//nolint:testpackage // exercises the unexported deviceNumberFromStat
package snapshot

import (
	"os"
	"path/filepath"
	"testing"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

// The device number a real backup reads is the same for two entries of
// one directory and differs between two filesystems. Without it no
// mount point is ever found. See
// https://git.eeqj.de/sneak/vaultik/issues/395.
func TestDeviceNumberFromStat(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	file := filepath.Join(dir, "file.txt")
	require.NoError(t, os.WriteFile(file, nil, 0o600))

	deviceOf := func(path string) uint64 {
		t.Helper()

		info, err := os.Stat(path)
		require.NoError(t, err)

		device, ok := deviceNumberFromStat(info)
		require.True(t, ok, "no device number read for %s", path)

		return device
	}

	assert.Equal(t, deviceOf(dir), deviceOf(file))

	// /dev is a different filesystem from the temp dir on Linux, macOS and in Docker.
	assert.NotEqual(t, deviceOf(dir), deviceOf("/dev"))
}