// drive.go — MS-RDPEFS 设备 I/O 响应的编码器：目录枚举条目
// （[MS-FSCC] FILE_*_DIRECTORY_INFORMATION）、文件/卷信息结构与 UTF-16
// 辅助。时间统一从 JS 侧的毫秒时间戳换算 Windows FILETIME。
package rdpdr

import (
	"encoding/binary"
	"encoding/json"
	"unicode/utf16"
)

// DirEntry 是桥接侧返回的单条目录/文件元数据。
type DirEntry struct {
	Name     string `json:"name"`
	Dir      bool   `json:"dir"`
	Size     int64  `json:"size"`
	Mtime    int64  `json:"mtime"`    // 毫秒时间戳（最后写入）
	Created  int64  `json:"created"`  // 毫秒时间戳（缺省取 Mtime）
	Accessed int64  `json:"accessed"` // 毫秒时间戳（缺省取 Mtime）
}

// FSCC 信息类（本实现支持的子集）。
const (
	FileDirectoryInformation     = 0x00000001
	FileFullDirectoryInformation = 0x00000002
	FileBothDirectoryInformation = 0x00000003
	FileNamesInformation         = 0x0000000C

	FileFsVolumeInformation     = 0x00000001
	FileFsSizeInformation       = 0x00000003
	FileFsDeviceInformation     = 0x00000004
	FileFsAttributeInformation  = 0x00000005
	FileFsFullSizeInformation   = 0x00000007

	FileBasicInformation      = 0x00000004
	FileStandardInformation   = 0x00000005
	FileNetworkOpenInformation = 0x00000022
)

// filetime 把毫秒 Unix 时间戳换算为 Windows FILETIME（100ns，1601 纪元）。
func filetime(ms int64) uint64 {
	const epochDelta = 116444736000000000 // 1601→1970 的 100ns 数
	if ms < 0 {
		ms = 0
	}
	return uint64(ms)*10000 + epochDelta
}

func utf16Bytes(s string) []byte {
	u := utf16.Encode([]rune(s))
	b := make([]byte, 2*len(u))
	for i, v := range u {
		binary.LittleEndian.PutUint16(b[2*i:], v)
	}
	return b
}

func utf16ToString(b []byte) string {
	if len(b)%2 != 0 {
		b = b[:len(b)-1]
	}
	u := make([]uint16, len(b)/2)
	for i := range u {
		u[i] = binary.LittleEndian.Uint16(b[2*i:])
	}
	runes := utf16.Decode(u)
	// 去掉结尾 NUL
	for n := len(runes) - 1; n >= 0; n-- {
		if runes[n] == 0 {
			runes = runes[:n]
		} else {
			break
		}
	}
	return string(runes)
}

// decodeEntries 解析桥接 JSON 数组。
func decodeEntries(jsonStr string) ([]DirEntry, error) {
	var entries []DirEntry
	if err := json.Unmarshal([]byte(jsonStr), &entries); err != nil {
		return nil, err
	}
	for i := range entries {
		fillTimes(&entries[i])
	}
	return entries, nil
}

// decodeEntry 解析桥接 JSON 单对象。
func decodeEntry(jsonStr string) (DirEntry, error) {
	var e DirEntry
	if err := json.Unmarshal([]byte(jsonStr), &e); err != nil {
		return e, err
	}
	fillTimes(&e)
	return e, nil
}

func fillTimes(e *DirEntry) {
	if e.Created == 0 {
		e.Created = e.Mtime
	}
	if e.Accessed == 0 {
		e.Accessed = e.Mtime
	}
}

func (e *DirEntry) attributes() uint32 {
	if e.Dir {
		return FILE_ATTRIBUTE_DIRECTORY
	}
	if e.Size == 0 {
		return FILE_ATTRIBUTE_NORMAL
	}
	return FILE_ATTRIBUTE_NORMAL | FILE_ATTRIBUTE_ARCHIVE
}

// encodeDirEntries 把一批条目编码为 FSCC 目录信息结构链。
// 支持 FileDirectoryInformation(1)/FileBothDirectoryInformation(3)/
// FileNamesInformation(0xC)；其它返回 nil（上层回 NOT_IMPLEMENTED）。
func encodeDirEntries(infoClass uint32, entries []DirEntry) []byte {
	if len(entries) == 0 {
		return []byte{}
	}
	var out []byte
	for i := range entries {
		e := &entries[i]
		name := utf16Bytes(e.Name)
		var raw []byte
		switch infoClass {
		case FileDirectoryInformation:
			// NextEntryOffset(4) FileIndex(4) Creation(8) Access(8) Write(8)
			// Change(8) EndOfFile(8) Allocation(8) Attributes(4) NameLen(4) = 64
			raw = make([]byte, 64+len(name))
			putTimes(raw, 8, e)
			binary.LittleEndian.PutUint64(raw[40:], uint64(e.Size))
			binary.LittleEndian.PutUint64(raw[48:], uint64(e.Size))
			binary.LittleEndian.PutUint32(raw[56:], e.attributes())
			binary.LittleEndian.PutUint32(raw[60:], uint32(len(name)))
			copy(raw[64:], name)
		case FileBothDirectoryInformation:
			// 64 字节同上 + EaSize(4) ShortNameLen(1) ShortName(24) = 93
			raw = make([]byte, 93+len(name))
			putTimes(raw, 8, e)
			binary.LittleEndian.PutUint64(raw[40:], uint64(e.Size))
			binary.LittleEndian.PutUint64(raw[48:], uint64(e.Size))
			binary.LittleEndian.PutUint32(raw[56:], e.attributes())
			binary.LittleEndian.PutUint32(raw[60:], uint32(len(name)))
			raw[68] = 0 // ShortNameLength
			// ShortName[24] 全 0（无短名）
			copy(raw[93:], name)
		case FileNamesInformation:
			// NextEntryOffset(4) FileIndex(4) FileNameLength(4) = 12
			raw = make([]byte, 12+len(name))
			binary.LittleEndian.PutUint32(raw[8:], uint32(len(name)))
			copy(raw[12:], name)
		default:
			return nil
		}
		if i == len(entries)-1 {
			// 末条：NextEntryOffset=0，无需对齐
			binary.LittleEndian.PutUint32(raw[0:], 0)
			out = append(out, raw...)
			continue
		}
		// 非末条：长度 4 字节对齐，补零
		next := (len(raw) + 3) &^ 3
		buf := make([]byte, next)
		copy(buf, raw)
		binary.LittleEndian.PutUint32(buf[0:], uint32(next))
		out = append(out, buf...)
	}
	return out
}

