modularize simulation

battlesnake/Cargo.toml

@@ -3,6 +3,7 @@ authors = ["Max Känner"]
 name = "battlesnake"
 version = "2.0.0"
 edition = "2024"
+rust-version = "1.86"
 
 readme = "README.md"
 repository = "https://git.mkaenner.de/max/battlesnake"
@@ -10,11 +11,21 @@ keywords = ["battlesnake"]
 description = """
 A simple Battlesnake written in Rust
 """
+default-run = "battlesnake"
 
 [lints.clippy]
 pedantic = "warn"
 nursery = "warn"
 
+[[bin]]
+name = "battlesnake"
+
+[[bin]]
+name = "seed-cracker"
+
+[[bin]]
+name = "generate"
+
 [dependencies]
 # server
 tokio = { version = "1.43", features = ["full"] }
@@ -31,6 +42,19 @@ enum-iterator = "2.1"
 rand = "0.9"
 float-ord = "0.3"
 futures-util = "0.3.31"
+az = "1.2.1"
+blanket = "0.4.0"
+hashbrown = "0.15.4"
+serde_json = "1.0.140"
+clap = { version = "4.5.39", features = ["derive"] }
+sqlx = { version = "0.8.6", features = ["runtime-tokio", "sqlite"] }
+enum_dispatch = "0.3.13"
+lru = "0.14.0"
+lfu_cache = "1.3.0"
+memmap2 = "0.9.5"
+bytemuck = "1.23.1"
+flame = "0.2.2"
+flamer = "0.5.0"
 
 [dev-dependencies]
 criterion = "0.5"

battlesnake/benches/simulation.rs

@@ -10,7 +10,7 @@ use criterion::{Bencher, BenchmarkId, Criterion, criterion_group, criterion_main
 
 use battlesnake::types::{
     Coord,
-    simulation::Board,
+    simulation::Game as Board,
     wire::{Battlesnake, Board as WireBoard, Game, Request, RoyaleSettings, Ruleset, Settings},
 };
 use rand::{SeedableRng, rngs::SmallRng};
@@ -78,13 +78,8 @@ fn standard(c: &mut Criterion) {
     let benchmark = |b: &mut Bencher, board: &Board| {
         b.iter(|| {
             let mut board = board.clone();
-            let turn = board.simulate_random(&mut SmallRng::from_os_rng(), |board| {
-                if board.num_snakes() <= 1 {
-                    Some(board.turn())
-                } else {
-                    None
-                }
-            });
+            board.simulate_random(&mut SmallRng::from_os_rng());
+            let turn = board.board.turn();
 
             if turn < turns_min.load(Ordering::Relaxed) {
                 turns_min.store(turn, Ordering::Relaxed);
@@ -155,13 +150,8 @@ fn constrictor(c: &mut Criterion) {
     let benchmark = |b: &mut Bencher, board: &Board| {
         b.iter(|| {
             let mut board = board.clone();
-            let turn = board.simulate_random(&mut SmallRng::from_os_rng(), |board| {
-                if board.num_snakes() <= 1 {
-                    Some(board.turn())
-                } else {
-                    None
-                }
-            });
+            board.simulate_random(&mut SmallRng::from_os_rng());
+            let turn = board.board.turn();
 
             if turn < turns_min.load(Ordering::Relaxed) {
                 turns_min.store(turn, Ordering::Relaxed);

battlesnake/src/main.rs

@@ -5,22 +5,26 @@ use std::{
 
 use axum::{
     Router,
-    extract::Json,
+    extract::{Json, State},
     response,
     routing::{get, post},
 };
 use battlesnake::types::{
     Direction,
-    simulation::Board,
+    simulation::{Board, Game},
     wire::{Request, Response},
 };
 use float_ord::FloatOrd;
 use futures_util::future::join_all;
+use hashbrown::HashMap;
 use log::{debug, error, info, trace, warn};
 use rand::prelude::*;
 use serde::Serialize;
 use tokio::{
+    fs::File,
+    io::AsyncWriteExt,
     net::TcpListener,
+    sync::mpsc::{UnboundedSender, unbounded_channel},
     time::{Duration, Instant},
 };
 
