//go:build darwin

package main

import (
	"slices"

	"golang.org/x/sys/unix"
)

// nonPersistentFilesystems returns the device ID of every mounted
// filesystem that is not persistent, with its type, from the system's
// list of mounted filesystems. The device ID is read with lstat on the
// mount point. Where one filesystem is mounted over another on the same
// mount point, the later one in the list counts. A mount point that
// lstat cannot reach is left out.
func nonPersistentFilesystems() (map[uint64]string, error) {
	// The first call counts the filesystems, the second lists them.
	n, err := unix.Getfsstat(nil, unix.MNT_NOWAIT)
	if err != nil {
		return nil, err
	}

	list := make([]unix.Statfs_t, n)

	n, err = unix.Getfsstat(list, unix.MNT_NOWAIT)
	if err != nil {
		return nil, err
	}

	mounts := make(map[string]string, n)

	for _, st := range list[:n] {
		mounts[unix.ByteSliceToString(st.Mntonname[:])] =
			unix.ByteSliceToString(st.Fstypename[:])
	}

	types := nonPersistentFilesystemTypes()
	devices := make(map[uint64]string)

	for mountPoint, fsType := range mounts {
		if !slices.Contains(types, fsType) {
			continue
		}

		if dev, ok := deviceOfPath(mountPoint); ok {
			devices[dev] = fsType
		}
	}

	return devices, nil
}