// Based on https://github.com/gogap/logrus_mate under License Apache License 2.0
package file

import (
	"bytes"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"
)

// RFC5424 log message levels.
const (
	LevelError = iota
	LevelWarn
	LevelInfo
	LevelDebug
)

const (
	y1  = `0123456789`
	y2  = `0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789`
	y3  = `0000000000111111111122222222223333333333444444444455555555556666666666777777777788888888889999999999`
	y4  = `0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789`
	mo1 = `000000000111`
	mo2 = `123456789012`
	d1  = `0000000001111111111222222222233`
	d2  = `1234567890123456789012345678901`
	h1  = `000000000011111111112222`
	h2  = `012345678901234567890123`
	mi1 = `000000000011111111112222222222333333333344444444445555555555`
	mi2 = `012345678901234567890123456789012345678901234567890123456789`
	s1  = `000000000011111111112222222222333333333344444444445555555555`
	s2  = `012345678901234567890123456789012345678901234567890123456789`
	ns1 = `0123456789`
)

// fileLogWriter implements LoggerInterface.
// It writes messages by lines limit, file size limit, or time frequency.
type fileLogWriter struct {
	sync.RWMutex // write log order by order and  atomic incr maxLinesCurLines and maxSizeCurSize
	// The opened file
	Filename   string
	fileWriter *os.File

	// Rotate at line
	MaxLines         int
	maxLinesCurLines int

	// Rotate at size
	MaxSize        int
	maxSizeCurSize int

	// Rotate daily
	Daily         bool
	MaxDays       int
	dailyOpenDate int
	dailyOpenTime time.Time

	Rotate     bool
	Perm       string
	RotatePerm string

	fileNameOnly, suffix string // like "project.log", project is fileNameOnly and .log is suffix
}

func InitFileLogWriter(c *ConfigStruct) (*fileLogWriter, error) {

	w := fileLogWriter{
		Filename:   c.Filename,
		MaxLines:   c.MaxLines,
		MaxSize:    c.MaxSize,
		Daily:      c.Daily,
		MaxDays:    c.MaxDays,
		Rotate:     c.Rotate,
		Perm:       c.Perm,
		RotatePerm: c.RotatePerm,
	}

	w.suffix = filepath.Ext(w.Filename)
	w.fileNameOnly = strings.TrimSuffix(w.Filename, w.suffix)
	if w.suffix == "" {
		w.suffix = ".log"
	}
	err := w.startLogger()
	return &w, err
}

// start file logger. create log file and set to locker-inside file writer.
func (w *fileLogWriter) startLogger() error {
	file, err := w.createLogFile()
	if err != nil {
		return err
	}
	if w.fileWriter != nil {
		w.fileWriter.Close()
	}
	w.fileWriter = file
	return w.initFd()
}

func (w *fileLogWriter) needRotate(size int, day int) bool {
	return (w.MaxLines > 0 && w.maxLinesCurLines >= w.MaxLines) ||
		(w.MaxSize > 0 && w.maxSizeCurSize >= w.MaxSize) ||
		(w.Daily && day != w.dailyOpenDate)

}

// WriteMsg write logger message into file.
func (w *fileLogWriter) WriteMsg(when time.Time, msg string, level int) error {
	h, d := formatTimeHeader(when)
	msg = string(h) + msg + "\n"
	if w.Rotate {
		w.RLock()
		if w.needRotate(len(msg), d) {
			w.RUnlock()
			w.Lock()
			if w.needRotate(len(msg), d) {
				if err := w.doRotate(when); err != nil {
					fmt.Fprintf(os.Stderr, "FileLogWriter(%q): %s\n", w.Filename, err)
				}
			}
			w.Unlock()
		} else {
			w.RUnlock()
		}
	}

	w.Lock()
	_, err := w.fileWriter.Write([]byte(msg))
	if err == nil {
		w.maxLinesCurLines++
		w.maxSizeCurSize += len(msg)
	}
	w.Unlock()
	return err
}

func (w *fileLogWriter) createLogFile() (*os.File, error) {
	// Open the log file
	perm, err := strconv.ParseInt(w.Perm, 8, 64)
	if err != nil {
		return nil, err
	}
	fd, err := os.OpenFile(w.Filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, os.FileMode(perm))
	if err == nil {
		// Make sure file perm is user set perm cause of `os.OpenFile` will obey umask
		os.Chmod(w.Filename, os.FileMode(perm))
	}
	return fd, err
}

func (w *fileLogWriter) initFd() error {
	fd := w.fileWriter
	fInfo, err := fd.Stat()
	if err != nil {
		return fmt.Errorf("get stat err: %s", err)
	}
	w.maxSizeCurSize = int(fInfo.Size())
	w.dailyOpenTime = time.Now()
	w.dailyOpenDate = w.dailyOpenTime.Day()
	w.maxLinesCurLines = 0
	if w.Rotate {
		if w.Daily {
			go w.dailyRotate(w.dailyOpenTime)
		}
		if fInfo.Size() > 0 && w.MaxLines > 0 {
			count, err := w.lines()
			if err != nil {
				return err
			}
			w.maxLinesCurLines = count
		}
	}
	return nil
}