@@ -30,12 +34,15 @@ static THREADS: AtomicUsize = AtomicUsize::new(1);
 async fn main() {
     env_logger::init();
 
+    let (sender, mut receiver) = unbounded_channel();
+
     debug!("Creating routes");
     let app = Router::new()
         .route("/", get(info))
         .route("/start", post(start))
         .route("/move", post(get_move))
-        .route("/end", post(end));
+        .route("/end", post(end))
+        .with_state(sender);
 
     let threads = env::var("THREADS")
         .ok()
@@ -51,6 +58,53 @@ async fn main() {
     debug!("Creating listener");
     let port = env::var("PORT").unwrap_or_else(|_| "8000".into());
     let listener = TcpListener::bind(format!("0.0.0.0:{port}")).await.unwrap();
+
+    debug!("Starting observer");
+    tokio::spawn(async move {
+        let mut games = HashMap::new();
+        while let Some((request_type, request)) = receiver.recv().await {
+            match request_type {
+                RequestType::Start => {
+                    let game_id = request.game.id.clone();
+                    info!("Got start request {game_id}");
+                    if let Some(old_requests) = games.insert(game_id, vec![request]) {
+                        warn!("evicted duplicate game: {old_requests:?}");
+                    }
+                }
+                RequestType::GetMove => {
+                    let game_id = request.game.id.clone();
+                    info!("Got move request {game_id}");
+                    games.entry(game_id).or_default().push(request);
+                }
+                RequestType::End => {
+                    let game_id = request.game.id.clone();
+                    info!("Got end request {game_id}");
+                    if let Some(mut requests) = games.remove(&game_id) {
+                        requests.push(request);
+                        let json = match serde_json::to_vec_pretty(&requests) {
+                            Ok(json) => json,
+                            Err(e) => {
+                                error!("Unable to serealize json: {e}");
+                                continue;
+                            }
+                        };
+                        match File::create_new(format!("games/{game_id}.json")).await {
+                            Ok(mut file) => {
+                                if let Err(e) = file.write_all(&json).await {
+                                    error!("Unable to write jsone: {e}");
+                                }
+                            }
+                            Err(e) => error!("Unable to open file: {e}"),
+                        }
+                    } else {
+                        warn!("end of game without game: {request:?}");
+                    }
+                }
+            }
+        }
+        warn!("Observer stopped");
+    });
+
     debug!("Starting server");
     axum::serve(listener, app).await.unwrap();
 }
@@ -77,22 +131,41 @@ struct Info {
     version: &'static str,
 }
 
-async fn start(request: Json<Request>) {
-    let board = Board::from(&*request);
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy)]
+enum RequestType {
+    Start,
+    GetMove,
+    End,
+}
+
+async fn start(
+    State(sender): State<UnboundedSender<(RequestType, Request)>>,
+    Json(request): Json<Request>,
+) {
+    if let Err(e) = sender.send((RequestType::Start, request.clone())) {
+        warn!("Unable to observe request: {e}");
+    }
+    let board = Board::from(&request);
     info!("got start request: {board}");
 }
 
