#include "config.hpp"
#include <atomic>
#include <cassert>
#include <csignal>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <inttypes.h>
#include <iostream>
#include <netdb.h>
#include <netinet/tcp.h>
#include <sys/epoll.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/un.h>
#include <thread>
#include <unistd.h>

#ifndef __has_feature
#define __has_feature(x) 0
#endif

// Adapted from getaddrinfo man page
int getListenFd(const char *node, const char *service) {

  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(node, service, &hints, &result);
  if (s != 0) {
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
    abort();
  }

  /* getaddrinfo() returns a list of address structures.
     Try each address until we successfully bind(2).
     If socket(2) (or bind(2)) fails, we (close the socket
     and) try the next 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;
    setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));

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

    close(sfd);
  }

  freeaddrinfo(result); /* No longer needed */

  if (rp == nullptr) { /* No address succeeded */
    fprintf(stderr, "Could not bind\n");
    abort();
  }

  int rv = listen(sfd, SOMAXCONN);
  if (rv) {
    perror("listen");
    abort();
  }

  return sfd;
}

int getAcceptFd(int listenFd, struct sockaddr *addr) {
  socklen_t addrlen = sizeof(sockaddr);
  int fd = accept4(listenFd, addr, &addrlen, SOCK_NONBLOCK);
  return fd;
}

// Connection lifecycle. Only one of these is the case at a time
//  - Created on an accept thread from a call to accept
//  - Waiting on connection fd to be readable/writable
//  - Owned by a network thread, which drains readable and writable bytes
//  - Owned by a thread in the request processing pipeline
//  - Closed by a network thread according to http protocol
//
// Since only one thread owns a connection at a time, no synchronization is
// necessary
struct Connection {
  const int fd;
  const int64_t id;
  struct sockaddr addr;

  Connection(struct sockaddr addr, int fd, int64_t id)
      : fd(fd), id(id), addr(addr) {}

  ~Connection() {
    int e = close(fd);
    if (e == -1) {
      perror("close");
      abort();
    }
  }

  struct Task {
    std::string s;
    bool closeConnection{false};
    int written = 0;
  };

  std::deque<Task> tasks;

  void readBytes() {
    for (;;) {
      // TODO make size configurable
      char buf[1024];
      int r = read(fd, buf, sizeof(buf));
      if (r == -1) {
        if (errno == EINTR) {
          continue;
        }
        if (errno == EAGAIN) {
          return;
        }
        perror("read");
        goto close_connection;
      }
      if (r == 0) {
        goto close_connection;
      }
      // pump parser
      tasks.emplace_back(std::string{buf, size_t(r)});
    }
  close_connection:
    tasks.emplace_back(std::string{}, true);
  }

  bool writeBytes() {
    while (!tasks.empty()) {
      auto &front = tasks.front();
      if (front.closeConnection) {
        return true;
      }
      int w;
      for (;;) {
        w = write(fd, front.s.data() + front.written,
                  front.s.size() - front.written);
        if (w == -1) {
          if (errno == EINTR) {
            continue;
          }
          if (errno == EAGAIN) {
            return false;
          }
          perror("write");
          return true;
        }
        break;
      }
      assert(w != 0);
      front.written += w;
      if (front.written == int(front.s.size())) {
        tasks.pop_front();
      }
    }
    return false;
  }

#if __has_feature(thread_sanitizer)
  void tsan_acquire() { tsan_sync.load(std::memory_order_acquire); }
  void tsan_release() { tsan_sync.store(0, std::memory_order_release); }
  std::atomic<int> tsan_sync;
#else
  void tsan_acquire() {}
  void tsan_release() {}
#endif
};

int main(int argc, char *argv[]) {
  std::string config_file = "config.toml";

  if (argc > 1) {
    config_file = argv[1];
  }

  auto config = weaseldb::ConfigParser::load_from_file(config_file);

  if (!config) {
    std::cerr << "Failed to load config from: " << config_file << std::endl;
    std::cerr << "Using default configuration..." << std::endl;
    config = weaseldb::Config{};
  }

