Control Output using Bluetooth on ESP32

// This example code is in the Public Domain (or CC0 licensed, at your option.)
// By Evandro Copercini - 2018
//
// This example creates a bridge between Serial and Classical Bluetooth (SPP)
// and also demonstrate that SerialBT have the same functionalities of a normal Serial
//
// The code displays the received data and controls the on board LED
//
// Connect your device to ESP32test
// Use Serial Bluetooth Terminal app.

// this library forms part of the ESP32 Boards Manager file
#include "BluetoothSerial.h"

#if !defined(CONFIG_BT_ENABLED) || !defined(CONFIG_BLUEDROID_ENABLED)
#error Bluetooth is not enabled! Please run `make menuconfig` to and enable it
#endif

#if !defined(CONFIG_BT_SPP_ENABLED)
#error Serial Bluetooth not available or not enabled. It is only available for the ESP32 chip.
#endif

// set variables and constants
BluetoothSerial SerialBT;                   // set the Object SerialBT
String text = "";                           // define the text variable to receive BT input
int LED_BUILTIN = 2;                        // the pin number of the onboard LED
bool LED_STATE = false;                     // set the LED Status to False

// set up a number array called BT.
// The assigned values are LED_ON = 0, LED_OFF = 1, TOGGLE = 2, UNDEFINED = 3
enum BT {LED_ON, LED_OFF, TOGGLE, UNDEFINED };   
int BT = LED_OFF;                            // set the enum array to 1

void setup() {
  Serial.begin(115200);                      // Serial Monitor
  SerialBT.begin("ESP32test");               // Bluetooth device name
  Serial.println("The device started, now you can pair it with bluetooth!");
  pinMode(LED_BUILTIN, OUTPUT);              // set up the onboard LED pin as output
}

void loop() {
  // This line sets the output from the PC to the BT device
  if (Serial.available()) {SerialBT.write(Serial.read()); }

  // This line sets the input from the device to the PC
  if (SerialBT.available() > 0) {
    // stripping transfer characters to get the actual text
    text = SerialBT.readStringUntil('\n');     // get the BT input upto CRLF
    text.trim();                               // remove whitespace

    // set the value of BT enum array dependent on the input text received
    if (text == "Led On"){ BT = LED_ON; }       // set BT to 0
    else if (text == "Led Off"){ BT = LED_OFF; }// set BT to 1
    else if (text == "Toggle"){ BT = TOGGLE; }  // set BT to 2
    else { BT = UNDEFINED; }                    // input not recognised
    //Serial.println(text);                     // show the received text in the monitor

    // this switch case statement uses the value of BT to decide which code to run 
    switch (BT) {
      case 0 :                                  // LED_ON
        LED_STATE = true;                       // set the variable to true
        Serial.println("LED ON");               // print to the Monitor
        digitalWrite(LED_BUILTIN, LED_STATE);   // turn on the LED
        break;                                  // break out of the switch case statement

      case 1 :                                  // LED_OFF
        LED_STATE = false;                      // set the variable to false
        Serial.println("LED OFF");              // print to the Monitor
        digitalWrite(LED_BUILTIN, LED_STATE);   // turn off the LED
        break;                                  // break out of the switch case statement

      case 2 :                                  // LED_TOGGLE
        LED_STATE = !LED_STATE;                 // set the variable. Toggle the previous state
        Serial.println("TOGGLE LED");           // print to the Monitor
        digitalWrite(LED_BUILTIN, LED_STATE);   // toggle the LED
        break;                                  // break out of the switch case statement

      case 3:                                   // UNDEFINED
        LED_STATE = false;                      // set the variable to false
        Serial.println("UNDEFINED INPUT");      // print to the Monitor
        digitalWrite(LED_BUILTIN, LED_STATE);   // turn off the LED
        break;                                  // break out of the switch case statement

      default :                                 // if BT is not in the correct range then this code is executed
        Serial.println("Unrecognised input received");
    }
  }
  // slight 20ms delay
  delay(20);
}