// 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 syscall

import (
	"sync"
)

// An Error can represent any printable error condition.
type Error interface {
	String() string
}

// Errno is the Windows error number.
type Errno uint64

func (e Errno) String() string { return Errstr(int(e)) }

// DLLError describes reasons for DLL load failures.
type DLLError struct {
	Errno   Errno
	ObjName string
	Msg     string
}

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

// Implemented in ../runtime/windows/syscall.goc.
func Syscall(trap, nargs, a1, a2, a3 uintptr) (r1, r2, err uintptr)
func Syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr)
func Syscall9(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2, err uintptr)
func Syscall12(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12 uintptr) (r1, r2, err uintptr)
func loadlibrary(filename *uint16) (handle, err uintptr)
func getprocaddress(handle uintptr, procname *uint8) (proc, err uintptr)

// A DLL implements access to a single DLL.
type DLL struct {
	Name   string
	Handle Handle
}

// LoadDLL loads DLL file into memory.
func LoadDLL(name string) (dll *DLL, err Error) {
	h, e := loadlibrary(StringToUTF16Ptr(name))
	if e != 0 {
		return nil, &DLLError{
			Errno:   Errno(e),
			ObjName: name,
			Msg:     "Failed to load " + name + ": " + Errstr(int(e)),
		}
	}
	d := &DLL{
		Name:   name,
		Handle: 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) {
	a, e := getprocaddress(uintptr(d.Handle), StringBytePtr(name))
	if e != 0 {
		return nil, &DLLError{
			Errno:   Errno(e),
			ObjName: name,
			Msg:     "Failed to find " + name + " procedure in " + d.Name + ": " + Errstr(int(e)),
		}
	}
	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
}

// Release unloads DLL d from memory.
func (d *DLL) Release() (err Errno) {
	return Errno(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
}

// Call executes procedure p with arguments a.
func (p *Proc) Call(a ...uintptr) (r1, r2, err uintptr) {
	switch len(a) {
	case 0:
		return Syscall(p.Addr(), uintptr(len(a)), 0, 0, 0)
	case 1:
		return Syscall(p.Addr(), uintptr(len(a)), a[0], 0, 0)
	case 2:
		return Syscall(p.Addr(), uintptr(len(a)), a[0], a[1], 0)
	case 3:
		return Syscall(p.Addr(), uintptr(len(a)), a[0], a[1], a[2])
	case 4:
		return Syscall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], 0, 0)
	case 5:
		return Syscall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], 0)
	case 6:
		return Syscall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5])
	case 7:
		return 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 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 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 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 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 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])
	default:
		panic("Call " + p.Name + " with too many arguments " + itoa(len(a)) + ".")
	}
	return
}

// 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 {
	mu   sync.Mutex
	dll  *DLL // non nil once DLL is loaded
	Name string
}

// 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 {
	if d.dll == nil {
		d.mu.Lock()
		defer d.mu.Unlock()
		if d.dll == nil {
			dll, e := LoadDLL(d.Name)
			if e != nil {
				return e
			}
			d.dll = 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}
}

// A LazyProc implements access to a procedure inside a LazyDLL.
// It delays the lookup until the Addr method is called.
type LazyProc struct {
	mu   sync.Mutex
	Name string
	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 {
	if 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
			}
			p.proc = 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.
func (p *LazyProc) Addr() uintptr {
	p.mustFind()
	return p.proc.Addr()
}

// Call executes procedure p with arguments a.
func (p *LazyProc) Call(a ...uintptr) (r1, r2, err uintptr) {
	p.mustFind()
	return p.proc.Call(a...)
}