// ESP32 Series BLE Library
#include <BLEDevice.h>  
#include <BLEUtils.h>
#include <BLEServer.h> 

//UUIDs for the Bluetooth service and characteristic
#define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"

//Class to handle when a data is received from smart phone
class onReceive: public BLECharacteristicCallbacks {
    void onWrite(BLECharacteristic *pCharacteristic) {
        // Retrieve the value written to the characteristic and Convert to Arduino String
        String value = pCharacteristic->getValue().c_str(); 

        // If the value length is greater than 0, print it to the Serial Monitor
        if (value.length() > 0) {
            Serial.println("*********");
            Serial.print("New value: ");
            for (int i = 0; i < value.length(); i++)
                Serial.print(value[i]); // Print each character of the received value
            Serial.println();
            Serial.println("*********");
        }
    }
};

void setup() {

    Serial.begin(115200);  // Initialize the Serial Monitor
    // Initialize BLE device with the name "GLYPHC3"
    BLEDevice::init("GLYPHC3");
  
    // Create a BLE server
    BLEServer *pServer = BLEDevice::createServer();
    // Create a BLE service with the defined UUID
    BLEService *pService = pServer->createService(SERVICE_UUID);
    // Create a BLE characteristic with the defined UUID
    BLECharacteristic *pCharacteristic = pService->createCharacteristic(
                                         CHARACTERISTIC_UUID,
                                         BLECharacteristic::PROPERTY_READ |
                                         BLECharacteristic::PROPERTY_WRITE
                                       );

    // Set the function that as to be called when data is received 
    pCharacteristic->setCallbacks(new onReceive());

    // Set an initial value for the characteristic
    pCharacteristic->setValue("Hello World");
    pService->start();  // Start the service

    // Start advertising the BLE service
    BLEAdvertising *pAdvertising = pServer->getAdvertising();
    pAdvertising->start();

    // Print message indicating that the server has started
    Serial.println("BLE Server started, advertising...");
}

void loop() {
    //The main loop doesn't do anything until the data is received by the BLE 
    delay(2000);  // Wait for 2 seconds
}