const INPUT: &str = include_str!("../../data/day3");

struct Forest {
	pub rows: usize,
	stride: usize,
	trees: Vec<bool>,
}

impl Forest {
	fn parse(text: &str) -> Self {
		let first_line = text.lines().next().unwrap();
		let stride = first_line.len();
		let mut trees = Vec::new();
		let mut rows = 0;
		for line in text.lines() {
			assert_eq!(line.len(), stride);
			trees.extend(line.as_bytes().iter().map(|&c| c == b'#'));
			rows += 1;
		}
		Self {
			rows,
			stride,
			trees,
		}
	}

	fn is_tree(&self, row: usize, column: u64) -> bool {
		assert!(row < self.rows);
		let column = (column % self.stride as u64) as usize;
		self.trees[column + row * self.stride]
	}

	fn hit_trees(&self, slope_y: usize, slope_x: u64) -> u64 {
		let mut row = slope_y;
		let mut col = slope_x;
		let mut hits = 0;
		while row < self.rows {
			if self.is_tree(row, col) {
				hits += 1;
			}
			row += slope_y;
			col += slope_x;
		}
		hits
	}
}

const TEST_SLOPES: &[(usize, u64)] = &[
	(1, 1),
	(1, 3),
	(1, 5),
	(1, 7),
	(2, 1),
];

fn main() {
	let forest = Forest::parse(INPUT);
	println!("Hit trees: {}", forest.hit_trees(1, 3));
	println!(
		"Hit product: {}",
		TEST_SLOPES.iter().map(|(slope_y, slope_x)| {
			forest.hit_trees(*slope_y, *slope_x)
		}).product::<u64>(),
	);
}