// Package win32 封装 Fyne 未提供的 Windows 原生能力：
// 显示器枚举、窗口置顶/移动、全局热键、DPI 查询。
package win32

import (
	"fmt"
	"sync"
	"syscall"
	"unsafe"

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

var (
	user32 = windows.NewLazySystemDLL("user32.dll")
	shcore = windows.NewLazySystemDLL("shcore.dll")

	procFindWindowW         = user32.NewProc("FindWindowW")
	procFindWindowExW       = user32.NewProc("FindWindowExW")
	procGetWindowRect       = user32.NewProc("GetWindowRect")
	procSetWindowPos        = user32.NewProc("SetWindowPos")
	procGetCursorPos        = user32.NewProc("GetCursorPos")
	procEnumDisplayMonitors = user32.NewProc("EnumDisplayMonitors")
	procGetMonitorInfoW     = user32.NewProc("GetMonitorInfoW")
	procGetDpiForMonitor    = shcore.NewProc("GetDpiForMonitor")
)

const (
	swpNoSize     = 0x0001
	swpNoMove     = 0x0002
	swpNoZOrder   = 0x0004
	swpNoActivate = 0x0010
	swpShowWindow = 0x0040

	hwndTopMost        = ^uintptr(0) // (HWND)-1
	mdtEffectiveDPI    = 0
	monitorInfoPrimary = 1
)

// Rect 是以物理像素表示的屏幕矩形。
type Rect struct {
	Left, Top, Right, Bottom int
}

// Width 返回矩形宽度。
func (r Rect) Width() int { return r.Right - r.Left }

// Height 返回矩形高度。
func (r Rect) Height() int { return r.Bottom - r.Top }

// Contains 判断点是否落在矩形内。
func (r Rect) Contains(x, y int) bool {
	return x >= r.Left && x < r.Right && y >= r.Top && y < r.Bottom
}

type nativeRect struct {
	Left, Top, Right, Bottom int32
}

// Monitor 描述一台显示器。
type Monitor struct {
	Index   int
	Rect    Rect // 完整屏幕区域（物理像素）
	Work    Rect // 去掉任务栏的可用区域
	Primary bool
	Scale   float64 // 系统缩放，例如 1.25
}

type nativeMonitorInfo struct {
	CbSize    uint32
	RcMonitor nativeRect
	RcWork    nativeRect
	DwFlags   uint32
}

type point struct {
	X, Y int32
}

var (
	enumMu       sync.Mutex
	enumSink     *[]Monitor
	enumCallback uintptr
)

// Monitors 枚举当前所有显示器，坐标已换算为物理像素。
func Monitors() []Monitor {
	enumMu.Lock()
	defer enumMu.Unlock()

	var out []Monitor
	enumSink = &out
	if enumCallback == 0 {
		enumCallback = windows.NewCallback(enumProc)
	}
	procEnumDisplayMonitors.Call(0, 0, enumCallback, 0)
	enumSink = nil

	for i := range out {
		out[i].Index = i
	}
	return out
}

func enumProc(hMonitor, _, _, _ uintptr) uintptr {
	if enumSink == nil {
		return 1
	}
	info := nativeMonitorInfo{CbSize: uint32(unsafe.Sizeof(nativeMonitorInfo{}))}
	if r, _, _ := procGetMonitorInfoW.Call(hMonitor, uintptr(unsafe.Pointer(&info))); r == 0 {
		return 1
	}
	m := Monitor{
		Rect: Rect{
			Left:   int(info.RcMonitor.Left),
			Top:    int(info.RcMonitor.Top),
			Right:  int(info.RcMonitor.Right),
			Bottom: int(info.RcMonitor.Bottom),
		},
		Work: Rect{
			Left:   int(info.RcWork.Left),
			Top:    int(info.RcWork.Top),
			Right:  int(info.RcWork.Right),
			Bottom: int(info.RcWork.Bottom),
		},
		Primary: info.DwFlags&monitorInfoPrimary != 0,
		Scale:   1,
	}
	var dpiX, dpiY uint32
	if hr, _, _ := procGetDpiForMonitor.Call(hMonitor, mdtEffectiveDPI,
		uintptr(unsafe.Pointer(&dpiX)), uintptr(unsafe.Pointer(&dpiY))); hr == 0 && dpiX > 0 {
		m.Scale = float64(dpiX) / 96
	}
	*enumSink = append(*enumSink, m)
	return 1
}

