logcorrelator/internal/observability/logger.go

package observability

import (
	"fmt"
	"log"
	"os"
	"strings"
	"sync"
)

// LogLevel represents the severity of a log message.
type LogLevel int

const (
	DEBUG LogLevel = iota
	INFO
	WARN
	ERROR
)

// ParseLogLevel converts a string to LogLevel.
func ParseLogLevel(level string) LogLevel {
	switch strings.ToUpper(level) {
	case "DEBUG":
		return DEBUG
	case "INFO":
		return INFO
	case "WARN", "WARNING":
		return WARN
	case "ERROR":
		return ERROR
	default:
		return INFO
	}
}

// String returns the string representation of LogLevel.
func (l LogLevel) String() string {
	switch l {
	case DEBUG:
		return "DEBUG"
	case INFO:
		return "INFO"
	case WARN:
		return "WARN"
	case ERROR:
		return "ERROR"
	default:
		return "INFO"
	}
}

// Logger provides structured logging.
type Logger struct {
	mu      sync.Mutex
	logger  *log.Logger
	prefix  string
	fields  map[string]any
	minLevel LogLevel
}

// NewLogger creates a new logger with INFO level by default.
func NewLogger(prefix string) *Logger {
	return &Logger{
		logger:   log.New(os.Stderr, "", log.LstdFlags|log.Lmicroseconds),
		prefix:   prefix,
		fields:   make(map[string]any),
		minLevel: INFO,
	}
}

// NewLoggerWithLevel creates a new logger with specified minimum level.
func NewLoggerWithLevel(prefix string, level string) *Logger {
	return &Logger{
		logger:   log.New(os.Stderr, "", log.LstdFlags|log.Lmicroseconds),
		prefix:   prefix,
		fields:   make(map[string]any),
		minLevel: ParseLogLevel(level),
	}
}

// SetLevel sets the minimum log level.
func (l *Logger) SetLevel(level string) {
	l.mu.Lock()
	defer l.mu.Unlock()
	l.minLevel = ParseLogLevel(level)
}

// ShouldLog returns true if the given level should be logged.
func (l *Logger) ShouldLog(level LogLevel) bool {
	l.mu.Lock()
	defer l.mu.Unlock()
	return level >= l.minLevel
}

// WithFields returns a new logger with additional fields.
func (l *Logger) WithFields(fields map[string]any) *Logger {
	l.mu.Lock()
	minLevel := l.minLevel
	l.mu.Unlock()
	
	newLogger := &Logger{
		logger:   l.logger,
		prefix:   l.prefix,
		fields:   make(map[string]any),
		minLevel: minLevel,
	}
	for k, v := range l.fields {
		newLogger.fields[k] = v
	}
	for k, v := range fields {
		newLogger.fields[k] = v
	}
	return newLogger
}

// Info logs an info message.
func (l *Logger) Info(msg string) {
	if !l.ShouldLog(INFO) {
		return
	}
	l.mu.Lock()
	defer l.mu.Unlock()
	l.log("INFO", msg)
}

// Warn logs a warning message.
func (l *Logger) Warn(msg string) {
	if !l.ShouldLog(WARN) {
		return
	}
	l.mu.Lock()
	defer l.mu.Unlock()
	l.log("WARN", msg)
}

// Error logs an error message.
func (l *Logger) Error(msg string, err error) {
	if !l.ShouldLog(ERROR) {
		return
	}
	l.mu.Lock()
	defer l.mu.Unlock()
	if err != nil {
		l.log("ERROR", msg+" "+err.Error())
	} else {
		l.log("ERROR", msg)
	}
}

// Debug logs a debug message (only if debug level is enabled).
func (l *Logger) Debug(msg string) {
	if !l.ShouldLog(DEBUG) {
		return
	}
	l.mu.Lock()
	defer l.mu.Unlock()
	l.log("DEBUG", msg)
}

// Debugf logs a formatted debug message (only if debug level is enabled).
func (l *Logger) Debugf(msg string, args ...any) {
	if !l.ShouldLog(DEBUG) {
		return
	}
	l.mu.Lock()
	defer l.mu.Unlock()
	l.log("DEBUG", fmt.Sprintf(msg, args...))
}

// Warnf logs a formatted warning message.
func (l *Logger) Warnf(msg string, args ...any) {
	if !l.ShouldLog(WARN) {
		return
	}
	l.mu.Lock()
	defer l.mu.Unlock()
	l.log("WARN", fmt.Sprintf(msg, args...))
}

// Infof logs a formatted info message.
func (l *Logger) Infof(msg string, args ...any) {
	if !l.ShouldLog(INFO) {
		return
	}
	l.mu.Lock()
	defer l.mu.Unlock()
	l.log("INFO", fmt.Sprintf(msg, args...))
}

func (l *Logger) log(level, msg string) {
	prefix := l.prefix
	if prefix != "" {
		prefix = "[" + prefix + "] "
	}

	l.logger.SetPrefix(prefix + level + " ")
	
	var args []any
	for k, v := range l.fields {
		args = append(args, k, v)
	}
	
	if len(args) > 0 {
		l.logger.Printf(msg+" %+v", args...)
	} else {
		l.logger.Print(msg)
	}
}