//go:build windows

package win32

import (
	"fmt"
	"syscall"
	"time"
	"unicode/utf16"
	"unsafe"

	"golang.org/x/sys/windows"
)

// SetClipboardText copies s onto the Windows clipboard as CF_UNICODETEXT.
// OpenClipboard may transiently fail if another process holds the
// clipboard; we retry a few times before giving up.
func SetClipboardText(s string) error {
	const cfUnicodeText = 13
	utf := utf16.Encode([]rune(s + "\x00"))
	size := len(utf) * 2

	hMem, _, e := procGlobalAlloc.Call(0x0042 /*GMEM_MOVEABLE|GMEM_ZEROINIT*/, uintptr(size))
	if hMem == 0 {
		return fmt.Errorf("win32: GlobalAlloc: %w", e)
	}
	dst, _, _ := procGlobalLock.Call(hMem)
	if dst == 0 {
		procGlobalFree.Call(hMem)
		return fmt.Errorf("win32: GlobalLock failed")
	}
	dstSlice := unsafe.Slice((*uint16)(unsafe.Pointer(dst)), len(utf))
	copy(dstSlice, utf)
	procGlobalUnlock.Call(hMem)

	if err := openClipboardRetry(0); err != nil {
		procGlobalFree.Call(hMem)
		return err
	}
	procEmptyClipboard.Call()
	r, _, ce := procSetClipboardData.Call(cfUnicodeText, hMem)
	if r == 0 {
		procCloseClipboard.Call()
		procGlobalFree.Call(hMem)
		return fmt.Errorf("win32: SetClipboardData: %w", ce)
	}
	// Ownership of hMem transfers to the system on success — do not free.
	procCloseClipboard.Call()
	return nil
}

func openClipboardRetry(hwnd uintptr) error {
	var last error
	for i := 0; i < 8; i++ {
		r, _, e := procOpenClipboard.Call(hwnd)
		if r != 0 {
			return nil
		}
		last = e
		time.Sleep(20 * time.Millisecond)
	}
	return fmt.Errorf("win32: OpenClipboard: %w", last)
}

// GetForegroundWindow returns the HWND that currently has keyboard
// focus. Use this to remember the target window before the user clicks
// into winauth-go (which itself becomes foreground and would otherwise
// receive injected keystrokes).
func GetForegroundWindow() uintptr {
	r, _, _ := procGetForegroundWindow.Call()
	return r
}

// FocusWindow restores hwnd to the foreground. Hits the well-known
// SetForegroundWindow restriction (only the foreground process may
// hand focus to another); we work around it by attaching to the target
// thread's input queue briefly, the trick documented in MSDN's
// "AttachThreadInput" page.
func FocusWindow(hwnd uintptr) error {
	if hwnd == 0 {
		return fmt.Errorf("win32: FocusWindow: nil hwnd")
	}
	curTID, _, _ := procGetCurrentThreadId.Call()
	targetTID, _, _ := procGetWindowThreadProcessId.Call(hwnd, 0)
	if targetTID == 0 {
		return fmt.Errorf("win32: GetWindowThreadProcessId failed")
	}
	if curTID != targetTID {
		procAttachThreadInput.Call(curTID, targetTID, 1)
		defer procAttachThreadInput.Call(curTID, targetTID, 0)
	}
	procSetForegroundWindowProc.Call(hwnd)
	procShowWindowProc.Call(hwnd, 9 /*SW_RESTORE*/)
	procBringWindowToTop.Call(hwnd)
	return nil
}

// TypeUnicode injects s as Unicode characters using SendInput KEYEVENTF_UNICODE.
// Special characters in s pass through transparently; no translation
// of newlines / tabs happens. If you need an Enter at the end, pass
// "\n" and let the caller append it explicitly.
func TypeUnicode(s string) error {
	if s == "" {
		return nil
	}
	utf := utf16.Encode([]rune(s))
	// Each rune becomes 2 inputs (keydown + keyup).
	inputs := make([]inputUnion, 0, len(utf)*2)
	for _, u := range utf {
		inputs = append(inputs,
			makeUnicodeInput(u, false),
			makeUnicodeInput(u, true),
		)
	}
	r, _, e := procSendInput.Call(
		uintptr(len(inputs)),
		uintptr(unsafe.Pointer(&inputs[0])),
		unsafe.Sizeof(inputs[0]),
	)
	if int(r) != len(inputs) {
		if errno, ok := e.(syscall.Errno); ok && errno != 0 {
			return fmt.Errorf("win32: SendInput: sent %d/%d: %w", r, len(inputs), errno)
		}
		return fmt.Errorf("win32: SendInput: sent %d/%d", r, len(inputs))
	}
	return nil
}

