aurganize-backend/backend/pkg/logger/logger.go

package logger

import (
	"io"
	"os"
	"time"

	"github.com/rs/zerolog"
	"github.com/rs/zerolog/log"
)

const (
	LevelDebug = "debug"
	LevelInfo  = "info"
	LevelWarn  = "warn"
	LevelError = "error"
)

// Init initializes the global logger with environment-specific settings.
// Call this once at application startup.
//
// Environment determines output format:
//   - development: Pretty console output with colors
//   - staging/production: JSON output for log aggregation
//
// Example:
//
//	logger.Init("development")
//	log.Info().Msg("Application started")
func Init(enviroment string) {

	// Configuring the time format for loggin
	// Unix style timestamp in production for efficiency
	// Humar-readable in development
	if enviroment == "production" {
		// This is the unixtimestamp format used in production for efficiency : 1732632645
		zerolog.TimeFieldFormat = zerolog.TimeFormatUnix
	} else {
		zerolog.TimeFieldFormat = time.RFC3339
		// This is format for human readable format : 2025-11-26T10:30:45-05:00
	}

	var output io.Writer = os.Stdout

	if enviroment == "development" {
		output = zerolog.ConsoleWriter{
			Out:        os.Stdout,
			TimeFormat: time.RFC3339, // 2025-11-26T10:30:45-05:00
			NoColor:    false,        // Enabling Colours
		}
	}

	// Production uses default JSON output to stdout

	// Set global logger
	// Caller() : this caused adtional overhead as runtime.Caller() is called, which is worth
	// for debugging value, should disable in production
	log.Logger = zerolog.New(output).
		With().
		Timestamp().
		Caller(). // This line is to add file and line number information into the log
		Logger()

	// set global log level
	// Debug (most verbose)
	//  ↓
	// Info
	//  ↓
	// Warn
	//  ↓
	// Error
	//  ↓
	// Fatal (least verbose)
	switch enviroment {
	case "production":
		zerolog.SetGlobalLevel(zerolog.InfoLevel)
	case "UAT":
		zerolog.SetGlobalLevel(zerolog.InfoLevel)
	case "staging":
		zerolog.SetGlobalLevel(zerolog.InfoLevel)
	case "test":
		zerolog.SetGlobalLevel(zerolog.DebugLevel)
	case "development":
		zerolog.SetGlobalLevel(zerolog.DebugLevel)
	}

	// Log initialization
	log.Info().
		Str("environment", enviroment).
		Str("log_level", zerolog.GlobalLevel().String()).
		Msg("logger initialized")
}

func InitWithLevel(environment, level string) {
	Init(environment)

	switch level {
	case LevelDebug:
		zerolog.SetGlobalLevel(zerolog.DebugLevel)
	case LevelInfo:
		zerolog.SetGlobalLevel(zerolog.InfoLevel)
	case LevelWarn:
		zerolog.SetGlobalLevel(zerolog.WarnLevel)
	case LevelError:
		zerolog.SetGlobalLevel(zerolog.ErrorLevel)
	default:
		log.Warn().
			Str("provided_level", level).
			Str("using_level", zerolog.GlobalLevel().String()).
			Msg("Invalid log level, using default")
	}

	log.Info().
		Str("environment", environment).
		Str("log_level", zerolog.GlobalLevel().String()).
		Msg("Logger initialized with custom level")
}

// GetLogger returns the global logger instance.
// Use this to get a logger with additional context.
//
// Example :
//
//	logger := logger.GetLogger().
//					With().
//					Str("module","auth").
//					Logger()
//	logger.Info().Msg("Auth module started")
func GetLogger() *zerolog.Logger {
	return &log.Logger
}

// WithContext returns a logger with additional context fields.
// Useful for adding request-specific context.
//
// Example:
//
//	contextLogger := logger.WithContext(map[string]interface{}{
//	    "request_id": "abc-123",
//	    "user_id": "user-456",
//	})
//	contextLogger.Info().Msg("Processing request")
func WithContext(fields map[string]interface{}) *zerolog.Logger {
	logger := log.Logger
	for key, value := range fields {
		logger = logger.With().Interface(key, value).Logger()
	}

	return &logger
}

// Example Usage log functions (for familiarizing its usage)

// LogDebug logs debug information (these are verbose, development only)
func ExampleDebug() {
	log.Debug().
		Str("function", "ExampleDebug").
		Int("iteration", 1).
		Msg("Debug information")
}

func ExampleInfo() {
	log.Info().
		Str("user_id", "123").
		Str("reason", "invalid_token").
		Msg("User logged in successfully")
}

func ExampleError() {
	log.Error().
		Err(nil). // we add the actual error here
		Str("user_id", "123").
		Str("operation", "database_query").
		Msg("Failed to fetch user data")
}

// Log Fatal logs fatal erros and exits the application
// user sparingly - only for unrecoverable errors
func ExmapleFatal() {
	// log.Fatal().
	// 	Err(err).
	// 	Msg("Cannot connect to database")
	// -- Application exits after this
}

// Log with fields demonstrated logging mutliple fields
func ExampleWithFields() {
	log.Info().
		Str("user_id", "123").
		Str("email", "user@example.com").
		Int("login_attemtps", 3).
		Bool("success", true).
		Dur("duration", 150*time.Millisecond).
		Msg("login completed")
}

// Log with SubLogger demonstrates creating sub-loggers
func ExampleSubLogger() {

	// create a sub-logger for a specific module
	authLogger := log.With().
		Str("module", "auth").
		Str("version", "v1").
		Logger()

	authLogger.Info().Msg("Auth module initialized")
	authLogger.Debug().Msg("Loading auth configuration")
}