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

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), connection_registry_() {}

Server::~Server() {
  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;
  }

  // Close all epoll instances
  for (int epollfd : epoll_fds_) {
    if (epollfd != -1) {
      close(epollfd);
    }
  }
  epoll_fds_.clear();

  if (listen_sockfd_ != -1) {
    close(listen_sockfd_);
    listen_sockfd_ = -1;
  }

  // Clean up unix socket file if it exists
  if (!config_.server.unix_socket_path.empty()) {
    unlink(config_.server.unix_socket_path.c_str());
  }
}

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

  listen_sockfd_ = create_listen_socket();

  create_epoll_instances();

  // Create I/O threads locally in this call frame
  // CRITICAL: By owning threads in run()'s call frame, we guarantee they are
  // joined before run() returns, eliminating any race conditions in ~Server()
  std::vector<std::thread> threads;
  start_io_threads(threads);

  // Wait for all threads to complete before returning
  // This ensures all I/O threads are fully stopped before the Server
  // destructor can be called, preventing race conditions during connection
  // cleanup
  for (auto &thread : threads) {
    thread.join();
  }

  // At this point, all threads are joined and it's safe to destroy the Server
}

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 - pass unique_ptr directly
    server->receiveConnectionBack(std::move(connection));
  }

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

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

  // Re-add the connection to epoll for continued processing
  struct epoll_event event{};

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

  connection->tsan_release();
  int fd = connection->getFd();
  event.data.fd = fd;

  // Store connection in registry before adding to epoll
  // This mirrors the pattern used in process_connection_batch
  size_t epoll_index = connection->getEpollIndex();
  int epollfd = epoll_fds_[epoll_index];
  connection_registry_.store(fd, std::move(connection));

  if (epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &event) == -1) {
    perror("epoll_ctl MOD in receiveConnectionBack");
    // Remove from registry and clean up on failure
    (void)connection_registry_.remove(fd);
  }
}

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() {
  int sfd;

  // Check if unix socket path is specified
  if (!config_.server.unix_socket_path.empty()) {
    // Create unix socket
    sfd = socket(AF_UNIX, SOCK_STREAM, 0);
    if (sfd == -1) {
      perror("socket");
      throw std::runtime_error("Failed to create unix socket");
    }

    // Remove existing socket file if it exists
    unlink(config_.server.unix_socket_path.c_str());

    struct sockaddr_un addr;
    memset(&addr, 0, sizeof(addr));
    addr.sun_family = AF_UNIX;

    if (config_.server.unix_socket_path.length() >= sizeof(addr.sun_path)) {
      close(sfd);
      throw std::runtime_error("Unix socket path too long");
    }

    strncpy(addr.sun_path, config_.server.unix_socket_path.c_str(),
            sizeof(addr.sun_path) - 1);

    // Set socket to non-blocking for graceful shutdown
    int flags = fcntl(sfd, F_GETFL, 0);
    if (flags == -1) {
      perror("fcntl F_GETFL");
      close(sfd);
      throw std::runtime_error("Failed to get socket flags");
    }
    if (fcntl(sfd, F_SETFL, flags | O_NONBLOCK) == -1) {
      perror("fcntl F_SETFL");
      close(sfd);
      throw std::runtime_error("Failed to set socket non-blocking");
    }

    if (bind(sfd, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
      perror("bind");
      close(sfd);
      throw std::runtime_error("Failed to bind unix socket");
    }

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

    return sfd;
  }

  // TCP socket creation (original code)
  struct addrinfo hints;
  struct addrinfo *result, *rp;
  int 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 (only for TCP sockets)
    if (rp->ai_family == AF_INET || rp->ai_family == AF_INET6) {
      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::create_epoll_instances() {
  // Create multiple epoll instances to reduce contention
  epoll_fds_.resize(config_.server.epoll_instances);

  for (int i = 0; i < config_.server.epoll_instances; ++i) {
    epoll_fds_[i] = epoll_create1(EPOLL_CLOEXEC);
    if (epoll_fds_[i] == -1) {
      perror("epoll_create");
      throw std::runtime_error("Failed to create epoll instance");
    }

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

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

    // Add listen socket to each epoll instance with EPOLLEXCLUSIVE to prevent
    // thundering herd
    struct epoll_event listen_event;
    listen_event.events = EPOLLIN | EPOLLEXCLUSIVE;
    listen_event.data.fd = listen_sockfd_;
    if (epoll_ctl(epoll_fds_[i], EPOLL_CTL_ADD, listen_sockfd_,
                  &listen_event) == -1) {
      perror("epoll_ctl listen socket");
      throw std::runtime_error("Failed to add listen socket to epoll");
    }
  }
}

int Server::get_epoll_for_thread(int thread_id) const {
  // Round-robin assignment of threads to epoll instances
  return epoll_fds_[thread_id % epoll_fds_.size()];
}

void Server::start_io_threads(std::vector<std::thread> &threads) {
  int io_threads = config_.server.io_threads;

