// SPDX-FileCopyrightText: 2026 LINUXexpert-org
// SPDX-License-Identifier: GPL-3.0-or-later

package backup

import (
	"fmt"
	"os"
)

// PreserveBinary moves the currently-installed binary aside to
// "<binaryPath>.v<sourceVersion>" so cutover can install the new one at the
// original path while the exact old binary stays on disk - an operator
// putting the machine back by hand needs it, and re-downloading a specific
// old release is not something to be doing under pressure. It never deletes
// the old binary, and it's idempotent: if a prior attempt at this run
// already preserved it, calling this again just returns the existing
// preserved path rather than erroring on a missing source file.
func PreserveBinary(binaryPath, sourceVersion string) (preservedPath string, err error) {
	if sourceVersion == "" {
		return "", fmt.Errorf("backup: cannot preserve %s without a source version to suffix it with", binaryPath)
	}
	preservedPath = binaryPath + ".v" + sourceVersion

	if _, statErr := os.Stat(preservedPath); statErr == nil {
		return preservedPath, nil
	} else if !os.IsNotExist(statErr) {
		return "", fmt.Errorf("backup: stat %s: %w", preservedPath, statErr)
	}

	if err := os.Rename(binaryPath, preservedPath); err != nil {
		return "", fmt.Errorf("backup: preserve %s as %s: %w", binaryPath, preservedPath, err)
	}
	return preservedPath, nil
}