#! /usr/bin/env python3
from collections import namedtuple


Seat = namedtuple("Seat", ["row", "column", "id"])


def partition_search(partitions, start, end, lower, upper):
    if start == end:
        return start
    assert partitions
    assert start < end
    assert all((lower, upper))
    # print(f"Searching: range {start}:{end} {partitions[0]}")

    mid = (end - start) / 2
    direction = partitions.pop(0)
    if direction == lower:
        return partition_search(partitions, start, start + mid - .5, lower, upper)
    elif direction == upper:
        return partition_search(partitions, start + mid + .5, end, lower, upper)

    raise ValueError(f"Unknown direction {direction}")


def parse_seat(code, total_rows=128, total_cols=8):
    if len(code) != 10:
        raise ValueError(f"Invalid code length: {code}")
    row_partitions = list(code[:7])
    row = partition_search(row_partitions, 0, total_rows-1, "F", "B")
    col_partitions = list(code[7:])
    col = partition_search(col_partitions, 0, total_cols-1, "L", "R")
    return Seat(int(row), int(col), int(row*8+col))


def part1():
    with open("input.txt") as f:
        max_seat = max((parse_seat(line.strip()).id
                        for line in f))
    print(f"Max seat id: {max_seat}")


def part2():
    seats = []
    with open("input.txt") as f:
        seats = list(sorted((parse_seat(line.strip()).id
                        for line in f)))
    last_id = None
    for id in seats:
        # print("Seat:", id)
        if last_id is None:
            last_id = id
            continue
        if id == last_id + 2:
            print(f"My seat: {last_id+1}")
            return
        last_id = id
    else:
        print("Didn't find seat")


if __name__ == "__main__":
    # print(parse_seat("FBFBBFFRLR"))
    part1()
    part2()