package log

import (
	"io"
	"os"
	"sync"
)

type WriteSyncer interface {
	io.Writer
	Sync() error
}

// WrapOsFile wraps an *os.File in a WriteSyncer.
//
// To support multithreaded logging and to support
// flushing the buffer before the program exits.
func WrapOsFile(f *os.File) WriteSyncer {
	return Lock(f)
}

// AddSync converts an io.Writer to a WriteSyncer. It attempts to be
// intelligent: if the concrete type of the io.Writer implements WriteSyncer,
// we'll use the existing Sync method. If it doesn't, we'll add a no-op Sync.
func AddSync(w io.Writer) WriteSyncer {
	switch w := w.(type) {
	case WriteSyncer:
		return w
	default:
		return writerWrapper{w}
	}
}

type lockedWriteSyncer struct {
	sync.Mutex
	ws WriteSyncer
}

// Lock wraps a WriteSyncer in a mutex to make it safe for concurrent use. In
// particular, *os.Files must be locked before use.
func Lock(ws WriteSyncer) WriteSyncer {
	if _, ok := ws.(*lockedWriteSyncer); ok {
		// no need to layer on another lock
		return ws
	}
	return &lockedWriteSyncer{ws: ws}
}

func (s *lockedWriteSyncer) Write(bs []byte) (int, error) {
	s.Lock()
	n, err := s.ws.Write(bs)
	s.Unlock()
	return n, err
}

func (s *lockedWriteSyncer) Sync() error {
	s.Lock()
	err := s.ws.Sync()
	s.Unlock()
	return err
}

type writerWrapper struct {
	io.Writer
}

func (w writerWrapper) Sync() error {
	return nil
}