refactor: Add config validation, defaults, and unit tests

config/config.go

@@ -18,6 +18,15 @@ const (
 	EnvResponseTimeout = "RESPONSE_TIMEOUT"
 )
 
+// Default configuration values
+const (
+	DefaultLogLevel        = zerolog.InfoLevel
+	DefaultNumWorkers      = 5
+	DefaultWorkerBatchSize = 100
+	DefaultMaxResponseSize = 1048576 // 1MB
+	DefaultResponseTimeout = 30      // seconds
+)
+
 // Config holds the application configuration loaded from environment variables
 type Config struct {
 	LogLevel        zerolog.Level // Logging level (debug, info, warn, error)
@@ -28,6 +37,14 @@ type Config struct {
 	WorkerBatchSize int          // Batch size for worker processing
 }
 
+// String returns a string representation of the configuration
+func (c *Config) String() string {
+	return fmt.Sprintf(
+		"Config{LogLevel: %s, RootPath: %s, MaxResponseSize: %d, NumWorkers: %d, ResponseTimeout: %d, WorkerBatchSize: %d}",
+		c.LogLevel, c.RootPath, c.MaxResponseSize, c.NumOfWorkers, c.ResponseTimeout, c.WorkerBatchSize,
+	)
+}
+
 var CONFIG Config
 
 // parsePositiveInt parses and validates positive integer values
@@ -57,6 +74,9 @@ func GetConfig() *Config {
 			return nil
 		},
 		EnvRootPath: func(v string) error {
+			if _, err := os.Stat(v); err != nil {
+				return fmt.Errorf("invalid root path: %w", err)
+			}
 			config.RootPath = v
 			return nil
 		},