//go:build windows

package main

import (
	"errors"
	"fmt"
	"io"
	"os"
	"strings"
	"unicode/utf8"
)

const truncatedLogRecord = "\n[Слишком длинная запись сокращена]\n"

type rotatingLog struct {
	file        *os.File
	path        string
	limit, size int64
}

func openRotatingLog(path string, limit int64) (*rotatingLog, error) {
	if limit < int64(len(truncatedLogRecord)+16) {
		return nil, fmt.Errorf("log size limit is too small")
	}
	for _, name := range []string{path, path + ".1"} {
		info, err := os.Lstat(name)
		if errors.Is(err, os.ErrNotExist) {
			continue
		}
		if err != nil {
			return nil, err
		}
		if !info.Mode().IsRegular() {
			return nil, fmt.Errorf("log target is not a regular file")
		}
		if name != path {
			if err = os.Remove(name); err != nil {
				return nil, err
			}
		}
	}
	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0600)
	if err != nil {
		return nil, err
	}
	return &rotatingLog{file: f, path: path, limit: limit}, nil
}
func (w *rotatingLog) Write(text string) error {
	if w.file == nil {
		return os.ErrClosed
	}
	if text == "" {
		return nil
	}
	if !utf8.ValidString(text) {
		text = strings.ToValidUTF8(text, "?")
	}
	if int64(len(text)) > w.limit {
		end := int(w.limit) - len(truncatedLogRecord)
		for end > 0 && !utf8.ValidString(text[:end]) {
			end--
		}
		text = text[:end] + truncatedLogRecord
	}
	if w.size > 0 && w.size+int64(len(text)) > w.limit {
		if err := w.rotate(); err != nil {
			return err
		}
	}
	n, err := w.file.WriteString(text)
	w.size += int64(n)
	if err == nil && n != len(text) {
		return io.ErrShortWrite
	}
	return err
}
func (w *rotatingLog) rotate() error {
	err := w.file.Close()
	w.file = nil
	if err != nil {
		return err
	}
	if info, e := os.Lstat(w.path + ".1"); e == nil {
		if !info.Mode().IsRegular() {
			return fmt.Errorf("log archive is not a regular file")
		}
		if e = os.Remove(w.path + ".1"); e != nil {
			return e
		}
	} else if !errors.Is(e, os.ErrNotExist) {
		return e
	}
	if err = os.Rename(w.path, w.path+".1"); err != nil {
		return err
	}
	w.file, err = os.OpenFile(w.path, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0600)
	w.size = 0
	return err
}
func (w *rotatingLog) Close() error {
	if w.file == nil {
		return nil
	}
	e := errors.Join(w.file.Sync(), w.file.Close())
	w.file = nil
	return e
}