#!/usr/bin/env python

import re
import argparse

RE_CPY = re.compile(r'^cpy (.*) (.)')
RE_INC = re.compile(r'^inc (.)')
RE_DEC = re.compile(r'^dec (.)')
RE_JNZ = re.compile(r'^jnz (.*) (-?\d+)')

INSTRUCTIONS = []
REGISTER = {'a': 0, 'b': 0, 'c': 1, 'd': 0 }

def instruction_cpy(k, v):
    global REGISTER
    if v in REGISTER:
        v = REGISTER[v]
    REGISTER[k] = int(v)
    return 1

def instruction_inc(k):
    global REGISTER
    REGISTER[k] += 1
    return 1

def instruction_dec(k):
    global REGISTER
    REGISTER[k] -= 1
    return 1

def instruction_jnz(k, v):
    global REGISTER
    if k in REGISTER:
        if REGISTER[k]:
            return v
    elif(int(k)):
        return v
    return 1


def load_file(filename):
    with open(filename) as f:
        for line in f:
            yield line.strip()

def main(args):
    for LINE in load_file(args.input):
        match = RE_CPY.match(LINE)
        if match:
            INSTRUCTIONS.append({'values': [match.group(2), match.group(1)], 'function': instruction_cpy})
            continue
        match = RE_INC.match(LINE)
        if match:
            INSTRUCTIONS.append({'values': [match.group(1)], 'function': instruction_inc})
            continue
        match = RE_DEC.match(LINE)
        if match:
            INSTRUCTIONS.append({'values': [match.group(1)], 'function': instruction_dec})
            continue
        match = RE_JNZ.match(LINE)
        if match:
            INSTRUCTIONS.append({'values': [match.group(1), int(match.group(2))], 'function': instruction_jnz})
            continue
        raise Exception("line not parsable: {}". format(LINE))

    line = 0
    while True:
        if line >= len(INSTRUCTIONS):
            break
        code = INSTRUCTIONS[line]
        line += code['function'](*code['values'])

    print(REGISTER['a'])

if __name__ == "__main__":
    parser = argparse.ArgumentParser(description='AdventOfCode 2016 Day 01')
    parser.add_argument('--input', '-i', action='store',  required=True, help='input file')
    args = parser.parse_args()

    main(args)