#include "pen_channel.h"

#include <flutter/encodable_value.h>
#include <flutter/event_channel.h>
#include <flutter/event_stream_handler_functions.h>
#include <flutter/flutter_engine.h>
#include <flutter/standard_method_codec.h>

#include <memory>

namespace {

std::unique_ptr<flutter::EventSink<flutter::EncodableValue>> g_pen_sink;

std::unique_ptr<flutter::EventChannel<flutter::EncodableValue>> g_pen_channel;

// Diagnostic counters so the Dart side can see WHAT the observer receives:
//  - g_ptr_msgs:   WM_POINTER* messages seen (is WM_POINTER reaching us at all?)
//  - g_pen_msgs:   of those, PT_PEN with a successful GetPointerPenInfo
//  - g_mouse_msgs: legacy mouse/touch input messages (Flutter on the old path?)
int g_ptr_msgs = 0;
int g_pen_msgs = 0;
int g_mouse_msgs = 0;
int g_last_msg = 0;

}  // namespace

void RegisterPenChannel(flutter::FlutterEngine* engine) {
  g_pen_channel =
      std::make_unique<flutter::EventChannel<flutter::EncodableValue>>(
          engine->messenger(), "badnote/pen",
          &flutter::StandardMethodCodec::GetInstance());

  auto handler = std::make_unique<
      flutter::StreamHandlerFunctions<flutter::EncodableValue>>(
      [](const flutter::EncodableValue* arguments,
         std::unique_ptr<flutter::EventSink<flutter::EncodableValue>>&&
             events)
          -> std::unique_ptr<
              flutter::StreamHandlerError<flutter::EncodableValue>> {
        g_pen_sink = std::move(events);
        return nullptr;
      },
      [](const flutter::EncodableValue* arguments)
          -> std::unique_ptr<
              flutter::StreamHandlerError<flutter::EncodableValue>> {
        g_pen_sink = nullptr;
        return nullptr;
      });

  g_pen_channel->SetStreamHandler(std::move(handler));
}

void ObservePenMessage(UINT message, WPARAM wparam, LPARAM lparam) {
  if (!g_pen_sink) {
    return;
  }

  const bool is_pointer =
      message == WM_POINTERENTER || message == WM_POINTERDOWN ||
      message == WM_POINTERUPDATE || message == WM_POINTERUP;
  // Legacy input path: if Flutter is feeding us mouse/touch instead of pointer
  // messages, these tell us so (so we know WM_POINTER never arrives here).
  const bool is_legacy_input =
      message == WM_LBUTTONDOWN || message == WM_LBUTTONUP ||
      message == WM_MOUSEMOVE || message == WM_TOUCH;

  if (!is_pointer && !is_legacy_input) {
    return;
  }
  g_last_msg = static_cast<int>(message);
  if (is_legacy_input) {
    ++g_mouse_msgs;
  }

  int flags = 0;
  double tilt_x = 0.0;
  double tilt_y = 0.0;

  if (is_pointer) {
    ++g_ptr_msgs;
    UINT32 pointerId = GET_POINTERID_WPARAM(wparam);
    POINTER_INPUT_TYPE type = PT_POINTER;
    if (GetPointerType(pointerId, &type) && type == PT_PEN) {
      POINTER_PEN_INFO ppi{};
      if (GetPointerPenInfo(pointerId, &ppi)) {
        ++g_pen_msgs;
        if (ppi.penFlags & PEN_FLAG_BARREL)   flags |= 1;
        if (ppi.penFlags & PEN_FLAG_INVERTED) flags |= 2;
        if (ppi.penFlags & PEN_FLAG_ERASER)   flags |= 4;
        tilt_x = static_cast<double>(ppi.tiltX);
        tilt_y = static_cast<double>(ppi.tiltY);
      }
    }
    if (message == WM_POINTERUP) {
      flags = 0;  // lift-off clears held flags
    }
  }

  // Always emit the diagnostic counters so the Dart overlay can show whether
  // WM_POINTER / PT_PEN ever reach this observer.
  flutter::EncodableMap payload{
      {flutter::EncodableValue("flags"), flutter::EncodableValue(flags)},
      {flutter::EncodableValue("tiltX"), flutter::EncodableValue(tilt_x)},
      {flutter::EncodableValue("tiltY"), flutter::EncodableValue(tilt_y)},
      {flutter::EncodableValue("diagPtr"), flutter::EncodableValue(g_ptr_msgs)},
      {flutter::EncodableValue("diagPen"), flutter::EncodableValue(g_pen_msgs)},
      {flutter::EncodableValue("diagMouse"), flutter::EncodableValue(g_mouse_msgs)},
      {flutter::EncodableValue("diagMsg"), flutter::EncodableValue(g_last_msg)},
  };
  g_pen_sink->Success(flutter::EncodableValue(payload));
}