// Package jsonfilelog provides the default Logger implementation for
// Docker logging. This logger logs to files on the host server in the
// JSON format.
package jsonfilelog

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"strconv"
	"sync"
	"time"

	"gopkg.in/fsnotify.v1"

	"github.com/Sirupsen/logrus"
	"github.com/docker/docker/daemon/logger"
	"github.com/docker/docker/pkg/ioutils"
	"github.com/docker/docker/pkg/jsonlog"
	"github.com/docker/docker/pkg/pubsub"
	"github.com/docker/docker/pkg/tailfile"
	"github.com/docker/docker/pkg/timeutils"
	"github.com/docker/docker/pkg/units"
)

const (
	// Name is the name of the file that the jsonlogger logs to.
	Name               = "json-file"
	maxJSONDecodeRetry = 10
)

// JSONFileLogger is Logger implementation for default Docker logging.
type JSONFileLogger struct {
	buf          *bytes.Buffer
	f            *os.File   // store for closing
	mu           sync.Mutex // protects buffer
	capacity     int64      //maximum size of each file
	n            int        //maximum number of files
	ctx          logger.Context
	readers      map[*logger.LogWatcher]struct{} // stores the active log followers
	notifyRotate *pubsub.Publisher
}

func init() {
	if err := logger.RegisterLogDriver(Name, New); err != nil {
		logrus.Fatal(err)
	}
	if err := logger.RegisterLogOptValidator(Name, ValidateLogOpt); err != nil {
		logrus.Fatal(err)
	}
}

// New creates new JSONFileLogger which writes to filename passed in
// on given context.
func New(ctx logger.Context) (logger.Logger, error) {
	log, err := os.OpenFile(ctx.LogPath, os.O_RDWR|os.O_APPEND|os.O_CREATE, 0600)
	if err != nil {
		return nil, err
	}
	var capval int64 = -1
	if capacity, ok := ctx.Config["max-size"]; ok {
		var err error
		capval, err = units.FromHumanSize(capacity)
		if err != nil {
			return nil, err
		}
	}
	var maxFiles = 1
	if maxFileString, ok := ctx.Config["max-file"]; ok {
		maxFiles, err = strconv.Atoi(maxFileString)
		if err != nil {
			return nil, err
		}
		if maxFiles < 1 {
			return nil, fmt.Errorf("max-file cannot be less than 1")
		}
	}
	return &JSONFileLogger{
		f:            log,
		buf:          bytes.NewBuffer(nil),
		ctx:          ctx,
		capacity:     capval,
		n:            maxFiles,
		readers:      make(map[*logger.LogWatcher]struct{}),
		notifyRotate: pubsub.NewPublisher(0, 1),
	}, nil
}

// Log converts logger.Message to jsonlog.JSONLog and serializes it to file.
func (l *JSONFileLogger) Log(msg *logger.Message) error {
	l.mu.Lock()
	defer l.mu.Unlock()

	timestamp, err := timeutils.FastMarshalJSON(msg.Timestamp)
	if err != nil {
		return err
	}
	err = (&jsonlog.JSONLogs{Log: append(msg.Line, '\n'), Stream: msg.Source, Created: timestamp}).MarshalJSONBuf(l.buf)
	if err != nil {
		return err
	}
	l.buf.WriteByte('\n')
	_, err = writeLog(l)
	return err
}

func writeLog(l *JSONFileLogger) (int64, error) {
	if l.capacity == -1 {
		return writeToBuf(l)
	}
	meta, err := l.f.Stat()
	if err != nil {
		return -1, err
	}
	if meta.Size() >= l.capacity {
		name := l.f.Name()
		if err := l.f.Close(); err != nil {
			return -1, err
		}
		if err := rotate(name, l.n); err != nil {
			return -1, err
		}
		file, err := os.OpenFile(name, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0666)
		if err != nil {
			return -1, err
		}
		l.f = file
		l.notifyRotate.Publish(struct{}{})
	}
	return writeToBuf(l)
}

func writeToBuf(l *JSONFileLogger) (int64, error) {
	i, err := l.buf.WriteTo(l.f)
	if err != nil {
		l.buf = bytes.NewBuffer(nil)
	}
	return i, err
}

func rotate(name string, n int) error {
	if n < 2 {
		return nil
	}
	for i := n - 1; i > 1; i-- {
		oldFile := name + "." + strconv.Itoa(i)
		replacingFile := name + "." + strconv.Itoa(i-1)
		if err := backup(oldFile, replacingFile); err != nil {
			return err
		}
	}
	if err := backup(name+".1", name); err != nil {
		return err
	}
	return nil
}

// backup renames a file from curr to old, creating an empty file curr if it does not exist.
func backup(old, curr string) error {
	if _, err := os.Stat(old); !os.IsNotExist(err) {
		err := os.Remove(old)
		if err != nil {
			return err
		}
	}
	if _, err := os.Stat(curr); os.IsNotExist(err) {
		f, err := os.Create(curr)
		if err != nil {
			return err
		}
		f.Close()
	}
	return os.Rename(curr, old)
}

// ValidateLogOpt looks for json specific log options max-file & max-size.
func ValidateLogOpt(cfg map[string]string) error {
	for key := range cfg {
		switch key {
		case "max-file":
		case "max-size":
		default:
			return fmt.Errorf("unknown log opt '%s' for json-file log driver", key)
		}
	}
	return nil
}

