//! Day 10 of 2021.

use crate::prelude::*;

/// Get the solution for day 10 of 2021.
pub fn solution() -> Solution {
  Solution::new(Day::new(10, 2021), part_1, part_2)
    .with_expected(387363, 4330777059_i64)
}

/// The logic to solve part one.
fn part_1(input: &str) -> Result<String> {
  let mut syntax_error_score = 0;

  for line in input.lines() {
    let mut tokens = VecDeque::new();

    for token in line.chars() {
      if ['(', '[', '{', '<'].contains(&token) {
        tokens.push_back(token);
        continue;
      }

      let expected_close = match tokens.pop_back() {
        Some('(') => ')',
        Some('[') => ']',
        Some('{') => '}',
        Some('<') => '>',
        _ => unreachable!(),
      };

      if token != expected_close {
        syntax_error_score += match token {
          ')' => 3,
          ']' => 57,
          '}' => 1197,
          '>' => 25137,
          _ => unreachable!(),
        };
      }
    }
  }

  Ok(syntax_error_score.to_string())
}

/// The logic to solve part two.
fn part_2(input: &str) -> Result<String> {
  let mut scores = vec![];

  'line_loop: for line in input.lines() {
    let mut line_score: isize = 0;
    let mut tokens = VecDeque::new();

    for token in line.chars() {
      if ['(', '[', '{', '<'].contains(&token) {
        tokens.push_back(token);
        continue;
      }

      let expected_close = match tokens.pop_back() {
        Some('(') => ')',
        Some('[') => ']',
        Some('{') => '}',
        Some('<') => '>',
        _ => unreachable!(),
      };

      if token != expected_close {
        continue 'line_loop;
      }
    }

    for token in tokens.into_iter().rev() {
      let token_score = match token {
        '(' => 1,
        '[' => 2,
        '{' => 3,
        '<' => 4,
        _ => unreachable!(),
      };

      line_score *= 5;
      line_score += token_score;
    }

    scores.push(line_score);
  }

  scores.sort();
  Ok(scores[scores.len() / 2].to_string())
}