Optional audible-alert investigation

/*
  ESP32 Plant Monitoring Learning Kit
  Project 6: Optional audible-alert investigation

  Wiring: optional DIY-016 active buzzer - signal GPIO27, VCC 3V3 (check
  the module's rating; it is sold as a 5 V part), GND. Soil sensor on GPIO34.

  What you learn: an alert should be rare and clear. The sketch beeps
  twice when the soil percentage drops below DRY_SOIL_PERCENT, then stays
  quiet for QUIET_MINUTES so it does not nag; a recovered plant resets it.
  Endpoints are fixed here - take yours from project 2.
*/

const int BUZZER_PIN = 27;
const int SOIL_PIN = 34;
const int DRY_RAW = 3200;          // from your calibration study
const int WET_RAW = 1400;
const int DRY_SOIL_PERCENT = 30;
const unsigned long QUIET_MINUTES = 1;   // 1 min here; 60 for a real plant
const unsigned long SAMPLE_MS = 1000;

unsigned long lastSample = 0, lastAlert = 0;
bool alertArmed = true;

void beep(int times) {
  for (int i = 0; i < times; i++) {
    digitalWrite(BUZZER_PIN, HIGH); delay(120);
    digitalWrite(BUZZER_PIN, LOW);  delay(120);
  }
}

void setup() {
  Serial.begin(115200);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(SOIL_PIN, INPUT);
  analogReadResolution(12);
  Serial.println("t_s,soil_raw,soil_pct,state");
}

void loop() {
  if (millis() - lastSample < SAMPLE_MS) return;
  lastSample = millis();
  int raw = analogRead(SOIL_PIN);
  int percent = constrain(map(raw, DRY_RAW, WET_RAW, 0, 100), 0, 100);
  bool dry = percent < DRY_SOIL_PERCENT;
  const char *state = "OK";
  if (dry) {
    if (alertArmed) {
      beep(2);
      lastAlert = millis();
      alertArmed = false;
      state = "ALERT";
      Serial.println("ALERT: soil is dry - water the plant");
    } else if (millis() - lastAlert > QUIET_MINUTES * 60000UL) {
      alertArmed = true;        // the quiet period is over: remind once more
      state = "DRY";
    } else state = "DRY (quiet)";
  } else {
    alertArmed = true;          // watered: the next dry spell alerts again
  }
  Serial.print(millis() / 1000); Serial.print(",");
  Serial.print(raw); Serial.print(",");
  Serial.print(percent); Serial.print(",");
  Serial.println(state);
}