 #[allow(clippy::too_many_lines)]
-async fn get_move(request: Json<Request>) -> response::Json<Response> {
+async fn get_move(
+    State(sender): State<UnboundedSender<(RequestType, Request)>>,
+    Json(request): Json<Request>,
+) -> response::Json<Response> {
     let start = Instant::now();
-    let board = Board::from(&*request);
+    if let Err(e) = sender.send((RequestType::GetMove, request.clone())) {
+        warn!("Unable to observe request: {e}");
+    }
+    let board = Game::from(&request);
     let timeout = Duration::from_millis(u64::from(request.game.timeout));
-    let id = board.get_id(&request.you.id).unwrap_or_else(|| {
+    let id = board.board.get_id(&request.you.id).unwrap_or_else(|| {
         error!("My id is not in the simulation board");
         0
     });
-    debug!("got move request: {board}");
-    let actions = board.valid_actions(id).collect::<Vec<_>>();
+    debug!("got move request: {}", board.board);
+    let actions = board.board.valid_actions(id).collect::<Vec<_>>();
     if actions.len() <= 1 {
         info!(
             "only one possible action. Fast forwarding {:?}",
@@ -111,10 +184,6 @@ async fn get_move(request: Json<Request>) -> response::Json<Response> {
             start.elapsed().as_millis()
         );
     }
-    let end_condition: fn(&Board) -> Option<()> = match &*request.game.ruleset.name {
-        "solo" => end_solo,
-        _ => end_standard,
-    };
     let score_fn: fn(&Board, u8) -> u32 = match &*request.game.ruleset.name {
         "solo" => score_solo,
         _ => score_standard,
@@ -132,22 +201,25 @@ async fn get_move(request: Json<Request>) -> response::Json<Response> {
             let mut mcts_actions = Vec::new();
             while start.elapsed() < timeout * 4 / 5 {
                 let mut board = board.clone();
-                while end_condition(&board).is_none() {
+                let mut game_over = false;
+                while !game_over {
                     mcts_actions.clear();
                     mcts_actions.extend(mcts_managers.iter_mut().filter_map(|mcts_manager| {
                         mcts_manager
-                            .next_action(&board, c, &mut rng)
+                            .next_action(&board.board, c, &mut rng)
                             .map(|action| (mcts_manager.snake, action))
                     }));
-                    board.next_turn(&mcts_actions, &mut rng);
+                    game_over = board.next_turn_random(&mcts_actions, &mut rng);
                     if mcts_actions.is_empty() {
                         break;
                     }
                 }
-                board.simulate_random(&mut rng, end_condition);
+                if !game_over {
+                    board.simulate_random(&mut rng);
+                }
                 for mcts_manager in &mut mcts_managers {
                     let id = mcts_manager.snake;
-                    let score = score_fn(&board, id);
+                    let score = score_fn(&board.board, id);
                     mcts_manager.apply_score(score);
                 }
             }
@@ -200,16 +272,8 @@ async fn get_move(request: Json<Request>) -> response::Json<Response> {
     })
 }
 
-fn end_solo(board: &Board) -> Option<()> {
-    (board.valid_actions(0).count() == 0).then_some(())
-}
-
-fn end_standard(board: &Board) -> Option<()> {
-    (board.num_snakes() <= 1).then_some(())
-}
-
-fn score_solo(board: &Board, id: u8) -> u32 {
-    u32::try_from(board.length(id)).unwrap_or(0)
+const fn score_solo(board: &Board, _id: u8) -> u32 {
+    board.turn()
 }
 
 fn score_standard(board: &Board, id: u8) -> u32 {
@@ -220,8 +284,14 @@ fn score_standard(board: &Board, id: u8) -> u32 {
     }
 }
 
-async fn end(request: Json<Request>) {
-    let board = Board::from(&*request);
+async fn end(
+    State(sender): State<UnboundedSender<(RequestType, Request)>>,
+    Json(request): Json<Request>,
+) {
+    if let Err(e) = sender.send((RequestType::End, request.clone())) {
+        warn!("Unable to observe request: {e}");
+    }
+    let board = Board::from(&request);
     info!("got end request: {board}");
 }
 

battlesnake/src/types/mod.rs

@@ -1,10 +1,12 @@
+use std::fmt::Display;
+
 use enum_iterator::Sequence;
 use serde::{Deserialize, Serialize};
 
 pub mod simulation;
 pub mod wire;
 
-#[derive(Debug, PartialEq, Eq, Clone, Copy, Deserialize)]
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Deserialize, Serialize)]
 pub struct Coord {
     pub x: u8,
     pub y: u8,
@@ -33,6 +35,12 @@ impl Coord {
     }
 }
 
