advanced move safety check

Cargo.lock

@@ -148,6 +148,7 @@ dependencies = [
 name = "battlesnake"
 version = "1.0.0"
 dependencies = [
+ "enum-iterator",
  "env_logger",
  "log",
  "rand",
@@ -275,6 +276,26 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "enum-iterator"
+version = "2.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c280b9e6b3ae19e152d8e31cf47f18389781e119d4013a2a2bb0180e5facc635"
+dependencies = [
+ "enum-iterator-derive",
+]
+
+[[package]]
+name = "enum-iterator-derive"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1ab991c1362ac86c61ab6f556cff143daa22e5a15e4e189df818b2fd19fe65b"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "env_filter"
 version = "0.1.2"

battlesnake/Cargo.toml

@@ -22,3 +22,4 @@ serde_json = "1.0.59"
 log = "0.4.0"
 env_logger = "0.11.5"
 rand = "0.8.4"
+enum-iterator = "2.1"

battlesnake/src/logic.rs

@@ -13,9 +13,52 @@
 use log::info;
 use rand::seq::SliceRandom;
 use serde_json::{json, Value};
-use std::collections::HashMap;
 
-use crate::{Battlesnake, Board, Coord, Direction, Game, Move};
+use crate::{Battlesnake, Board, Direction, Game, Move};
+
+impl Battlesnake {
+    /// Check if moving the snake in `direction` is safe.
+    #[must_use]
+    pub fn is_direction_safe(&self, direction: Direction, game: &Game, board: &Board) -> bool {
+        let target = self.head.move_to(direction);
+
+        // check if target is out of bounds
+        if !((0..board.width).contains(&target.x) && (0..board.height).contains(&target.y)) {
+            return false;
+        }
+
+        // check if target is inside a snake
+        if board
+            .snakes
+            .iter()
+            .filter(|snake| {
+                !(game.ruleset.settings.squad.allow_body_collisions && self.squad == snake.squad)
+            })
+            .flat_map(|snake| snake.body.iter())
+            .any(|&coord| target == coord)
+        {
+            return false;
+        }
+
+        // check if a bigger snake could move to this square
+        if board
+            .snakes
+            .iter()
+            .filter(|snake| snake.id != self.id && self.length < snake.length)
+            .flat_map(|snake| enum_iterator::all().map(|dir| snake.head.move_to(dir)))
+            .any(|coord| target == coord)
+        {
+            return false;
+        }
+
+        // check for hazards
+        if board.hazards.iter().any(|&coord| target == coord) {
+            return false;
+        }
+
+        true
+    }
+}
 
 // info is called when you create your Battlesnake on play.battlesnake.com
 // and controls your Battlesnake's appearance
@@ -45,87 +88,15 @@ pub fn end(_game: &Game, _turn: i32, _board: &Board, _you: &Battlesnake) {
 // move is called on every turn and returns your next move
 // Valid moves are "up", "down", "left", or "right"
 // See https://docs.battlesnake.com/api/example-move for available data
-pub fn get_move(_game: &Game, turn: i32, board: &Board, you: &Battlesnake) -> Move {
-    use Direction::{Down, Left, Right, Up};
-
-    let mut is_move_safe: HashMap<_, _> =
-        vec![(Up, true), (Down, true), (Left, true), (Right, true)]
-            .into_iter()
-            .collect();
-
-    // We've included code to prevent your Battlesnake from moving backwards
-    let my_head = &you.body[0]; // Coordinates of your head
-    let my_neck = &you.body[1]; // Coordinates of your "neck"
-
-    if my_neck.x < my_head.x {
-        // Neck is left of head, don't move left
-        is_move_safe.insert(Left, false);
-    } else if my_neck.x > my_head.x {
-        // Neck is right of head, don't move right
-        is_move_safe.insert(Right, false);
-    } else if my_neck.y < my_head.y {
-        // Neck is below head, don't move down
-        is_move_safe.insert(Down, false);
-    } else if my_neck.y > my_head.y {
-        // Neck is above head, don't move up
-        is_move_safe.insert(Up, false);
-    }
-
-    // TODO: Step 1 - Prevent your Battlesnake from moving out of bounds
-    if my_head.x == 0 {
-        is_move_safe.insert(Left, false);
-    }
-    if my_head.x == board.width - 1 {
-        is_move_safe.insert(Right, false);
-    }
-    if my_head.y == 0 {
-        is_move_safe.insert(Down, false);
-    }
-    if my_head.y == board.height - 1 {
-        is_move_safe.insert(Up, false);
-    }
-
-    // TODO: Step 2 - Prevent your Battlesnake from colliding with itself
-    if you.body.contains(&Coord {
-        x: my_head.x - 1,
-        y: my_head.y,
-    }) {
-        is_move_safe.insert(Left, false);
-    }
-    if you.body.contains(&Coord {
-        x: my_head.x + 1,
-        y: my_head.y,
-    }) {
-        is_move_safe.insert(Right, false);
-    }
-    if you.body.contains(&Coord {
-        x: my_head.x,
-        y: my_head.y - 1,
-    }) {
-        is_move_safe.insert(Down, false);
-    }
-    if you.body.contains(&Coord {
-        x: my_head.x,
-        y: my_head.y + 1,
-    }) {
-        is_move_safe.insert(Up, false);
-    }
-
-    // TODO: Step 3 - Prevent your Battlesnake from colliding with other Battlesnakes
-    // let opponents = &board.snakes;
-
-    // Are there any safe moves left?
-    let safe_moves = is_move_safe
-        .into_iter()
-        .filter(|&(_, v)| v)
-        .map(|(k, _)| k)
+pub fn get_move(game: &Game, turn: i32, board: &Board, you: &Battlesnake) -> Move {
+    let safe_moves = enum_iterator::all()
+        .filter(|&direction| you.is_direction_safe(direction, game, board))
         .collect::<Vec<_>>();
 
     // Choose a random move from the safe ones
-    let chosen = safe_moves.choose(&mut rand::thread_rng()).unwrap_or(&Up);
-
-    // TODO: Step 4 - Move towards food instead of random, to regain health and survive longer
-    // let food = &board.food;
+    let chosen = safe_moves
+        .choose(&mut rand::thread_rng())
+        .unwrap_or(&Direction::Up);
 
     info!("MOVE {}: {:?}", turn, chosen);
     Move {

battlesnake/src/main.rs

@@ -1,5 +1,6 @@
 #![allow(clippy::needless_pass_by_value)]
 
+use enum_iterator::Sequence;
 use log::info;
 use rocket::fairing::AdHoc;
 use rocket::http::Status;
@@ -14,7 +15,7 @@ mod logic;
 // API and Response Objects
 // See https://docs.battlesnake.com/api
 
-#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy, Deserialize, Serialize)]
+#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy, Deserialize, Serialize, Sequence)]
 pub enum Direction {
     /// Move left (-x)
     #[serde(rename = "left")]
@@ -165,6 +166,18 @@ pub struct Coord {
     y: i32,
 }
 
+impl Coord {
+    const fn move_to(mut self, direction: Direction) -> Self {
+        match direction {
+            Direction::Left => self.x -= 1,
+            Direction::Up => self.y += 1,
+            Direction::Right => self.x += 1,
+            Direction::Down => self.y -= 1,
+        }
+        self
+    }
+}
+
 #[derive(Deserialize, Serialize, Debug)]
 pub struct GameState {
     game: Game,