"errors"

type DirEntry struct {
	IsDirectory bool
	Name        string
	Encoding    string
	Inode       *Block
}
func dirEntry(data []byte) ([]byte, DirEntry, error) {
	var d DirEntry
	var err error
	data, d.IsDirectory, err = mapValue(uint16LE, func(n uint16) bool {
		return n&0x200 != 0
	})(data)
	if err != err {
		return data, d, err
	}
	_, _, err = tuple(
		assign(&d.Name, toString(lengthData(uint64LE))),
		assign(&d.Encoding, mapValue(option(toString(lengthData(uint64LE))), func(p *string) string {
			if p == nil {
				return ""
			}
			return *p
		})),
	)(data)
	if err != nil {
		d.Name = string(data)
	}
	return nil, d, nil
}
func ReadDir(dirInode *Block) ([]DirEntry, error) {
	var entries []DirEntry
	for _, e := range dirInode.Edges {
		if e.Flag&EdgeFlagsDeleted != 0 {
			continue
		}
		if e.Flag&EdgeFlagsFolder == 0 {
			return nil, errors.New("ReadDir: found an edge that doesn't have Folder flag set")
		}
		b := e.To
		_, entry, err := dirEntry(b.Content)
		if err != nil {
			return nil, fmt.Errorf("not a valid directory entry: %q", b.Content)
		}
		for _, inodeEdge := range b.Edges {
			if inodeEdge.Flag&EdgeFlagsDeleted != 0 {
				continue
			}
			if inodeEdge.Flag&EdgeFlagsFolder == 0 {
				return nil, fmt.Errorf("directory entry for %s has an edge without Folder flag", entry.Name)
			}
			entry.Inode = inodeEdge.To
			break
		}
		if entry.Inode == nil {
			return nil, fmt.Errorf("directory entry for %s has no inode", entry.Name)
		}
		entries = append(entries, entry)
	}
	return entries, nil
}

func uint16LE(input []byte) ([]byte, uint16, error) {
	if len(input) < 2 {
		return input, 0, fmt.Errorf("need 2 bytes to parse a 16-bit integer; only got %d", len(input))
	}
	return input[2:], binary.LittleEndian.Uint16(input), nil
}