boxon/src/main.rs

use std::{env::args, fs};

fn main() {
	let file = args().nth(1).expect("Usage : boxon <file>");
	let content = fs::read_to_string(&file).unwrap_or_else(|_| panic!("Could not read file '{file}'."));
	let mut grid = Grid::from(content);
	grid.fix();
	let content: String = grid.into();
	fs::write(&file, content).unwrap_or_else(|_| panic!("Could not write result to file '{file}'."));
}

#[derive(Debug, Clone)]
struct Grid(Vec<Vec<char>>);

impl<T: AsRef<str>> From<T> for Grid {
	fn from(value: T) -> Self {
		Self(value.as_ref().lines().map(str::chars).map(Iterator::collect).collect())
	}
}

impl From<Grid> for String {
	fn from(val: Grid) -> Self {
		val.0
			.iter()
			.map(|l| l.iter().collect::<String>())
			.collect::<Vec<_>>()
			.join("\n")
	}
}

impl Grid {
	fn fix(&mut self) -> usize {
		let mut result = 0;
		let copy = self.clone();
		for (y, line) in self.0.iter_mut().enumerate() {
			for (x, character) in line.iter_mut().enumerate() {
				if let Some(cross) = copy.cross_at(x as i32, y as i32) {
					let new_char = match cross {
						Cross(
							((), MM, ()), //
							(MM, MM, MM), //
							((), MM, ()), //
						) => '┼',
						Cross(
							((), MM, ()), //
							(F_, MM, MM), //
							((), MM, ()), //
						) => '├',
						Cross(
							((), MM, ()), //
							(MM, MM, F_), //
							((), MM, ()), //
						) => '┤',
						Cross(
							((), MM, ()), //
							(MM, MM, MM), //
							((), F_, ()), //
						) => '┴',
						Cross(
							((), F_, ()), //
							(MM, MM, MM), //
							((), MM, ()), //
						) => '┬',
						Cross(
							((), F_, ()), //
							(MM, MM, MM), //
							((), F_, ()), //
						) => '─',
						Cross(
							((), MM, ()), //
							(F_, MM, F_), //
							((), MM, ()), //
						) => '│',
						Cross(
							((), MM, ()), //
							(MM, MM, F_), //
							((), F_, ()), //
						) => '┘',
						Cross(
							((), F_, ()), //
							(MM, MM, F_), //
							((), MM, ()), //
						) => '┐',
						Cross(
							((), F_, ()), //
							(F_, MM, MM), //
							((), MM, ()), //
						) => '┌',
						Cross(
							((), MM, ()), //
							(F_, MM, MM), //
							((), F_, ()), //
						) => '└',
						_ => continue,
					};
					*character = new_char;
					result += 1;
				}
			}
		}
		result
	}

    #[rustfmt::skip]
	fn cross_at(&self, x: i32, y: i32) -> Option<Cross> {
		fn at(g: &Grid, x: i32, y: i32) -> Option<Cross> {
            if x < 0 || y < 0 {
                None
            } else {
                Some(connects(*g.0.get(y as usize)?.get(x as usize)?))
            }
		}
        let get = |x: i32, y: i32| -> Cross {
            at(self, x, y).unwrap_or(connects(' '))
        };
        let c = get(x, y);        
		let its_y = y;
		Some(Cross(
			(                        (), get(x, y - 1).d() && c.u(),                ()),
			(get(x - 1, y).r() && c.l(), get(x, its_y).c(), get(x + 1, y).l() && c.r()),
			(                        (), get(x, y + 1).u() && c.d(),                ()),
		))
	}
}

fn connects(c: char) -> Cross {
	match c {
		'-' => Cross(
			((), F_, ()), //
			(MM, MM, MM), //
			((), F_, ()), //
		),
		'|' => Cross(
			((), MM, ()), //
			(F_, MM, F_), //
			((), MM, ()), //
		),
		'+' => Cross(
			((), MM, ()), //
			(MM, MM, MM), //
			((), MM, ()), //
		),
		'┼' => Cross(
			((), MM, ()), //
			(MM, MM, MM), //
			((), MM, ()), //
		),
		'├' => Cross(
			((), MM, ()), //
			(F_, MM, MM), //
			((), MM, ()), //
		),
		'┤' => Cross(
			((), MM, ()), //
			(MM, MM, F_), //
			((), MM, ()), //
		),
		'┴' => Cross(
			((), MM, ()), //
			(MM, MM, MM), //
			((), F_, ()), //
		),
		'┬' => Cross(
			((), F_, ()), //
			(MM, MM, MM), //
			((), MM, ()), //
		),
		'─' => Cross(
			((), F_, ()), //
			(MM, MM, MM), //
			((), F_, ()), //
		),
		'│' => Cross(
			((), MM, ()), //
			(F_, MM, F_), //
			((), MM, ()), //
		),
		'┘' => Cross(
			((), MM, ()), //
			(MM, MM, F_), //
			((), F_, ()), //
		),
		'┐' => Cross(
			((), F_, ()), //
			(MM, MM, F_), //
			((), MM, ()), //
		),
		'┌' => Cross(
			((), F_, ()), //
			(F_, MM, MM), //
			((), MM, ()), //
		),
		'└' => Cross(
			((), MM, ()), //
			(F_, MM, MM), //
			((), F_, ()), //
		),
		_ => Cross(
			((), F_, ()), //
			(F_, F_, F_), //
			((), F_, ()), //
		),
	}
}

const F_: bool = false;
const MM: bool = true;
type Empt = ();
struct Cross(
	(Empt, bool, Empt), //
	(bool, bool, bool), //
	(Empt, bool, Empt), //
);

impl Cross {
	fn u(&self) -> bool {
		self.0.1
	}

	fn d(&self) -> bool {
		self.2.1
	}

	fn l(&self) -> bool {
		self.1.0
	}

	fn r(&self) -> bool {
		self.1.2
	}

	fn c(&self) -> bool {
		self.1.1
	}
}