+impl Display for Coord {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "({}, {})", self.x, self.y)
+    }
+}
+
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Serialize, Sequence)]
 #[serde(rename_all = "lowercase")]
 pub enum Direction {

battlesnake/src/types/simulation/maps/mod.rs

@@ -0,0 +1,43 @@
+mod royale;
+mod standard;
+
+use blanket::blanket;
+use enum_dispatch::enum_dispatch;
+use rand::Rng;
+use royale::Royale;
+use standard::Standard;
+
+use crate::types::wire::Game;
+
+use super::Board;
+
+#[blanket(derive(Ref, Arc, Mut, Box))]
+#[enum_dispatch(Maps)]
+pub trait Map {
+    /// Called before the board is updated
+    fn pre_update(&self, board: &mut Board, rng: &mut impl Rng);
+
+    /// Called after the board is updated
+    fn post_update(&self, board: &mut Board, rng: &mut impl Rng);
+}
+
+#[enum_dispatch]
+#[derive(Debug, Clone, Copy)]
+pub enum Maps {
+    Standard,
+    Royale,
+}
+
+pub trait MapId {
+    /// ID of the map for detection
+    const ID: &str;
+}
+
+impl From<&Game> for Maps {
+    fn from(value: &Game) -> Self {
+        match value.map.as_ref() {
+            Royale::ID => Royale::from(&value.ruleset.settings).into(),
+            _ => Standard::from(&value.ruleset.settings).into(),
+        }
+    }
+}

battlesnake/src/types/simulation/maps/royale.rs

@@ -0,0 +1,86 @@
+use rand::{Rng, seq::IteratorRandom};
+
+use crate::types::{Coord, Direction, simulation::Board, wire::Settings};
+
+use super::{Map, MapId, standard::Standard};
+
+#[derive(Debug, Clone, Copy)]
+pub struct Royale {
+    standard: Standard,
+    shrink_every_n_turns: u8,
+}
+
+impl Map for Royale {
+    fn pre_update(&self, board: &mut Board, rng: &mut impl Rng) {
+        self.standard.pre_update(board, rng);
+    }
+
+    fn post_update(&self, board: &mut Board, rng: &mut impl Rng) {
+        self.standard.post_update(board, rng);
+
+        // Royale uses the current turn to generate hazards, not the previous turn that's in the
+        // board state
+        let turn = board.turn + 1;
+
+        if turn < u32::from(self.shrink_every_n_turns) {
+            return;
+        }
+
+        let side = enum_iterator::all::<Direction>()
+            .choose(rng)
+            .unwrap_or(Direction::Up);
+        match side {
+            Direction::Up => {
+                if let Some(i) = board.hazard.first_zero() {
+                    let y = board.linear_to_coord(i).y;
+                    for x in 0..board.width {
+                        let i = board.coord_to_linear(Coord { x, y });
+                        board.hazard.set(i, true);
+                    }
+                }
+            }
+            Direction::Down => {
+                if let Some(i) = board.hazard.last_zero() {
+                    let y = board.linear_to_coord(i).y;
+                    for x in 0..board.width {
+                        let i = board.coord_to_linear(Coord { x, y });
+                        board.hazard.set(i, true);
+                    }
+                }
+            }
+            Direction::Left => {
+                if let Some(i) = board.hazard.first_zero() {
+                    let x = board.linear_to_coord(i).y;
+                    for y in 0..board.height {
+                        let i = board.coord_to_linear(Coord { x, y });
+                        board.hazard.set(i, true);
+                    }
+                }
+            }
+            Direction::Right => {
+                if let Some(i) = board.hazard.last_zero() {
+                    let x = board.linear_to_coord(i).y;
+                    for y in 0..board.height {
+                        let i = board.coord_to_linear(Coord { x, y });
+                        board.hazard.set(i, true);
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl MapId for Royale {
+    const ID: &str = "royale";
+}
+
+impl From<&Settings> for Royale {
+    fn from(value: &Settings) -> Self {
+        let standard = Standard::from(value);
+        let shrink_every_n_turns = value.royale.shrink_every_n_turns;
+        Self {
+            standard,
+            shrink_every_n_turns,
+        }
+    }
+}

