from machine import Pin, time_pulse_us
import time

# Pin definitions
TRIG_PIN = 19
ECHO_PIN = 18
BUZZER_PIN = 17
LED_PIN = 16
BUTTON_PIN = 15 

# Initialize pins
trig = Pin(TRIG_PIN, Pin.OUT)
echo = Pin(ECHO_PIN, Pin.IN)
buzzer = Pin(BUZZER_PIN, Pin.OUT)
led = Pin(LED_PIN, Pin.OUT)
button = Pin(BUTTON_PIN, Pin.IN, Pin.PULL_UP)

def measure_distance():
    trig.low()
    time.sleep_us(2)
    trig.high()
    time.sleep_us(10)
    trig.low()
    duration = time_pulse_us(echo, 1, 30000)
    if duration < 0: return None
    return (duration * 0.0343) / 2

def main():
    last_distance = None
    unchanged_start_time = time.time()
    last_sensor_read = 0
    
    # SETTINGS
    DISTANCE_THRESHOLD = 2.0  # Only jumps bigger than 2cm reset the timer
    TIMEOUT_SECONDS = 10      # Alert after 10 seconds of "stillness"
    
    alert_active = False 

    print("System Active. Monitoring for jumps > 2cm...")

    while True:
        current_time = time.time()

        # 1. CHECK THE BUTTON CONSTANTLY (No delay here!)
        if button.value() == 0:
            print("!!! BUTTON RESET !!!")
            buzzer.value(0)
            led.value(0)
            alert_active = False
            last_distance = None 
            unchanged_start_time = time.time()
            time.sleep(0.3) # Short debounce so it doesn't double-trigger
            continue

        # 2. ONLY MEASURE DISTANCE EVERY 1 SECOND
        if current_time - last_sensor_read >= 1:
            last_sensor_read = current_time
            distance = measure_distance()
            
            if distance is None:
                print("Sensor error")
                continue

            if last_distance is None:
                last_distance = distance
                print(f"Initial Level: {distance:.2f} cm")
            else:
                diff = abs(distance - last_distance)
                
                # Only reset if the jump is SIGNIFICANT (e.g., > 2cm)
                if diff > DISTANCE_THRESHOLD:
                    unchanged_start_time = current_time
                    last_distance = distance # Update reference to the new level
                    print(f"Significant Change: {diff:.2f} cm. Timer Reset.")
                else:
                    # Small ripples (< 2cm) are ignored, timer keeps ticking
                    elapsed = current_time - unchanged_start_time
                    print(f"Stable ({distance:.2f} cm) - Idle: {elapsed:.0f}s")

                    if elapsed >= TIMEOUT_SECONDS and not alert_active:
                        buzzer.value(1)
                        led.value(1)
                        alert_active = True
                        print("!!! STAGNANT WATER ALERT !!!")

        # Small sleep so the CPU doesn't catch fire, 
        # but fast enough to catch every button press.
        time.sleep(0.05) 

if __name__ == "__main__":
    main()