// Copyright (C) 2010, Kyle Lemons <kyle@kylelemons.net>.  All rights reserved.

package log4go

import (
	"bytes"
	"fmt"
	"io"
	"os"
	"time"
)

// This log writer sends output to a file
type FileLogWriter struct {
	rec  chan *LogRecord
	rot  chan bool
	done chan bool

	// The opened file
	filename string
	file     *os.File

	// The logging format
	format string

	// File header/trailer
	header, trailer string

	// Rotate at linecount
	maxlines          int
	maxlines_curlines int

	// Rotate at size
	maxsize         int
	maxsize_cursize int

	// Rotate daily
	daily          bool
	daily_opendate int

	// Keep old logfiles (.001, .002, etc)
	rotate    bool
	maxbackup int
}

// This is the FileLogWriter's output method
func (w *FileLogWriter) LogWrite(rec *LogRecord) {
	w.rec <- rec
}

func (w *FileLogWriter) Close() {
	close(w.rec)
	<-w.done
}

// NewFileLogWriter creates a new LogWriter which writes to the given file and
// has rotation enabled if rotate is true.
//
// If rotate is true, any time a new log file is opened, the old one is renamed
// with a .### extension to preserve it.  The various Set* methods can be used
// to configure log rotation based on lines, size, and daily.
//
// The standard log-line format is:
//   [%D %T] [%L] (%S) %M
func NewFileLogWriter(fname string, rotate bool) *FileLogWriter {
	w := &FileLogWriter{
		rec:       make(chan *LogRecord, LogBufferLength),
		rot:       make(chan bool),
		done:      make(chan bool),
		filename:  fname,
		format:    "[%D %T] [%L] (%S) %M",
		rotate:    rotate,
		maxbackup: 999,
	}

	// open the file for the first time
	if err := w.intRotate(); err != nil {
		fmt.Fprintf(os.Stderr, "FileLogWriter(%q): %s\n", w.filename, err)
		return nil
	}

	go func() {
		defer func() {
			if w.file != nil {
				fmt.Fprint(w.file, FormatLogRecord(w.trailer, &LogRecord{Created: time.Now()}))
				w.file.Sync()
				w.file.Close()
			}
			close(w.done)
		}()

		for {
			select {
			case <-w.rot:
				if err := w.intRotate(); err != nil {
					fmt.Fprintf(os.Stderr, "FileLogWriter(%q): %s\n", w.filename, err)
					return
				}
			case rec, ok := <-w.rec:
				if !ok {
					return
				}
				now := time.Now()
				if (w.maxlines > 0 && w.maxlines_curlines >= w.maxlines) ||
					(w.maxsize > 0 && w.maxsize_cursize >= w.maxsize) ||
					(w.daily && now.Day() != w.daily_opendate) {
					if err := w.intRotate(); err != nil {
						fmt.Fprintf(os.Stderr, "FileLogWriter(%q): %s\n", w.filename, err)
						return
					}
				}

				// Perform the write
				n, err := fmt.Fprint(w.file, FormatLogRecord(w.format, rec))
				if err != nil {
					fmt.Fprintf(os.Stderr, "FileLogWriter(%q): %s\n", w.filename, err)
					return
				}

				// Update the counts
				w.maxlines_curlines++
				w.maxsize_cursize += n
			}
		}
	}()

	return w
}

// Request that the logs rotate
func (w *FileLogWriter) Rotate() {
	w.rot <- true
}

// If this is called in a threaded context, it MUST be synchronized
func (w *FileLogWriter) intRotate() error {
	// Close any log file that may be open
	if w.file != nil {
		fmt.Fprint(w.file, FormatLogRecord(w.trailer, &LogRecord{Created: time.Now()}))
		w.file.Close()
	}

	// If we are keeping log files, move it to the next available number
	if w.rotate {
		_, err := os.Lstat(w.filename)
		if err == nil { // file exists
			// Find the next available number
			num := 1
			fname := ""
			if w.daily && time.Now().Day() != w.daily_opendate {
				yesterday := time.Now().AddDate(0, 0, -1).Format("2006-01-02")

				for ; err == nil && num <= 999; num++ {
					fname = w.filename + fmt.Sprintf(".%s.%03d", yesterday, num)
					_, 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\n", w.filename)
				}
			} else {
				num = w.maxbackup - 1
				for ; num >= 1; num-- {
					fname = w.filename + fmt.Sprintf(".%d", num)
					nfname := w.filename + fmt.Sprintf(".%d", num+1)
					_, err = os.Lstat(fname)
					if err == nil {
						os.Rename(fname, nfname)
					}
				}
			}

