Release 0.2.0

- new language: go
- new shops: cybertek.fr, mediamarkt.ch
- deprecated shops: alternate.be, minershop.eu
- improved database transaction management
- better web parsing library (ferret, requires headless chrome browser)
- include or exclude products by applying regex on their names
- check for PID file to avoid running the bot twice
- hastags are now configurable

Signed-off-by: Julien Riou <julien@riou.xyz>

pid.go

@@ -0,0 +1,74 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"os"
+	"strconv"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// writePid writes current process ID into a file
+func writePid(file string) error {
+	if file == "" {
+		return nil
+	}
+	log.Debugf("writing PID to %s", file)
+	pid := strconv.Itoa(os.Getpid())
+	f, err := os.OpenFile(file, os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	_, err = f.WriteString(pid)
+	return err
+}
+
+// removePid removes file containing the process ID
+func removePid(file string) error {
+	if file == "" {
+		return nil
+	}
+	if _, err := os.Stat(file); err == nil {
+		log.Debugf("removing PID file %s", file)
+		return os.Remove(file)
+	}
+	return nil
+}
+
+// waitPid check if another instance is running and eventually wait for it to terminate (with a timeout)
+func waitPid(pidFile string, waitTimeout int) error {
+	if pidFile == "" {
+		return nil
+	}
+
+	waitTime := 100 * time.Millisecond // initial backoff time for waiting
+	maxBackoffTime := 1000             // maximum time in millisecond to add between each waiting runs
+
+	timeout := false
+	maxTime := time.Now().Add(time.Second * time.Duration(waitTimeout))
+
+	for {
+		if _, err := os.Stat(pidFile); err == nil {
+			// PID file exists
+			log.Debugf("waiting %s before checking PID again", waitTime)
+			time.Sleep(waitTime)
+			waitTime = waitTime + time.Duration(rand.Intn(maxBackoffTime))*time.Millisecond
+		} else {
+			// file does not exist
+			break
+		}
+		if time.Now().After(maxTime) {
+			timeout = true
+			break
+		}
+	}
+
+	if timeout {
+		return fmt.Errorf("timeout waiting for PID file")
+	}
+
+	return nil
+}