battlesnake/src/types/simulation/maps/standard.rs

@@ -0,0 +1,78 @@
+use az::SaturatingAs;
+use rand::{Rng, seq::SliceRandom};
+
+use crate::types::{Coord, simulation::Board, wire::Settings};
+
+use super::{Map, MapId};
+
+#[derive(Debug, Clone, Copy)]
+pub struct Standard {
+    min_food: u16,
+    food_spawn_chance: u8,
+}
+
+impl Map for Standard {
+    fn pre_update(&self, _board: &mut Board, _rng: &mut impl Rng) {}
+
+    fn post_update(&self, board: &mut Board, rng: &mut impl Rng) {
+        let food_needed = self.check_food_needing_placement(board, rng);
+        if food_needed > 0 {
+            Self::place_food_randomly(board, rng, food_needed);
+        }
+    }
+}
+
+impl MapId for Standard {
+    const ID: &str = "standard";
+}
+
+impl From<&Settings> for Standard {
+    fn from(value: &Settings) -> Self {
+        let min_food = value.minimum_food;
+        let food_spawn_chance = value.food_spawn_chance;
+        Self {
+            min_food,
+            food_spawn_chance,
+        }
+    }
+}
+
+impl Standard {
+    fn check_food_needing_placement(self, board: &Board, rng: &mut impl rand::Rng) -> u16 {
+        let num_current_food: u16 = board.food.count_ones().saturating_as();
+
+        if num_current_food < self.min_food {
+            return self.min_food - num_current_food;
+        }
+        if self.food_spawn_chance > 0 && (100 - rng.random_range(0..100)) < self.food_spawn_chance {
+            return 1;
+        }
+        0
+    }
+
+    fn place_food_randomly(board: &mut Board, rng: &mut impl rand::Rng, food_needed: u16) {
+        let mut unoccupied_points: Vec<_> = board.get_unoccupied_points(false, false).collect();
+        Self::place_food_ramdomly_at_positions(
+            board,
+            rng,
+            food_needed,
+            unoccupied_points.as_mut_slice(),
+        );
+    }
+
+    fn place_food_ramdomly_at_positions(
+        board: &mut Board,
+        rng: &mut impl rand::Rng,
+        food_needed: u16,
+        positions: &mut [Coord],
+    ) {
+        let food_needed = usize::from(food_needed).min(positions.len());
+
+        positions.shuffle(rng);
+
+        for tile in &positions[..food_needed] {
+            let i = board.coord_to_linear(*tile);
+            board.food.set(i, true);
+        }
+    }
+}

battlesnake/src/types/simulation/mod.rs

@@ -1,3 +1,6 @@
+mod maps;
+mod rules;
+
 use std::{
     collections::VecDeque,
     fmt::Display,
@@ -6,9 +9,12 @@ use std::{
     sync::Arc,
 };
 
+use az::SaturatingAs;
 use bitvec::prelude::*;
 use log::{error, warn};
+use maps::{Map, Maps};
 use rand::prelude::*;
+use rules::{Ruleset, Rulesets};
 
 use super::{Coord, Direction, wire::Request};
 