// LogPath returns the location the given json logger logs to.
func (l *JSONFileLogger) LogPath() string {
	return l.ctx.LogPath
}

// Close closes underlying file and signals all readers to stop.
func (l *JSONFileLogger) Close() error {
	l.mu.Lock()
	err := l.f.Close()
	for r := range l.readers {
		r.Close()
		delete(l.readers, r)
	}
	l.mu.Unlock()
	return err
}

// Name returns name of this logger.
func (l *JSONFileLogger) Name() string {
	return Name
}

func decodeLogLine(dec *json.Decoder, l *jsonlog.JSONLog) (*logger.Message, error) {
	l.Reset()
	if err := dec.Decode(l); err != nil {
		return nil, err
	}
	msg := &logger.Message{
		Source:    l.Stream,
		Timestamp: l.Created,
		Line:      []byte(l.Log),
	}
	return msg, nil
}

// ReadLogs implements the logger's LogReader interface for the logs
// created by this driver.
func (l *JSONFileLogger) ReadLogs(config logger.ReadConfig) *logger.LogWatcher {
	logWatcher := logger.NewLogWatcher()

	go l.readLogs(logWatcher, config)
	return logWatcher
}

func (l *JSONFileLogger) readLogs(logWatcher *logger.LogWatcher, config logger.ReadConfig) {
	defer close(logWatcher.Msg)

	pth := l.ctx.LogPath
	var files []io.ReadSeeker
	for i := l.n; i > 1; i-- {
		f, err := os.Open(fmt.Sprintf("%s.%d", pth, i-1))
		if err != nil {
			if !os.IsNotExist(err) {
				logWatcher.Err <- err
				break
			}
			continue
		}
		defer f.Close()
		files = append(files, f)
	}

	latestFile, err := os.Open(pth)
	if err != nil {
		logWatcher.Err <- err
		return
	}
	defer latestFile.Close()

	files = append(files, latestFile)
	tailer := ioutils.MultiReadSeeker(files...)

	if config.Tail != 0 {
		tailFile(tailer, logWatcher, config.Tail, config.Since)
	}

	if !config.Follow {
		return
	}

	if config.Tail >= 0 {
		latestFile.Seek(0, os.SEEK_END)
	}

	l.mu.Lock()
	l.readers[logWatcher] = struct{}{}
	l.mu.Unlock()

	notifyRotate := l.notifyRotate.Subscribe()
	followLogs(latestFile, logWatcher, notifyRotate, config.Since)

	l.mu.Lock()
	delete(l.readers, logWatcher)
	l.mu.Unlock()

	l.notifyRotate.Evict(notifyRotate)
}

func tailFile(f io.ReadSeeker, logWatcher *logger.LogWatcher, tail int, since time.Time) {
	var rdr io.Reader = f
	if tail > 0 {
		ls, err := tailfile.TailFile(f, tail)
		if err != nil {
			logWatcher.Err <- err
			return
		}
		rdr = bytes.NewBuffer(bytes.Join(ls, []byte("\n")))
	}
	dec := json.NewDecoder(rdr)
	l := &jsonlog.JSONLog{}
	for {
		msg, err := decodeLogLine(dec, l)
		if err != nil {
			if err != io.EOF {
				logWatcher.Err <- err
			}
			return
		}
		if !since.IsZero() && msg.Timestamp.Before(since) {
			continue
		}
		logWatcher.Msg <- msg
	}
}

func followLogs(f *os.File, logWatcher *logger.LogWatcher, notifyRotate chan interface{}, since time.Time) {
	dec := json.NewDecoder(f)
	l := &jsonlog.JSONLog{}
	fileWatcher, err := fsnotify.NewWatcher()
	if err != nil {
		logWatcher.Err <- err
		return
	}
	defer fileWatcher.Close()
	if err := fileWatcher.Add(f.Name()); err != nil {
		logWatcher.Err <- err
		return
	}

	var retries int
	for {
		msg, err := decodeLogLine(dec, l)
		if err != nil {
			if err != io.EOF {
				// try again because this shouldn't happen
				if _, ok := err.(*json.SyntaxError); ok && retries <= maxJSONDecodeRetry {
					dec = json.NewDecoder(f)
					retries++
					continue
				}
				logWatcher.Err <- err
				return
			}

			select {
			case <-fileWatcher.Events:
				dec = json.NewDecoder(f)
				continue
			case <-fileWatcher.Errors:
				logWatcher.Err <- err
				return
			case <-logWatcher.WatchClose():
				return
			case <-notifyRotate:
				fileWatcher.Remove(f.Name())

				f, err = os.Open(f.Name())
				if err != nil {
					logWatcher.Err <- err
					return
				}
				if err := fileWatcher.Add(f.Name()); err != nil {
					logWatcher.Err <- err
				}
				dec = json.NewDecoder(f)
				continue
			}
		}

		retries = 0 // reset retries since we've succeeded
		if !since.IsZero() && msg.Timestamp.Before(since) {
			continue
		}
		select {
		case logWatcher.Msg <- msg:
		case <-logWatcher.WatchClose():
			logWatcher.Msg <- msg
			for {
				msg, err := decodeLogLine(dec, l)
				if err != nil {
					return
				}
				if !since.IsZero() && msg.Timestamp.Before(since) {
					continue
				}
				logWatcher.Msg <- msg
			}
		}
	}
}