// SPDX-License-Identifier: LGPL-2.1-or-later
#include "reader_events.h"
#include <condition_variable>
#include <cstdio>
#include <deque>
#include <mutex>
#include <string>

struct ReaderEventQueue::State {
  State(GDBusConnection *bus, const ReaderEndpoint &reader)
      : connection(G_DBUS_CONNECTION(g_object_ref(bus))), endpoint(reader),
        calls(g_cancellable_new()) {}
  ~State() {
    clear();
    g_object_unref(calls);
    g_object_unref(connection);
  }
  GDBusConnection *connection;
  const ReaderEndpoint endpoint;
  GCancellable *calls;
  std::mutex mutex;
  std::condition_variable changed;
  std::deque<GVariant *> pending;
  bool stopping = false, overflowReported = false;

  void clear() {
    for (auto *parameters : pending) g_variant_unref(parameters);
    pending.clear();
  }
  bool send(GVariant *parameters, unsigned &failures) {
    GError *error = nullptr;
    GVariant *reply = g_dbus_connection_call_sync(
        connection, endpoint.busName, endpoint.objectPath,
        endpoint.interfaceName, "PresentAccessibleEvent", parameters,
        G_VARIANT_TYPE("(b)"), G_DBUS_CALL_FLAGS_NONE, 500, calls, &error);
    // A false reply can simply mean filtered/duplicate feedback. Only a
    // failed exchange warrants diagnostics. Never include event contents.
    const bool delivered = reply != nullptr;
    if (!delivered && !g_cancellable_is_cancelled(calls)) {
      if (++failures == 1)
        std::fprintf(stderr, "wine-access: reader event reply failed (domain %s, code %d)\n",
                     error ? g_quark_to_string(error->domain) : "unknown", error ? error->code : 0);
    } else if (delivered && failures) {
      std::fprintf(stderr, "wine-access: reader event replies resumed after %u failed calls\n", failures);
      failures = 0;
    }
    if (reply) g_variant_unref(reply);
    if (error) g_error_free(error);
    return delivered;
  }
  static DWORD WINAPI work(LPVOID pointer) {
    std::unique_ptr<std::shared_ptr<State>> retained(
        static_cast<std::shared_ptr<State> *>(pointer));
    auto state = *retained;
    unsigned failures = 0;
    std::unique_ptr<GVariant, decltype(&g_variant_unref)> focus(nullptr, g_variant_unref);
    std::string focusSource;
    bool focusDelivered = false;
    for (;;) {
      GVariant *parameters;
      {
        std::unique_lock<std::mutex> lock(state->mutex);
        state->changed.wait(lock, [&] { return state->stopping || !state->pending.empty(); });
        if (state->stopping) break;
        parameters = state->pending.front();
        state->pending.pop_front();
      }
      const char *source = nullptr, *kind = nullptr;
      g_variant_get_child(parameters, 0, "&s", &source);
      g_variant_get_child(parameters, 1, "&s", &kind);
      if (std::string(kind) == "focus") {
        focus.reset(g_variant_ref(parameters));
        focusSource = source;
        focusDelivered = state->send(parameters, failures);
      } else {
        // A lost focus exchange must not strand later editor actions. Replay
        // only the focus dependency, never a timed-out ordered text action.
        if (std::string(kind) == "text" && !focusDelivered && focus && focusSource == source)
          focusDelivered = state->send(focus.get(), failures);
        if (std::string(kind) != "text" || focusDelivered) {
          if (!state->send(parameters, failures)) focusDelivered = false;
        }
      }
      g_variant_unref(parameters);
    }
    return 0;
  }
};

ReaderEventQueue::~ReaderEventQueue() { stop(); }

bool ReaderEventQueue::start(GDBusConnection *connection, const ReaderEndpoint &endpoint) {
  if (state_) return false;
  state_ = std::make_shared<State>(connection, endpoint);
  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;
}

bool ReaderEventQueue::submit(GVariant *parameters) {
  parameters = g_variant_ref_sink(parameters);
  if (state_) {
    std::lock_guard<std::mutex> lock(state_->mutex);
    // Keep memory bounded if the reader remains unavailable. Do not reorder
    // actions or evict the focus on which queued editor actions depend.
    if (!state_->stopping && state_->pending.size() < 128) {
      state_->pending.push_back(parameters);
      state_->changed.notify_one();
      return true;
    }
    if (!state_->stopping && !state_->overflowReported) {
      std::fprintf(stderr, "wine-access: reader event queue full; feedback dropped\n");
      state_->overflowReported = true;
    }
  }
  g_variant_unref(parameters);
  return false;
}

void ReaderEventQueue::stop() {
  if (!state_) return;
  {
    std::lock_guard<std::mutex> lock(state_->mutex);
    state_->stopping = true;
    state_->clear();
    state_->changed.notify_one();
  }
  g_cancellable_cancel(state_->calls);
  // The worker retains its connection and queue state if cancellation has
  // not completed yet; it never references event-thread globals.
  WaitForSingleObject(worker_, 100);
  CloseHandle(worker_);
  worker_ = nullptr;
  state_.reset();
}