// Copyright 2011 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.

package windows

import (

	"sync"

	"sync/atomic"

	"syscall"

	"unsafe"

)

// We need to use LoadLibrary and GetProcAddress from the Go runtime, because

// the these symbols are loaded by the system linker and are required to

// dynamically load additional symbols. Note that in the Go runtime, these

// return syscall.Handle and syscall.Errno, but these are the same, in fact,

// as windows.Handle and windows.Errno, and we intend to keep these the same.

//go:linkname syscall_loadlibrary syscall.loadlibrary

func syscall_loadlibrary(filename *uint16) (handle Handle, err Errno)

//go:linkname syscall_getprocaddress syscall.getprocaddress

func syscall_getprocaddress(handle Handle, procname *uint8) (proc uintptr, err Errno)

// DLLError describes reasons for DLL load failures.

type DLLError struct {

	Err     error

	ObjName string

	Msg     string

}

func (e *DLLError) Error() string { return e.Msg }

func (e *DLLError) Unwrap() error { return e.Err }

// A DLL implements access to a single DLL.

type DLL struct {

	Name   string

	Handle Handle

}

// LoadDLL loads DLL file into memory.

//

// Warning: using LoadDLL without an absolute path name is subject to

// DLL preloading attacks. To safely load a system DLL, use LazyDLL

// with System set to true, or use LoadLibraryEx directly.

func LoadDLL(name string) (dll *DLL, err error) {

	namep, err := UTF16PtrFromString(name)

	if err != nil {

		return nil, err

	}

	h, e := syscall_loadlibrary(namep)

	if e != 0 {

		return nil, &DLLError{

			Err:     e,

			ObjName: name,

			Msg:     "Failed to load " + name + ": " + e.Error(),

		}

	}

	d := &DLL{

		Name:   name,

		Handle: h,

	}

	return d, nil

}

// MustLoadDLL is like LoadDLL but panics if load operation failes.

func MustLoadDLL(name string) *DLL {

	d, e := LoadDLL(name)

	if e != nil {

		panic(e)

	}

	return d

}

// FindProc searches DLL d for procedure named name and returns *Proc

// if found. It returns an error if search fails.

func (d *DLL) FindProc(name string) (proc *Proc, err error) {

	namep, err := BytePtrFromString(name)

	if err != nil {

		return nil, err

	}

	a, e := syscall_getprocaddress(d.Handle, namep)

	if e != 0 {

		return nil, &DLLError{

			Err:     e,

			ObjName: name,

			Msg:     "Failed to find " + name + " procedure in " + d.Name + ": " + e.Error(),

		}

	}

	p := &Proc{

		Dll:  d,

		Name: name,

		addr: a,

	}

	return p, nil

}

// MustFindProc is like FindProc but panics if search fails.

func (d *DLL) MustFindProc(name string) *Proc {

	p, e := d.FindProc(name)

	if e != nil {

		panic(e)

	}

	return p

}

// FindProcByOrdinal searches DLL d for procedure by ordinal and returns *Proc

// if found. It returns an error if search fails.

func (d *DLL) FindProcByOrdinal(ordinal uintptr) (proc *Proc, err error) {

	a, e := GetProcAddressByOrdinal(d.Handle, ordinal)

	name := "#" + itoa(int(ordinal))

	if e != nil {

		return nil, &DLLError{

			Err:     e,

			ObjName: name,

			Msg:     "Failed to find " + name + " procedure in " + d.Name + ": " + e.Error(),

		}

	}

	p := &Proc{

		Dll:  d,

		Name: name,

		addr: a,

	}

	return p, nil

}

// MustFindProcByOrdinal is like FindProcByOrdinal but panics if search fails.

func (d *DLL) MustFindProcByOrdinal(ordinal uintptr) *Proc {

	p, e := d.FindProcByOrdinal(ordinal)

	if e != nil {

		panic(e)

	}

	return p

}

// Release unloads DLL d from memory.

func (d *DLL) Release() (err error) {

	return FreeLibrary(d.Handle)

}

// A Proc implements access to a procedure inside a DLL.

type Proc struct {

	Dll  *DLL

	Name string

	addr uintptr

}

// Addr returns the address of the procedure represented by p.