			w.file.Close()
			// Rename the file to its newfound home
			err = os.Rename(w.filename, fname)
			if err != nil {
				return fmt.Errorf("Rotate: %s\n", err)
			}
		}
	}

	lineCount := 0
	byteCount := 0

	// If the file exists, open for reading and set our line/byte counts
	// On failure, just assume the file doesn't exist
	if fd, err := os.OpenFile(w.filename, os.O_RDONLY, 0440); err == nil {
		lineCount, _ = lineCounter(fd)

		fi, err := fd.Stat()
		if err == nil {
			byteCount = int(fi.Size())
		}

		fd.Close()
	}

	fd, err := os.OpenFile(w.filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0660)
	if err != nil {
		return err
	}
	w.file = fd

	now := time.Now()
	fmt.Fprint(w.file, FormatLogRecord(w.header, &LogRecord{Created: now}))

	// Set the daily open date to the current date
	w.daily_opendate = now.Day()

	// initialize rotation values
	w.maxlines_curlines = lineCount
	w.maxsize_cursize = byteCount

	return nil
}

// Taken from https://stackoverflow.com/a/24563853
func lineCounter(r io.Reader) (int, error) {
	buf := make([]byte, 32*1024)
	count := 0
	lineSep := []byte{'\n'}

	for {
		c, err := r.Read(buf)
		count += bytes.Count(buf[:c], lineSep)

		switch {
		case err == io.EOF:
			return count, nil

		case err != nil:
			return count, err
		}
	}
}

// Set the logging format (chainable).  Must be called before the first log
// message is written.
func (w *FileLogWriter) SetFormat(format string) *FileLogWriter {
	w.format = format
	return w
}

// Set the logfile header and footer (chainable).  Must be called before the first log
// message is written.  These are formatted similar to the FormatLogRecord (e.g.
// you can use %D and %T in your header/footer for date and time).
func (w *FileLogWriter) SetHeadFoot(head, foot string) *FileLogWriter {
	w.header, w.trailer = head, foot
	if w.maxlines_curlines == 0 {
		fmt.Fprint(w.file, FormatLogRecord(w.header, &LogRecord{Created: time.Now()}))
	}
	return w
}

// Set rotate at linecount (chainable). Must be called before the first log
// message is written.
func (w *FileLogWriter) SetRotateLines(maxlines int) *FileLogWriter {
	//fmt.Fprintf(os.Stderr, "FileLogWriter.SetRotateLines: %v\n", maxlines)
	w.maxlines = maxlines
	return w
}

// Set rotate at size (chainable). Must be called before the first log message
// is written.
func (w *FileLogWriter) SetRotateSize(maxsize int) *FileLogWriter {
	//fmt.Fprintf(os.Stderr, "FileLogWriter.SetRotateSize: %v\n", maxsize)
	w.maxsize = maxsize
	return w
}

// Set rotate daily (chainable). Must be called before the first log message is
// written.
func (w *FileLogWriter) SetRotateDaily(daily bool) *FileLogWriter {
	//fmt.Fprintf(os.Stderr, "FileLogWriter.SetRotateDaily: %v\n", daily)
	w.daily = daily
	return w
}

// Set max backup files. Must be called before the first log message
// is written.
func (w *FileLogWriter) SetRotateMaxBackup(maxbackup int) *FileLogWriter {
	w.maxbackup = maxbackup
	return w
}

// SetRotate changes whether or not the old logs are kept. (chainable) Must be
// called before the first log message is written.  If rotate is false, the
// files are overwritten; otherwise, they are rotated to another file before the
// new log is opened.
func (w *FileLogWriter) SetRotate(rotate bool) *FileLogWriter {
	//fmt.Fprintf(os.Stderr, "FileLogWriter.SetRotate: %v\n", rotate)
	w.rotate = rotate
	return w
}

// NewXMLLogWriter is a utility method for creating a FileLogWriter set up to
// output XML record log messages instead of line-based ones.
func NewXMLLogWriter(fname string, rotate bool) *FileLogWriter {
	return NewFileLogWriter(fname, rotate).SetFormat(
		`	<record level="%L">
		<timestamp>%D %T</timestamp>
		<source>%S</source>
		<message>%M</message>
	</record>`).SetHeadFoot("<log created=\"%D %T\">", "</log>")
}