Blink and read a button

/*
  01 — Blink and read a button
  Kit: ESP32 & ESP8266 IoT Automation Kit (DIY KIT UAE)
  Boards: ESP32 or NodeMCU V3 ESP8266 development board — same sketch, pick the board in the IDE.
  Parts: onboard LED, tactile switch, breadboard, jumper wires. No library.
  Optional: a 5 mm LED from the kit in series with a 220 ohm resistor, long leg
  to the pin below and short leg to GND — then change LED_PIN to that pin
  (ESP32: GPIO 26; NodeMCU: D1) and LED_ON to HIGH.

  Wiring (button): one leg to the pin below, the other leg to GND.
  The internal pull-up holds the pin HIGH; pressing pulls it LOW.
    ESP32:   button -> GPIO 27      LED = onboard, GPIO 2 (HIGH = on)
    NodeMCU: button -> D5           LED = onboard, D4  (LOW  = on)

  What you learn: digital output, digital input with a pull-up, and why one
  press can register as three (contact bounce) — fixed with a 30 ms debounce.
*/

#if defined(ESP32)
  const int BUTTON_PIN = 27;
  const int LED_PIN    = 2;
  const bool LED_ON    = HIGH;
#elif defined(ESP8266)
  const int BUTTON_PIN = D5;
  const int LED_PIN    = LED_BUILTIN;   // D4 on NodeMCU
  const bool LED_ON    = LOW;           // wired between 3V3 and the pin, so LOW lights it
#else
  #error "Select an ESP32 or ESP8266 board"
#endif

bool ledState = false;
int  lastReading = HIGH;
int  stableState = HIGH;
unsigned long lastChange = 0;
const unsigned long DEBOUNCE_MS = 30;

void setup() {
  Serial.begin(115200);
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);

  // Part 1: no wiring at all — blink the onboard LED three times.
  for (int i = 0; i < 3; i++) {
    digitalWrite(LED_PIN, LED_ON);  delay(200);
    digitalWrite(LED_PIN, !LED_ON); delay(200);
  }
  Serial.println("Press the button to toggle the LED.");
}

void loop() {
  // Part 2: the button toggles the LED — one toggle per press, debounced.
  int reading = digitalRead(BUTTON_PIN);
  if (reading != lastReading) {
    lastChange = millis();          // contact is bouncing: restart the timer
    lastReading = reading;
  }
  if (millis() - lastChange > DEBOUNCE_MS && reading != stableState) {
    stableState = reading;          // it has been steady long enough to trust
    if (stableState == LOW) {       // LOW = pressed (pull-up)
      ledState = !ledState;
      digitalWrite(LED_PIN, ledState ? LED_ON : !LED_ON);
      Serial.println(ledState ? "LED on" : "LED off");
    }
  }
}