// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// +build windows

package registry

import (
	"errors"
	"io"
	"syscall"
	"unicode/utf16"
	"unsafe"
)

const (
	// Registry value types.
	NONE                       = 0
	SZ                         = 1
	EXPAND_SZ                  = 2
	BINARY                     = 3
	DWORD                      = 4
	DWORD_BIG_ENDIAN           = 5
	LINK                       = 6
	MULTI_SZ                   = 7
	RESOURCE_LIST              = 8
	FULL_RESOURCE_DESCRIPTOR   = 9
	RESOURCE_REQUIREMENTS_LIST = 10
	QWORD                      = 11
)

var (
	// ErrShortBuffer is returned when the buffer was too short for the operation.
	ErrShortBuffer = syscall.ERROR_MORE_DATA

	// ErrNotExist is returned when a registry key or value does not exist.
	ErrNotExist = syscall.ERROR_FILE_NOT_FOUND

	// ErrUnexpectedType is returned by Get*Value when the value's type was unexpected.
	ErrUnexpectedType = errors.New("unexpected key value type")
)

// GetValue retrieves the type and data for the specified value associated
// with an open key k. It fills up buffer buf and returns the retrieved
// byte count n. If buf is too small to fit the stored value it returns
// ErrShortBuffer error along with the required buffer size n.
// If no buffer is provided, it returns true and actual buffer size n.
// If no buffer is provided, GetValue returns the value's type only.
// If the value does not exist, the error returned is ErrNotExist.
//
// GetValue is a low level function. If value's type is known, use the appropriate
// Get*Value function instead.
func (k Key) GetValue(name string, buf []byte) (n int, valtype uint32, err error) {
	pname, err := syscall.UTF16PtrFromString(name)
	if err != nil {
		return 0, 0, err
	}
	var pbuf *byte
	if len(buf) > 0 {
		pbuf = (*byte)(unsafe.Pointer(&buf[0]))
	}
	l := uint32(len(buf))
	err = syscall.RegQueryValueEx(syscall.Handle(k), pname, nil, &valtype, pbuf, &l)
	if err != nil {
		return int(l), valtype, err
	}
	return int(l), valtype, nil
}

func (k Key) getValue(name string, buf []byte) (date []byte, valtype uint32, err error) {
	p, err := syscall.UTF16PtrFromString(name)
	if err != nil {
		return nil, 0, err
	}
	var t uint32
	n := uint32(len(buf))
	for {
		err = syscall.RegQueryValueEx(syscall.Handle(k), p, nil, &t, (*byte)(unsafe.Pointer(&buf[0])), &n)
		if err == nil {
			return buf[:n], t, nil
		}
		if err != syscall.ERROR_MORE_DATA {
			return nil, 0, err
		}
		if n <= uint32(len(buf)) {
			return nil, 0, err
		}
		buf = make([]byte, n)
	}
}

// GetStringValue retrieves the string value for the specified
// value name associated with an open key k. It also returns the value's type.
// If value does not exist, GetStringValue returns ErrNotExist.
// If value is not SZ or EXPAND_SZ, it will return the correct value
// type and ErrUnexpectedType.
func (k Key) GetStringValue(name string) (val string, valtype uint32, err error) {
	data, typ, err2 := k.getValue(name, make([]byte, 64))
	if err2 != nil {
		return "", typ, err2
	}
	switch typ {
	case SZ, EXPAND_SZ:
	default:
		return "", typ, ErrUnexpectedType
	}
	if len(data) == 0 {
		return "", typ, nil
	}
	u := (*[1 << 10]uint16)(unsafe.Pointer(&data[0]))[:]
	return syscall.UTF16ToString(u), typ, nil
}

// ExpandString expands environment-variable strings and replaces
// them with the values defined for the current user.
// Use ExpandString to expand EXPAND_SZ strings.
func ExpandString(value string) (string, error) {
	if value == "" {
		return "", nil
	}
	p, err := syscall.UTF16PtrFromString(value)
	if err != nil {
		return "", err
	}
	r := make([]uint16, 100)
	for {
		n, err := expandEnvironmentStrings(p, &r[0], uint32(len(r)))
		if err != nil {
			return "", err
		}
		if n <= uint32(len(r)) {
			u := (*[1 << 15]uint16)(unsafe.Pointer(&r[0]))[:]
			return syscall.UTF16ToString(u), nil
		}
		r = make([]uint16, n)
	}
}

// GetStringsValue retrieves the []string value for the specified
// value name associated with an open key k. It also returns the value's type.
// If value does not exist, GetStringsValue returns ErrNotExist.
// If value is not MULTI_SZ, it will return the correct value
// type and ErrUnexpectedType.
func (k Key) GetStringsValue(name string) (val []string, valtype uint32, err error) {
	data, typ, err2 := k.getValue(name, make([]byte, 64))
	if err2 != nil {
		return nil, typ, err2
	}
	if typ != MULTI_SZ {
		return nil, typ, ErrUnexpectedType
	}
	if len(data) == 0 {
		return nil, typ, nil
	}
	p := (*[1 << 24]uint16)(unsafe.Pointer(&data[0]))[:len(data)/2]
	if len(p) == 0 {
		return nil, typ, nil
	}
	if p[len(p)-1] == 0 {
		p = p[:len(p)-1] // remove terminating null
	}
	val = make([]string, 0, 5)
	from := 0
	for i, c := range p {
		if c == 0 {
			val = append(val, string(utf16.Decode(p[from:i])))
			from = i + 1
		}
	}
	return val, typ, nil
}

