# main.py
# Water-level style monitor: HC-SR04 -> Pico
# SAFE if distance <= 200 cm -> green LED ON and "SAFE" on LCD
# DANGER if distance > 200 cm -> red LED blinks and "DANGER" on LCD

from machine import Pin, I2C
import utime
from i2c_lcd import I2cLcd

# ----- CONFIGURE PINS (change these if your wiring differs) -----
TRIG_PIN = 3    # GP3 on Pico
ECHO_PIN = 2    # GP2 on Pico
SDA_PIN  = 4    # GP4 (I2C SDA)
SCL_PIN  = 5    # GP5 (I2C SCL)
GREEN_LED = 14  # GP14
RED_LED   = 15  # GP15

# ----- SETUP HARDWARE -----
TRIG = Pin(TRIG_PIN, Pin.OUT)
ECHO = Pin(ECHO_PIN, Pin.IN)
green = Pin(GREEN_LED, Pin.OUT)
red   = Pin(RED_LED, Pin.OUT)

# Setup I2C and LCD (if available)
i2c = I2C(0, scl=Pin(SCL_PIN), sda=Pin(SDA_PIN), freq=100000)
devices = i2c.scan()
lcd = None
if len(devices) == 0:
    # no I2C device found
    print("No I2C device found. LCD will be disabled.")
else:
    addr = devices[0]
    print("I2C device(s) found:", [hex(a) for a in devices], "-> using", hex(addr))
    lcd = I2cLcd(i2c, addr, 2, 16)

# ----- ULTRASONIC HELPER (with timeouts) -----
def get_distance(timeout_us=30000):
    """
    Returns distance in cm or None if timeout / no echo.
    timeout_us default 30000 (~30 ms) which corresponds to ~5 meters return time safe limit.
    """
    TRIG.value(0)
    utime.sleep_us(2)
    TRIG.value(1)
    utime.sleep_us(10)
    TRIG.value(0)

    start = utime.ticks_us()
    # wait for ECHO to go high
    while ECHO.value() == 0:
        if utime.ticks_diff(utime.ticks_us(), start) > timeout_us:
            return None
    t1 = utime.ticks_us()

    # wait for ECHO to go low
    while ECHO.value() == 1:
        if utime.ticks_diff(utime.ticks_us(), t1) > timeout_us:
            return None
    t2 = utime.ticks_us()

    dt = utime.ticks_diff(t2, t1)  # microseconds
    # sound speed 343 m/s => 0.0343 cm/us ; distance = (dt * 0.0343) / 2
    distance_cm = (dt * 0.0343) / 2.0
    return distance_cm

# ----- MAIN LOOP -----
THRESHOLD = 200.0  # cm

def show_on_lcd(line1, line2=""):
    if lcd:
        lcd.move_to(0,0)
        lcd.putstr(line1.ljust(16)[:16])
        lcd.move_to(0,1)
        lcd.putstr(line2.ljust(16)[:16])

# initial state
green.value(0)
red.value(0)
utime.sleep(0.1)

while True:
    dist = get_distance()
    if dist is None:
        # no echo / sensor error
        print("No echo (timeout). Check wiring / power.")
        show_on_lcd("Distance: --.-- cm", "No Echo")
        green.value(0)
        red.value(0)
        utime.sleep(1.0)
        continue

    # round for display
    dstr = "{:6.1f} cm".format(dist)
    print("Distance:", dstr)

    if dist <= THRESHOLD:
        # SAFE
        green.value(1)
        red.value(0)
        show_on_lcd("Distance: " + dstr, "SAFE")
        utime.sleep(0.8)   # slower update while safe
    else:
        # DANGER: blink red
        green.value(0)
        show_on_lcd("Distance: " + dstr, "DANGER")
        # blink once
        red.value(1)
        utime.sleep(0.35)
        red.value(0)
        utime.sleep(0.35)