docker-compose-backup/internal/backup/retention.go

package backup

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

// RetentionPolicy defines how many backups to keep.
type RetentionPolicy struct {
	Count int // keep at most N most recent backups
	Days  int // also delete backups older than N days (0 = disabled)
}

// ApplyRetention removes old backups from the project's backup directory.
// Returns the number of files removed.
func ApplyRetention(backupDir, projectName string, policy RetentionPolicy) (int, error) {
	dir := filepath.Join(backupDir, projectName)

	entries, err := os.ReadDir(dir)
	if err != nil {
		if os.IsNotExist(err) {
			return 0, nil
		}
		return 0, err
	}

	type fileInfo struct {
		name    string
		modTime time.Time
	}

	var backups []fileInfo
	for _, entry := range entries {
		if entry.IsDir() || !isBackupArchive(projectName, entry.Name()) {
			continue
		}
		info, err := entry.Info()
		if err != nil {
			continue
		}
		backups = append(backups, fileInfo{
			name:    entry.Name(),
			modTime: info.ModTime(),
		})
	}

	if len(backups) == 0 {
		return 0, nil
	}

	// Sort newest-first by modification time.
	sort.Slice(backups, func(i, j int) bool {
		return backups[i].modTime.After(backups[j].modTime)
	})

	removed := 0

	// Enforce count-based retention.
	if policy.Count > 0 && len(backups) > policy.Count {
		for _, b := range backups[policy.Count:] {
			path := filepath.Join(dir, b.name)
			if err := os.Remove(path); err == nil {
				removed++
			}
		}
		// Trim the list for the next check.
		backups = backups[:policy.Count]
	}

	// Enforce age-based retention.
	if policy.Days > 0 {
		cutoff := time.Now().AddDate(0, 0, -policy.Days)
		for _, b := range backups {
			if b.modTime.Before(cutoff) {
				path := filepath.Join(dir, b.name)
				if err := os.Remove(path); err == nil {
					removed++
				}
			}
		}
	}

	return removed, nil
}

func isBackupArchive(projectName, name string) bool {
	return IsBackupArchive(projectName, name)
}

// IsBackupArchive reports whether name is a backup archive for the project.
func IsBackupArchive(projectName, name string) bool {
	return strings.HasPrefix(name, projectName+"-") && strings.HasSuffix(name, ".tar.gz")
}