// Embedded Heater Control System - ESP32
#include <DHT.h>

#define DHTPIN 13          // DHT Sensor Pin
#define DHTTYPE DHT22     // DHT 22 (AM2302)
#define HEATER_PIN 2      // Heater Control (simulated LED)
#define LED_PIN 4         // State Indicator LED
#define BUZZER_PIN 5      // Overheat Buzzer

DHT dht(DHTPIN, DHTTYPE);

// Temperature thresholds
const float HEAT_ON_TEMP = 30.0;
const float STABILIZE_TEMP = 35.0;
const float OVERHEAT_TEMP = 40.0;

// State Enum
enum HeaterState {
  IDLE,
  HEATING,
  STABILIZING,
  TARGET_REACHED,
  OVERHEAT
};

HeaterState currentState = IDLE;
bool buzzerState = false;
unsigned long previousMillis = 0;
const long buzzerInterval = 500; // milliseconds

void setup() {
  Serial.begin(115200);
  dht.begin();

  pinMode(HEATER_PIN, OUTPUT);
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);

  digitalWrite(HEATER_PIN, LOW);
  digitalWrite(LED_PIN, LOW);
  digitalWrite(BUZZER_PIN, LOW);
}

void loop() {
  float temp = dht.readTemperature();

  if (isnan(temp)) {
    Serial.println("Failed to read from DHT sensor!");
    delay(1000);
    return;
  }

  updateState(temp);
  logStatus(temp);
  handleBuzzer();

  delay(2000); // Read every 2 seconds
}

void updateState(float temp) {
  if (temp > OVERHEAT_TEMP) {
    currentState = OVERHEAT;
    digitalWrite(HEATER_PIN, LOW);
    digitalWrite(LED_PIN, LOW);
  }
  else if (temp >= STABILIZE_TEMP) {
    currentState = TARGET_REACHED;
    digitalWrite(HEATER_PIN, LOW);
    digitalWrite(LED_PIN, LOW);
    digitalWrite(BUZZER_PIN, LOW);
  }
  else if (temp >= HEAT_ON_TEMP && temp < STABILIZE_TEMP) {
    currentState = STABILIZING;
    digitalWrite(HEATER_PIN, LOW);
    digitalWrite(LED_PIN, HIGH);
    digitalWrite(BUZZER_PIN, LOW);
  }
  else if (temp < HEAT_ON_TEMP) {
    currentState = HEATING;
    digitalWrite(HEATER_PIN, HIGH);
    digitalWrite(LED_PIN, HIGH);
    digitalWrite(BUZZER_PIN, LOW);
  }
  else {
    currentState = IDLE;
    digitalWrite(HEATER_PIN, LOW);
    digitalWrite(LED_PIN, LOW);
    digitalWrite(BUZZER_PIN, LOW);
  }
}

void handleBuzzer() {
  if (currentState == OVERHEAT) {
    unsigned long currentMillis = millis();
    if (currentMillis - previousMillis >= buzzerInterval) {
      previousMillis = currentMillis;
      buzzerState = !buzzerState;
      digitalWrite(BUZZER_PIN, buzzerState);
    }
  } else {
    digitalWrite(BUZZER_PIN, LOW);
    buzzerState = false;
  }
}

void logStatus(float temp) {
  String stateStr;
  switch (currentState) {
    case IDLE: stateStr = "Idle"; break;
    case HEATING: stateStr = "Heating"; break;
    case STABILIZING: stateStr = "Stabilizing"; break;
    case TARGET_REACHED: stateStr = "Target Reached"; break;
    case OVERHEAT: stateStr = "Overheat"; break;
  }

  Serial.print("Temperature: ");
  Serial.print(temp);
  Serial.print(" °C | State: ");
  Serial.println(stateStr);
}