// -*- mode: c++; c-basic-offset: 2; -*-

#include "common.hh"

#include <list>
#include <poll.h>
#include <vector>

#include "looper.hh"

namespace {

int const read_events = POLLIN | POLLPRI
#ifdef POLLRDHUP
  | POLLRDHUP
#endif
  ;
int const write_events = POLLOUT;
int const error_events = POLLERR | POLLNVAL;
int const hup_events = POLLHUP;

class LooperImpl : public Looper {
public:
  LooperImpl()
    : fds_to_remove_(0), fds_protected_(0), quit_(false) {
  }

  ~LooperImpl() override {
    for (auto& timeout : timeouts_) {
      delete timeout;
    }
  }

  void add(int fd, uint8_t events, FdCallback const& callback) override {
    if (fd < 0) {
      assert(false);
      return;
    }
    for (auto it = fds_.begin(); it != fds_.end(); ++it) {
      if (it->fd == fd) {
        size_t index = it - fds_.begin();
        auto& entry = fdentries_[index];
        if (index >= fds_protected_) {
          entry.callback = callback;
          it->events = pollevents(events);
          return;
        } else {
          // Don't call new callback this run, so add it at the end but
          // remove the old callback as it would be replaced
          if (!entry.removed) {
            entry.removed = true;
            fds_to_remove_++;
          }
        }
      }
    }

    fds_.emplace_back((struct pollfd) { fd, pollevents(events), 0 });
    fdentries_.emplace_back(callback);
  }

  void modify(int fd, uint8_t events) override {
    if (fd < 0) {
      assert(false);
      return;
    }
    for (auto it = fds_.begin(); it != fds_.end(); ++it) {
      if (it->fd == fd) {
        size_t index = it - fds_.begin();
        if (index < fds_protected_) {
          auto entry = fdentries_.begin() + index;
          // If entry is removed we need to write to the later one
          if (entry->removed) {
            continue;
          }
        }
        it->events = pollevents(events);
        return;
      }
    }
    assert(false);
  }

  void remove(int fd) override {
    if (fd < 0) return;
    for (auto it = fds_.begin(); it != fds_.end(); ++it) {
      if (it->fd == fd) {
        size_t index = it - fds_.begin();
        auto entry = fdentries_.begin() + index;
        if (index < fds_protected_) {
          if (!entry->removed) {
            entry->removed = true;
            fds_to_remove_++;
          }
        } else {
          fds_.erase(it);
          fdentries_.erase(entry);
        }
        return;
      }
    }
    assert(false);
  }

  void* schedule(float delay_s, ScheduleCallback const& callback) override {
    clock::time_point target = clock::now()
      + std::chrono::duration_cast<clock::duration>(
          std::chrono::duration<float>(delay_s));
    auto timeout = new Timeout(target, callback);
    for (auto it = timeouts_.begin(); it != timeouts_.end(); ++it) {
      if (target < (*it)->target) {
        timeouts_.insert(it, timeout);
        return timeout;
      }
    }
    timeouts_.push_back(timeout);
    return timeout;
  }

  void cancel(void* handle) override {
    auto timeout = reinterpret_cast<Timeout*>(handle);
    if (!timeout) {
      assert(false);
      return;
    }
    if (timeout->expired) return;
    for (auto it = timeouts_.begin(); it != timeouts_.end(); ++it) {
      if (*it == timeout) {
        timeouts_.erase(it);
        delete timeout;
        return;
      }
    }
    assert(false);
  }

  void quit() override {
    quit_ = true;
  }

  bool run() override {
    std::vector<Timeout*> expired;

    while (!quit_) {
      int timeout = -1;
      if (!timeouts_.empty()) {
        auto dur = std::chrono::duration_cast<std::chrono::milliseconds>(
            timeouts_.front()->target - clock::now());
        if (dur.count() <= 0) {
          timeout = 0;
        } else if (dur.count() < std::numeric_limits<int>::max()) {
          timeout = dur.count();
        } else {
          timeout = std::numeric_limits<int>::max();
        }
      }
      auto ret = poll(fds_.data(), fds_.size(), timeout);
      if (ret < 0) {
        if (errno == EINTR) continue;
        return false;
      }
      now_ = clock::now();
      fds_protected_ = fds_.size();

      if (!timeouts_.empty()) {
        while (timeouts_.front()->target <= now_) {
          auto timeout = timeouts_.front();
          timeouts_.pop_front();
          timeout->expired = true;
          expired.push_back(timeout);
          if (timeouts_.empty()) break;
        }

        for (auto& timeout : expired) {
          timeout->callback(timeout);
        }
        for (auto& timeout : expired) {
          delete timeout;
        }
        expired.clear();
      }

      // Not using iterators here as that would be unsafe with
      // add() and remove() modifying the vector outside protected range
      // while callbacks are called
      size_t i;
      for (i = 0; ret > 0 && i < fds_protected_; ++i) {
        if (fds_[i].revents) {
          --ret;
          if (!fdentries_[i].removed) {
            fdentries_[i].callback(fds_[i].fd, unpollevents(fds_[i].revents));
          }
        }
      }
      assert(ret == 0);
      assert(fds_.size() >= fds_protected_);
      assert(fdentries_.size() >= fds_protected_);
      for (i = fds_protected_; fds_to_remove_ > 0 && i > 0; --i) {
        if (fdentries_[i - 1].removed) {
          --fds_to_remove_;
          fds_.erase(fds_.begin() + i - 1);
          fdentries_.erase(fdentries_.begin() + i - 1);
        }
      }
      assert(fds_to_remove_ == 0);
      fds_protected_ = 0;
    }
    return true;
  }

  clock::time_point now() const override {
    return now_;
  }

private:
  struct FdEntry {
    FdCallback callback;
    bool removed;

    FdEntry(FdCallback const& callback)
      : callback(callback), removed(false) {
    }
  };

  struct Timeout {
    clock::time_point target;
    ScheduleCallback callback;
    bool expired;

    Timeout(clock::time_point target, ScheduleCallback const& callback)
      : target(target), callback(callback), expired(false) {
    }
  };

  static uint8_t unpollevents(short events) {
    uint8_t ret = 0;
    if (events & read_events) {
      ret |= EVENT_READ;
    }
    if (events & write_events) {
      ret |= EVENT_WRITE;
    }
    if (events & error_events) {
      ret |= EVENT_ERROR;
    }
    if (events & hup_events) {
      ret |= EVENT_HUP;
    }
    return ret;
  }

  static short pollevents(uint8_t events) {
    int ret = 0;
    if (events & EVENT_READ) {
      ret |= read_events;
    }
    if (events & EVENT_WRITE) {
      ret |= write_events;
    }
    return ret;
  }

  std::vector<struct pollfd> fds_;
  std::vector<FdEntry> fdentries_;
  size_t fds_to_remove_;
  size_t fds_protected_;
  std::list<Timeout*> timeouts_;
  bool quit_;
  clock::time_point now_;
};

}  // namespace

// static
Looper* Looper::create() {
  return new LooperImpl();
}

// static
const uint8_t Looper::EVENT_READ = 1 << 0;
// static
const uint8_t Looper::EVENT_WRITE = 1 << 1;
// static
const uint8_t Looper::EVENT_ERROR = 1 << 2;
// static
const uint8_t Looper::EVENT_HUP = 1 << 3;