feat: implement core of the game

Cargo.toml

@@ -3,6 +3,5 @@ name = "rust-wasm-snake"
 version = "0.1.0"
 edition = "2021"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
-
 [dependencies]
+rand = "0.8.5"

src/lib.rs

@@ -1,8 +1,126 @@
+use std::collections::VecDeque;
+
+use rand::prelude::*;
+
+pub type Position = (usize, usize);
+
+#[derive(Debug, PartialEq)]
+pub enum Direction {
+	Up,
+	Down,
+	Left,
+	Right,
+}
+
+#[derive(Debug)]
+pub struct SnakeGame {
+	width: usize,
+	height: usize,
+	snake: VecDeque<Position>,
+	snake_direction: Direction,
+	food: Position,
+	game_over: bool
+}
+
+fn rand_position(width: usize, height: usize) -> Position {
+	let mut rng = thread_rng();
+	(rng.gen_range(0..width), rng.gen_range(0..height))
+}
+
+fn get_opposite_direction(direction: &Direction) -> Direction {
+	match direction {
+		Direction::Up => Direction::Down,
+		Direction::Down => Direction::Up,
+		Direction::Right => Direction::Left,
+		Direction::Left => Direction::Right,
+	}
+}
+
+impl SnakeGame {
+	pub fn new(width: usize, height: usize) -> SnakeGame {
+		Self {
+			width,
+			height,
+			snake: VecDeque::from([(width / 2, height / 2)]),
+			snake_direction: Direction::Left,
+			food: rand_position(width, height),
+			game_over: false
+		}
+	}
+
+	pub fn change_direction(&mut self, direction: Direction) {
+		// Because you can't start going in the opposite direction you are
+		// currently going
+		if get_opposite_direction(&self.snake_direction) == direction {
+			return;
+		}
+
+		self.snake_direction = direction
+	}
+
+	fn is_valid_move(&self, (x, y): Position, dx: i32, dy: i32) -> bool {
+		let new_x = x as i32 + dx;
+		let new_y = y as i32 + dy;
+		0 <= new_x && new_x < self.width as i32 && 0 <= new_y && new_y < self.height as i32
+	}
+
+	fn get_unoccupied_position(&self) -> Option<Position> {
+		let mut rng = thread_rng();
+		(0..self.height)
+			.flat_map(|y| (0..self.width).map(move |x| (x, y)))
+			.filter(|pos| !self.snake.contains(pos))
+			.choose(&mut rng)
+	}
+
+	pub fn tick(&mut self) {
+		if self.game_over {
+			return;
+		}
+
+		let head = self.snake.front();
+		if head.is_none() {
+			return;
+		}
+		let head = *head.unwrap();
+
+		let (dx, dy): (i32, i32) = match &self.snake_direction {
+			Direction::Up => (-1, 0),
+			Direction::Down => (1, 0),
+			Direction::Left => (-1, 0),
+			Direction::Right => (1, 0),
+		};
+
+		if !self.is_valid_move(head, dx, dy) {
+			self.game_over = true;
+			return;
+		}
+
+		let new_head = (
+			(head.0 as i32 + dx) as usize,
+			(head.1 as i32 + dy) as usize
+		);
+		self.snake.push_front(new_head);
+
+		if new_head == self.food {
+			let new_food = self.get_unoccupied_position();
+			if let Some(new_food) = new_food {
+				self.food = new_food;
+			} else {
+				self.game_over = true;
+			}
+		} else {
+			self.snake.pop_back();
+		}
+	}
+}
+
 #[cfg(test)]
 mod tests {
+	use super::*;
 	#[test]
 	fn it_works() {
-        let result = 2 + 2;
-        assert_eq!(result, 4);
+		let game = SnakeGame::new(10, 10);
+
+		println!("{:?}", game);
 	}
 }