package snapshot

import (
	"os"
	"syscall"
	"time"
)

// getCTime extracts the inode change time (ctime) from os.FileInfo.
//
// On Linux, this returns the inode change time (Ctim) from the underlying
// syscall.Stat_t. Linux ctime is updated whenever file metadata (permissions,
// ownership, link count) or content changes. It is NOT the file creation
// (birth) time.
//
// Note: Linux ext4 (kernel 4.11+) and btrfs do track birth time via the
// statx() syscall, but this is not exposed through Go's os.FileInfo.Sys().
// The inode change time is the best available approximation through standard
// Go APIs.
//
// Falls back to modification time if the underlying Sys() data is not a
// *syscall.Stat_t (e.g. when using in-memory filesystems for testing).
func getCTime(info os.FileInfo) time.Time {
	stat, ok := info.Sys().(*syscall.Stat_t)
	if !ok {
		return info.ModTime()
	}
	return time.Unix(stat.Ctim.Sec, stat.Ctim.Nsec).UTC()
}