#include <iostream>
#include <sstream>
#include <vector>

using namespace std;

class BaseState
{
public:
  BaseState() = default;
  virtual ~BaseState() = default;
  virtual void eval(istream& sequence) const = 0;
private:
};


class State : public BaseState
{
public:
  State() : signals(10) {}
  State(State &&) = default;
  State(State const&) = default;
  State& operator=(State const&) = default;
  State& operator=(State &&) = default;

  void add_signal(BaseState* state, int condition)
  {
    signals.at(condition) = state;
  }

  void eval(istream& sequence) const override
  {
    int next_number;
    sequence >> next_number;
    try
    {
      BaseState* next = signals.at(next_number);
      if ( next != nullptr )
        next -> eval(sequence);
      return;
    }
    catch ( out_of_range const& oor )
    {
      return;
    }
  }
private:
  vector<BaseState*> signals;
};

class EndState : public BaseState
{
public:
  using BaseState::BaseState;

  void eval(istream& sequence) const override
  {
    // cout << "evaling end" << endl;
    if ( sequence.peek() == std::istream::traits_type::eof() )
    {
      cout << "Sequence is correct" << endl;
    }
  }
private:
};

int main()
{
  State start{};
  State alpha{};
  EndState end{};

  start.add_signal(&alpha, 1);
  alpha.add_signal(&start, 2);
  alpha.add_signal(&end, 1);

  try
  {
    alpha.add_signal(&end, -1);
  }
  catch(std::exception& e)
  {
    cerr << "tried to add signal out of range" << endl;
  }
    
  { // Test first sequence (correct)
    stringstream sequence{"1 1"};
    cout << "testing sequence: " << sequence.str() << endl;
    start.eval(sequence);
  }

  { // Test second sequence (correct)
    stringstream sequence{"1 2 1 2 1 1"};
    cout << "testing sequence: " << sequence.str() << endl;
    start.eval(sequence);
  }

  { // Test third sequence (incorrect)
    stringstream sequence{"1 1 1 2 1 1"};
    cout << "testing sequence: " << sequence.str() << endl;
    start.eval(sequence);
  }

  { // Test fourth sequence (incorrect)
    stringstream sequence{"1 1 1"};
    cout << "testing sequence: " << sequence.str() << endl;
    start.eval(sequence);
  }

  { // Test fifth sequence (incorrect)
    stringstream sequence{"1 5 1"};
    cout << "testing sequence: " << sequence.str() << endl;
    start.eval(sequence);
  }

  { // Test sixth sequence (incorrect)
    stringstream sequence{"1 25 1"};
    cout << "testing sequence: " << sequence.str() << endl;
    start.eval(sequence);
  }
  
}