//! Day 12 of 2020.

use crate::prelude::*;

mod extra;

use extra::*;

/// Get the solution for day 12 of 2020.
pub fn solution() -> Solution {
  Solution::new(Day::new(12, 2020), part_1, part_2).with_expected(1496, 63843)
}

/// Parse the list of [`Instruction`]s based on the puzzle input.
fn parse_instructions(input: &str) -> Vec<Instruction> {
  input.lines().map(Into::into).collect()
}

/// The logic to solve part one.
fn part_1(input: &str) -> Result<String> {
  let instructions = parse_instructions(input);
  let mut horizontal = 0;
  let mut vertical = 0;
  let mut direction: i32 = 90;

  for instruction in instructions {
    match instruction.action {
      Action::Forward => {
        match direction {
          90 => horizontal += instruction.value,
          270 => horizontal -= instruction.value,
          180 => vertical += instruction.value,
          0 => vertical -= instruction.value,
          _ => unreachable!("{direction}"),
        };
      }
      Action::Left => direction -= instruction.value,
      Action::Right => direction += instruction.value,
      Action::East => horizontal += instruction.value,
      Action::West => horizontal -= instruction.value,
      Action::South => vertical += instruction.value,
      Action::North => vertical -= instruction.value,
    };

    direction = match direction % 360 {
      -270 => 90,
      -90 => 270,
      0 => 0,
      value => value.abs(),
    };
  }

  Ok((horizontal.abs() + vertical.abs()).to_string())
}

/// The logic to solve part two.
fn part_2(input: &str) -> Result<String> {
  let instructions = parse_instructions(input);

  let mut horizontal = 0;
  let mut vertical = 0;

  let mut wp_horizontal = 10;
  let mut wp_vertical = -1;

  for instruction in instructions {
    match instruction.action {
      Action::Forward => {
        horizontal += wp_horizontal * instruction.value;
        vertical += wp_vertical * instruction.value;
      }
      Action::East => wp_horizontal += instruction.value,
      Action::West => wp_horizontal -= instruction.value,
      Action::South => wp_vertical += instruction.value,
      Action::North => wp_vertical -= instruction.value,
      _ => (),
    };

    match (&instruction.action, instruction.value) {
      (Action::Left, 90) | (Action::Right, 270) => {
        let intermediate_vertical = wp_vertical;
        wp_vertical = -wp_horizontal;
        wp_horizontal = intermediate_vertical;
      }
      (Action::Left, 180) | (Action::Right, 180) => {
        wp_horizontal = -wp_horizontal;
        wp_vertical = -wp_vertical;
      }
      (Action::Left, 270) | (Action::Right, 90) => {
        let intermediate_horizontal = wp_horizontal;
        wp_horizontal = -wp_vertical;
        wp_vertical = intermediate_horizontal;
      }
      _ => (),
    };
  }

  Ok((horizontal.abs() + vertical.abs()).to_string())
}