// The return value can be passed to Syscall to run the procedure.

func (p *Proc) Addr() uintptr {

	return p.addr

}

//go:uintptrescapes

// Call executes procedure p with arguments a. It will panic, if more than 15 arguments

// are supplied.

//

// The returned error is always non-nil, constructed from the result of GetLastError.

// Callers must inspect the primary return value to decide whether an error occurred

// (according to the semantics of the specific function being called) before consulting

// the error. The error will be guaranteed to contain windows.Errno.

func (p *Proc) Call(a ...uintptr) (r1, r2 uintptr, lastErr error) {

	switch len(a) {

	case 0:

		return syscall.Syscall(p.Addr(), uintptr(len(a)), 0, 0, 0)

	case 1:

		return syscall.Syscall(p.Addr(), uintptr(len(a)), a[0], 0, 0)

	case 2:

		return syscall.Syscall(p.Addr(), uintptr(len(a)), a[0], a[1], 0)

	case 3:

		return syscall.Syscall(p.Addr(), uintptr(len(a)), a[0], a[1], a[2])

	case 4:

		return syscall.Syscall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], 0, 0)

	case 5:

		return syscall.Syscall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], 0)

	case 6:

		return syscall.Syscall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5])

	case 7:

		return syscall.Syscall9(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], 0, 0)

	case 8:

		return syscall.Syscall9(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], 0)

	case 9:

		return syscall.Syscall9(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8])

	case 10:

		return syscall.Syscall12(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], 0, 0)

	case 11:

		return syscall.Syscall12(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], 0)

	case 12:

		return syscall.Syscall12(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], a[11])

	case 13:

		return syscall.Syscall15(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], a[11], a[12], 0, 0)

	case 14:

		return syscall.Syscall15(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], a[11], a[12], a[13], 0)

	case 15:

		return syscall.Syscall15(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], a[11], a[12], a[13], a[14])

	default:

		panic("Call " + p.Name + " with too many arguments " + itoa(len(a)) + ".")

	}

}

// A LazyDLL implements access to a single DLL.

// It will delay the load of the DLL until the first

// call to its Handle method or to one of its

// LazyProc's Addr method.

type LazyDLL struct {

	Name string

	// System determines whether the DLL must be loaded from the

	// Windows System directory, bypassing the normal DLL search

	// path.

	System bool

	mu  sync.Mutex

	dll *DLL // non nil once DLL is loaded

}

// Load loads DLL file d.Name into memory. It returns an error if fails.

// Load will not try to load DLL, if it is already loaded into memory.

func (d *LazyDLL) Load() error {

	// Non-racy version of:

	// if d.dll != nil {

	if atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&d.dll))) != nil {

		return nil

	}

	d.mu.Lock()

	defer d.mu.Unlock()

	if d.dll != nil {

		return nil

	}

	// kernel32.dll is special, since it's where LoadLibraryEx comes from.

	// The kernel already special-cases its name, so it's always

	// loaded from system32.

	var dll *DLL

	var err error

	if d.Name == "kernel32.dll" {

		dll, err = LoadDLL(d.Name)

	} else {

		dll, err = loadLibraryEx(d.Name, d.System)

	}

	if err != nil {

		return err

	}

	// Non-racy version of:

	// d.dll = dll

	atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&d.dll)), unsafe.Pointer(dll))

	return nil

}

// mustLoad is like Load but panics if search fails.

func (d *LazyDLL) mustLoad() {

	e := d.Load()

	if e != nil {

		panic(e)

	}

}

// Handle returns d's module handle.

func (d *LazyDLL) Handle() uintptr {

	d.mustLoad()

	return uintptr(d.dll.Handle)

}

// NewProc returns a LazyProc for accessing the named procedure in the DLL d.

func (d *LazyDLL) NewProc(name string) *LazyProc {

	return &LazyProc{l: d, Name: name}

}

// NewLazyDLL creates new LazyDLL associated with DLL file.

func NewLazyDLL(name string) *LazyDLL {

	return &LazyDLL{Name: name}

}

// NewLazySystemDLL is like NewLazyDLL, but will only

// search Windows System directory for the DLL if name is

// a base name (like "advapi32.dll").

func NewLazySystemDLL(name string) *LazyDLL {

	return &LazyDLL{Name: name, System: true}

}

// A LazyProc implements access to a procedure inside a LazyDLL.

