
}
err := clock.read()
if err != nil {
return nil, err
}
return clock, nil
}
// Increment is used to return the value of the lamport clock and increment it afterwards
func (c *Persisted) Increment() (Time, error) {
time := c.Clock.Increment()
return time, c.Write()
}
// Witness is called to update our local clock if necessary after
// witnessing a clock value received from another process
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 {
data := []byte(fmt.Sprintf("%d", c.counter))
return ioutil.WriteFile(c.filePath, data, 0644)
}
