package main

import "fmt"

const (
	ERR    = 3
	NOTICE = 5
	DEBUG  = 7
)

type Logger interface {
	WriteMessage(msg string)
}

type ChainLogger struct {
	logger Logger
	next   *ChainLogger
	mask   int
}

func NewChainLogger(mask int, logger Logger) *ChainLogger {
	return &ChainLogger{logger, nil, mask}
}

func (self *ChainLogger) SetNext(nextChainLogger *ChainLogger) *ChainLogger {
	if self.next == nil {
		self.next = nextChainLogger
	} else {
		self.next.SetNext(nextChainLogger)
	}
	return self
}

func (self *ChainLogger) Message(msg string, priority int) {
	if priority <= self.mask {
		self.logger.WriteMessage(msg)
		if self.next != nil {
			self.next.Message(msg, priority)
		}
	}
}

type StdoutLogger struct {
}

func (self *StdoutLogger) WriteMessage(msg string) {
	fmt.Println("Writting to stdout: ", msg)
}

type EmailLogger struct {
}

func (self *EmailLogger) WriteMessage(msg string) {
	fmt.Println("Sending via email :", msg)
}

type StderrLogger struct {
}

func (self *StderrLogger) WriteMessage(msg string) {
	fmt.Println("Sending to stderr :", msg)
}

func main() {
	l := NewChainLogger(DEBUG, &StdoutLogger{}).SetNext(
		NewChainLogger(NOTICE, &EmailLogger{})).SetNext(
		NewChainLogger(ERR, &StderrLogger{}))

	l.Message("Entering function y.", DEBUG)
	l.Message("Step1 Completed.", NOTICE)
	l.Message("Ab error has occurred.", ERR)
}