#include "callback_manager.h"

#include <iterator>
#include <list>
#include <utility>
#include <vector>

#include "absl/functional/any_invocable.h"
#include "absl/log/check.h"
#include "absl/log/log.h"
#include "absl/synchronization/mutex.h"

namespace safepower_agent {

CallbackManager::Handle::Handle(PrivateToken, CallbackManager& manager,
                                std::list<Callback>::iterator it)
    : manager_(&manager), it_(it) {}

CallbackManager::Handle::~Handle() {
  if (manager_ == nullptr) return;
  absl::MutexLock lock(manager_->mutex_);
  manager_->callbacks_.erase(it_);
}

CallbackManager::Handle::Handle(Handle&& other) {
  manager_ = other.manager_;
  it_ = other.it_;
  other.manager_ = nullptr;
}

CallbackManager::Handle& CallbackManager::Handle::operator=(Handle&& other) {
  if (manager_ != nullptr) {
    absl::MutexLock lock(manager_->mutex_);
    manager_->callbacks_.erase(it_);
  }
  manager_ = other.manager_;
  it_ = other.it_;
  other.manager_ = nullptr;
  return *this;
}

bool CallbackManager::Handle::pending() const {
  if (manager_ == nullptr) return false;
  absl::MutexLock lock_running(manager_->running_mutex_);
  absl::MutexLock lock(manager_->mutex_);
  return *it_ != nullptr;
}

bool CallbackManager::Handle::TryCancel() {
  if (manager_ == nullptr) return false;
  absl::MutexLock lock_running(manager_->running_mutex_);
  absl::MutexLock lock(manager_->mutex_);
  if (*it_ == nullptr) return false;
  *it_ = nullptr;
  return true;
}

CallbackManager::~CallbackManager() {
  if (!mutex_.try_lock()) {
    LOG(DFATAL) << "CallbackManager destroyed while mutex was held";
    return;
  }
  for (Callback& callback : callbacks_) {
    if (callback) {
      LOG(DFATAL) << "CallbackManager destroyed with pending callbacks";
      break;
    }
  }
  mutex_.unlock();
}

CallbackManager::Handle CallbackManager::RunFirst(Callback callback) {
  absl::MutexLock lock(mutex_);
  callbacks_.push_front(std::move(callback));
  return Handle({}, *this, callbacks_.begin());
}

CallbackManager::Handle CallbackManager::RunLast(Callback callback) {
  absl::MutexLock lock(mutex_);
  callbacks_.push_back(std::move(callback));
  return Handle({}, *this, std::prev(callbacks_.end()));
}

void CallbackManager::RunCallbacks() {
  // We need to move the callbacks out of the list because we will run them
  // outside of the lock. This allows the callback to install / remove other
  // callbacks.
  std::vector<Callback> callbacks_to_run;
  {
    absl::MutexLock lock(mutex_);
    for (auto& callback : callbacks_) {
      if (callback) {
        callbacks_to_run.push_back(std::move(callback));
      }
    }
  }
  absl::MutexLock lock(running_mutex_);
  for (auto& callback : callbacks_to_run) {
    std::move(callback)();
  }
}

}  // namespace safepower_agent