#!/usr/bin/env python3

from intcode import defaultlist
from operator import mul


def str_of_signal(signal):
    return ''.join(map(str, signal))

def apply_pattern(signal, offset=0):
    sums = [None] * (len(signal)-1) + [signal[-1]]
    for i in range(len(signal)-2, -1, -1):
        sums[i] = sums[i+1] + signal[i]

    sums = defaultlist(sums, lambda : 0)
    new = []
    for i in range(len(signal)):
        step = i + offset + 1
        n = 0
        for block in range(i, len(signal), 4*step):
            n += sums[block] - sums[block + step]
            n -= sums[block + 2*step] - sums[block + 3*step]
        new.append(abs(n)%10)
    return new

def phase(signal, n, offset=0):
    signal = signal[offset:]
    for i in range(n):
        signal = apply_pattern(signal, offset)
    return signal

def preproc(puzzle_input):
    return list(map(int, puzzle_input))

def partI(signal):
    return str_of_signal(phase(signal, 100)[:8])

def partII(signal):
    signal = signal * 10**4
    offset = int(str_of_signal(signal[:7]))

    return str_of_signal(phase(signal, 100, offset)[:8])