logging/logging.go

package logging

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

// higher log level means more logging...
const (
	ERROR = iota
	WARNING
	INFO
	DEBUG
	TRACE
)

const (
	LoggerCreated       int = iota // return code if the logger creates a new logger
	LoggerExists                   // retun cde in the case that there is already a logger
	ErrorCreatingLogger            // in case of error creating the logger
)

var logLevelStringMap = map[string]int{
	"error":   ERROR,
	"warning": WARNING,
	"info":    INFO,
	"debug":   DEBUG,
	"trace":   TRACE,
}

type logOutput interface {
	Printf(format string, a ...interface{})
	// Println(format string, a ...interface{})
	init(m *io.Writer, s string, ll int)
}

type logStream struct {
	s        *log.Logger
	logLevel int
}

var (
	Trace         logStream
	Debug         logStream
	Info          logStream
	Warning       logStream
	Error         logStream
	DefaultLogger logStream
	LogLevel      int
)

func (l *logStream) Printf(format string, a ...interface{}) {
	// describe(a)
	if LogLevel < l.logLevel {
		return
	}

	// if no specific logger is configured for this logstrea, write to stdout...
	if l.s == nil {
		fmt.Printf(format, a...)
		return
	}

	l.s.Printf(format, a...)
}

func (l *logStream) init(m io.Writer, s string, ll int) {
	l.s = log.New(m, s, log.Ldate|log.Ltime|log.Lshortfile)
	l.logLevel = ll
}

// function to parse string representation of log level into integer - if there
// is no match of the string, it will return 0 which maps to error only
// logging...perhaps this could be made more explicit
func determineLogLevel(lstr string) int {
	lstrLowerCase := strings.ToLower(lstr)
	return logLevelStringMap[lstrLowerCase]
}

func InitLogger(logFile string, logLevelStr string, logToConsole bool) {

	LogLevel = determineLogLevel(logLevelStr)

	file, err := os.OpenFile(logFile, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)

	var multi io.Writer

	if err != nil {
		log.Println("Failed to open log file:", logFile, ":", err)
		multi = io.MultiWriter(os.Stdout)
	} else {
		if logToConsole {
			multi = io.MultiWriter(file, os.Stdout)
		} else {
			multi = io.MultiWriter(file)
		}
	}

	Trace.init(multi, "   TRACE: ", TRACE)
	Debug.init(multi, "  DEBUG: ", DEBUG)
	Info.init(multi, "   INFO: ", INFO)
	Warning.init(multi, "WARNING: ", WARNING)
	Error.init(multi, "  ERROR: ", ERROR)
}