From a04a36bf90b2ac82c4a1411a8f03f0e39252a4e2 Mon Sep 17 00:00:00 2001
From: Gregory Eremin <g@erem.in>
Date: Sat, 29 Aug 2015 16:25:40 +0300
Subject: [PATCH] Handle file system events to reload config

---
 secondly.go | 47 +++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 45 insertions(+), 2 deletions(-)

diff --git a/secondly.go b/secondly.go
index b0d70ee..0e14cc9 100644
--- a/secondly.go
+++ b/secondly.go
@@ -6,8 +6,12 @@ import (
 	"log"
 	"os"
 	"os/signal"
+	"path/filepath"
 	"reflect"
+	"strings"
 	"syscall"
+
+	"github.com/howeyc/fsnotify"
 )
 
 var (
@@ -17,8 +21,8 @@ var (
 	initialized bool
 )
 
-// SetFlags sets up Confection configuration flags.
-func SetFlags() {
+// SetupFlags sets up Confection configuration flags.
+func SetupFlags() {
 	flag.StringVar(&configFile, "config", "config.json", "Path to config file")
 }
 
@@ -46,6 +50,41 @@ func HandleSIGHUP() {
 	}()
 }
 
+// HandleFSEvents listens to file system events and reloads configuration when
+// config file is modified.
+func HandleFSEvents() {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		panic(err)
+	}
+	if err := watcher.WatchFlags(filepath.Dir(configFile), fsnotify.FSN_MODIFY); err != nil {
+		panic(err)
+	}
+
+	fname := configFile
+	if ss := strings.Split(configFile, "/"); len(ss) > 1 {
+		fname = ss[len(ss)-1]
+	}
+
+	go func() {
+		for {
+			select {
+			case e := <-watcher.Event:
+				if e.Name != fname {
+					continue
+				}
+				if !e.IsModify() {
+					continue
+				}
+				log.Println("Config file was modified, reloading")
+				readConfig()
+			case err := <-watcher.Error:
+				log.Println("fsnotify error:", err)
+			}
+		}
+	}()
+}
+
 // OnChange adds a callback function that is triggered every time a value of
 // a field changes.
 func OnChange(field string, fun func(oldVal, newVal interface{})) {
@@ -103,6 +142,10 @@ func triggerCallbacks(oldConf, newConf interface{}) {
 		return
 	}
 
+	if len(callbacks) == 0 {
+		return
+	}
+
 	for fname, d := range diff(oldConf, newConf) {
 		if cbs, ok := callbacks[fname]; ok {
 			for _, cb := range cbs {