#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>

BLECharacteristic *pBatteryCharacteristic;
BLEServer *pServer;

#define SERVICE_UUID "180F"
#define CHARACTERISTIC_UUID_BATTERY "2A19"

void setup() {
  Serial.begin(115200);
  BLEDevice::init("ESP32 Battery Monitor");

  pServer = BLEDevice::createServer();
  BLEService *pService = pServer->createService(SERVICE_UUID);

  pBatteryCharacteristic = pService->createCharacteristic(
      CHARACTERISTIC_UUID_BATTERY,
      BLECharacteristic::PROPERTY_READ | BLECharacteristic::PROPERTY_NOTIFY
  );

  pBatteryCharacteristic->addDescriptor(new BLE2902());
  pService->start();

  BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
  pAdvertising->addServiceUUID(SERVICE_UUID);
  pAdvertising->start();
}

void loop() {
  int batteryLevel = getBatteryLevel();
  pBatteryCharacteristic->setValue(batteryLevel);
  pBatteryCharacteristic->notify();
  delay(60000);
}

int getBatteryLevel() {
  int rawValue = analogRead(34);
  float voltage = rawValue * (3.3 / 4095.0);
  int batteryLevel = (voltage / 3.3) * 100;
  return batteryLevel;
}