#include <WiFi.h>
#include <HTTPClient.h>
#include <ArduinoJson.h>
#include <DHT.h>

// WiFi credentials for Wokwi Simulator
const char* ssid = "Wokwi-GUEST";
const char* password = "";

// ====================================================================================
// CRITICAL: Update this URL with your public server address (e.g., from cloudflared or ngrok).
// The address 127.0.0.1 will NOT work from inside the Wokwi simulator.
// Example (cloudflared): "https://your-unique-name.trycloudflare.com/api/receive-data/"
// ====================================================================================
const char* apiEndpoint = "http://YOUR_PUBLIC_SERVER_ADDRESS/api/receive-data/";

// --- Sensor Pin Definitions ---
// Use `const int` for type safety, which is generally preferred in C++.
const int MQ2_PIN = 36; // VP pin on ESP32 DevKit V1
const int DHT_PIN = 2;  // D2 pin (GPIO2)
#define DHT_TYPE DHT22

// --- Sensor Objects ---
DHT dht(DHT_PIN, DHT_TYPE);

// --- Device Configuration ---
const String deviceId = "WOKWI_MQ2_001";
const String sensorName = "Kitchen Smoke Detector";
const String sensorType = "MQ2";
const String location = "kitchen";

void setup() {
  Serial.begin(115200);
  Serial.println("Starting ESP32 MQ2 Gas Sensor...");
  
  // Configure ADC for ESP32
  analogReadResolution(12);       // 12-bit resolution (0-4095)
  analogSetAttenuation(ADC_11db); // Full 0-3.3V range
  
  // Initialize DHT sensor
  dht.begin();
  
  // --- Connect to WiFi ---
  WiFi.begin(ssid, password);
  Serial.print("Connecting to WiFi");
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\nConnected to WiFi");
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());
}

void loop() {
  Serial.println("\n--- Reading Sensors ---");
  
  // --- Read MQ2 Sensor ---
  int analogValue = analogRead(MQ2_PIN);
  float voltage = analogValue * (3.3 / 4095.0); // Convert analog reading to voltage
  
  // Calculate gas concentration by passing the pre-calculated voltage.
  float gasConcentration = calculateGasConcentration(voltage);
  
  // --- Read DHT22 Sensor ---
  float temperature = dht.readTemperature();
  float humidity = dht.readHumidity();
  
  // Handle NaN (Not a Number) readings from DHT sensor, which indicates a failed read.
  if (isnan(temperature)) {
    temperature = 25.0; // Use a default value
    Serial.println("Warning: DHT22 temperature reading failed, using default value.");
  }
  if (isnan(humidity)) {
    humidity = 50.0; // Use a default value
    Serial.println("Warning: DHT22 humidity reading failed, using default value.");
  }
  
  // --- Print Readings to Serial Monitor for Debugging ---
  Serial.println("Sensor Readings:");
  Serial.println("  Analog Value: " + String(analogValue));
  Serial.println("  Voltage: " + String(voltage, 2) + "V");
  Serial.println("  Gas Concentration: " + String(gasConcentration, 2) + " PPM");
  Serial.println("  Temperature: " + String(temperature, 1) + "°C");
  Serial.println("  Humidity: " + String(humidity, 1) + "%");
  
  // --- Send Data to API ---
  sendSensorData(gasConcentration, analogValue, voltage, temperature, humidity);
  
  // Wait 30 seconds before the next reading cycle
  Serial.println("Waiting 30 seconds for next reading...");
  delay(30000);
}

/**
 * @brief Calculates gas concentration based on sensor voltage.
 * @param voltage The voltage read from the MQ2 sensor's analog output.
 * @return The calculated gas concentration in PPM (parts per million).
 */
float calculateGasConcentration(float voltage) {
  // Prevent division by zero if voltage is 0.
  if (voltage <= 0) return 0;

  // Calculate sensor resistance Rs (assuming a 10kOhm load resistor RL)
  // Formula derived from voltage divider: Vout = Vin * (RL / (Rs + RL))
  float resistance = (3.3 - voltage) / voltage * 10000.0;
  
  // MQ2 calibration formula for smoke detection.
  // NOTE: These values are approximations. For accurate readings, you must
  // calibrate the sensor against known gas concentrations.
  // The formula is derived from the log-log scale graph in the sensor datasheet.
  float ppm = 613.9 * pow(resistance / 1000.0, -2.074);
  
  // Ensure the PPM value stays within a reasonable range.
  return constrain(ppm, 0, 1000);
}

/**
 * @brief Sends sensor data to the Django server via an HTTP POST request.
 * @param gasConc The gas concentration value.
 * @param analogVal The raw analog value from the sensor.
 * @param volt The calculated voltage.
 * @param temp The temperature reading.
 * @param hum The humidity reading.
 */
void sendSensorData(float gasConc, int analogVal, float volt, float temp, float hum) {
  if (WiFi.status() == WL_CONNECTED) {
    HTTPClient http;
    http.begin(apiEndpoint);
    http.addHeader("Content-Type", "application/json");
    
    // Create JSON payload using ArduinoJson library
    StaticJsonDocument<400> doc;
    doc["sensor_name"] = sensorName;
    doc["device_id"] = deviceId;
    doc["sensor_type"] = sensorType;
    doc["location"] = location;
    doc["gas_concentration"] = round(gasConc * 100) / 100.0; // Round to 2 decimal places
    doc["analog_value"] = analogVal;
    doc["voltage"] = round(volt * 100) / 100.0;
    doc["temperature"] = round(temp * 10) / 10.0; // Round to 1 decimal place
    doc["humidity"] = round(hum * 10) / 10.0;
    
    String jsonString;
    serializeJson(doc, jsonString);
    
    Serial.println("Sending data to Django API:");
    Serial.println("  Endpoint: " + String(apiEndpoint));
    Serial.println("  JSON Data: " + jsonString);
    
    // Send the POST request
    int httpResponseCode = http.POST(jsonString);
    
    if (httpResponseCode > 0) {
      String response = http.getString();
      Serial.println("✅ HTTP Response Code: " + String(httpResponseCode));
      Serial.println("📡 Response: " + response);
      if (httpResponseCode == 201) {
        Serial.println("✅ Data sent successfully!");
      }
    } else {
      Serial.println("❌ Error sending data. HTTP Response Code: " + String(httpResponseCode));
      Serial.println("   Check if your server is running and the endpoint URL is correct.");
    }
    
    http.end(); // Free resources
  } else {
    Serial.println("❌ WiFi not connected - cannot send data.");
  }
}