/*
 * This file is part of PowerDNS or dnsdist.
 * Copyright -- PowerDNS.COM B.V. and its contributors
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * In addition, for the avoidance of any doubt, permission is granted to
 * link this program with OpenSSL and to (re)distribute the binaries
 * produced as the result of such linking.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
#pragma once
#include <boost/any.hpp>
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/hashed_index.hpp>
#include <boost/multi_index/key_extractors.hpp>
#include <vector>
#include <map>
#include <stdexcept>
#include <string>
#include <sys/time.h>

using namespace ::boost::multi_index;

class FDMultiplexerException : public std::runtime_error
{
public:
  FDMultiplexerException(const std::string& str) :
    std::runtime_error(str)
  {}
};

/** Very simple FD multiplexer, based on callbacks and boost::any parameters
    As a special service, this parameter is kept around and can be modified,
    allowing for state to be stored inside the multiplexer.

    It has some "interesting" semantics
*/

class FDMultiplexer
{
public:
  typedef boost::any funcparam_t;
  typedef std::function<void(int, funcparam_t&)> callbackfunc_t;
  enum class EventKind : uint8_t
  {
    Read,
    Write,
    Both
  };

protected:
  struct Callback
  {
    callbackfunc_t d_callback;
    mutable funcparam_t d_parameter;
    struct timeval d_ttd;
    int d_fd;
  };

public:
  virtual ~FDMultiplexer() = default;

  // The maximum number of events processed in a single run, not the maximum of watched descriptors
  static constexpr unsigned int s_maxevents = 1024;
  /* The maximum number of events processed in a single run will be capped to the
     minimum value of maxEventsHint and s_maxevents, to reduce memory usage. */
  static FDMultiplexer* getMultiplexerSilent(unsigned int maxEventsHint = s_maxevents);

  struct InRun
  {
    InRun(const InRun&) = delete;
    InRun(InRun&&) = delete;
    InRun& operator=(const InRun&) = delete;
    InRun& operator=(InRun&&) = delete;
    InRun(bool& ref) :
      d_inrun(ref)
    {
      if (d_inrun) {
        throw FDMultiplexerException("FDMultiplexer::run() is not reentrant!");
      }
      d_inrun = true;
    }
    ~InRun()
    {
      d_inrun = false;
    }
    bool& d_inrun;
  };

  /* tv will be updated to 'now' before run returns */
  /* timeout is in ms, 0 will return immediately, -1 will block until at
     least one descriptor is ready */
  /* returns 0 on timeout, -1 in case of error (but all implementations
     actually throw in that case) and the number of ready events otherwise.
     Note that We might have two events (read AND write) for the same descriptor */
  virtual int run(struct timeval* tv, int timeout = 500) = 0;

  /* timeout is in ms, 0 will return immediately, -1 will block until at least one FD is ready */
  virtual void getAvailableFDs(std::vector<int>& fds, int timeout) = 0;

  //! Add an fd to the read watch list - currently an fd can only be on one list at a time!
  void addReadFD(int fd, callbackfunc_t toDo, const funcparam_t& parameter = funcparam_t(), const struct timeval* ttd = nullptr)
  {
    bool alreadyWatched = d_writeCallbacks.count(fd) > 0;

    if (alreadyWatched) {
      this->alterFD(fd, EventKind::Write, EventKind::Both);
    }
    else {
      this->addFD(fd, EventKind::Read);
    }

    /* do the addition _after_ so the entry is not added if there is an error */
    accountingAddFD(d_readCallbacks, fd, std::move(toDo), parameter, ttd);
  }

  //! Add an fd to the write watch list - currently an fd can only be on one list at a time!
  void addWriteFD(int fd, callbackfunc_t toDo, const funcparam_t& parameter = funcparam_t(), const struct timeval* ttd = nullptr)
  {
    bool alreadyWatched = d_readCallbacks.count(fd) > 0;

    if (alreadyWatched) {
      this->alterFD(fd, EventKind::Read, EventKind::Both);
    }
    else {
      this->addFD(fd, EventKind::Write);
    }

    /* do the addition _after_ so the entry is not added if there is an error */
    accountingAddFD(d_writeCallbacks, fd, std::move(toDo), parameter, ttd);
  }

  //! Remove an fd from the read watch list. You can't call this function on an fd that is closed already!
  /** WARNING: references to 'parameter' become invalid after this function! */
  void removeReadFD(int fd)
  {
    const auto& iter = d_writeCallbacks.find(fd);
    accountingRemoveFD(d_readCallbacks, fd);

    if (iter != d_writeCallbacks.end()) {
      this->alterFD(fd, EventKind::Both, EventKind::Write);
    }
    else {
      this->removeFD(fd, EventKind::Read);
    }
  }

  //! Remove an fd from the write watch list. You can't call this function on an fd that is closed already!
  /** WARNING: references to 'parameter' become invalid after this function! */
  void removeWriteFD(int fd)
  {
    const auto& iter = d_readCallbacks.find(fd);
    accountingRemoveFD(d_writeCallbacks, fd);

    if (iter != d_readCallbacks.end()) {
      this->alterFD(fd, EventKind::Both, EventKind::Read);
    }
    else {
      this->removeFD(fd, EventKind::Write);
    }
  }

  void setReadTTD(int fd, struct timeval tv, int timeout)
  {
    const auto& it = d_readCallbacks.find(fd);
    if (it == d_readCallbacks.end()) {
      throw FDMultiplexerException("attempt to timestamp fd not in the multiplexer");
    }

    auto newEntry = *it;
    tv.tv_sec += timeout;
    newEntry.d_ttd = tv;
    d_readCallbacks.replace(it, newEntry);
  }

