// Week 08 — board functionality test (Week 06 XIAO RP2040 breakout).
// One button cycles the LED through three modes: OFF -> SLOW -> FAST -> OFF...
// Non-blocking (millis-based). Button is active-HIGH (external 10k pull-down).
//
// Pin mapping note (XIAO RP2040, Earle Philhower core):
//   silk D9  = GPIO4  -> the LED
//   silk D10 = GPIO3  -> the button
// Using the D9/D10 macros instead of raw integers keeps the code aligned with
// the board silk and removes the silk-vs-GPIO confusion entirely.

const int LED_PIN    = D9;   // silk D9  (GPIO4)
const int BUTTON_PIN = D10;  // silk D10 (GPIO3), external pull-down -> pressed = HIGH

const unsigned long DEBOUNCE_MS      = 30;   // stable window before a reading counts
const unsigned long SLOW_INTERVAL_MS = 500;  // half-period of the slow blink
const unsigned long FAST_INTERVAL_MS = 125;  // half-period of the fast blink

enum Mode { MODE_OFF, MODE_SLOW, MODE_FAST };
Mode currentMode = MODE_OFF;

bool ledState = false;                 // current LED output level
unsigned long lastBlinkTime    = 0;    // last LED toggle timestamp
unsigned long lastDebounceTime = 0;    // last raw-reading change timestamp
int lastButtonReading = LOW;           // previous raw reading (for change detection)
int buttonState       = LOW;           // debounced, stable button state

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT);          // external pull-down: do NOT use INPUT_PULLUP
  digitalWrite(LED_PIN, LOW);
  Serial.begin(115200);
}

void loop() {
  handleButton();   // detect a debounced press and advance the mode
  updateLed();       // drive the LED according to the current mode
}

// --- button: debounce + rising-edge detection ---
void handleButton() {
  int reading = digitalRead(BUTTON_PIN);

  if (reading != lastButtonReading) {
    lastDebounceTime = millis();       // input moved: restart the debounce timer
  }

  if (millis() - lastDebounceTime > DEBOUNCE_MS) {
    // the reading has been stable long enough to be trusted
    if (reading != buttonState) {
      buttonState = reading;
      if (buttonState == HIGH) {       // LOW -> HIGH transition = a real press
        advanceMode();
      }
    }
  }

  lastButtonReading = reading;
}

void advanceMode() {
  switch (currentMode) {
    case MODE_OFF:  currentMode = MODE_SLOW; break;
    case MODE_SLOW: currentMode = MODE_FAST; break;
    case MODE_FAST: currentMode = MODE_OFF;  break;
  }

  // start the new mode from a clean phase
  lastBlinkTime = millis();
  ledState = false;
  digitalWrite(LED_PIN, LOW);

  Serial.print("Mode -> ");
  Serial.println(currentMode == MODE_OFF  ? "OFF"
               : currentMode == MODE_SLOW ? "SLOW"
                                          : "FAST");
}

// --- LED: non-blocking blink according to the current mode ---
void updateLed() {
  if (currentMode == MODE_OFF) {
    if (ledState) {                    // make sure it ends up off
      ledState = false;
      digitalWrite(LED_PIN, LOW);
    }
    return;
  }

  unsigned long interval =
      (currentMode == MODE_SLOW) ? SLOW_INTERVAL_MS : FAST_INTERVAL_MS;

  if (millis() - lastBlinkTime >= interval) {
    lastBlinkTime = millis();
    ledState = !ledState;
    digitalWrite(LED_PIN, ledState ? HIGH : LOW);
  }
}