import time
from machine import Pin, ADC

# Ultrasonic Sensor (HC-SR04)
trigger = Pin(2, Pin.OUT)
echo = Pin(3, Pin.IN)

# LDR Module (AO pin connected to GPIO1)
ldr = ADC(Pin(1))
ldr.atten(ADC.ATTN_11DB)  # Full range 0-3.3V

# LEDs
red_led = Pin(4, Pin.OUT)    # Obstacle detected
yellow_led = Pin(5, Pin.OUT) # Low light detected

# Thresholds
OBSTACLE_DISTANCE = 20  # cm
LIGHT_THRESHOLD = 200 # Below this value = low light (0-4095)
TIMEOUT = 100000  # microseconds (100ms)

def measure_distance():
    # Send pulse
    trigger.value(0)
    time.sleep_us(2)
    trigger.value(1)
    time.sleep_us(10)
    trigger.value(0)
    
    # Initialize with timeout
    timeout_start = time.ticks_us()
    
    # Wait for echo start
    while echo.value() == 0:
        if time.ticks_diff(time.ticks_us(), timeout_start) > TIMEOUT:
            return -1  # Timeout
    
    pulse_start = time.ticks_us()
    
    # Wait for echo end
    while echo.value() == 1:
        if time.ticks_diff(time.ticks_us(), timeout_start) > TIMEOUT:
            return -1  # Timeout
    
    pulse_end = time.ticks_us()
    
    # Calculate distance
    pulse_duration = time.ticks_diff(pulse_end, pulse_start)
    return pulse_duration / 58.0  # cm

def read_light():
    return ldr.read()  # Returns 0-4095

while True:
    # Read sensors
    distance = measure_distance()
    light = read_light()
    
    # Reset LEDs
    red_led.value(0)
    yellow_led.value(0)
    
    # Check conditions
    if distance != -1 and distance <= OBSTACLE_DISTANCE:
        red_led.value(1)
        print(f"Obstacle Detected! Distance: {distance:.1f} cm")
    elif light < LIGHT_THRESHOLD:
        yellow_led.value(1)
        print("Low Light Detected.")
    else:
        print("Environment Clear.")
    
    time.sleep(1)