#!/usr/bin/python

# Busy Beaver Turing machine

# https://en.wikipedia.org/wiki/Busy_beaver

# Create GIF animation with ImageMagick:
# convert -delay 90 beaver_step*.png -loop 0 b.gif

from PIL import Image, ImageDraw, ImageFont

cell = 40 * [0]         # tape array
left, right = 19, 24    # plot limits

fs = 120
w, h = (right - left + 1) * 84, 3 * fs
fnt = ImageFont.truetype('Courier Prime.ttf', fs)

bp = len(cell) // 2     # starting position
bs = "A"                # initial state

# 3-state, 2-symbol
tab3  = {
"A": ["1RB", "1RH"],
"B": ["0RC", "1RB"],
"C": ["1LC", "1LA"],
}

# 4-state, 2-symbol
tab4 = {
"A": ["1RB", "1LB"],
"B": ["1LA", "0LC"],
"C": ["1RH", "1LD"],
"D": ["1RD", "0RA"],
}

# select table to use
tab = tab3
step = -1

while True:
    out = "".join([str(x) for x in cell])
    out2 = out[:bp] + bs + out[bp+1:]
    out  = out[left:right+1]
    out2 = out2[left:right+1]
    print(out2)

    step += 1
    im = Image.new('RGBA', (w, h), (0,0,0))
    d = ImageDraw.Draw(im)
    d.text((0, 0), out, font = fnt, fill = (255,255,0), align = "left")
    d.text((0, fs), (bp - left) * " " + bs, font = fnt, fill = (255,0,0), align = "left")
    d.text((0, 2 * fs), "STEP %u" % step, font = fnt, fill = (0,255,0), align = "left")
    im.save("beaver_step%04u.png" % step)

    if bs == "H":
        for n in range(step + 1, step + 3):
            im.save("beaver_step%04u.png" % n)
        break
    cmd = tab[bs][cell[bp]]
    cell[bp] = int(cmd[0])
    if cmd[1] == 'R':
        bp += 1
    if cmd[1] == 'L':
        bp -= 1
    bs = cmd[2]