func (w *fileLogWriter) dailyRotate(openTime time.Time) {
	y, m, d := openTime.Add(24 * time.Hour).Date()
	nextDay := time.Date(y, m, d, 0, 0, 0, 0, openTime.Location())
	tm := time.NewTimer(time.Duration(nextDay.UnixNano() - openTime.UnixNano() + 100))
	<-tm.C
	w.Lock()
	if w.needRotate(0, time.Now().Day()) {
		if err := w.doRotate(time.Now()); err != nil {
			fmt.Fprintf(os.Stderr, "FileLogWriter(%q): %s\n", w.Filename, err)
		}
	}
	w.Unlock()
}

func (w *fileLogWriter) lines() (int, error) {
	fd, err := os.Open(w.Filename)
	if err != nil {
		return 0, err
	}
	defer fd.Close()

	buf := make([]byte, 32768) // 32k
	count := 0
	lineSep := []byte{'\n'}

	for {
		c, err := fd.Read(buf)
		if err != nil && err != io.EOF {
			return count, err
		}

		count += bytes.Count(buf[:c], lineSep)

		if err == io.EOF {
			break
		}
	}

	return count, nil
}

// DoRotate means it need to write file in new file.
// new file name like xx.2013-01-01.log (daily) or xx.001.log (by line or size)
func (w *fileLogWriter) doRotate(logTime time.Time) error {
	// file exists
	// Find the next available number
	num := 1
	fName := ""
	rotatePerm, err := strconv.ParseInt(w.RotatePerm, 8, 64)
	if err != nil {
		return err
	}

	_, err = os.Lstat(w.Filename)
	if err != nil {
		//even if the file is not exist or other ,we should RESTART the logger
		goto RESTART_LOGGER
	}

	if w.MaxLines > 0 || w.MaxSize > 0 {
		for ; err == nil && num <= 999; num++ {
			fName = w.fileNameOnly + fmt.Sprintf(".%s.%03d%s", logTime.Format("2006-01-02"), num, w.suffix)
			_, err = os.Lstat(fName)
		}
	} else {
		fName = fmt.Sprintf("%s.%s%s", w.fileNameOnly, w.dailyOpenTime.Format("2006-01-02"), w.suffix)
		_, err = os.Lstat(fName)
		for ; err == nil && num <= 999; num++ {
			fName = w.fileNameOnly + fmt.Sprintf(".%s.%03d%s", w.dailyOpenTime.Format("2006-01-02"), num, w.suffix)
			_, err = os.Lstat(fName)
		}
	}
	// return error if the last file checked still existed
	if err == nil {
		return fmt.Errorf("Rotate: Cannot find free log number to rename %s", w.Filename)
	}

	// close fileWriter before rename
	w.fileWriter.Close()

	// Rename the file to its new found name
	// even if occurs error,we MUST guarantee to  restart new logger
	err = os.Rename(w.Filename, fName)
	if err != nil {
		goto RESTART_LOGGER
	}

	err = os.Chmod(fName, os.FileMode(rotatePerm))

RESTART_LOGGER:

	startLoggerErr := w.startLogger()
	go w.deleteOldLog()

	if startLoggerErr != nil {
		return fmt.Errorf("Rotate StartLogger: %s", startLoggerErr)
	}
	if err != nil {
		return fmt.Errorf("Rotate: %s", err)
	}
	return nil
}

func (w *fileLogWriter) deleteOldLog() {
	dir := filepath.Dir(w.Filename)
	filepath.Walk(dir, func(path string, info os.FileInfo, err error) (returnErr error) {
		defer func() {
			if r := recover(); r != nil {
				fmt.Fprintf(os.Stderr, "Unable to delete old log '%s', error: %v\n", path, r)
			}
		}()

		if info == nil {
			return
		}

		if !info.IsDir() && info.ModTime().Add(24*time.Hour*time.Duration(w.MaxDays)).Before(time.Now()) {
			if strings.HasPrefix(filepath.Base(path), filepath.Base(w.fileNameOnly)) &&
				strings.HasSuffix(filepath.Base(path), w.suffix) {
				os.Remove(path)
			}
		}
		return
	})
}

// Destroy close the file description, close file writer.
func (w *fileLogWriter) Destroy() {
	w.fileWriter.Close()
}

// Flush flush file logger.
// there are no buffering messages in file logger in memory.
// flush file means sync file from disk.
func (w *fileLogWriter) Flush() {
	w.fileWriter.Sync()
}

func formatTimeHeader(when time.Time) ([]byte, int) {
	y, mo, d := when.Date()
	h, mi, s := when.Clock()
	ns := when.Nanosecond() / 1000000
	//len("2006/01/02 15:04:05.123 ")==24
	var buf [24]byte

	buf[0] = y1[y/1000%10]
	buf[1] = y2[y/100]
	buf[2] = y3[y-y/100*100]
	buf[3] = y4[y-y/100*100]
	buf[4] = '/'
	buf[5] = mo1[mo-1]
	buf[6] = mo2[mo-1]
	buf[7] = '/'
	buf[8] = d1[d-1]
	buf[9] = d2[d-1]
	buf[10] = ' '
	buf[11] = h1[h]
	buf[12] = h2[h]
	buf[13] = ':'
	buf[14] = mi1[mi]
	buf[15] = mi2[mi]
	buf[16] = ':'
	buf[17] = s1[s]
	buf[18] = s2[s]
	buf[19] = '.'
	buf[20] = ns1[ns/100]
	buf[21] = ns1[ns%100/10]
	buf[22] = ns1[ns%10]

	buf[23] = ' '

	return buf[0:], d
}