  void setWriteTTD(int fd, struct timeval tv, int timeout)
  {
    const auto& it = d_writeCallbacks.find(fd);
    if (it == d_writeCallbacks.end()) {
      throw FDMultiplexerException("attempt to timestamp fd not in the multiplexer");
    }

    auto newEntry = *it;
    tv.tv_sec += timeout;
    newEntry.d_ttd = tv;
    d_writeCallbacks.replace(it, newEntry);
  }

  void alterFDToRead(int fd, callbackfunc_t toDo, const funcparam_t& parameter = funcparam_t(), const struct timeval* ttd = nullptr)
  {
    accountingRemoveFD(d_writeCallbacks, fd);
    this->alterFD(fd, EventKind::Write, EventKind::Read);
    accountingAddFD(d_readCallbacks, fd, std::move(toDo), parameter, ttd);
  }

  void alterFDToWrite(int fd, callbackfunc_t toDo, const funcparam_t& parameter = funcparam_t(), const struct timeval* ttd = nullptr)
  {
    accountingRemoveFD(d_readCallbacks, fd);
    this->alterFD(fd, EventKind::Read, EventKind::Write);
    accountingAddFD(d_writeCallbacks, fd, std::move(toDo), parameter, ttd);
  }

  std::vector<std::pair<int, funcparam_t>> getTimeouts(const struct timeval& tv, bool writes = false)
  {
    std::vector<std::pair<int, funcparam_t>> ret;
    const auto tied = std::tie(tv.tv_sec, tv.tv_usec);
    auto& idx = writes ? d_writeCallbacks.get<TTDOrderedTag>() : d_readCallbacks.get<TTDOrderedTag>();

    for (const auto& t : idx) {
      if (t.d_ttd.tv_sec == 0 || tied <= std::tie(t.d_ttd.tv_sec, t.d_ttd.tv_usec)) {
        break;
      }
      ret.emplace_back(t.d_fd, t.d_parameter);
    }

    return ret;
  }

  typedef FDMultiplexer* getMultiplexer_t(unsigned int);
  typedef std::multimap<int, getMultiplexer_t*> FDMultiplexermap_t;

  static FDMultiplexermap_t& getMultiplexerMap()
  {
    static FDMultiplexermap_t theMap;
    return theMap;
  }

  virtual std::string getName() const = 0;

  size_t getWatchedFDCount(bool writeFDs) const
  {
    return writeFDs ? d_writeCallbacks.size() : d_readCallbacks.size();
  }

  void runForAllWatchedFDs(void (*watcher)(bool isRead, int fd, const funcparam_t&, struct timeval))
  {
    for (const auto& entry : d_readCallbacks) {
      watcher(true, entry.d_fd, entry.d_parameter, entry.d_ttd);
    }
    for (const auto& entry : d_writeCallbacks) {
      watcher(false, entry.d_fd, entry.d_parameter, entry.d_ttd);
    }
  }

protected:
  struct FDBasedTag
  {
  };
  struct TTDOrderedTag
  {
  };
  struct ttd_compare
  {
    /* we want a 0 TTD (no timeout) to come _after_ everything else */
    bool operator()(const struct timeval& lhs, const struct timeval& rhs) const
    {
      /* special treatment if at least one of the TTD is 0,
         normal comparison otherwise */
      if (lhs.tv_sec == 0 && rhs.tv_sec == 0) {
        return false;
      }
      if (lhs.tv_sec == 0 && rhs.tv_sec != 0) {
        return false;
      }
      if (lhs.tv_sec != 0 && rhs.tv_sec == 0) {
        return true;
      }

      return std::tie(lhs.tv_sec, lhs.tv_usec) < std::tie(rhs.tv_sec, rhs.tv_usec);
    }
  };

  typedef multi_index_container<
    Callback,
    indexed_by<
      hashed_unique<tag<FDBasedTag>,
                    member<Callback, int, &Callback::d_fd>>,
      ordered_non_unique<tag<TTDOrderedTag>,
                         member<Callback, struct timeval, &Callback::d_ttd>,
                         ttd_compare>>>
    callbackmap_t;

  callbackmap_t d_readCallbacks, d_writeCallbacks;
  bool d_inrun{false};

  void accountingAddFD(callbackmap_t& cbmap, int fd, callbackfunc_t toDo, const funcparam_t& parameter, const struct timeval* ttd)
  {
    Callback cb;
    cb.d_fd = fd;
    cb.d_callback = std::move(toDo);
    cb.d_parameter = parameter;
    memset(&cb.d_ttd, 0, sizeof(cb.d_ttd));
    if (ttd) {
      cb.d_ttd = *ttd;
    }

    auto pair = cbmap.insert(std::move(cb));
    if (!pair.second) {
      throw FDMultiplexerException("Tried to add fd " + std::to_string(fd) + " to multiplexer twice");
    }
  }

  void accountingRemoveFD(callbackmap_t& cbmap, int fd)
  {
    if (!cbmap.erase(fd)) {
      throw FDMultiplexerException("Tried to remove unlisted fd " + std::to_string(fd) + " from multiplexer");
    }
  }

  virtual void addFD(int fd, EventKind kind) = 0;
  /* most implementations do not care about which event has to be removed, except for kqueue */
  virtual void removeFD(int fd, EventKind kind) = 0;
  /* most implementations do not care about which event has to be removed, except for kqueue */
  virtual void alterFD(int fd, EventKind from, EventKind to)
  {
    /* naive implementation */
    removeFD(fd, from);
    addFD(fd, to);
  }
};