// PressKey injects a single virtual-key down+up pair (e.g. VK_RETURN).
func PressKey(vk uint16) error {
	inputs := [2]inputUnion{
		makeVKInput(vk, false),
		makeVKInput(vk, true),
	}
	r, _, e := procSendInput.Call(
		uintptr(len(inputs)),
		uintptr(unsafe.Pointer(&inputs[0])),
		unsafe.Sizeof(inputs[0]),
	)
	if int(r) != len(inputs) {
		if errno, ok := e.(syscall.Errno); ok && errno != 0 {
			return fmt.Errorf("win32: SendInput (vk): %w", errno)
		}
		return fmt.Errorf("win32: SendInput (vk): short send")
	}
	return nil
}

// VK_RETURN is exposed for callers that want to press Enter after Auto-type.
const VK_RETURN uint16 = 0x0D

// -----------------------------------------------------------------------------
// raw syscalls + structs

var (
	procOpenClipboard            = user32.NewProc("OpenClipboard")
	procCloseClipboard           = user32.NewProc("CloseClipboard")
	procEmptyClipboard           = user32.NewProc("EmptyClipboard")
	procSetClipboardData         = user32.NewProc("SetClipboardData")
	procGetClipboardData         = user32.NewProc("GetClipboardData")
	procGetForegroundWindow      = user32.NewProc("GetForegroundWindow")
	procSetForegroundWindowProc  = user32.NewProc("SetForegroundWindow")
	procShowWindowProc           = user32.NewProc("ShowWindow")
	procBringWindowToTop         = user32.NewProc("BringWindowToTop")
	procGetWindowThreadProcessId = user32.NewProc("GetWindowThreadProcessId")
	procAttachThreadInput        = user32.NewProc("AttachThreadInput")
	procSendInput                = user32.NewProc("SendInput")

	kernel32               = windows.NewLazySystemDLL("kernel32.dll")
	procGlobalAlloc        = kernel32.NewProc("GlobalAlloc")
	procGlobalFree         = kernel32.NewProc("GlobalFree")
	procGlobalLock         = kernel32.NewProc("GlobalLock")
	procGlobalUnlock       = kernel32.NewProc("GlobalUnlock")
	procGlobalSize         = kernel32.NewProc("GlobalSize")
	procGetCurrentThreadId = kernel32.NewProc("GetCurrentThreadId")
)

// inputUnion is the Win32 INPUT structure, sized for KEYBDINPUT (the
// largest variant on x64 is MOUSEINPUT but KEYBDINPUT padded to 40
// works because INPUT_KEYBOARD never reads the extra trailing bytes).
type inputUnion struct {
	typ     uint32
	_pad    uint32 // alignment on 64-bit
	wVk     uint16
	wScan   uint16
	dwFlags uint32
	time    uint32
	dwExtra uintptr
	// 8 bytes of MOUSEINPUT-sized padding so the layout is large enough
	// for the union on amd64.
	_padTail [8]byte
}

const (
	inputKeyboard    uint32 = 1
	keyeventfKeyUp   uint32 = 0x0002
	keyeventfUnicode uint32 = 0x0004
)

func makeUnicodeInput(r uint16, up bool) inputUnion {
	flags := keyeventfUnicode
	if up {
		flags |= keyeventfKeyUp
	}
	return inputUnion{typ: inputKeyboard, wScan: r, dwFlags: flags}
}

func makeVKInput(vk uint16, up bool) inputUnion {
	var flags uint32
	if up {
		flags = keyeventfKeyUp
	}
	return inputUnion{typ: inputKeyboard, wVk: vk, dwFlags: flags}
}