#include <math.h>
#include <DHT.h>  // For temperature/humidity sensor

// ======================
// SENSOR CONFIGURATION
// ======================
#define OUTDOOR_DHT_PIN 16   // GPIO16 for outdoor sensor
#define INDOOR_DHT_PIN 17    // GPIO17 for indoor sensor
#define DHT_TYPE DHT22       // Sensor type (DHT11, DHT21, DHT22)

DHT outdoorSensor(OUTDOOR_DHT_PIN, DHT_TYPE);
DHT indoorSensor(INDOOR_DHT_PIN, DHT_TYPE);

// ======================
// HUMIDITY CALCULATION
// ======================
float calculateMinHumidity(float outdoorTemp, float outdoorRH, float indoorTemp) {
  // Handle invalid temperatures
  if (isnan(outdoorTemp) || isnan(indoorTemp) || outdoorTemp < -40 || indoorTemp < -40) {
    return NAN;
  }
  
  // Magnus formula calculation
  float termOut = outdoorTemp / (outdoorTemp + 243.5);
  float termIn = indoorTemp / (indoorTemp + 243.5);
  float exponent = 17.67 * (termOut - termIn);
  float minRH = outdoorRH * exp(exponent);
  
  // Constrain to physical limits
  return constrain(minRH, 0.0, 100.0);
}

// ======================
// SETUP & MAIN LOOP
// ======================
void setup() {
  Serial.begin(115200);
  outdoorSensor.begin();
  indoorSensor.begin();
  
  Serial.println("\nESP32 Minimum Humidity Calculator");
  Serial.println("=================================");
}

void loop() {
  // Read sensor data
  float outdoorTemp = outdoorSensor.readTemperature();     // °C
  float outdoorHumidity = outdoorSensor.readHumidity();    // %
  float indoorTemp = indoorSensor.readTemperature();       // °C
  
  // Check sensor readings
  if (isnan(outdoorTemp) || isnan(outdoorHumidity) || isnan(indoorTemp)) {
    Serial.println("Error: Failed to read sensors!");
    delay(2000);
    return;
  }
  
  // Calculate minimum achievable humidity
  float minHumidity = calculateMinHumidity(outdoorTemp, outdoorHumidity, indoorTemp);
  
  // Display results
  Serial.print("Outdoor: ");
  Serial.print(outdoorTemp, 1);
  Serial.print("°C, ");
  Serial.print(outdoorHumidity, 1);
  Serial.println("% RH");
  
  Serial.print("Indoor Temp: ");
  Serial.print(indoorTemp, 1);
  Serial.println("°C");
  
  Serial.print("Min Achievable RH: ");
  if (isnan(minHumidity)) {
    Serial.println("Calculation Error");
  } else {
    Serial.print(minHumidity, 1);
    Serial.println("%");
  }
  
  Serial.println("----------------------------");
  delay(5000);  // Update every 5 seconds
}