// SPDX-License-Identifier: LGPL-2.1-or-later
#include "msaa_events.h"
#include "msaa_states.h"
#include <oleacc.h>
#include <condition_variable>
#include <mutex>
#include <deque>
#include <atomic>
#include <utility>

namespace {
// MSAA notifications describe transient state, unlike ordered editor actions.
// Bound pending work and favor current focus if an application floods events.
constexpr size_t capacity = 32;
std::string text(BSTR value) {
  if (!value) return {};
  int size = WideCharToMultiByte(CP_UTF8, WC_ERR_INVALID_CHARS, value, -1, nullptr, 0, nullptr, nullptr);
  if (size <= 1) return {};
  std::string result(size, '\0');
  WideCharToMultiByte(CP_UTF8, WC_ERR_INVALID_CHARS, value, -1, result.data(), size, nullptr, nullptr);
  result.resize(size - 1);
  return result;
}
std::string property(IAccessible *object,
    HRESULT (STDMETHODCALLTYPE IAccessible::*getter)(VARIANT, BSTR *), VARIANT child) {
  BSTR value = nullptr;
  HRESULT hr = (object->*getter)(child, &value);
  auto result = SUCCEEDED(hr) ? text(value) : std::string{};
  SysFreeString(value);
  return result;
}
struct Accessible {
  IAccessible *object = nullptr;
  VARIANT child{};
  ~Accessible() { if (object) object->Release(); VariantClear(&child); }
};
}

bool msaa_event_in_foreground(HWND window) {
  HWND foreground = GetForegroundWindow();
  HWND root = GetAncestor(window, GA_ROOT);
  if (!foreground || !root) return false;
  if (root == foreground) return true;
  if (!IsWindowVisible(root) || !(GetWindowLongPtrW(root, GWL_STYLE) & WS_POPUP)) return false;
  // Bound traversal even if a malformed owner chain cycles. Owned popups can
  // expose MSAA focus while the foreground owner retains native keyboard focus.
  for (unsigned depth = 0; root && depth < 32; ++depth) {
    root = GetWindow(root, GW_OWNER);
    if (root == foreground) return true;
  }
  return false;
}

struct MsaaEventReader::State {
  std::mutex mutex;
  std::condition_variable changed;
  std::deque<MsaaEvent> pending;
  std::deque<MsaaResult> ready;
  std::atomic<bool> stopping{false};
  uint64_t generation = 0;
  bool current(const MsaaEvent &event) {
    if (stopping || GetTickCount64() >= event.deadline ||
        !msaa_event_in_foreground(event.window)) return false;
    std::lock_guard<std::mutex> lock(mutex);
    return generation == event.generation;
  }
  MsaaResult read(const MsaaEvent &event) {
    MsaaResult result; result.source = event;
    Accessible accessible;
    if (!current(event) || FAILED(AccessibleObjectFromEvent(event.window, event.object,
        event.child, &accessible.object, &accessible.child)) || !accessible.object)
      return result;
    if (!current(event)) return result;
    VARIANT role{};
    LONG roleId = 0;
    if (SUCCEEDED(accessible.object->get_accRole(accessible.child, &role))) {
      if (role.vt == VT_I4) {
        roleId = role.lVal;
        WCHAR label[128]{};
        if (GetRoleTextW(roleId, label, 128)) result.role = text(label);
        else result.role = std::to_string(roleId);
      } else if (role.vt == VT_BSTR) result.role = text(role.bstrVal);
    }
    VariantClear(&role);
    if (!current(event)) return result;
    VARIANT state{};
    if (SUCCEEDED(accessible.object->get_accState(accessible.child, &state)) && state.vt == VT_I4) {
      result.states = msaa_states(static_cast<DWORD>(state.lVal), roleId);
      result.password = state.lVal & STATE_SYSTEM_PROTECTED;
    }
    VariantClear(&state);
    if (!current(event)) return result;
    result.name = property(accessible.object, &IAccessible::get_accName, accessible.child);
    if (!current(event)) return result;
    // Protected values must be excluded before querying the provider.
    if (!result.password) result.value = property(accessible.object, &IAccessible::get_accValue, accessible.child);
    if (!current(event)) return result;
    result.description = property(accessible.object, &IAccessible::get_accDescription, accessible.child);
    if (!current(event)) return result;
    accessible.object->get_accChildCount(&result.count);
    result.native_client = accessible.child.vt == VT_I4 && accessible.child.lVal == CHILDID_SELF &&
        (result.role.empty() || roleId == ROLE_SYSTEM_CLIENT);
    result.available = true;
    return result;
  }
  static DWORD WINAPI work(LPVOID pointer) {
    std::unique_ptr<std::shared_ptr<State>> retained(static_cast<std::shared_ptr<State>*>(pointer));
    auto state = *retained;
    const HRESULT com = CoInitializeEx(nullptr, COINIT_APARTMENTTHREADED);
    for (;;) {
      MsaaEvent event;
      {
        std::unique_lock<std::mutex> lock(state->mutex);
        state->changed.wait(lock, [&] { return state->stopping || !state->pending.empty(); });
        if (state->stopping) break;
        event = state->pending.front(); state->pending.pop_front();
      }
      auto result = SUCCEEDED(com) ? state->read(event) : MsaaResult{};
      result.source = event;
      if (!state->current(event)) continue;
      std::lock_guard<std::mutex> lock(state->mutex);
      if (state->stopping || event.generation != state->generation) continue;
      if (state->ready.size() == capacity) state->ready.pop_front();
      state->ready.push_back(std::move(result));
    }
    if (SUCCEEDED(com)) CoUninitialize();
    return 0;
  }
};

MsaaEventReader::~MsaaEventReader() { stop(); }
bool MsaaEventReader::start() {
  if (state_) return false;
  state_ = std::make_shared<State>();
  auto retained = new std::shared_ptr<State>(state_);
  worker_ = CreateThread(nullptr, 0, State::work, retained, 0, nullptr);
  if (!worker_) { delete retained; state_.reset(); return false; }
  return true;
}
void MsaaEventReader::invalidate(uint64_t generation) {
  if (!state_) return;
  std::lock_guard<std::mutex> lock(state_->mutex);
  state_->generation = generation;
  state_->pending.clear(); state_->ready.clear();
}
void MsaaEventReader::submit(const MsaaEvent &event) {
  if (!state_) return;
  std::lock_guard<std::mutex> lock(state_->mutex);
  if (state_->stopping || state_->generation != event.generation) return;
  if (state_->pending.size() == capacity) state_->pending.pop_front();
  state_->pending.push_back(event); state_->changed.notify_one();
}
bool MsaaEventReader::take(MsaaResult &result) {
  if (!state_) return false;
  std::lock_guard<std::mutex> lock(state_->mutex);
  if (state_->ready.empty()) return false;
  result = std::move(state_->ready.front()); state_->ready.pop_front();
  return true;
}
void MsaaEventReader::stop() {
  if (!state_) return;
  {
    std::lock_guard<std::mutex> lock(state_->mutex);
    state_->stopping = true; state_->pending.clear(); state_->ready.clear();
    state_->changed.notify_one();
  }
  // A hung COM call cannot be safely terminated. It retains only its own
  // shared state and native references until completion or process exit.
  WaitForSingleObject(worker_, 100);
  CloseHandle(worker_); worker_ = nullptr;
  state_.reset();
}