chore(config): merge userConfig with defaultConfig and add a lock (#164)

* chore(config): merge userConfig with defaultConfig and add a lock

* chore(config): remove lock for LoadConfig

config.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"sync"
 )
 
 type WakeOnLanDevice struct {
@@ -40,25 +41,28 @@ var defaultConfig = &Config{
 	DisplayOffAfterSec:   1800, // 30 minutes
 }
 
-var config *Config
+var (
+	config     *Config
+	configLock = &sync.Mutex{}
+)
 
 func LoadConfig() {
 	if config != nil {
+		logger.Info("config already loaded, skipping")
 		return
 	}
 
 	file, err := os.Open(configPath)
 	if err != nil {
 		logger.Debug("default config file doesn't exist, using default")
-		config = defaultConfig
 		return
 	}
 	defer file.Close()
 
-	var loadedConfig Config
+	// load and merge the default config with the user config
+	loadedConfig := *defaultConfig
 	if err := json.NewDecoder(file).Decode(&loadedConfig); err != nil {
 		logger.Errorf("config file JSON parsing failed, %v", err)
-		config = defaultConfig
 		return
 	}
 
@@ -66,6 +70,9 @@ func LoadConfig() {
 }
 
 func SaveConfig() error {
+	configLock.Lock()
+	defer configLock.Unlock()
+
 	file, err := os.Create(configPath)
 	if err != nil {
 		return fmt.Errorf("failed to create config file: %w", err)