// Copyright 2015-2016 Luke Shumaker
//
// 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.

//go:generate make

package sd_daemon

import (
	"io"
	"os"
	"strings"
	"sync"
	"fmt"
	"log/syslog"
)

// Logger writes "<N>"-prefixed lines to an io.Writer, where N is a
// syslog priority number.  It implements mostly the same interface as
// "log/syslog".Writer.
//
// You probably don't need any instance of this other than the
// constant "Log", which uses os.Stderr as the writer.  It is
// implemented as a struct rather than a set of functions so that it
// can be passed around as an implementation of an interface.
type Logger struct{
	mu  sync.Mutex
	out io.Writer
}

func NewLogger(w io.Writer) Logger {
	return Logger{out: w}
}

// Log is a Logger that use used very similarly to
// "log/syslog".Writer, but writes to os.Stderr under the assumption
// that stderr is forwarded to syslog/journald.
//
// You are encouraged to use stderr unless you have a good reason to
// talk to syslog or journald directly.
var Log = Logger{out: os.Stderr}

// WriteString writes a message with the specified priority to the
// log.
func (l Logger) WriteBytes(level syslog.Priority, msg []byte) (n int, err error) {
	return l.WriteString(level, string(msg))
}

// WriteString writes a message with the specified priority to the
// log.
func (l Logger) WriteString(level syslog.Priority, msg string) (n int, err error) {
	l.mu.Lock()
	defer l.mu.Unlock()

	// BUG(lukeshu): Logger uses high-level string functions that
	// do many small allocations, making it insuitable for in
	// tight loops; it should use a buffer property to be
	// essentially zero-allocation.
	prefix := fmt.Sprintf("<%d>", level)
	buf := prefix + strings.Replace(strings.TrimSuffix(msg, "\n"), "\n", "\n"+prefix, -1)
	return io.WriteString(l.out, buf)
}

type loggerWriter struct {
	log   Logger
	level syslog.Priority
}

func (lw loggerWriter) Write(p []byte) (n int, err error) {
	return lw.log.WriteBytes(lw.level, p)
}

// Writer returns an io.Writer that writes messages with the specified
// priority to the log.
func (l Logger) Writer(level syslog.Priority) io.Writer {
	return loggerWriter{log: l, level: level}
}