// package rotatelogs is a port of File-RotateLogs from Perl
// (https://metacpan.org/release/File-RotateLogs), and it allows
// you to automatically rotate output files when you write to them
// according to the filename pattern that you can specify.
package rotatelogs

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"sync"
	"time"

	strftime "github.com/lestrrat-go/strftime"
	"github.com/pkg/errors"
)

func (c clockFn) Now() time.Time {
	return c()
}

// New creates a new RotateLogs object. A log filename pattern
// must be passed. Optional `Option` parameters may be passed
func New(p string, options ...Option) (*RotateLogs, error) {
	globPattern := p
	for _, re := range patternConversionRegexps {
		globPattern = re.ReplaceAllString(globPattern, "*")
	}

	pattern, err := strftime.New(p)
	if err != nil {
		return nil, errors.Wrap(err, `invalid strftime pattern`)
	}

	var clock Clock = Local
	rotationTime := 24 * time.Hour
	var rotationCount uint
	var linkName string
	var maxAge time.Duration

	for _, o := range options {
		switch o.Name() {
		case optkeyClock:
			clock = o.Value().(Clock)
		case optkeyLinkName:
			linkName = o.Value().(string)
		case optkeyMaxAge:
			maxAge = o.Value().(time.Duration)
			if maxAge < 0 {
				maxAge = 0
			}
		case optkeyRotationTime:
			rotationTime = o.Value().(time.Duration)
			if rotationTime < 0 {
				rotationTime = 0
			}
		case optkeyRotationCount:
			rotationCount = o.Value().(uint)
		}
	}

	if maxAge > 0 && rotationCount > 0 {
		return nil, errors.New("options MaxAge and RotationCount cannot be both set")
	}

	if maxAge == 0 && rotationCount == 0 {
		// if both are 0, give maxAge a sane default
		maxAge = 7 * 24 * time.Hour
	}

	return &RotateLogs{
		clock:         clock,
		globPattern:   globPattern,
		linkName:      linkName,
		maxAge:        maxAge,
		pattern:       pattern,
		rotationTime:  rotationTime,
		rotationCount: rotationCount,
	}, nil
}

func (rl *RotateLogs) genFilename() string {
	now := rl.clock.Now()
	diff := time.Duration(now.UnixNano()) % rl.rotationTime
	t := now.Add(time.Duration(-1 * diff))
	return rl.pattern.FormatString(t)
}

// Write satisfies the io.Writer interface. It writes to the
// appropriate file handle that is currently being used.
// If we have reached rotation time, the target file gets
// automatically rotated, and also purged if necessary.
func (rl *RotateLogs) Write(p []byte) (n int, err error) {
	// Guard against concurrent writes
	rl.mutex.Lock()
	defer rl.mutex.Unlock()

	out, err := rl.getWriter_nolock(false)
	if err != nil {
		return 0, errors.Wrap(err, `failed to acquite target io.Writer`)
	}

	return out.Write(p)
}

// must be locked during this operation
func (rl *RotateLogs) getWriter_nolock(bailOnRotateFail bool) (io.Writer, error) {
	// This filename contains the name of the "NEW" filename
	// to log to, which may be newer than rl.currentFilename
	filename := rl.genFilename()
	if rl.curFn == filename {
		// nothing to do
		return rl.outFh, nil
	}

	// if we got here, then we need to create a file
	fh, err := os.OpenFile(filename, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
	if err != nil {
		return nil, errors.Errorf("failed to open file %s: %s", rl.pattern, err)
	}

	if err := rl.rotate_nolock(filename); err != nil {
		err = errors.Wrap(err, "failed to rotate")
		if bailOnRotateFail {
			// Failure to rotate is a problem, but it's really not a great
			// idea to stop your application just because you couldn't rename
			// your log.
			// We only return this error when explicitly needed.
			return nil, err
		}
		fmt.Fprintf(os.Stderr, "%s\n", err.Error())
	}

	rl.outFh.Close()
	rl.outFh = fh
	rl.curFn = filename

	return fh, nil
}

// CurrentFileName returns the current file name that
// the RotateLogs object is writing to
func (rl *RotateLogs) CurrentFileName() string {
	rl.mutex.RLock()
	defer rl.mutex.RUnlock()
	return rl.curFn
}

var patternConversionRegexps = []*regexp.Regexp{
	regexp.MustCompile(`%[%+A-Za-z]`),
	regexp.MustCompile(`\*+`),
}

type cleanupGuard struct {
	enable bool
	fn     func()
	mutex  sync.Mutex
}

func (g *cleanupGuard) Enable() {
	g.mutex.Lock()
	defer g.mutex.Unlock()
	g.enable = true
}
func (g *cleanupGuard) Run() {
	g.fn()
}

// Rotate forcefully rotates the log files.
func (rl *RotateLogs) Rotate() error {
	rl.mutex.Lock()
	defer rl.mutex.Unlock()
	if _, err := rl.getWriter_nolock(true); err != nil {
		return err
	}
	return nil
}

func (rl *RotateLogs) rotate_nolock(filename string) error {
	lockfn := filename + `_lock`
	fh, err := os.OpenFile(lockfn, os.O_CREATE|os.O_EXCL, 0644)
	if err != nil {
		// Can't lock, just return
		return err
	}

	var guard cleanupGuard
	guard.fn = func() {
		fh.Close()
		os.Remove(lockfn)
	}
	defer guard.Run()

	if rl.linkName != "" {
		tmpLinkName := filename + `_symlink`
		if err := os.Symlink(filename, tmpLinkName); err != nil {
			return errors.Wrap(err, `failed to create new symlink`)
		}

		if err := os.Rename(tmpLinkName, rl.linkName); err != nil {
			return errors.Wrap(err, `failed to rename new symlink`)
		}
	}

	if rl.maxAge <= 0 && rl.rotationCount <= 0 {
		return errors.New("panic: maxAge and rotationCount are both set")
	}

	matches, err := filepath.Glob(rl.globPattern)
	if err != nil {
		return err
	}

	cutoff := rl.clock.Now().Add(-1 * rl.maxAge)
	var toUnlink []string
	for _, path := range matches {
		// Ignore lock files
		if strings.HasSuffix(path, "_lock") || strings.HasSuffix(path, "_symlink") {
			continue
		}

		fi, err := os.Stat(path)
		if err != nil {
			continue
		}

		fl, err := os.Lstat(path)
		if err != nil {
			continue
		}

		if rl.maxAge > 0 && fi.ModTime().After(cutoff) {
			continue
		}

		if rl.rotationCount > 0 && fl.Mode()&os.ModeSymlink == os.ModeSymlink {
			continue
		}
		toUnlink = append(toUnlink, path)
	}

	if rl.rotationCount > 0 {
		// Only delete if we have more than rotationCount
		if rl.rotationCount >= uint(len(toUnlink)) {
			return nil
		}

		toUnlink = toUnlink[:len(toUnlink)-int(rl.rotationCount)]
	}

	if len(toUnlink) <= 0 {
		return nil
	}

	guard.Enable()
	go func() {
		// unlink files on a separate goroutine
		for _, path := range toUnlink {
			os.Remove(path)
		}
	}()

	return nil
}

// Close satisfies the io.Closer interface. You must
// call this method if you performed any writes to
// the object.
func (rl *RotateLogs) Close() error {
	rl.mutex.Lock()
	defer rl.mutex.Unlock()

	if rl.outFh == nil {
		return nil
	}

	rl.outFh.Close()
	rl.outFh = nil
	return nil
}