// It delays the lookup until the Addr method is called.

type LazyProc struct {

	Name string

	mu   sync.Mutex

	l    *LazyDLL

	proc *Proc

}

// Find searches DLL for procedure named p.Name. It returns

// an error if search fails. Find will not search procedure,

// if it is already found and loaded into memory.

func (p *LazyProc) Find() error {

	// Non-racy version of:

	// if p.proc == nil {

	if atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&p.proc))) == nil {

		p.mu.Lock()

		defer p.mu.Unlock()

		if p.proc == nil {

			e := p.l.Load()

			if e != nil {

				return e

			}

			proc, e := p.l.dll.FindProc(p.Name)

			if e != nil {

				return e

			}

			// Non-racy version of:

			// p.proc = proc

			atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&p.proc)), unsafe.Pointer(proc))

		}

	}

	return nil

}

// mustFind is like Find but panics if search fails.

func (p *LazyProc) mustFind() {

	e := p.Find()

	if e != nil {

		panic(e)

	}

}

// Addr returns the address of the procedure represented by p.

// The return value can be passed to Syscall to run the procedure.

// It will panic if the procedure cannot be found.

func (p *LazyProc) Addr() uintptr {

	p.mustFind()

	return p.proc.Addr()

}

//go:uintptrescapes

// Call executes procedure p with arguments a. It will panic, if more than 15 arguments

// are supplied. It will also panic if the procedure cannot be found.

//

// The returned error is always non-nil, constructed from the result of GetLastError.

// Callers must inspect the primary return value to decide whether an error occurred

// (according to the semantics of the specific function being called) before consulting

// the error. The error will be guaranteed to contain windows.Errno.

func (p *LazyProc) Call(a ...uintptr) (r1, r2 uintptr, lastErr error) {

	p.mustFind()

	return p.proc.Call(a...)

}

var canDoSearchSystem32Once struct {

	sync.Once

	v bool

}

func initCanDoSearchSystem32() {

	// https://msdn.microsoft.com/en-us/library/ms684179(v=vs.85).aspx says:

	// "Windows 7, Windows Server 2008 R2, Windows Vista, and Windows

	// Server 2008: The LOAD_LIBRARY_SEARCH_* flags are available on

	// systems that have KB2533623 installed. To determine whether the

	// flags are available, use GetProcAddress to get the address of the

	// AddDllDirectory, RemoveDllDirectory, or SetDefaultDllDirectories

	// function. If GetProcAddress succeeds, the LOAD_LIBRARY_SEARCH_*

	// flags can be used with LoadLibraryEx."

	canDoSearchSystem32Once.v = (modkernel32.NewProc("AddDllDirectory").Find() == nil)

}

func canDoSearchSystem32() bool {

	canDoSearchSystem32Once.Do(initCanDoSearchSystem32)

	return canDoSearchSystem32Once.v

}

func isBaseName(name string) bool {

	for _, c := range name {

		if c == ':' || c == '/' || c == '\\' {

			return false

		}

	}

	return true

}

// loadLibraryEx wraps the Windows LoadLibraryEx function.

//

// See https://msdn.microsoft.com/en-us/library/windows/desktop/ms684179(v=vs.85).aspx

//

// If name is not an absolute path, LoadLibraryEx searches for the DLL

// in a variety of automatic locations unless constrained by flags.

// See: https://msdn.microsoft.com/en-us/library/ff919712%28VS.85%29.aspx

func loadLibraryEx(name string, system bool) (*DLL, error) {