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

      // Each thread uses its assigned epoll instance (round-robin)
      int epollfd = get_epoll_for_thread(thread_id);

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

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

        bool listenReady = false;
        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;
          }
          // Check for new connections
          if (events[i].data.fd == listen_sockfd_) {
            listenReady = true;
            continue;
          }

          // Handle existing connection events
          int fd = events[i].data.fd;
          std::unique_ptr<Connection> conn = connection_registry_.remove(fd);
          if (conn) {
            conn->tsan_acquire();
          }

          if (events[i].events & (EPOLLERR | EPOLLHUP)) {
            // unique_ptr will automatically delete on scope exit
            continue;
          }

          // Transfer ownership from registry to batch processing
          batch[batch_count] = std::move(conn);
          batch_events[batch_count] = events[i].events;
          batch_count++;
        }

        // Process existing connections in batch
        if (batch_count > 0) {
          process_connection_batch(epollfd, {batch, (size_t)batch_count},
                                   {batch_events, (size_t)batch_count}, false);
        }

        // Reuse same batch array for accepting connections
        if (listenReady) {
          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 &&
                active_connections_.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");
            }

            // Transfer ownership from registry to batch processing
            size_t epoll_index = thread_id % epoll_fds_.size();
            batch[batch_count] = std::unique_ptr<Connection>(new Connection(
                addr, fd,
                connection_id_.fetch_add(1, std::memory_order_relaxed),
                epoll_index, &handler_, weak_from_this()));
            batch_events[batch_count] =
                EPOLLIN; // New connections always start with read
            batch_count++;

            // Process batch if full
            if (batch_count == config_.server.event_batch_size) {
              process_connection_batch(epollfd, {batch, (size_t)batch_count},
                                       {batch_events, (size_t)batch_count},
                                       true);
              batch_count = 0;
            }
          }

          // Process remaining accepted connections
          if (batch_count > 0) {
            process_connection_batch(epollfd, {batch, (size_t)batch_count},
                                     {batch_events, (size_t)batch_count}, true);
            batch_count = 0;
          }
        }
      }
    });
  }
}

void Server::process_connection_io(std::unique_ptr<Connection> &conn,
                                   int events) {
  assert(conn);
  // Handle EPOLLIN - read data and process it
  if (events & EPOLLIN) {
    auto buf_size = config_.server.read_buffer_size;
    char buf[buf_size];
    int r = conn->readBytes(buf, buf_size);

    if (r < 0) {
      // Error or EOF - connection should be closed
      conn.reset();
      return;
    }

    if (r == 0) {
      // No data available (EAGAIN) - skip read processing but continue
      return;
    }

    // Call handler with unique_ptr - handler can take ownership if needed
    handler_.on_data_arrived(std::string_view{buf, size_t(r)}, conn);

    // If handler took ownership (conn is now null), return true to indicate
    // processing is done
    if (!conn) {
      return;
    }
  }

  // Send immediately if we have outgoing messages (either from EPOLLOUT or
  // after reading)
  if ((events & EPOLLOUT) || ((events & EPOLLIN) && conn->hasMessages())) {
    bool error = conn->writeBytes();
    if (error) {
      conn.reset(); // Connection should be closed
      return;
    }

    // Call handler with unique_ptr - handler can take ownership if needed
    handler_.on_write_progress(conn);
    // If handler took ownership (conn is now null), return true to indicate
    // processing is done
    if (!conn) {
      return;
    }

    // Check if we should close the connection according to application
    if (!conn->hasMessages() && conn->closeConnection_) {
      conn.reset(); // Connection should be closed
      return;
    }
  }
}

void Server::process_connection_batch(
    int epollfd, std::span<std::unique_ptr<Connection>> batch,
    std::span<const int> events, bool is_new) {
  // First process I/O for each connection
  for (size_t i = 0; i < batch.size(); ++i) {
    if (batch[i]) {
      process_connection_io(batch[i], events[i]);
    }
  }

  // Call post-batch handler - handlers can take ownership here
  handler_.on_post_batch(batch);

  // Transfer all remaining connections back to epoll
  for (auto &conn_ptr : batch) {
    if (conn_ptr) {
      int fd = conn_ptr->getFd();

      struct epoll_event event{};
      if (!conn_ptr->hasMessages()) {
        event.events = EPOLLIN | EPOLLONESHOT;
      } else {
        event.events = EPOLLOUT | EPOLLONESHOT;
      }

      conn_ptr->tsan_release();
      event.data.fd = fd; // Use file descriptor for epoll
      // Put connection back in registry since handler didn't take ownership.
      // Must happen before epoll_ctl
      connection_registry_.store(fd, std::move(conn_ptr));
      int epoll_op = is_new ? EPOLL_CTL_ADD : EPOLL_CTL_MOD;
      if (epoll_ctl(epollfd, epoll_op, fd, &event) == -1) {
        perror(is_new ? "epoll_ctl ADD" : "epoll_ctl MOD");
        (void)connection_registry_.remove(fd);
      }
    }
  }
}