cpp_design_patterns/Behavioral/state/handmade_fsm.cpp at master · mpavezb/cpp_design_patterns · GitHub

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#include <iostream>
#include <map>
#include <string>
#include <vector>
using namespace std;

// states
enum class State { OffHook, Connecting, Connected, OnHold, OnHook };

// events to triger transitions
enum class Trigger {
  CallDialed,
  HungUp,
  CallConnected,
  PlacedOnHold,
  TakenOffHold,
  LeftMessage,
  StopUsingPhone
};

inline ostream &operator<<(ostream &os, const State &s) {
  switch (s) {
  case State::OffHook:
    os << "off the hook";
    break;
  case State::Connecting:
    os << "connecting";
    break;
  case State::Connected:
    os << "connected";
    break;
  case State::OnHold:
    os << "on hold";
    break;
  case State::OnHook:
    os << "on the hook";
    break;
  }
  return os;
}

inline ostream &operator<<(ostream &os, const Trigger &t) {
  switch (t) {
  case Trigger::CallDialed:
    os << "call dialed";
    break;
  case Trigger::HungUp:
    os << "hung up";
    break;
  case Trigger::CallConnected:
    os << "call connected";
    break;
  case Trigger::PlacedOnHold:
    os << "placed on hold";
    break;
  case Trigger::TakenOffHold:
    os << "taken off hold";
    break;
  case Trigger::LeftMessage:
    os << "left message";
    break;
  case Trigger::StopUsingPhone:
    os << "putting phone on hook";
    break;
  default:
    break;
  }
  return os;
}

typedef pair<Trigger, State> Transition;
typedef vector<Transition> Transitions;

int main() {

  // FSM: Each State is connected to some transitions
  map<State, Transitions> rules;

  rules[State::OffHook] = {{Trigger::CallDialed, State::Connecting},
                           {Trigger::StopUsingPhone, State::OnHook}};

  rules[State::Connecting] = {{Trigger::HungUp, State::OffHook},
                              {Trigger::CallConnected, State::Connected}};

  rules[State::Connected] = {{Trigger::LeftMessage, State::OffHook},
                             {Trigger::HungUp, State::OffHook},
                             {Trigger::PlacedOnHold, State::OnHold}};

  rules[State::OnHold] = {{Trigger::TakenOffHold, State::Connected},
                          {Trigger::HungUp, State::OffHook}};

  State currentState{State::OffHook};
  State exitState{State::OnHook};

  while (true) {
    cout << "The phone is currently " << currentState << endl;
  select_trigger:

    // Display available states:
    cout << "Select a trigger:"
         << "\n";

    int i = 0;
    for (auto item : rules[currentState]) {
      cout << i++ << ". " << item.first << "\n";
    }

    // Read selected action
    size_t input;
    cin >> input;

    // handle errors
    if ((input + 1) > rules[currentState].size()) {
      cout << "Incorrect option. Please try again."
           << "\n";
      goto select_trigger;
    }

    // Update state based on the transition.
    currentState = rules[currentState][input].second;
    if (currentState == exitState)
      break;
  }

  cout << "We are done using the phone"
       << "\n";

  return 0;
}