import time
import board
import digitalio

# SET PARAMETERS

x = 60              # Max count value (stopwatch reset after 60)
interval = 0.2      # Time delay between counts (speed of counting)

# BUTTON INPUTS

sw1 = digitalio.DigitalInOut(board.GP15)        # Start button (SW1)
sw1.direction = digitalio.Direction.INPUT       # Set as input
sw1.pull = digitalio.Pull.UP                    # Enable pull-up (pressed = low)

sw2 = digitalio.DigitalInOut(board.GP16)        # Reset button (SW2)
sw2.direction = digitalio.Direction.INPUT       # Set as input
sw2.pull = digitalio.Pull.UP                    # Enable pull-up (pressed = low)

# SHARED BCD DATA LINES (D0-D3)

A = digitalio.DigitalInOut(board.GP2)   # BCD bit 0 #MSB
B = digitalio.DigitalInOut(board.GP3)   # BCD bit 1
C = digitalio.DigitalInOut(board.GP4)   # BCD bit 2
D = digitalio.DigitalInOut(board.GP5)   # BCD bit 3 #LSB

# Set all BCD pin as output
for pin in [A, B, C, D]:
    pin.direction = digitalio.Direction.OUTPUT

bcd_pins = [A, B, C, D]     # Store BCD pins for easy looping
 
# LATCH ENABLE PINS (CD4511 control)

s72 = digitalio.DigitalInOut(board.GP0)     # Control tens display
s72.direction = digitalio.Direction.OUTPUT

s71 = digitalio.DigitalInOut(board.GP1)     # Control ones display
s71.direction = digitalio.Direction.OUTPUT

# BCD FUNCTION
def send_bcd(value):
    # Send 4-bit binary value to CD4511 decoder
    for i in reversed (range(4)):
         bcd_pins[i].value = (value >> i) & 1    # Extract each bit

def latch(pin):
    # Send pulse to latch data into 7-segment display
    pin.value = 0       # Enable latch (active low)
    time.sleep(0.001)   # Small delay for hardware stability
    pin.value = 1       # disable latch

def display_number(num):
    # Split number into tens and ones digits
    tens = num // 10
    ones = num % 10

    # Send tens digit to left display
    send_bcd(tens)
    latch(s72)

    # Send ones digit to right display
    send_bcd(ones)
    latch(s71)

def display_off():
    # Turn OFF both segment
    for pin in bcd_pins:
        pin.value = 0       # Clear BCD input

    # Turn OFF both display
    latch(s72)
    latch(s71)

# MAIN VARIABLES
count = x            # Current stopwatch value
running = False      # State of stopwatch (false = stopped, True = running)

# Initial display OFF
display_off()

# MAIN LOOP
while True:

    # Always update display with current count
    display_number(count)

    # START BUTTON (SW1)
    if not sw1.value:       # Button pressed (low signal)
        count = x           
        running = True      # Start counting
        print("START COUNTDOWN")
        time.sleep(0.3)     # Debounce delay

    # RESET BUTTON (SW2)
    if not sw2.value:       # Button pressed
        running = False     # Stop counting
        count = x           # Reset value to 0
        display_off()
        print("RESET -> DISPLAY OFF")
        time.sleep(0.3)     # Debounce delay

    # COUNTING PROCESS
    if running:                 # Only count when stopwatch is running
        time.sleep(interval)    # Wait before increasing count
        count -= 1              # Increase count by 1

        # MAX VALUE CONDITION
        if count <= 0:           # If count exceed max value
            count = 0           # Reset back to 0
            running = False
            print("TIME UP -> RESET")

        # Display formatted output(always 2 digit)
        print("Time: {:02d}".format(count))