#include "server.hpp"
#include "connection.hpp"
#include <csignal>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fcntl.h>
#include <netdb.h>
#include <netinet/tcp.h>
#include <pthread.h>
#include <stdexcept>
#include <sys/epoll.h>
#include <sys/socket.h>
#include <unistd.h>

extern std::atomic<int> activeConnections;

std::shared_ptr<Server> Server::create(const weaseldb::Config &config,
                                       ConnectionHandler &handler) {
  // Use std::shared_ptr constructor with private access
  // We can't use make_shared here because constructor is private
  return std::shared_ptr<Server>(new Server(config, handler));
}

Server::Server(const weaseldb::Config &config, ConnectionHandler &handler)
    : config_(config), handler_(handler) {}

Server::~Server() { cleanup_resources(); }

void Server::run() {
  setup_shutdown_pipe();

  listen_sockfd_ = create_listen_socket();

  // Create epoll instances
  network_epollfd_ = epoll_create1(EPOLL_CLOEXEC);
  if (network_epollfd_ == -1) {
    perror("epoll_create network");
    throw std::runtime_error("Failed to create network epoll instance");
  }

  accept_epollfd_ = epoll_create1(EPOLL_CLOEXEC);
  if (accept_epollfd_ == -1) {
    perror("epoll_create accept");
    throw std::runtime_error("Failed to create accept epoll instance");
  }

  // Add shutdown pipe to both epoll instances
  struct epoll_event shutdown_event;
  shutdown_event.events = EPOLLIN;
  shutdown_event.data.fd = shutdown_pipe_[0];

  if (epoll_ctl(network_epollfd_, EPOLL_CTL_ADD, shutdown_pipe_[0],
                &shutdown_event) == -1) {
    perror("epoll_ctl add shutdown to network");
    throw std::runtime_error("Failed to add shutdown pipe to network epoll");
  }

  if (epoll_ctl(accept_epollfd_, EPOLL_CTL_ADD, shutdown_pipe_[0],
                &shutdown_event) == -1) {
    perror("epoll_ctl add shutdown to accept");
    throw std::runtime_error("Failed to add shutdown pipe to accept epoll");
  }

  // Add listen socket to accept epoll
  struct epoll_event listen_event;
  listen_event.events = EPOLLIN | EPOLLEXCLUSIVE;
  listen_event.data.fd = listen_sockfd_;
  if (epoll_ctl(accept_epollfd_, EPOLL_CTL_ADD, listen_sockfd_,
                &listen_event) == -1) {
    perror("epoll_ctl add listen socket");
    throw std::runtime_error("Failed to add listen socket to accept epoll");
  }

  start_network_threads();
  start_accept_threads();

  // Wait for all threads to complete
  for (auto &thread : threads_) {
    thread.join();
  }
}

void Server::shutdown() {
  if (shutdown_pipe_[1] != -1) {
    char val = 1;
    // write() is async-signal-safe per POSIX - safe to use in signal handler
    // Write single byte to avoid partial write complexity
    while (write(shutdown_pipe_[1], &val, 1) == -1) {
      if (errno != EINTR) {
        abort(); // graceful shutdown didn't work. Let's go ungraceful.
      }
    }
  }
}

void Server::releaseBackToServer(std::unique_ptr<Connection> connection) {
  if (!connection) {
    return; // Nothing to release
  }

  // Try to get the server from the connection's weak_ptr
  if (auto server = connection->server_.lock()) {
    // Server still exists - release raw pointer and let server take over
    Connection *raw_conn = connection.release();
    server->receiveConnectionBack(raw_conn);
  }

  // If server is gone, connection will be automatically cleaned up when
  // unique_ptr destructs
}

void Server::receiveConnectionBack(Connection *connection) {
  // Re-add the connection to epoll for continued processing
  struct epoll_event event{};

  if (!connection->hasMessages()) {
    event.events = EPOLLIN | EPOLLONESHOT | EPOLLRDHUP;
  } else {
    event.events = EPOLLOUT | EPOLLONESHOT | EPOLLRDHUP;
  }

  connection->tsan_release();
  event.data.ptr = connection;

  if (epoll_ctl(network_epollfd_, EPOLL_CTL_ADD, connection->getFd(), &event) ==
      -1) {
    perror("epoll_ctl ADD in receiveConnectionBack");
    delete connection; // Clean up on failure
  }
}

void Server::setup_shutdown_pipe() {
  if (pipe(shutdown_pipe_) == -1) {
    perror("pipe");
    throw std::runtime_error("Failed to create shutdown pipe");
  }

