package snapshot

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

// fileCTime returns the inode change time on Linux.
//
// On Linux, "ctime" refers to the inode change time — the last time the
// file's metadata (permissions, ownership, link count, etc.) was modified.
// This is NOT the file creation time; Linux did not expose birth time until
// the statx(2) syscall was added in kernel 4.11, and Go's syscall package
// does not yet surface it.
//
// This differs from macOS/Darwin where "ctime" means birth time (file
// creation time). See ctime_darwin.go for details.
//
// If the underlying stat information is unavailable (e.g. when using a
// virtual filesystem like afero.MemMapFs), this falls back to mtime.
func fileCTime(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()
}