state.h

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/* Diagnostic Client library
 * Copyright (C) 2024  Avijit Dey
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
#ifndef DIAGNOSTIC_CLIENT_LIB_LIB_UTILITY_UTILITY_STATE_H
#define DIAGNOSTIC_CLIENT_LIB_LIB_UTILITY_UTILITY_STATE_H
 
#include <atomic>
#include <cstdint>
#include <map>
#include <memory>
#include <mutex>
#include <string>
#include <utility>
 
namespace utility {
namespace state {
template<typename EnumState>
class State {
 public:
  // ctor
  explicit State(EnumState state) : state_{state} {}
 
  // dtor
  virtual ~State() = default;
 
  // start the state
  virtual void Start() = 0;
 
  // Update the state
  virtual void Stop() = 0;
 
  // Handle invoked asynchronously
  // Todo:: Delete this methods, no used anywhere
  virtual void HandleMessage() {}
 
  // Get the State index
  auto GetState() const noexcept -> EnumState { return state_; }
 
 protected:
  // state index number
  EnumState state_;
};
 
template<typename EnumState>
class StateContext {
 public:
  // ctor
  StateContext() : current_state_{nullptr}, state_map_{} {}
 
  // dtor
  ~StateContext() = default;
 
  // Add the needed state
  void AddState(EnumState state, std::unique_ptr<State<EnumState>> state_ptr) {
    state_map_.insert(std::pair<EnumState, std::unique_ptr<State<EnumState>>>(state, std::move(state_ptr)));
  }
 
  // Get the current state
  auto GetActiveState() noexcept -> State<EnumState> & {
    std::lock_guard<std::mutex> const lck{state_lock};
    return *current_state_;
  }
 
  // Function to transition state to provided state
  void TransitionTo(EnumState state) {
    // stop the current state
    Stop();
    // Update to new state
    Update(state);
    // Start new state
    Start();
  }
 
  // Get Context
  auto GetContext() noexcept -> StateContext * { return this; }
 
 private:
  // Start the current state
  void Start() {
    if (this->current_state_ != nullptr) { this->current_state_->Start(); }
  }
 
  // Stop the current state
  void Stop() {
    if (this->current_state_ != nullptr) { this->current_state_->Stop(); }
  }
 
  // Update to new state
  void Update(EnumState state) {
    std::lock_guard<std::mutex> const lck{state_lock};
    auto it = state_map_.find(state);
    if (it != state_map_.end()) {
      this->current_state_ = it->second.get();
    } else {
      // failure condition
    }
  }
 
  // mutex to protect transition
  std::mutex state_lock;
 
  // pointer to store the active state
  State<EnumState> *current_state_;
  // mapping of state to state ref
  std::map<EnumState, std::unique_ptr<State<EnumState>>> state_map_;
};
}  // namespace state
}  // namespace utility
#endif  // DIAGNOSTIC_CLIENT_LIB_LIB_UTILITY_UTILITY_STATE_H