"""Digital Stream, by Al Sweigart al@inventwithpython.com
A screensaver in the style of The Matrix movie's visuals.
This code is available at https://nostarch.com/big-book-small-python-programming
Tags: tiny, artistic, beginner, scrolling"""

import random, shutil, sys, time

# Set up the constants:
MIN_STREAM_LENGTH = 6  # (!) Try changing this to 1 or 50.
MAX_STREAM_LENGTH = 14  # (!) Try changing this to 100.
PAUSE = 0.1  # (!) Try changing this to 0.0 or 2.0.
STREAM_CHARS = ['0', '1']  # (!) Try changing this to other characters.

# Density can range from 0.0 to 1.0:
DENSITY = 0.02  # (!) Try changing this to 0.10 or 0.30.

# Get the size of the terminal window:
WIDTH = shutil.get_terminal_size()[0]
# We can't print to the last column on Windows without it adding a
# newline automatically, so reduce the width by one:
WIDTH -= 1

print('Digital Stream, by Al Sweigart al@inventwithpython.com')
print('Press Ctrl-C to quit.')
time.sleep(2)

try:
    # For each column, when the counter is 0, no stream is shown.
    # Otherwise, it acts as a counter for how many times a 1 or 0
    # should be displayed in that column.
    columns = [0] * WIDTH
    while True:
        # Set up the counter for each column:
        for i in range(WIDTH):
            if columns[i] == 0:
                if random.random() <= DENSITY:
                    # Restart a stream on this column.
                    columns[i] = random.randint(MIN_STREAM_LENGTH,
                                                MAX_STREAM_LENGTH)

            # Display an empty space or a 1/0 character.
            if columns[i] > 0:
                print(random.choice(STREAM_CHARS), end='')
                columns[i] -= 1
            else:
                print(' ', end='')
        print()  # Print a newline at the end of the row of columns.
        sys.stdout.flush()  # Make sure text appears on the screen.
        time.sleep(PAUSE)
except KeyboardInterrupt:
    sys.exit()  # When Ctrl-C is pressed, end the program.