From 1c0d39018c08c1189aceaf37fbb715ca52d5eccd Mon Sep 17 00:00:00 2001
From: Daniel Theophanes <Daniel Theophanes@localhost>
Date: Fri, 20 Sep 2013 09:58:18 -0700
Subject: [PATCH] Add configuration helper.

---
 config/config.go | 134 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 134 insertions(+)
 create mode 100644 config/config.go

diff --git a/config/config.go b/config/config.go
new file mode 100644
index 0000000..ed38119
--- /dev/null
+++ b/config/config.go
@@ -0,0 +1,134 @@
+// A simple and consistent method to extract a configuration from a file.
+// This doesn't contain any method to actually decode the file. The actual
+// decoding is done in an external function.
+package config
+
+import (
+	"bitbucket.org/kardianos/osext"
+	"code.google.com/p/go.exp/fsnotify"
+	"encoding/json"
+	"io"
+	"os"
+	"path/filepath"
+)
+
+const DefaultPostfix = "_config.json"
+
+// Simple JSON based configuration decoder.
+func DecodeJsonConfig(r io.Reader, v interface{}) error {
+	d := json.NewDecoder(r)
+	return d.Decode(v)
+}
+
+// Return a configuration file path. If baseName is empty,
+// then the current executable name without the extension
+// is used. If postfix is empty then DefaultPostfix is used.
+func GetConfigFilePath(baseName, postfix string) (string, error) {
+	if len(postfix) == 0 {
+		postfix = DefaultPostfix
+	}
+	path, err := osext.Executable()
+	if err != nil {
+		return "", err
+	}
+	path, exeName := filepath.Split(path)
+	if len(baseName) == 0 {
+		exeName = exeName[:len(exeName)-len(filepath.Ext(exeName))]
+	} else {
+		exeName = baseName
+	}
+	configPath := filepath.Join(path, exeName+postfix)
+	return configPath, nil
+}
+
+type DecodeConfig func(r io.Reader, v interface{}) error
+type EncodeConfig func(w io.Writer, v interface{}) error
+
+type WatchConfig struct {
+	// Notified here if the file changes.
+	C chan *WatchConfig
+
+	filepath string
+	watch    *fsnotify.Watcher
+	decode   DecodeConfig
+
+	close chan struct{}
+}
+
+// Create a new configuration watcher. Adds a notification if the configuration file changes
+// so it may be reloaded. If defaultConfig is not nil and encode is not nil, the
+// configuration file path is checked if a file exists or not. If it doesn't exist
+// the default configuration is written to the file.
+func NewWatchConfig(filepath string, decode DecodeConfig, defaultConfig interface{}, encode EncodeConfig) (*WatchConfig, error) {
+	if defaultConfig != nil && encode != nil {
+		f, err := os.Open(filepath)
+		if f != nil {
+			f.Close()
+		}
+		if os.IsNotExist(err) {
+			f, err = os.Create(filepath)
+			if err != nil {
+				return nil, err
+			}
+			err = encode(f, defaultConfig)
+			f.Close()
+			if err != nil {
+				return nil, err
+			}
+		}
+	}
+	watch, err := fsnotify.NewWatcher()
+	if err != nil {
+		return nil, err
+	}
+	err = watch.WatchFlags(filepath, fsnotify.FSN_MODIFY|fsnotify.FSN_CREATE)
+	if err != nil {
+		return nil, err
+	}
+
+	wc := &WatchConfig{
+		C: make(chan *WatchConfig),
+
+		filepath: filepath,
+		watch:    watch,
+		decode:   decode,
+
+		close: make(chan struct{}, 0),
+	}
+	go wc.run()
+
+	return wc, nil
+}
+
+func (wc *WatchConfig) run() {
+	for {
+		select {
+		case <-wc.close:
+			return
+		case <-wc.watch.Event:
+			wc.C <- wc
+		}
+	}
+}
+
+// Send a notification as if the configuration file has changed.
+func (wc *WatchConfig) TriggerC() {
+	wc.C <- wc
+}
+
+// Load the configuration from the file into the provided value.
+func (wc *WatchConfig) Load(v interface{}) error {
+	f, err := os.Open(wc.filepath)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	return wc.decode(f, v)
+}
+
+// Stop the watch and any loops that are running.
+func (wc *WatchConfig) Close() error {
+	wc.close <- struct{}{}
+	return wc.watch.Close()
+}