#include <ThingSpeak.h> // include the ThingSpeak library

#define TRIG_PIN   23 // ESP32 pin GPIO26 connected to Ultrasonic Sensor's TRIG pin
#define ECHO_PIN   22 // ESP32 pin GPIO25 connected to Ultrasonic Sensor's ECHO pin
#define BUZZER_PIN 2 // ESP32 pin GPIO17 connected to Piezo Buzzer's pin
#define DISTANCE_THRESHOLD 50 // centimeters

// ThingSpeak settings
char ssid[] = "your_wifi_ssid"; // your network SSID (name)
char pass[] = "your_wifi_password"; // your network password
const unsigned long postingInterval = 10 * 1000; // post data every 10 seconds
unsigned long lastConnectionTime = 0;

// variables will change:
float duration_us, distance_cm;

void setup() {
  Serial.begin (9600);         // initialize serial port
  pinMode(TRIG_PIN, OUTPUT);   // set ESP32 pin to output mode
  pinMode(ECHO_PIN, INPUT);    // set ESP32 pin to input mode
  pinMode(BUZZER_PIN, OUTPUT); // set ESP32 pin to output mode
  
  // initialize ThingSpeak
  ThingSpeak.begin(client);
}

void loop() {
  // generate 10-microsecond pulse to TRIG pin
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // measure duration of pulse from ECHO pin
  duration_us = pulseIn(ECHO_PIN, HIGH);
  // calculate the distance
  distance_cm = 0.017 * duration_us;

  if (distance_cm < DISTANCE_THRESHOLD)
    digitalWrite(BUZZER_PIN, HIGH); // turn on Piezo Buzzer
  else
    digitalWrite(BUZZER_PIN, LOW);  // turn off Piezo Buzzer

  // print the value to Serial Monitor
  Serial.print("distance: ");
  Serial.print(distance_cm);
  Serial.println(" cm");

  // Check if it's time to send data to ThingSpeak
  if (millis() - lastConnectionTime >= postingInterval) {
    sendToThingSpeak(distance_cm);
    lastConnectionTime = millis();
  }

  delay(500);
}

void sendToThingSpeak(float distance) {
  // Connect to WiFi
  WiFi.begin(ssid, pass);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  // Update ThingSpeak fields
  ThingSpeak.setField(1, distance);

  // Write the fields that you've set all at once.
  ThingSpeak.writeFields(2499149, "G688R6I26B1RWSDY");
  
  // Disconnect WiFi
  WiFi.disconnect();
}