import time
import board
import digitalio

# ----------------------------
# SET PARAMETERS
# ----------------------------
x = 30          # Initial countdown value (e.g., 30, 45, or 60 seconds)
interval = 1.0  # Countdown speed (1 second per count)

# ----------------------------
# BUTTON INPUTS
# ----------------------------
sw1 = digitalio.DigitalInOut(board.GP15)  # Start button (SW1)
sw1.direction = digitalio.Direction.INPUT
sw1.pull = digitalio.Pull.UP              # Pressed = LOW

sw2 = digitalio.DigitalInOut(board.GP16)  # Reset/Stop button (SW2)
sw2.direction = digitalio.Direction.INPUT
sw2.pull = digitalio.Pull.UP              # Pressed = LOW

# ----------------------------
# SHARED BCD DATA LINES (D0-D3)
# ----------------------------
A = digitalio.DigitalInOut(board.GP2)     # BCD bit 0 (LSB)
B = digitalio.DigitalInOut(board.GP3)     # BCD bit 1
C = digitalio.DigitalInOut(board.GP4)     # BCD bit 2
D = digitalio.DigitalInOut(board.GP5)     # BCD bit 3 (MSB)

for pin in [A, B, C, D]:
    pin.direction = digitalio.Direction.OUTPUT

bcd_pins = [A, B, C, D]

# ----------------------------
# LATCH ENABLE PINS (CD4511 control)
# ----------------------------
s72 = digitalio.DigitalInOut(board.GP0)   # TENS display latch
s72.direction = digitalio.Direction.OUTPUT

s71 = digitalio.DigitalInOut(board.GP1)   # ONES display latch
s71.direction = digitalio.Direction.OUTPUT

# ----------------------------
# BCD FUNCTIONS
# ----------------------------
def send_bcd(value):
    """Send 4-bit BCD value to CD4511"""
    for i in range(4):
        bcd_pins[i].value = (value >> i) & 1

def latch(pin):
    """Latch data into 7-segment display"""
    pin.value = 0          # Enable latch (active low)
    time.sleep(0.001)      # Hardware stability delay
    pin.value = 1          # Disable latch

def display_number(num):
    """Display a 2-digit number on the 7-segment displays"""
    tens = num // 10
    ones = num % 10
    
    send_bcd(tens)
    latch(s72)
    
    send_bcd(ones)
    latch(s71)

def display_off():
    send_bcd(15)
    latch(s72)
    send_bcd(15)
    latch(s71)

# ----------------------------
# MAIN VARIABLES
# ----------------------------
count = x          # Start from initial value x
running = False    # Timer state (False = stopped, True = counting down)

display_off()      # Initial blank display

# ----------------------------
# EDGE DETECTION VARIABLES
# ----------------------------
last_sw1_state = True
last_sw2_state = True

# ----------------------------
# MAIN LOOP
# ----------------------------
while True:
    # Read current button states (True = not pressed, False = pressed)
    sw1_pressed = not sw1.value
    sw2_pressed = not sw2.value
    
    # START BUTTON (SW1) - Rising edge detection
    if sw1_pressed and not last_sw1_state:
        if not running:
            running = True
            print(f"COUNTDOWN STARTED from {count:02d}")
    
    # RESET/STOP BUTTON (SW2) - Rising edge detection
    if sw2_pressed and not last_sw2_state:
        running = False
        count = x
        display_off()
        print(f"STOPPED & RESET to {x:02d} (Display OFF)")
    
    # Update button states for next iteration
    last_sw1_state = sw1_pressed
    last_sw2_state = sw2_pressed
    
    # COUNTDOWN PROCESS
    if running:
        # Update display with current count
        display_number(count)
        
        # Countdown logic (decrement every 'interval' seconds)
        time.sleep(interval)
        
        if count > 0:
            count -= 1
            print(f"Time remaining: {count:02d}")
        
        # REACHED ZERO - Auto stop
        if count == 0:
            running = False
            print("COUNTDOWN COMPLETE! Time's up! 🎯")
            display_number(0)  # Show "00" momentarily
            time.sleep(0.5)    # Brief pause to see "00"
            display_off()      # Turn off displays
            count = x          # Reset for next run
            print(f"System stopped. Press SW1 to start from {x:02d}")
    
    else:
        # When not running, keep display OFF (per lab requirement)
        # Small delay to prevent excessive looping
        time.sleep(0.05)