logcorrelator/internal/observability/logger.go

package observability

import (
	"fmt"
	"log"
	"os"
	"sort"
	"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.RWMutex
	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.RLock()
	defer l.mu.RUnlock()
	return level >= l.minLevel
}

// WithFields returns a new logger with additional fields.
func (l *Logger) WithFields(fields map[string]any) *Logger {
	l.mu.RLock()
	minLevel := l.minLevel
	prefix := l.prefix
	existing := make(map[string]any, len(l.fields))
	for k, v := range l.fields {
		existing[k] = v
	}
	l.mu.RUnlock()

	for k, v := range fields {
		existing[k] = v
	}

	return &Logger{
		logger:   l.logger,
		prefix:   prefix,
		fields:   existing,
		minLevel: minLevel,
	}
}

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

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

// Error logs an error message.
func (l *Logger) Error(msg string, err error) {
	if !l.ShouldLog(ERROR) {
		return
	}
	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.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.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.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.log("INFO", fmt.Sprintf(msg, args...))
}

func (l *Logger) log(level, msg string) {
	l.mu.RLock()
	prefix := l.prefix
	fields := make(map[string]any, len(l.fields))
	for k, v := range l.fields {
		fields[k] = v
	}
	l.mu.RUnlock()

	var b strings.Builder
	if prefix != "" {
		b.WriteString("[")
		b.WriteString(prefix)
		b.WriteString("] ")
	}
	b.WriteString(level)
	b.WriteString(" ")
	b.WriteString(msg)

	if len(fields) > 0 {
		keys := make([]string, 0, len(fields))
		for k := range fields {
			keys = append(keys, k)
		}
		sort.Strings(keys)

		for _, k := range keys {
			b.WriteString(" ")
			b.WriteString(k)
			b.WriteString("=")
			b.WriteString(fmt.Sprintf("%v", fields[k]))
		}
	}

	l.logger.Print(b.String())
}