package database

import (
	"os"
	"path/filepath"
	"slices"
	"strings"
	"time"
)

type backupFile struct {
	path     string
	modified time.Time
}

func newBackupTarget(directory string, now time.Time, extension string) (string, error) {
	if err := os.MkdirAll(directory, os.ModePerm); err != nil {
		return "", err
	}
	target := filepath.Join(directory, backupFilePrefix+now.UTC().Format(backupTimeLayout)+extension)
	if _, err := os.Stat(target); err == nil {
		return "", errBackupExists
	}
	return target, nil
}

func pruneBackups(directory string, extension string) error {
	entries, err := os.ReadDir(directory)
	if err != nil {
		return err
	}
	files := make([]backupFile, 0, len(entries))
	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), extension) {
			continue
		}
		info, err := entry.Info()
		if err != nil {
			return err
		}
		files = append(files, backupFile{path: filepath.Join(directory, entry.Name()), modified: info.ModTime()})
	}
	slices.SortFunc(files, func(a, b backupFile) int {
		if byTime := b.modified.Compare(a.modified); byTime != 0 {
			return byTime
		}
		return strings.Compare(b.path, a.path)
	})
	for _, stale := range files[min(backupsToKeep, len(files)):] {
		if err := os.Remove(stale.path); err != nil {
			return err
		}
	}
	return nil
}