// VirtualScreen 返回所有显示器的并集，作为虚拟桌面坐标参考。
func VirtualScreen() Rect {
	ms := Monitors()
	if len(ms) == 0 {
		return Rect{}
	}
	union := ms[0].Rect
	for _, m := range ms[1:] {
		if m.Rect.Left < union.Left {
			union.Left = m.Rect.Left
		}
		if m.Rect.Top < union.Top {
			union.Top = m.Rect.Top
		}
		if m.Rect.Right > union.Right {
			union.Right = m.Rect.Right
		}
		if m.Rect.Bottom > union.Bottom {
			union.Bottom = m.Rect.Bottom
		}
	}
	return union
}

// CursorPos 返回鼠标当前位置（物理像素）。
func CursorPos() (int, int) {
	var p point
	if r, _, _ := procGetCursorPos.Call(uintptr(unsafe.Pointer(&p))); r == 0 {
		return 0, 0
	}
	return int(p.X), int(p.Y)
}

// MonitorAt 返回包含指定点的显示器，找不到时退化为第一台。
func MonitorAt(x, y int) (Monitor, bool) {
	ms := Monitors()
	for _, m := range ms {
		if m.Rect.Contains(x, y) {
			return m, true
		}
	}
	if len(ms) > 0 {
		return ms[0], false
	}
	return Monitor{}, false
}

// MonitorAtCursor 返回鼠标所在的显示器。
func MonitorAtCursor() (Monitor, bool) {
	x, y := CursorPos()
	return MonitorAt(x, y)
}

// FindWindowByTitle 按标题查找顶层窗口句柄。
func FindWindowByTitle(title string) (syscall.Handle, error) {
	p, err := windows.UTF16PtrFromString(title)
	if err != nil {
		return 0, err
	}
	r, _, e := procFindWindowW.Call(0, uintptr(unsafe.Pointer(p)))
	if r == 0 {
		return 0, fmt.Errorf("未找到标题为 %q 的窗口: %w", title, e)
	}
	return syscall.Handle(r), nil
}

// FindWindowByClass 按窗口类名查找顶层窗口句柄。
func FindWindowByClass(class string) (syscall.Handle, error) {
	p, err := windows.UTF16PtrFromString(class)
	if err != nil {
		return 0, err
	}
	r, _, e := procFindWindowExW.Call(0, 0, uintptr(unsafe.Pointer(p)), 0)
	if r == 0 {
		return 0, fmt.Errorf("未找到类名为 %q 的窗口: %w", class, e)
	}
	return syscall.Handle(r), nil
}

// WindowRect 返回窗口在屏幕上的物理像素矩形。
func WindowRect(hwnd syscall.Handle) (Rect, error) {
	var r nativeRect
	if ok, _, e := procGetWindowRect.Call(uintptr(hwnd), uintptr(unsafe.Pointer(&r))); ok == 0 {
		return Rect{}, fmt.Errorf("GetWindowRect 失败: %w", e)
	}
	return Rect{Left: int(r.Left), Top: int(r.Top), Right: int(r.Right), Bottom: int(r.Bottom)}, nil
}

// SetTopMost 让窗口保持置顶但不抢焦点。
func SetTopMost(hwnd syscall.Handle) error {
	if ok, _, e := procSetWindowPos.Call(uintptr(hwnd), hwndTopMost, 0, 0, 0, 0,
		swpNoMove|swpNoSize|swpNoActivate); ok == 0 {
		return fmt.Errorf("SetWindowPos(TOPMOST) 失败: %w", e)
	}
	return nil
}

// MoveTo 把窗口移动到指定物理矩形（不改变 Z 序）。
func MoveTo(hwnd syscall.Handle, r Rect) error {
	if ok, _, e := procSetWindowPos.Call(uintptr(hwnd), 0,
		uintptr(r.Left), uintptr(r.Top),
		uintptr(r.Width()), uintptr(r.Height()),
		swpNoZOrder|swpNoActivate|swpShowWindow); ok == 0 {
		return fmt.Errorf("SetWindowPos(MoveTo) 失败: %w", e)
	}
	return nil
}