battlesnake/src/logic.rs

@@ -14,71 +14,99 @@ use log::info;
 use rand::seq::SliceRandom;
 use serde_json::{json, Value};
 
-use crate::{Battlesnake, Board, Direction, Game, Move};
-
-const MAX_HEALTH: i32 = 100;
+use crate::{Battlesnake, Board, Coord, Direction, Game, Move};
 
 impl Battlesnake {
-    fn possible_moves_without_heads<'a>(
-        &'a self,
-        game: &'a Game,
-        board: &'a Board,
-    ) -> impl Iterator<Item = Direction> + 'a {
-        enum_iterator::all::<Direction>()
-            .filter(|direction| {
-                // filter out directions that would go outside the field
-                let target = self.head.move_to(*direction);
-                (0..board.width).contains(&target.x) && (0..board.height).contains(&target.y)
-            })
-            .filter(|direction| {
-                let target = self.head.move_to(*direction);
-                // don't collide with any snake
-                !board
+    /// Check if moving the snake in `direction` is safe.
+    #[must_use]
+    pub fn is_direction_safe(&self, direction: Direction, game: &Game, board: &Board) -> bool {
+        if self.is_direction_death(direction, game, board) {
+            return false;
+        }
+
+        let target = self.head.move_to(direction);
+
+        // check if a bigger snake could move to this square
+        if board
             .snakes
             .iter()
-                    .filter(|snake| {
-                        // filter out snakes that are in our squad if body collisions are allowed
-                        !(game.ruleset.settings.squad.allow_body_collisions
-                            && self.squad == snake.squad
-                            && self.id != snake.id)
-                    })
-                    .flat_map(|snake| {
-                        // get all coordinates of the snake body. The tail of the body can be ignored
-                        // if the snake hasn't just eaten, as it will move out of the way
-                        let has_eaten = snake.health == MAX_HEALTH;
-                        snake.body[..snake.body.len() - usize::from(!has_eaten)].iter()
-                    })
-                    .any(|&coord| coord == target)
-            })
+            .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
     }
 
     #[must_use]
-    pub fn possible_moves(&self, game: &Game, board: &Board) -> Vec<Direction> {
-        self.possible_moves_without_heads(game, board)
-            .filter(|direction| {
-                // don't go into spots where a bigger snake must go
-                let target = self.head.move_to(*direction);
-                !board
+    pub fn is_direction_death(&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 true;
+        }
+
+        // check if target is inside a snake
+        if board
             .snakes
             .iter()
             .filter(|snake| {
-                        // The other snake must be bigger than we are
-                        snake.length > self.length
+                !(game.ruleset.settings.squad.allow_body_collisions && self.squad == snake.squad)
             })
-                    .filter_map(|snake| {
-                        // get all snakes movement options
-                        let moves = snake
-                            .possible_moves_without_heads(game, board)
-                            .collect::<Vec<_>>();
-                        // only snakes that have a single option
-                        match moves[..] {
-                            [direction] => Some(snake.head.move_to(direction)),
-                            _ => None,
+            .flat_map(|snake| snake.body.iter())
+            .any(|&coord| target == coord)
+        {
+            return true;
         }
+        false
+    }
+
+    #[must_use]
+    pub fn health_cost(&self, tile: Coord, game: &Game, board: &Board) -> i32 {
+        // we can't leave the board
+        if !((0..board.width).contains(&tile.x) && (0..board.height).contains(&tile.y)) {
+            return self.health;
+        }
+
+        // we can't move into other snakes
+        if board
+            .snakes
+            .iter()
+            .filter(|snake| {
+                !(game.ruleset.settings.squad.allow_body_collisions && self.squad == snake.squad)
             })
-                    .any(|coord| coord == target)
-            })
-            .collect()
+            .flat_map(|snake| snake.body.iter())
+            .any(|&coord| tile == coord)
+        {
+            return self.health;
+        }
+
+        // every step costs us one health point
+        let mut cost = 1;
+
+        // hazards increase the health loss
+        if board.hazards.iter().any(|&hazard| tile == hazard) {
+            cost += game.ruleset.settings.hazard_damage_per_turn;
+        }
+
+        // check for bigger snakes that can move into this square
+        for snake in board
+            .snakes
+            .iter()
+            .filter(|snake| snake.id != self.id && self.length <= snake.length)
+        {
+            let moves = enum_iterator::all().map(|dir| snake.head.move_to(dir));
+        }
+
+        cost
     }
 }
 
@@ -111,13 +139,19 @@ pub fn end(_game: &Game, _turn: i32, _board: &Board, _you: &Battlesnake) {
 // 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) -> Option<Move> {
-    let moves = you.possible_moves(game, board);
-    if moves.is_empty() {
-        return None;
-    }
+    let moves = enum_iterator::all()
+        .filter(|&direction| !you.is_direction_death(direction, game, board))
+        .collect::<Vec<_>>();
+    let safe_moves = moves
+        .iter()
+        .copied()
+        .filter(|&direction| you.is_direction_safe(direction, game, board))
+        .collect::<Vec<_>>();
 
     // Choose a random move from the safe ones
-    let chosen = moves.choose(&mut rand::thread_rng())?;
+    let chosen = safe_moves
+        .choose(&mut rand::thread_rng())
+        .or_else(|| moves.choose(&mut rand::thread_rng()))?;
 
     info!("MOVE {}: {:?}", turn, chosen);
     Some(Move {

battlesnake/src/main.rs

@@ -30,9 +30,7 @@ pub enum Direction {
 
 #[derive(Debug, Deserialize, Serialize)]
 pub struct Move {
-    /// In which direction the snake should move
     r#move: Direction,
-    /// Say something to the other snakes
     #[serde(default, skip_serializing_if = "is_default")]
     shout: Option<String>,
 }