/*
  Forum: https://forum.arduino.cc/t/changing-led-state-with-ir-sensors/1434325/2
  Wokwi: https://wokwi.com/projects/457942657328082945

  Simple Signal Light, both directions, considering that the release my be triggered several times while the train
  passes the end of block

    starts with green signal
    press red or green button (train enters block from LEFT or RIGHT)
    signal switches to red
    press green or red button (train starts leaving block to the RIGHT or to the LEFT)
    release green or red button for at least minReleaseTime (train hast completely left the block)
    signal switches to green again

    If the button that signalizes the leaving of a block is pressed again within minReleaseTime the block will
    be considered to be still occupied.

  ec2021

*/

constexpr byte redPin   {12};
constexpr byte greenPin {11};
constexpr byte blockLeftPin  {7};
constexpr byte blockRightPin {6};
constexpr unsigned long minReleaseTime {1000}; // The time that is required after a release to change state back to FREE
enum class BLOCK {FREE, OCCUPIED, INTERRUPTED};

BLOCK blockState = BLOCK::FREE;
unsigned long releaseTime;

class blockSensor {
  private:
    byte pin;
    byte state = HIGH;
    byte lastState = HIGH;
    unsigned long lastChange = 0;
    boolean changed() {
      byte actState = digitalRead(pin);
      if (actState != lastState) {
        lastChange = millis();
        lastState = actState;
      }
      if (actState != state && millis() - lastChange > 30) {
        state = actState;
        return true;
      }
      return false;
    };
  public:
    void init(byte Pin) {
      pin = Pin;
      pinMode(pin, INPUT_PULLUP);
    };
    boolean pressed() {
      if (changed()) {
        return !state;
      } else {
        return false;
      }
    };
    boolean released() {
      if (changed()) {
        return state;
      } else {
        return false;
      }
    };
};

blockSensor blockLeft, blockRight;
blockSensor *blockPtr;

void setup() {
  Serial.begin(115200);
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  blockLeft.init(blockLeftPin);
  blockRight.init(blockRightPin);
  signalToGreen();
  Serial.println("Start");
}

void loop() {
  stateMachine();
}

void signalToRed() {
  digitalWrite(redPin, HIGH);
  digitalWrite(greenPin, LOW);
}

void signalToGreen() {
  digitalWrite(redPin, LOW);
  digitalWrite(greenPin, HIGH);
}

void stateMachine() {
  switch (blockState) {
    case BLOCK::FREE:
      if (blockLeft.pressed()) {
        blockOccupied("LEFT");
        blockPtr = &blockRight;
      }
      if (blockRight.pressed()) {
        blockOccupied("RIGHT");
        blockPtr = &blockLeft;
      }
      break;
    case BLOCK::OCCUPIED:
      if (blockPtr->released()) {
        Serial.println("Sensor released ...");
        releaseTime = millis();
        blockState = BLOCK::INTERRUPTED;
      }
      break;
    case BLOCK::INTERRUPTED:
      if (millis() - releaseTime >= minReleaseTime) {
        Serial.println("Train left block ...");
        signalToGreen();
        blockState = BLOCK::FREE;
      }
      if (blockPtr->pressed()) {
        //if the sensor triggers again let's go back to occupied
        Serial.println("Oops, train still in block ...");
        blockState = BLOCK::OCCUPIED;
      }
      break;

  }
}

void blockOccupied(char *msg) {
  Serial.print("Train entered block from ");
  Serial.println(msg);
  signalToRed();
  blockState = BLOCK::OCCUPIED;
}