import network
import time
from umqtt.simple import MQTTClient
from machine import Pin

# WiFi Config
SSID = "Wokwi-GUEST"
PASSWORD = ""

# MQTT Config
BROKER = "broker.emqx.io"
PORT = 1883
TOPIC = b"sensor/distance"
CLIENT_ID = b"ultrasonic-subscriber"

# Alert LED
led = Pin(2, Pin.OUT)

# Connect WiFi
def connect_wifi():
    wlan = network.WLAN(network.STA_IF)
    wlan.active(True)
    wlan.connect(SSID, PASSWORD)
    print("🔌 Connecting WiFi...", end="")
    while not wlan.isconnected():
        print(".", end="")
        time.sleep(0.5)
    print("\n✅ Connected:", wlan.ifconfig())

# Callback when message received
def message_callback(topic, msg):
    distance = float(msg.decode())  # convert to number
    print(f"📩 Distance received: {distance} cm")

    # Alert system
    if distance < 30:   # Threshold = 30 cm
        print("⚠️ ALERT: Object too close!")
        led.value(1)   # Turn LED ON
    else:
        led.value(0)   # Turn LED OFF

# Subscribe loop
def subscribe_loop():
    client = MQTTClient(CLIENT_ID, BROKER, PORT)
    client.set_callback(message_callback)
    client.connect()
    print("✅ Connected to MQTT Broker")
    
    client.subscribe(TOPIC)
    print(f"📡 Subscribed to {TOPIC.decode()}")
    
    try:
        while True:
            client.wait_msg()  # block until message arrives
    finally:
        client.disconnect()

# Run
connect_wifi()
subscribe_loop()