// Package applog persists the activity log independently of the webview cache.
package applog

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"time"
)

const maxFileBytes = 2 * 1024 * 1024
const maxEntryBytes = 64 * 1024
const recentLines = 2000

type Service struct {
	mu      sync.Mutex
	dir     string
	initErr error
	limit   int64
}

func NewService() *Service {
	dir, err := os.UserConfigDir()
	return &Service{dir: filepath.Join(dir, "iTuoke", "logs"), initErr: err, limit: maxFileBytes}
}

func (s *Service) files() ([]string, error) {
	if s.initErr != nil {
		return nil, s.initErr
	}
	info, err := os.Stat(s.dir)
	if errors.Is(err, os.ErrNotExist) {
		return []string{}, nil
	}
	if err != nil {
		return nil, err
	}
	if !info.IsDir() {
		return nil, fmt.Errorf("日志目录不可用: %s", s.dir)
	}
	entries, err := os.ReadDir(s.dir)
	if err != nil {
		return nil, err
	}
	var files []string
	for _, e := range entries {
		name := e.Name()
		if e.Type().IsRegular() && (name == "runtime.log" || (strings.HasPrefix(name, "runtime-") && strings.HasSuffix(name, ".log"))) {
			files = append(files, filepath.Join(s.dir, name))
		}
	}
	sort.Strings(files) // Timestamped archives first, active runtime.log last.
	return files, nil
}

// Read restores the latest 2000 lines; older files remain available on disk.
func (s *Service) Read() ([]string, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	files, err := s.files()
	if err != nil {
		return nil, fmt.Errorf("读取日志失败: %w", err)
	}
	lines := []string{}
	for i := len(files) - 1; i >= 0 && len(lines) < recentLines; i-- {
		f, err := os.Open(files[i])
		if err != nil {
			return nil, fmt.Errorf("读取日志失败: %w", err)
		}
		part := []string{}
		scanner := bufio.NewScanner(f)
		scanner.Buffer(make([]byte, 4096), maxEntryBytes+1)
		for scanner.Scan() {
			part = append(part, scanner.Text())
		}
		err = scanner.Err()
		closeErr := f.Close()
		if err != nil {
			return nil, fmt.Errorf("读取日志失败: %w", err)
		}
		if closeErr != nil {
			return nil, closeErr
		}
		remaining := recentLines - len(lines)
		if len(part) > remaining {
			part = part[len(part)-remaining:]
		}
		lines = append(part, lines...)
	}
	return lines, nil
}

// Append rotates before a complete entry would exceed 2 MiB. No archives are
// discarded automatically, and each completed call has synced its entry.
func (s *Service) Append(line string) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.initErr != nil {
		return s.initErr
	}
	line = strings.ReplaceAll(strings.ReplaceAll(line, "\r", "\\r"), "\n", "\\n")
	if len(line) > maxEntryBytes {
		return fmt.Errorf("单条日志超过 64 KB")
	}
	data := []byte(line + "\n")
	if err := os.MkdirAll(s.dir, 0700); err != nil {
		return fmt.Errorf("保存日志失败: %w", err)
	}
	path := filepath.Join(s.dir, "runtime.log")
	info, err := os.Stat(path)
	if err != nil && !errors.Is(err, os.ErrNotExist) {
		return err
	}
	if info != nil && info.Size() > 0 && info.Size()+int64(len(data)) > s.limit {
		// CreateTemp guarantees unique archive names even within the same tick.
		archive, err := os.CreateTemp(s.dir, "runtime-"+time.Now().UTC().Format("20060102-150405.000000000")+"-*.log")
		if err != nil {
			return err
		}
		name := archive.Name()
		if err := archive.Close(); err != nil {
			return err
		}
		// Windows requires a non-existing destination for some rename variants.
		if err := os.Remove(name); err != nil {
			return err
		}
		if err := os.Rename(path, name); err != nil {
			return fmt.Errorf("日志分卷失败: %w", err)
		}
	}
	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0600)
	if err != nil {
		return fmt.Errorf("保存日志失败: %w", err)
	}
	defer f.Close()
	start, err := f.Seek(0, io.SeekEnd)
	if err != nil {
		return err
	}
	n, err := f.Write(data)
	if err == nil && n != len(data) {
		err = io.ErrShortWrite
	}
	if err == nil {
		err = f.Sync()
	}
	if err != nil {
		// Leave no incomplete record for a later retry.
		if rollback := f.Truncate(start); rollback != nil {
			return fmt.Errorf("保存日志失败: %v；回滚失败: %w", err, rollback)
		}
		return fmt.Errorf("保存日志失败: %w", err)
	}
	return nil
}

// Clear only removes this logger's current and archived files.
func (s *Service) Clear() error {
	s.mu.Lock()
	defer s.mu.Unlock()
	files, err := s.files()
	if err != nil {
		return err
	}
	for _, path := range files {
		if err := os.Remove(path); err != nil {
			return fmt.Errorf("清空日志失败: %w", err)
		}
	}
	return nil
}