// ===============================
// Pin Definitions
// ===============================
#define LED_RUN           2
#define LED_IDLE          3
#define LED_FAULT         4
#define STARTER_RELAY1    5
#define ENGINE_RUN        6

#define SENSE             7
#define KEY_RUN           8
#define KEY_START         9
#define EMERG_STOP_BTN    10

// ===============================
// Timing Constants
// ===============================
const unsigned long CRANK_TIME   = 5000;   // 5 seconds
const unsigned long WAIT_TIME    = 10000;  // 10 seconds
const unsigned long BLINK_TIME   = 500;    // 500ms blink

// ===============================
// State Machine
// ===============================
enum State {
  IDLE,
  CRANKING,
  WAIT_FOR_RUN,
  RUNNING,
  FAULT,
  EMERGENCY
};

State state = IDLE;

unsigned long stateStartTime = 0;
unsigned long blinkTimer = 0;

int attemptCount = 0;
bool blinkState = false;
bool emergencyLatched = false;

// ===============================
// Setup
// ===============================
void setup() {

  pinMode(LED_RUN, OUTPUT);
  pinMode(LED_IDLE, OUTPUT);
  pinMode(LED_FAULT, OUTPUT);
  pinMode(STARTER_RELAY1, OUTPUT);
  pinMode(ENGINE_RUN, OUTPUT);

  pinMode(SENSE, INPUT);
  pinMode(KEY_RUN, INPUT_PULLUP);
  pinMode(KEY_START, INPUT_PULLUP);
  pinMode(EMERG_STOP_BTN, INPUT_PULLUP);

  resetOutputs();
}

// ===============================
// Main Loop
// ===============================
void loop() {

  bool sense = digitalRead(SENSE) == LOW;           // Active LOW
  bool keyRun = digitalRead(KEY_RUN) == LOW;
  bool keyStart = digitalRead(KEY_START) == LOW;
  bool emerg = digitalRead(EMERG_STOP_BTN) == LOW;

  unsigned long now = millis();

  // ============================
  // Emergency Stop Latch
  // ============================
  if (emerg) {
    emergencyLatched = true;
    state = EMERGENCY;
  }

  if (emergencyLatched) {
    handleEmergency(now);
    return;
  }

  // ============================
  // State Machine
  // ============================
  switch (state) {

    case IDLE:
      resetOutputs();
      digitalWrite(LED_IDLE, HIGH);
      attemptCount = 0;

      if (keyRun) {
        digitalWrite(ENGINE_RUN, HIGH);
        if (keyStart) {
          state = CRANKING;
          stateStartTime = now;
        }
      }
      break;

    case CRANKING:
      digitalWrite(ENGINE_RUN, HIGH);
      digitalWrite(STARTER_RELAY1, HIGH);

      if (sense) {
        digitalWrite(STARTER_RELAY1, LOW);
        state = RUNNING;
      }
      else if (now - stateStartTime >= CRANK_TIME) {
        digitalWrite(STARTER_RELAY1, LOW);
        state = WAIT_FOR_RUN;
        stateStartTime = now;
      }
      break;

    case WAIT_FOR_RUN:
      digitalWrite(ENGINE_RUN, HIGH);

      if (sense) {
        state = RUNNING;
      }
      else if (now - stateStartTime >= WAIT_TIME) {
        attemptCount++;

        if (attemptCount >= 4) {
          state = FAULT;
        } else {
          state = CRANKING;
          stateStartTime = now;
        }
      }
      break;

    case RUNNING:
      digitalWrite(ENGINE_RUN, HIGH);
      digitalWrite(LED_RUN, HIGH);

      if (!keyRun) {
        state = IDLE;
      }
      break;

    case FAULT:
      digitalWrite(LED_FAULT, HIGH);
      digitalWrite(ENGINE_RUN, LOW);

      if (!keyRun) {
        state = IDLE;
      }
      break;

    case EMERGENCY:
      // handled separately
      break;
  }
}

// ===============================
// Emergency Handler
// ===============================
void handleEmergency(unsigned long now) {

  digitalWrite(ENGINE_RUN, LOW);
  digitalWrite(STARTER_RELAY1, LOW);
  digitalWrite(LED_IDLE, LOW);
  digitalWrite(LED_RUN, LOW);

  if (now - blinkTimer >= BLINK_TIME) {
    blinkTimer = now;
    blinkState = !blinkState;
    digitalWrite(LED_FAULT, blinkState);
  }
}

// ===============================
// Reset All Outputs
// ===============================
void resetOutputs() {
  digitalWrite(LED_RUN, LOW);
  digitalWrite(LED_IDLE, LOW);
  digitalWrite(LED_FAULT, LOW);
  digitalWrite(STARTER_RELAY1, LOW);
  digitalWrite(ENGINE_RUN, LOW);
}