// GetIntegerValue retrieves the integer value for the specified
// value name associated with an open key k. It also returns the value's type.
// If value does not exist, GetIntegerValue returns ErrNotExist.
// If value is not DWORD or QWORD, it will return the correct value
// type and ErrUnexpectedType.
func (k Key) GetIntegerValue(name string) (val uint64, valtype uint32, err error) {
	data, typ, err2 := k.getValue(name, make([]byte, 8))
	if err2 != nil {
		return 0, typ, err2
	}
	switch typ {
	case DWORD:
		if len(data) != 4 {
			return 0, typ, errors.New("DWORD value is not 4 bytes long")
		}
		return uint64(*(*uint32)(unsafe.Pointer(&data[0]))), DWORD, nil
	case QWORD:
		if len(data) != 8 {
			return 0, typ, errors.New("QWORD value is not 8 bytes long")
		}
		return uint64(*(*uint64)(unsafe.Pointer(&data[0]))), QWORD, nil
	default:
		return 0, typ, ErrUnexpectedType
	}
}

// GetBinaryValue retrieves the binary value for the specified
// value name associated with an open key k. It also returns the value's type.
// If value does not exist, GetBinaryValue returns ErrNotExist.
// If value is not BINARY, it will return the correct value
// type and ErrUnexpectedType.
func (k Key) GetBinaryValue(name string) (val []byte, valtype uint32, err error) {
	data, typ, err2 := k.getValue(name, make([]byte, 64))
	if err2 != nil {
		return nil, typ, err2
	}
	if typ != BINARY {
		return nil, typ, ErrUnexpectedType
	}
	return data, typ, nil
}

func (k Key) setValue(name string, valtype uint32, data []byte) error {
	p, err := syscall.UTF16PtrFromString(name)
	if err != nil {
		return err
	}
	if len(data) == 0 {
		return regSetValueEx(syscall.Handle(k), p, 0, valtype, nil, 0)
	}
	return regSetValueEx(syscall.Handle(k), p, 0, valtype, &data[0], uint32(len(data)))
}

// SetDWordValue sets the data and type of a name value
// under key k to value and DWORD.
func (k Key) SetDWordValue(name string, value uint32) error {
	return k.setValue(name, DWORD, (*[4]byte)(unsafe.Pointer(&value))[:])
}

// SetQWordValue sets the data and type of a name value
// under key k to value and QWORD.
func (k Key) SetQWordValue(name string, value uint64) error {
	return k.setValue(name, QWORD, (*[8]byte)(unsafe.Pointer(&value))[:])
}

func (k Key) setStringValue(name string, valtype uint32, value string) error {
	v, err := syscall.UTF16FromString(value)
	if err != nil {
		return err
	}
	buf := (*[1 << 10]byte)(unsafe.Pointer(&v[0]))[:len(v)*2]
	return k.setValue(name, valtype, buf)
}

// SetStringValue sets the data and type of a name value
// under key k to value and SZ. The value must not contain a zero byte.
func (k Key) SetStringValue(name, value string) error {
	return k.setStringValue(name, SZ, value)
}

// SetExpandStringValue sets the data and type of a name value
// under key k to value and EXPAND_SZ. The value must not contain a zero byte.
func (k Key) SetExpandStringValue(name, value string) error {
	return k.setStringValue(name, EXPAND_SZ, value)
}

// SetStringsValue sets the data and type of a name value
// under key k to value and MULTI_SZ. The value strings
// must not contain a zero byte.
func (k Key) SetStringsValue(name string, value []string) error {
	ss := ""
	for _, s := range value {
		for i := 0; i < len(s); i++ {
			if s[i] == 0 {
				return errors.New("string cannot have 0 inside")
			}
		}
		ss += s + "\x00"
	}
	v := utf16.Encode([]rune(ss + "\x00"))
	buf := (*[1 << 10]byte)(unsafe.Pointer(&v[0]))[:len(v)*2]
	return k.setValue(name, MULTI_SZ, buf)
}

// SetBinaryValue sets the data and type of a name value
// under key k to value and BINARY.
func (k Key) SetBinaryValue(name string, value []byte) error {
	return k.setValue(name, BINARY, value)
}

// DeleteValue removes a named value from the key k.
func (k Key) DeleteValue(name string) error {
	return regDeleteValue(syscall.Handle(k), syscall.StringToUTF16Ptr(name))
}

// ReadValueNames returns the value names of key k.
// The parameter n controls the number of returned names,
// analogous to the way os.File.Readdirnames works.
func (k Key) ReadValueNames(n int) ([]string, error) {
	ki, err := k.Stat()
	if err != nil {
		return nil, err
	}
	names := make([]string, 0, ki.ValueCount)
	buf := make([]uint16, ki.MaxValueNameLen+1) // extra room for terminating null character
loopItems:
	for i := uint32(0); ; i++ {
		if n > 0 {
			if len(names) == n {
				return names, nil
			}
		}
		l := uint32(len(buf))
		for {
			err := regEnumValue(syscall.Handle(k), i, &buf[0], &l, nil, nil, nil, nil)
			if err == nil {
				break
			}
			if err == syscall.ERROR_MORE_DATA {
				println(len(buf), l)
				// Double buffer size and try again.
				l = uint32(2 * len(buf))
				buf = make([]uint16, l)
				continue
			}
			if err == _ERROR_NO_MORE_ITEMS {
				break loopItems
			}
			return names, err
		}
		names = append(names, syscall.UTF16ToString(buf[:l]))
	}
	if n > len(names) {
		return names, io.EOF
	}
	return names, nil
}
