//go:build windows

package win32

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

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

// HotkeyManager owns a dedicated OS thread that runs a GetMessageW
// pump. RegisterHotKey can only be called from the thread that will
// receive the messages, so all register/unregister/dispatch operations
// are serialized onto that goroutine via the cmd channel.
type HotkeyManager struct {
	cmd    chan hkCmd
	events chan HotkeyEvent

	mu      sync.Mutex
	nextID  int32
	stopped bool
}

type hkCmd struct {
	kind   hkCmdKind
	id     int32
	hotkey Hotkey
	reply  chan error
}

type hkCmdKind int

const (
	hkCmdRegister hkCmdKind = iota
	hkCmdUnregister
	hkCmdStop
)

// NewHotkeyManager starts the dedicated thread and returns a manager
// ready to accept Register calls. Events() yields presses; the channel
// is closed on Stop().
func NewHotkeyManager() *HotkeyManager {
	m := &HotkeyManager{
		cmd:    make(chan hkCmd),
		events: make(chan HotkeyEvent, 16),
		nextID: 1,
	}
	started := make(chan struct{})
	go m.run(started)
	<-started
	return m
}

// Events returns the read-only event channel.
func (m *HotkeyManager) Events() <-chan HotkeyEvent { return m.events }

// Register adds a global hotkey and returns its assigned id. Re-registering
// a combination that is already taken by another application returns an
// error; the caller should surface it to the user.
func (m *HotkeyManager) Register(h Hotkey) (int32, error) {
	m.mu.Lock()
	if m.stopped {
		m.mu.Unlock()
		return 0, fmt.Errorf("win32: hotkey manager stopped")
	}
	id := m.nextID
	m.nextID++
	m.mu.Unlock()

	reply := make(chan error, 1)
	m.cmd <- hkCmd{kind: hkCmdRegister, id: id, hotkey: h, reply: reply}
	if err := <-reply; err != nil {
		return 0, err
	}
	return id, nil
}

// Unregister removes a previously registered hotkey.
func (m *HotkeyManager) Unregister(id int32) error {
	reply := make(chan error, 1)
	m.cmd <- hkCmd{kind: hkCmdUnregister, id: id, reply: reply}
	return <-reply
}

// Stop tears down the message pump and closes Events(). Subsequent
// Register calls fail.
func (m *HotkeyManager) Stop() {
	m.mu.Lock()
	if m.stopped {
		m.mu.Unlock()
		return
	}
	m.stopped = true
	m.mu.Unlock()
	reply := make(chan error, 1)
	m.cmd <- hkCmd{kind: hkCmdStop, reply: reply}
	<-reply
}

// run is the dedicated-thread loop. It owns the message queue that
// RegisterHotKey targets.
func (m *HotkeyManager) run(started chan struct{}) {
	runtime.LockOSThread()
	defer runtime.UnlockOSThread()

	// Force the message queue to exist before anybody tries to post to
	// us. PeekMessage with PM_NOREMOVE is the canonical incantation.
	var msg msgStruct
	procPeekMessageW.Call(
		uintptr(unsafe.Pointer(&msg)),
		0, 0, 0, 0, // PM_NOREMOVE
	)
	close(started)

	for {
		// Non-blocking message pump: drain hotkey messages first, then
		// service one cmd, then sleep briefly. A blocking GetMessage
		// would freeze the cmd intake.
		for {
			r, _, _ := procPeekMessageW.Call(
				uintptr(unsafe.Pointer(&msg)),
				0, 0, 0, 1, // PM_REMOVE
			)
			if r == 0 {
				break
			}
			if msg.message == wmHotKey {
				select {
				case m.events <- HotkeyEvent{ID: int32(msg.wParam)}:
				default:
					// Listener slow — drop to avoid stalling the pump.
				}
			}
		}

		select {
		case c := <-m.cmd:
			switch c.kind {
			case hkCmdRegister:
				err := registerHotKey(0, c.id, c.hotkey.Mods, c.hotkey.VK)
				c.reply <- err
			case hkCmdUnregister:
				err := unregisterHotKey(0, c.id)
				c.reply <- err
			case hkCmdStop:
				close(m.events)
				c.reply <- nil
				return
			}
		default:
			// brief sleep so we don't busy-loop. 30ms is well under any
			// human-perceptible hotkey latency.
			windows.SleepEx(30, false)
		}
	}
}

// -----------------------------------------------------------------------------
// raw syscalls

var (
	procRegisterHotKey   = user32.NewProc("RegisterHotKey")
	procUnregisterHotKey = user32.NewProc("UnregisterHotKey")
	procPeekMessageW     = user32.NewProc("PeekMessageW")
)

const wmHotKey uint32 = 0x0312

type msgStruct struct {
	hwnd    uintptr
	message uint32
	wParam  uintptr
	lParam  uintptr
	time    uint32
	pt      struct{ x, y int32 }
}

func registerHotKey(hwnd uintptr, id int32, mods, vk uint32) error {
	r, _, e := procRegisterHotKey.Call(
		hwnd, uintptr(id), uintptr(mods), uintptr(vk),
	)
	if r == 0 {
		if errno, ok := e.(syscall.Errno); ok && errno != 0 {
			return fmt.Errorf("win32: RegisterHotKey: %w", errno)
		}
		return fmt.Errorf("win32: RegisterHotKey: unknown failure")
	}
	return nil
}

func unregisterHotKey(hwnd uintptr, id int32) error {
	r, _, e := procUnregisterHotKey.Call(hwnd, uintptr(id))
	if r == 0 {
		if errno, ok := e.(syscall.Errno); ok && errno != 0 {
			return fmt.Errorf("win32: UnregisterHotKey: %w", errno)
		}
	}
	return nil
}