// Copyright 2026 Amber Hu
#include "EventManager.h"

#include <iostream>

#include <unistd.h>

EventManager::EventManager() {
  // Create a set to populate with file descriptors we want to wait on
  // The number passed in does not matter, see man epoll_create
  epoll_fd_ = epoll_create(42);
}

void EventManager::RegisterCallback(int fd, CallbackFn callback) {
  struct CallbackData cb_data;
  cb_data.callback = callback;
  cb_data.fd = fd;
  this->active_list_.push_front(cb_data);

  struct epoll_event event_data;
  event_data.data.ptr = &(this->active_list_.front());
  event_data.events = EPOLLIN;
  epoll_ctl(this->epoll_fd_, EPOLL_CTL_ADD, fd, &event_data);
}

void EventManager::RemoveCallback(int fd) {
  epoll_ctl(this->epoll_fd_, EPOLL_CTL_DEL, fd, NULL);
  // This uses an anonymous function, similar to lambda x: x == y in Python
  this->active_list_.remove_if(
              [fd](const CallbackData& curr){ return curr.fd == fd;});
}

void EventManager::WaitAndDispatch() {
  struct epoll_event res;
  epoll_wait(this->epoll_fd_, &res, 1, -1);  // Timeout is -1 (no timeout)
  // Retrieve the data we tucked away when we registered the callback 
  struct CallbackData* cb_data = reinterpret_cast<CallbackData*>(res.data.ptr);

  // That CallbackData told us which fn to invoke and which fd to pass in
  cb_data->callback(cb_data->fd);
}

EventManager::~EventManager() {
  // Close all open file descriptors before shutting down
  for (auto curr : this->active_list_) {
    std::cout << "Closing fd " << curr.fd << std::endl;
    close(curr.fd);
  }
  close(this->epoll_fd_);
}