import sys
import os

in_file = sys.argv[1]
out_file = sys.argv[2]

def get_page_order(N):
    Nquadro = N // 4
    for q in reversed(range(Nquadro)):
        yield q*4 + 3
        yield q*4 + 0
    for q in range(Nquadro):
        yield q*4 + 1
        yield q*4 + 2

def echo_and_do(cmd_line):
    print(cmd_line)
    os.system(cmd_line)

# rotate & split pages into _s/p%d.jpg
#cmd_line = 'mkdir -p _s && convert -density 200 -quality 85 -rotate 270 -crop 50%x100% '+in_file+' _s/p%d.jpg'
cmd_line = 'mkdir -p _s && convert -density 200 -quality 85 -rotate 0 -crop 50%x100% '+in_file+' _s/p%d.jpg'
echo_and_do(cmd_line)

# reorder pages and merge into single output
from PyPDF2 import PdfFileReader
N = PdfFileReader(open(in_file, "rb")).getNumPages() * 2

cmd_line = 'convert '
for i in get_page_order(N):
    cmd_line = cmd_line + '_s/p%d.jpg ' % i
cmd_line = cmd_line + out_file
echo_and_do(cmd_line)

cmd_line = 'rm -r _s'
echo_and_do(cmd_line)