import board
import time
import busio
import digitalio
import lcd                      
import i2c_pcf8574_interface    

# Initialize I2C and LCD
i2c = busio.I2C(scl=board.GP5, sda=board.GP4)  
address = 0x27  
i2c = i2c_pcf8574_interface.I2CPCF8574Interface(i2c, address)  
display = lcd.LCD(i2c, num_rows=2, num_cols=16) 
display.set_backlight(True)  
display.set_display_enabled(True)  

# Clear display initially 
display.clear()

# Define messages for each line
line1_message = "Line 1 Scrolling Right"
line2_message = "Line 2 Scrolling Left"

# Add spaces before and after to create proper smooth scrolling effect
padding = " " * 16  # Create 16 spaces for padding (width of LCD)
line1_padded = padding + line1_message + padding  # Add padding to both sides of message
line2_padded = padding + line2_message + padding

# Get total length for scrolling calculations
line1_length = len(line1_padded)
line2_length = len(line2_padded)

# Initialize position counters - these track the current "window" position in the padded strings
line1_pos = 0
line2_pos = 0

while True:
    # Clear display for new content 
    display.clear()  

    # Display current window of line 1 (scrolling right)
    display.set_cursor_pos(0, 0)  # Set cursor to first line 
    # Extract 16 characters from the current position for line 1
    display.print(line1_padded[line1_pos:line1_pos+16])  # Show current 16-char window

    # Display current window of line 2 (scrolling left)
    display.set_cursor_pos(1, 0)  # Set cursor to second line 
    # Extract 16 characters from the current position for line 2
    display.print(line2_padded[line2_pos:line2_pos+16])  # Show current 16-char window

    # Update positions for next iteration with opposite directions
    line1_pos = (line1_pos - 1) % (line1_length - 16) #Scroll right by decrementing position
    line2_pos = (line2_pos + 1) % (line2_length - 16) #Scroll left by incrementing position
    
    # CRITICAL: Handle negative index for line1_pos
    if line1_pos < 0:
        line1_pos = line1_length - 17  # Wrap around to end of string when position becomes negative
        # Subtract 17 instead of 16 to account for the next decrement

    # Delay for smooth scrolling 
    time.sleep(0.2)