  std::cout << "Configuration loaded successfully:" << std::endl;
  std::cout << "Server bind address: " << config->server.bind_address
            << std::endl;
  std::cout << "Server port: " << config->server.port << std::endl;
  std::cout << "Max request size: " << config->server.max_request_size_bytes
            << " bytes" << std::endl;
  std::cout << "Min request ID length: " << config->commit.min_request_id_length
            << std::endl;
  std::cout << "Request ID retention: "
            << config->commit.request_id_retention_hours.count() << " hours"
            << std::endl;
  std::cout << "Subscription buffer size: "
            << config->subscription.max_buffer_size_bytes << " bytes"
            << std::endl;
  std::cout << "Keepalive interval: "
            << config->subscription.keepalive_interval.count() << " seconds"
            << std::endl;

  signal(SIGPIPE, SIG_IGN);

  int sockfd = getListenFd(config->server.bind_address.c_str(),
                           std::to_string(config->server.port).c_str());
  std::vector<std::thread> threads;
  int epollfd = epoll_create(/*ignored*/ 1);
  if (epollfd == -1) {
    perror("epoll_create");
    abort();
  }

  // Network threads
  // TODO make configurable
  int networkThreads = 1;
  // TODO make configurable
  constexpr int kEventBatchSize = 10;
  for (int i = 0; i < networkThreads; ++i) {
    threads.emplace_back([epollfd, i]() {
      pthread_setname_np(pthread_self(),
                         ("network-" + std::to_string(i)).c_str());
      for (;;) {
        struct epoll_event events[kEventBatchSize]{};
        int eventCount;
        for (;;) {
          eventCount =
              epoll_wait(epollfd, events, kEventBatchSize, /*no timeout*/ -1);
          if (eventCount == -1) {
            if (errno == EINTR) {
              continue;
            }
            perror("epoll_wait");
            abort();
          }
          break;
        }

        for (int i = 0; i < eventCount; ++i) {
          std::unique_ptr<Connection> conn{
              static_cast<Connection *>(events[i].data.ptr)};
          conn->tsan_acquire();
          events[i].data.ptr = nullptr;
          const int fd = conn->fd;

          if (events[i].events & EPOLLERR) {
            // Done with connection
            continue;
          }
          if (events[i].events & EPOLLOUT) {
            // Write bytes, maybe close connection
            bool finished = conn->writeBytes();
            if (finished) {
              // Done with connection
              continue;
            }
          }

          if (events[i].events & EPOLLIN) {
            conn->readBytes();
          }

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

          if (conn->tasks.empty()) {
            // Transfer back to epoll instance. This thread or another thread
            // will wake when fd is ready
            events[i].events = EPOLLIN | EPOLLONESHOT;
          } else {
            events[i].events = EPOLLOUT | EPOLLONESHOT;
          }
          conn->tsan_release();
          events[i].data.ptr = conn.release();
          int e = epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &events[i]);
          if (e == -1) {
            perror("epoll_ctl");
            abort();
          }
        }
      }
    });
  }

  std::atomic<int64_t> connectionId{0};

  // TODO make configurable
  int acceptThreads = 1;
  for (int i = 0; i < acceptThreads; ++i) {
    threads.emplace_back([epollfd, i, sockfd, &connectionId]() {
      pthread_setname_np(pthread_self(),
                         ("accept-" + std::to_string(i)).c_str());
      // Call accept in a loop
      for (;;) {
        struct sockaddr addr;
        int fd = getAcceptFd(sockfd, &addr);
        if (fd == -1) {
          perror("accept4");
          continue;
        }
        auto conn = std::make_unique<Connection>(
            addr, fd, connectionId.fetch_add(1, std::memory_order_relaxed));
        // Post to epoll instance
        struct epoll_event event{};
        event.events = EPOLLIN | EPOLLONESHOT;
        conn->tsan_release();
        event.data.ptr = conn.release();
        int e = epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event);
        if (e == -1) {
          perror("epoll_ctl");
          abort();
        }
      }
    });
  }

  for (auto &t : threads) {
    t.join();
  }

  return 0;
}