// putTimes 在 off 处写 Creation/Access/Write/Change 四个 FILETIME（32 字节）。
func putTimes(b []byte, off int, e *DirEntry) {
	binary.LittleEndian.PutUint64(b[off:], filetime(e.Created))
	binary.LittleEndian.PutUint64(b[off+8:], filetime(e.Accessed))
	binary.LittleEndian.PutUint64(b[off+16:], filetime(e.Mtime))
	binary.LittleEndian.PutUint64(b[off+24:], filetime(e.Mtime))
}

// encodeFileInfo 编码 QUERY_INFORMATION 响应体（不含 Length 前缀）。
func encodeFileInfo(infoClass uint32, e DirEntry) []byte {
	switch infoClass {
	case FileBasicInformation:
		// Creation(8) Access(8) Write(8) Change(8) Attributes(4) Reserved(4) = 40
		b := make([]byte, 40)
		putTimes(b, 0, &e)
		binary.LittleEndian.PutUint32(b[32:], e.attributes())
		return b
	case FileStandardInformation:
		// AllocationSize(8) EndOfFile(8) NumberOfLinks(4) DeletePending(1) Directory(1) = 22
		b := make([]byte, 22)
		binary.LittleEndian.PutUint64(b[0:], uint64(e.Size))
		binary.LittleEndian.PutUint64(b[8:], uint64(e.Size))
		binary.LittleEndian.PutUint32(b[16:], 1)
		b[20] = 0
		if e.Dir {
			b[21] = 1
		}
		return b
	case FileNetworkOpenInformation:
		// Creation(8) Access(8) Write(8) Change(8) Allocation(8) EndOfFile(8) Attributes(4) = 56
		b := make([]byte, 56)
		putTimes(b, 0, &e)
		binary.LittleEndian.PutUint64(b[32:], uint64(e.Size))
		binary.LittleEndian.PutUint64(b[40:], uint64(e.Size))
		binary.LittleEndian.PutUint32(b[48:], e.attributes())
		return b
	default:
		return nil
	}
}

// encodeVolumeInfo 编码 QUERY_VOLUME_INFORMATION 响应体（不含 Length 前缀）。
func encodeVolumeInfo(infoClass uint32, label string) []byte {
	switch infoClass {
	case FileFsVolumeInformation:
		// VolumeCreationTime(8) SerialNumber(4) LabelLength(4) SupportsObjects(1) Label
		vol := utf16Bytes(label)
		b := make([]byte, 17+len(vol))
		binary.LittleEndian.PutUint32(b[8:], 0x1ABCF2D8) // 任意固定序列号
		binary.LittleEndian.PutUint32(b[12:], uint32(len(vol)))
		copy(b[17:], vol)
		return b
	case FileFsSizeInformation, FileFsFullSizeInformation:
		// TotalAllocationUnits(8) Available(8) SectorsPerUnit(4) BytesPerSector(4) = 24
		// （Win10 服务器挂载设备时常探测 FullSize——缺失会致设备"不支持"）
		b := make([]byte, 24)
		binary.LittleEndian.PutUint64(b[0:], 0x00100000)
		binary.LittleEndian.PutUint64(b[8:], 0x00080000)
		binary.LittleEndian.PutUint32(b[16:], 8)
		binary.LittleEndian.PutUint32(b[20:], 512)
		return b
	case FileFsDeviceInformation:
		// DeviceType(4)=FILE_DEVICE_DISK Characteristics(4) = 8
		b := make([]byte, 8)
		binary.LittleEndian.PutUint32(b[0:], 7)
		return b
	case FileFsAttributeInformation:
		// Attributes(4) MaxComponentLen(4) NameLength(4) Name（"FAT32"，规避
		// 服务端按 NTFS 语义发起的 ACL/重解析点等操作——mstsc/FreeRDP 同款选择）
		fs := utf16Bytes("FAT32")
		b := make([]byte, 12+len(fs))
		binary.LittleEndian.PutUint32(b[0:], 0x00000007) // CASE_SENSITIVE_SEARCH|CASE_PRESERVED_NAMES|UNICODE_ON_DISK
		binary.LittleEndian.PutUint32(b[4:], 255)
		binary.LittleEndian.PutUint32(b[8:], uint32(len(fs)))
		copy(b[12:], fs)
		return b
	default:
		return nil
	}
}