// Fab Academy 2026 — Week 14 — Individual assignment
// XIAO RP2040 ↔ Node-RED over USB serial
//
// Hardware (Week 06 PCB):
//   D9  → LED (output, active HIGH)
//   D10 → push button via external 10k pull-down to GND, switch closes to 3V3
//         → pressed = HIGH, released = LOW
//
// Protocol (newline-terminated plain text):
//   Board → host: "PRESSED\n"  on rising edge  (button pushed down, debounced)
//                 "RELEASED\n" on falling edge (button let go,    debounced)
//   Host → board: "ON\n"  → LED on
//                 "OFF\n" → LED off

const int LED_PIN     = D9;
const int BUTTON_PIN  = D10;

const unsigned long DEBOUNCE_MS = 50;
int           lastStableState   = LOW;    // external pull-down: LOW = released
int           lastReadState     = LOW;
unsigned long lastChangeMs      = 0;

String  inputBuffer = "";

void setup() {
  pinMode(LED_PIN,    OUTPUT);
  pinMode(BUTTON_PIN, INPUT);   // external pull-down on the PCB, no internal pull needed
  digitalWrite(LED_PIN, LOW);
  Serial.begin(9600);
}

void loop() {
  handleButton();
  handleSerial();
}

void handleButton() {
  int reading = digitalRead(BUTTON_PIN);

  if (reading != lastReadState) {
    lastChangeMs  = millis();
    lastReadState = reading;
  }

  if ((millis() - lastChangeMs) > DEBOUNCE_MS) {
    if (reading != lastStableState) {
      lastStableState = reading;
      if (lastStableState == HIGH) {
        Serial.println("PRESSED");
      } else {
        Serial.println("RELEASED");
      }
    }
  }
}

void handleSerial() {
  while (Serial.available() > 0) {
    char c = Serial.read();
    if (c == '\n' || c == '\r') {
      if (inputBuffer.length() > 0) {
        if      (inputBuffer == "ON")  digitalWrite(LED_PIN, HIGH);
        else if (inputBuffer == "OFF") digitalWrite(LED_PIN, LOW);
        inputBuffer = "";
      }
    } else {
      inputBuffer += c;
    }
  }
}