// Copyright 2015 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package log provides a universal logger for martian packages.
package log

import (
	"fmt"
	"log"
	"sync"
)

const (
	// Silent is a level that logs nothing.
	Silent int = iota
	// Error is a level that logs error logs.
	Error
	// Info is a level that logs error, and info logs.
	Info
	// Debug is a level that logs error, info, and debug logs.
	Debug
)

// Default log level is Error.
var (
	level      = Error
	lock       sync.Mutex
	currLogger Logger = &logger{}
)

type Logger interface {
	Infof(format string, args ...interface{})
	Debugf(format string, args ...interface{})
	Errorf(format string, args ...interface{})
}

// SetLogger changes the default logger. This must be called very first,
// before interacting with rest of the martian package. Changing it at
// runtime is not supported.
func SetLogger(l Logger) {
	currLogger = l
}

// SetLevel sets the global log level.
func SetLevel(l int) {
	lock.Lock()
	defer lock.Unlock()

	level = l
}

// Infof logs an info message.
func Infof(format string, args ...interface{}) {
	currLogger.Infof(format, args...)
}

// Debugf logs a debug message.
func Debugf(format string, args ...interface{}) {
	currLogger.Debugf(format, args...)
}

// Errorf logs an error message.
func Errorf(format string, args ...interface{}) {
	currLogger.Errorf(format, args...)
}

type logger struct{}

func (l *logger) Infof(format string, args ...interface{}) {
	lock.Lock()
	defer lock.Unlock()

	if level < Info {
		return
	}

	msg := fmt.Sprintf("INFO: %s", format)
	if len(args) > 0 {
		msg = fmt.Sprintf(msg, args...)
	}

	log.Println(msg)
}

func (l *logger) Debugf(format string, args ...interface{}) {
	lock.Lock()
	defer lock.Unlock()

	if level < Debug {
		return
	}

	msg := fmt.Sprintf("DEBUG: %s", format)
	if len(args) > 0 {
		msg = fmt.Sprintf(msg, args...)
	}

	log.Println(msg)
}

func (l *logger) Errorf(format string, args ...interface{}) {
	lock.Lock()
	defer lock.Unlock()

	if level < Error {
		return
	}

	msg := fmt.Sprintf("ERROR: %s", format)
	if len(args) > 0 {
		msg = fmt.Sprintf(msg, args...)
	}

	log.Println(msg)
}