#!/usr/bin/env python
# -*- encoding: utf-8; py-indent-offset: 4 -*-

# Author: Sebastian Mark
# CC-BY-SA (https://creativecommons.org/licenses/by-sa/4.0/deed.de)

# pylint: disable=missing-module-docstring,missing-function-docstring,consider-using-f-string

import re
import copy

DIRECTION = {
    "^": (-1, 0),
    "v": (1, 0),
    "<": (0, -1),
    ">": (0, 1),
}


def readinput():
    with open("input", "r", encoding="utf-8") as file:
        lines = file.readlines()
        sep = lines.index("\n")

        warehouse = []
        for line in lines[:sep]:
            warehouse.append(list(line.strip()))

        directions = ""
        for line in lines[sep + 1 :]:
            directions += line.strip()

    return warehouse, directions


def find_robot(warehouse: list) -> tuple:
    for y, line in enumerate(warehouse):
        try:
            x = line.index("@")
        except ValueError:
            continue

        return (y, x)


def run_robot_run(warehouse: list, robot: tuple, directions: list) -> list:
    sorted_warehouse = copy.deepcopy(warehouse)
    roboty, robotx = robot

    for d in directions:
        dy, dx = DIRECTION[d]

        nxty = roboty + dy
        nxtx = robotx + dx

        # check for border in front of robot
        if sorted_warehouse[nxty][nxtx] == "#":
            continue

        # check stack of boxes
        boxes = []
        bxchky, bxchkx = nxty, nxtx
        while sorted_warehouse[bxchky][bxchkx] == "O":
            boxes.append((bxchky, bxchkx))
            bxchky += dy
            bxchkx += dx

        # check for border after last box
        if sorted_warehouse[bxchky][bxchkx] == "#":
            continue

        # move boxes
        for box in boxes:
            sorted_warehouse[box[0] + dy][box[1] + dx] = "O"

        # move robot
        sorted_warehouse[roboty][robotx] = "."
        sorted_warehouse[nxty][nxtx] = "@"
        roboty, robotx = nxty, nxtx

    return sorted_warehouse


def calc_gps_sum(warehouse: list) -> int:
    gps_sum = 0
    for y, line in enumerate(warehouse):
        boxes = re.finditer("O", "".join(line))
        for box in boxes:
            gps_sum += 100 * y + box.start()

    return gps_sum


def print_area(area: list):
    for line in area:
        print("".join(line))


def main():
    warehouse, directions = readinput()

    # part 1
    robot = find_robot(warehouse)
    unclutterd_warehouse = run_robot_run(warehouse, robot, directions)
    gps_sum = calc_gps_sum(unclutterd_warehouse)
    print("GPS sum: %d" % gps_sum)


if __name__ == "__main__":
    main()