"""Advent of Code 2016 day 1 solutions"""


import re


NORTH = (0, 1)
EXAMPLE_STEPS = [('R', 8), ('R', 4), ('R', 4), ('R', 8)]


def turn(direction, side):
    """
        Turns direction vector left or right by 90 degrees

        >>> turn(NORTH, 'L')
        (-1, 0)
        >>> turn(NORTH, 'R')
        (1, 0)
    """

    d_x, d_y = direction
    if side == 'L':
        return -d_y, d_x
    elif side == 'R':
        return d_y, -d_x
    else:
        raise ValueError('Invalid side: %s' % side)


def teleport(steps):
    """
        The last coordinates of Santa

        >>> teleport(EXAMPLE_STEPS)
        (4, 4)
    """

    coords = (0, 0)
    direction = NORTH
    for (side, distance) in steps:
        direction = turn(direction, side)
        c_x, c_y = coords
        d_x, d_y = direction
        coords = (c_x + d_x * distance, c_y + d_y * distance)
    return coords


def walk(steps):
    """
        The path of Santa

        >>> steps = [('R', 2), ('L', 2)]
        >>> list(walk(steps))
        [(1, 0), (2, 0), (2, 1), (2, 2)]
    """

    coords = (0, 0)
    direction = NORTH
    for (side, distance) in steps:
        direction = turn(direction, side)
        for _ in range(distance):
            c_x, c_y = coords
            d_x, d_y = direction
            coords = (c_x + d_x, c_y + d_y)
            yield coords


def find_first_duplicate(iteratable):
    """
        Finds the first duplicate in iteratable

        >>> find_first_duplicate([0, 1, 2, 1, 2])
        1
    """

    visited = set()
    for elem in iteratable:
        if elem in visited:
            return elem
        visited.add(elem)


def manhattan_distance_from_origin(coords):
    """
        Manhattan's distance to (0, 0)

        >>> manhattan_distance_from_origin((4, -4))
        8
    """

    c_x, c_y = coords
    return abs(c_x) + abs(c_y)


def main():
    """Main function"""
    with open('input.txt', 'r') as handle:
        pattern = r'([RL])(\d+)'
        matches = re.findall(pattern, handle.read())
    steps = [(side, int(distance)) for (side, distance) in matches]

    part1 = teleport(steps)
    print('Part 1:', manhattan_distance_from_origin(part1))

    path = walk(steps)
    part2 = find_first_duplicate(path)
    print('Part 2:', manhattan_distance_from_origin(part2))


if __name__ == '__main__':
    main()