// Package backup builds a downloadable, optionally encrypted snapshot of
// the jsondb directory (servers, clients, users, settings - everything
// needed to restore this installation). It never transmits data anywhere
// on its own; the archive is only ever returned to an authenticated admin
// as an HTTP download, never uploaded automatically.
package backup

import (
	"archive/tar"
	"bytes"
	"compress/gzip"
	"os"
	"path/filepath"
)

// BuildArchive tars+gzips every regular file under dbPath into memory,
// preserving paths relative to dbPath so restoring means extracting into a
// fresh, empty db directory.
func BuildArchive(dbPath string) ([]byte, error) {
	var buf bytes.Buffer
	gzw := gzip.NewWriter(&buf)
	tw := tar.NewWriter(gzw)

	err := filepath.Walk(dbPath, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if info.IsDir() {
			return nil
		}
		relPath, err := filepath.Rel(dbPath, path)
		if err != nil {
			return err
		}
		data, err := os.ReadFile(path)
		if err != nil {
			return err
		}
		header := &tar.Header{
			Name:    relPath,
			Mode:    int64(info.Mode().Perm()),
			Size:    int64(len(data)),
			ModTime: info.ModTime(),
		}
		if err := tw.WriteHeader(header); err != nil {
			return err
		}
		_, err = tw.Write(data)
		return err
	})
	if err != nil {
		return nil, err
	}
	if err := tw.Close(); err != nil {
		return nil, err
	}
	if err := gzw.Close(); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}