package rotatemanage

import (
	"compress/gzip"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"
)

type Options struct {
	MaxBackups int
	MaxAge     time.Duration
	Compress   bool
	Pattern    string
}

type backupFileMeta struct {
	path    string
	modTime time.Time
}

func Apply(archivePath string, currentPath string, options Options) error {
	if archivePath == "" || currentPath == "" {
		return nil
	}
	if options.Compress {
		if _, err := gzipBackupFile(archivePath); err != nil {
			return err
		}
	}
	backups, err := listManagedBackups(currentPath, options.Pattern)
	if err != nil {
		return err
	}
	return cleanupManagedBackups(backups, options)
}

func listManagedBackups(currentPath string, pattern string) ([]backupFileMeta, error) {
	dir := filepath.Dir(currentPath)
	base := filepath.Base(currentPath)
	stem := strings.TrimSuffix(base, filepath.Ext(base))
	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil, err
	}
	backups := make([]backupFileMeta, 0, len(entries))
	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		name := entry.Name()
		if name == base {
			continue
		}
		matched, err := IsManagedBackupName(name, base, stem, pattern)
		if err != nil {
			return nil, err
		}
		if !matched {
			continue
		}
		info, err := entry.Info()
		if err != nil {
			return nil, err
		}
		backups = append(backups, backupFileMeta{
			path:    filepath.Join(dir, name),
			modTime: info.ModTime(),
		})
	}
	return backups, nil
}

func IsManagedBackupName(name string, base string, stem string, pattern string) (bool, error) {
	if pattern != "" {
		return filepath.Match(pattern, name)
	}
	prefixes := []string{
		base + ".",
		base + "_",
		base + "-",
	}
	if stem != "" && stem != base {
		prefixes = append(prefixes,
			stem+".",
			stem+"_",
			stem+"-",
		)
	}
	for _, prefix := range prefixes {
		if !strings.HasPrefix(name, prefix) {
			continue
		}
		if isLikelyManagedBackupSuffix(strings.TrimPrefix(name, prefix)) {
			return true, nil
		}
	}
	return false, nil
}

func isLikelyManagedBackupSuffix(suffix string) bool {
	suffix = strings.TrimSpace(strings.ToLower(suffix))
	if suffix == "" {
		return false
	}
	suffix = strings.TrimSuffix(suffix, ".gz")
	suffix = strings.TrimSuffix(suffix, ".zip")
	if suffix == "" {
		return false
	}
	if strings.Contains(suffix, "bak") {
		return true
	}
	for _, ch := range suffix {
		if ch >= '0' && ch <= '9' {
			return true
		}
	}
	return false
}

func cleanupManagedBackups(backups []backupFileMeta, options Options) error {
	var firstErr error
	now := time.Now()
	kept := make([]backupFileMeta, 0, len(backups))
	for _, item := range backups {
		if options.MaxAge > 0 && now.Sub(item.modTime) > options.MaxAge {
			if err := os.Remove(item.path); err != nil && firstErr == nil {
				firstErr = err
			}
			continue
		}
		kept = append(kept, item)
	}
	if options.MaxBackups > 0 && len(kept) > options.MaxBackups {
		sort.Slice(kept, func(i, j int) bool {
			return kept[i].modTime.After(kept[j].modTime)
		})
		for _, item := range kept[options.MaxBackups:] {
			if err := os.Remove(item.path); err != nil && firstErr == nil {
				firstErr = err
			}
		}
	}
	return firstErr
}

func gzipBackupFile(path string) (string, error) {
	if strings.HasSuffix(path, ".gz") {
		return path, nil
	}
	source, err := os.Open(path)
	if err != nil {
		return "", err
	}

	destination := path + ".gz"
	temp := destination + ".tmp"
	target, err := os.Create(temp)
	if err != nil {
		_ = source.Close()
		return "", err
	}

	gzWriter := gzip.NewWriter(target)
	if _, err = io.Copy(gzWriter, source); err != nil {
		_ = source.Close()
		_ = gzWriter.Close()
		_ = target.Close()
		_ = os.Remove(temp)
		return "", err
	}
	if err = gzWriter.Close(); err != nil {
		_ = source.Close()
		_ = target.Close()
		_ = os.Remove(temp)
		return "", err
	}
	if err = target.Close(); err != nil {
		_ = source.Close()
		_ = os.Remove(temp)
		return "", err
	}
	if err = source.Close(); err != nil {
		_ = os.Remove(temp)
		return "", err
	}
	if err = os.Rename(temp, destination); err != nil {
		_ = os.Remove(temp)
		return "", err
	}
	if err = os.Remove(path); err != nil {
		return "", err
	}
	return destination, nil
}