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//! # Day 1: Not Quite Lisp
//!
//! Santa was hoping for a white Christmas, but his weather machine's "snow" function is powered by
//! stars, and he's fresh out! To save Christmas, he needs you to collect **fifty stars** by
//! December 25th.
//!
//! Collect stars by helping Santa solve puzzles. Two puzzles will be made available on each day in
//! the Advent calendar; the second puzzle is unlocked when you complete the first. Each puzzle
//! grants **one star**. Good luck!
//!
//! Here's an easy puzzle to warm you up.
//!
//! Santa is trying to deliver presents in a large apartment building, but he can't find the right
//! floor - the directions he got are a little confusing. He starts on the ground floor (floor `0`)
//! and then follows the instructions one character at a time.
//!
//! An opening parenthesis, `(`, means he should go up one floor, and a closing parenthesis, `)`,
//! means he should go down one floor.
//!
//! The apartment building is very tall, and the basement is very deep; he will never find the top
//! or bottom floors.
//!
//! For example:
//!
//! - `(())` and `()()` both result in floor `0`.
//! - `(((` and `(()(()(` both result in floor `3`.
//! - `))(((((` also results in floor `3`.
//! - `())` and `))(` both result in floor `-1` (the first basement level).
//! - `)))` and `)())())` both result in floor `-3`.
//!
//! To **what floor** do the instructions take Santa?
//!
//! ## Part Two
//!
//! Now, given the same instructions, find the **position** of the first character that causes him
//! to enter the basement (floor `-1`). The first character in the instructions has position `1`,
//! the second character has position `2`, and so on.
//!
//! For example:
//!
//! - `)` causes him to enter the basement at character position `1`.
//! - `()())` causes him to enter the basement at character position `5`.
//!
//! What is the **position** of the character that causes Santa to first enter the basement?

use anyhow::{bail, Result};

pub const INPUT: &str = include_str!("d01.txt");

pub fn solve_part_one(input: &str) -> Result<i64> {
    Ok(input.chars().fold(0, |f, c| f + if c == '(' { 1 } else { -1 }))
}

pub fn solve_part_two(input: &str) -> Result<i64> {
    let mut floor = 0;

    for (i, c) in input.chars().enumerate() {
        floor += if c == '(' { 1 } else { -1 };
        if floor == -1 {
            return Ok(i as i64 + 1);
        }
    }

    bail!("never going to the basement")
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn part_one() {
        assert_eq!(0, solve_part_one("(())").unwrap());
        assert_eq!(0, solve_part_one("()()").unwrap());
        assert_eq!(3, solve_part_one("(((").unwrap());
        assert_eq!(3, solve_part_one("(()(()(").unwrap());
        assert_eq!(3, solve_part_one("))(((((").unwrap());
        assert_eq!(-1, solve_part_one("())").unwrap());
        assert_eq!(-1, solve_part_one("))(").unwrap());
        assert_eq!(-3, solve_part_one(")))").unwrap());
        assert_eq!(-3, solve_part_one(")())())").unwrap());
    }

    #[test]
    fn part_two() {
        assert_eq!(1, solve_part_two(")").unwrap());
        assert_eq!(5, solve_part_two("()())").unwrap());
    }
}