  // Set both ends to close-on-exec
  if (fcntl(shutdown_pipe_[0], F_SETFD, FD_CLOEXEC) == -1 ||
      fcntl(shutdown_pipe_[1], F_SETFD, FD_CLOEXEC) == -1) {
    perror("fcntl FD_CLOEXEC");
    throw std::runtime_error("Failed to set close-on-exec for shutdown pipe");
  }
}

int Server::create_listen_socket() {
  struct addrinfo hints;
  struct addrinfo *result, *rp;
  int sfd, s;

  memset(&hints, 0, sizeof(hints));
  hints.ai_family = AF_UNSPEC;     /* Allow IPv4 or IPv6 */
  hints.ai_socktype = SOCK_STREAM; /* stream socket */
  hints.ai_flags = AI_PASSIVE;     /* For wildcard IP address */
  hints.ai_protocol = 0;           /* Any protocol */
  hints.ai_canonname = nullptr;
  hints.ai_addr = nullptr;
  hints.ai_next = nullptr;

  s = getaddrinfo(config_.server.bind_address.c_str(),
                  std::to_string(config_.server.port).c_str(), &hints, &result);
  if (s != 0) {
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
    throw std::runtime_error("Failed to resolve bind address");
  }

  for (rp = result; rp != nullptr; rp = rp->ai_next) {
    sfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
    if (sfd == -1) {
      continue;
    }

    int val = 1;
    if (setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val)) == -1) {
      perror("setsockopt SO_REUSEADDR");
      close(sfd);
      continue;
    }

    // Enable TCP_NODELAY for low latency
    if (setsockopt(sfd, IPPROTO_TCP, TCP_NODELAY, &val, sizeof(val)) == -1) {
      perror("setsockopt TCP_NODELAY");
      close(sfd);
      continue;
    }

    // Set socket to non-blocking for graceful shutdown
    int flags = fcntl(sfd, F_GETFL, 0);
    if (flags == -1) {
      perror("fcntl F_GETFL");
      close(sfd);
      continue;
    }
    if (fcntl(sfd, F_SETFL, flags | O_NONBLOCK) == -1) {
      perror("fcntl F_SETFL");
      close(sfd);
      continue;
    }

    if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0) {
      break; /* Success */
    }

    close(sfd);
  }

  freeaddrinfo(result);

  if (rp == nullptr) {
    throw std::runtime_error("Could not bind to any address");
  }

  if (listen(sfd, SOMAXCONN) == -1) {
    perror("listen");
    close(sfd);
    throw std::runtime_error("Failed to listen on socket");
  }

  return sfd;
}

void Server::start_network_threads() {
  int network_threads = config_.server.network_threads;

  for (int thread_id = 0; thread_id < network_threads; ++thread_id) {
    threads_.emplace_back([this, thread_id]() {
      pthread_setname_np(pthread_self(),
                         ("network-" + std::to_string(thread_id)).c_str());

      struct epoll_event events[config_.server.event_batch_size];
      std::unique_ptr<Connection> batch[config_.server.event_batch_size];

      for (;;) {
        int event_count = epoll_wait(network_epollfd_, events,
                                     config_.server.event_batch_size, -1);
        if (event_count == -1) {
          if (errno == EINTR) {
            continue;
          }
          perror("epoll_wait");
          abort();
        }

        int batch_count = 0;
        for (int i = 0; i < event_count; ++i) {
          // Check for shutdown event
          if (events[i].data.fd == shutdown_pipe_[0]) {
            return;
          }

          // Take ownership from epoll: raw pointer -> unique_ptr
          std::unique_ptr<Connection> conn{
              static_cast<Connection *>(events[i].data.ptr)};
          conn->tsan_acquire();
          events[i].data.ptr = nullptr;

          if (events[i].events & (EPOLLERR | EPOLLHUP | EPOLLRDHUP)) {
            continue; // Connection closed - unique_ptr destructor cleans up
          }

          if (events[i].events & EPOLLIN) {
            std::string_view data =
                conn->readBytes(config_.server.max_request_size_bytes,
                                config_.server.read_buffer_size);

            if (data.empty()) {
              // No data, error, or EOF - connection should be closed
              continue;
            }

            // Call handler with unique_ptr - handler can take ownership if
            // needed
            handler_.on_data_arrived(data, conn);

            // If handler took ownership (conn is now null), don't continue
            // processing
            if (!conn) {
              continue;
            }
          }

          if (events[i].events & EPOLLOUT) {
            bool error = conn->writeBytes();
            if (error) {
              continue;
            }

            // Call handler with unique_ptr - handler can take ownership if
            // needed
            handler_.on_write_progress(conn);
            // If handler took ownership (conn is now null), don't continue
            // processing
            if (!conn) {
              continue;
            }

            // Check if we should close the connection according to application
            if (!conn->hasMessages() && conn->closeConnection_) {
              continue;
            }
          }
          batch[batch_count++] = std::move(conn);
        }

        handler_.on_post_batch({batch, (size_t)batch_count});

        for (int i = 0; i < batch_count; ++i) {
          auto &conn = batch[i];
          if (!conn) {
            continue;
          }
          // Determine next epoll interest
          struct epoll_event event{};
          if (!conn->hasMessages()) {
            event.events = EPOLLIN | EPOLLONESHOT | EPOLLRDHUP;
          } else {
            event.events = EPOLLOUT | EPOLLONESHOT | EPOLLRDHUP;
          }

          // Transfer ownership back to epoll
          conn->tsan_release();
          Connection *raw_conn = conn.release();
          event.data.ptr = raw_conn;

          if (epoll_ctl(network_epollfd_, EPOLL_CTL_MOD, raw_conn->getFd(),
                        &event) == -1) {
            perror("epoll_ctl MOD");
            delete raw_conn;
            continue;
          }
        }
      }
    });
  }
}

void Server::start_accept_threads() {
  int accept_threads = config_.server.accept_threads;

  for (int thread_id = 0; thread_id < accept_threads; ++thread_id) {
    threads_.emplace_back([this, thread_id]() {
      pthread_setname_np(pthread_self(),
                         ("accept-" + std::to_string(thread_id)).c_str());

      for (;;) {
        struct epoll_event events[2]; // listen socket + shutdown pipe
        int ready = epoll_wait(accept_epollfd_, events, 2, -1);

        if (ready == -1) {
          if (errno == EINTR)
            continue;
          perror("epoll_wait accept");
          abort();
        }

        for (int i = 0; i < ready; ++i) {
          if (events[i].data.fd == shutdown_pipe_[0]) {
            return; // Shutdown signal
          }

          if (events[i].data.fd == listen_sockfd_) {
            // Accept new connections
            for (;;) {
              struct sockaddr_storage addr;
              socklen_t addrlen = sizeof(addr);
              int fd = accept4(listen_sockfd_, (struct sockaddr *)&addr,
                               &addrlen, SOCK_NONBLOCK);

              if (fd == -1) {
                if (errno == EAGAIN || errno == EWOULDBLOCK)
                  break;
                if (errno == EINTR)
                  continue;
                perror("accept4");
                abort();
              }

              // Check connection limit
              if (config_.server.max_connections > 0 &&
                  activeConnections.load(std::memory_order_relaxed) >=
                      config_.server.max_connections) {
                close(fd);
                continue;
              }

              // Enable keepalive
              int keepalive = 1;
              if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &keepalive,
                             sizeof(keepalive)) == -1) {
                perror("setsockopt SO_KEEPALIVE");
              }

              auto conn = Connection::createForServer(
                  addr, fd,
                  connection_id_.fetch_add(1, std::memory_order_relaxed),
                  &handler_, weak_from_this());

              // Transfer to network epoll
              struct epoll_event event{};
              event.events = EPOLLIN | EPOLLONESHOT | EPOLLRDHUP;
              conn->tsan_release();
              Connection *raw_conn = conn.release();
              event.data.ptr = raw_conn;

              if (epoll_ctl(network_epollfd_, EPOLL_CTL_ADD, fd, &event) ==
                  -1) {
                perror("epoll_ctl ADD");
                delete raw_conn;
                continue;
              }
            }
          }
        }
      }
    });
  }
}

void Server::cleanup_resources() {
  if (shutdown_pipe_[0] != -1) {
    close(shutdown_pipe_[0]);
    shutdown_pipe_[0] = -1;
  }
  if (shutdown_pipe_[1] != -1) {
    close(shutdown_pipe_[1]);
    shutdown_pipe_[1] = -1;
  }
  if (network_epollfd_ != -1) {
    close(network_epollfd_);
    network_epollfd_ = -1;
  }
  if (accept_epollfd_ != -1) {
    close(accept_epollfd_);
    accept_epollfd_ = -1;
  }
  if (listen_sockfd_ != -1) {
    close(listen_sockfd_);
    listen_sockfd_ = -1;
  }
}