@@ -58,19 +64,79 @@ impl DerefMut for SmallBitBox {
     }
 }
 
+#[derive(Clone)]
+pub struct Game {
+    pub board: Board,
+    map: Maps,
+    ruleset: Rulesets,
+}
+
+impl From<&Request> for Game {
+    fn from(value: &Request) -> Self {
+        let board = value.into();
+        let map = (&value.game).into();
+        let ruleset = (&value.game.ruleset).into();
+        Self {
+            board,
+            map,
+            ruleset,
+        }
+    }
+}
+
+impl Game {
+    pub fn simulate_random(&mut self, rng: &mut impl Rng) {
+        loop {
+            let random_actions: Vec<_> = (0..self.board.snakes.len())
+                .filter_map(|i| {
+                    self.board
+                        .valid_actions_index(i)
+                        .choose(rng)
+                        .map(|direction| (i.saturating_as(), direction))
+                })
+                .collect();
+            if self.next_turn(&random_actions, rng) {
+                break;
+            }
+        }
+    }
+
+    pub fn next_turn_random(&mut self, actions: &[(u8, Direction)], rng: &mut impl Rng) -> bool {
+        let random_actions: Vec<_> = (0..self.board.snakes.len())
+            .filter_map(|i| {
+                actions
+                    .iter()
+                    .find(|(j, _)| i == usize::from(*j))
+                    .copied()
+                    .or_else(|| {
+                        self.board
+                            .valid_actions_index(i)
+                            .choose(rng)
+                            .map(|direction| (i.saturating_as(), direction))
+                    })
+            })
+            .collect();
+        self.next_turn(&random_actions, rng)
+    }
+
+    pub fn next_turn(&mut self, actions: &[(u8, Direction)], rng: &mut impl Rng) -> bool {
+        self.map.pre_update(&mut self.board, rng);
+        let game_over = self.ruleset.execute(&mut self.board, actions);
+        self.map.post_update(&mut self.board, rng);
+        self.board.turn += 1;
+        game_over
+    }
+}
+
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub struct Board {
     width: u8,
     height: u8,
-    hazard_damage: u8,
-    food_spawn_chance: u8,
-    min_food: u16,
     turn: u32,
     food: SmallBitBox,
     hazard: SmallBitBox,
     free: SmallBitBox,
     snakes: Vec<Snake>,
-    constrictor: bool,
     id_map: Arc<[(u8, Arc<str>)]>,
 }
 
@@ -94,15 +160,11 @@ impl From<&Request> for Board {
         let mut board = Self {
             width,
             height,
-            hazard_damage: value.game.ruleset.settings.hazard_damage_per_turn,
-            food_spawn_chance: value.game.ruleset.settings.food_spawn_chance,
-            min_food: value.game.ruleset.settings.minimum_food,
             turn: value.turn,
             food: SmallBitBox::new(false, fields),
             hazard: SmallBitBox::new(false, fields),
             free: SmallBitBox::new(true, fields),
             snakes: Vec::with_capacity(value.board.snakes.len()),
-            constrictor: &*value.game.ruleset.name == "constrictor",
             id_map: id_map.into(),
         };
 
@@ -116,11 +178,12 @@ impl From<&Request> for Board {
             board.hazard.set(index, true);
         }
 
+        let constrictor = value.game.ruleset.name.as_ref() == "constrictor";
         for (id, snake) in value.board.snakes.iter().enumerate() {
             for &tile in snake
                 .body
                 .iter()
-                .take(snake.body.len() - usize::from(!board.constrictor))
+                .take(snake.body.len() - usize::from(!constrictor))
             {
                 let index = board.coord_to_linear(tile);
                 board.free.set(index, false);
@@ -139,17 +202,7 @@ impl From<&Request> for Board {
 
 impl Display for Board {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        writeln!(
-            f,
-            "{} {}x{} {}% ({}) {}dmg @ {}",
-            if self.constrictor { "constrictor" } else { "" },
-            self.width,
-            self.height,
-            self.food_spawn_chance,
-            self.min_food,
-            self.hazard_damage,
-            self.turn
-        )?;
+        writeln!(f, "{}x{} @ {}", self.width, self.height, self.turn)?;
 
         for y in (0..self.height).rev() {
             for x in 0..self.width {
@@ -279,30 +332,6 @@ impl Board {
         })
     }
 
-    pub fn simulate_random<T>(
-        &mut self,
-        rng: &mut impl RngCore,
-        stop: impl Fn(&Self) -> Option<T>,
-    ) -> T {
-        loop {
-            if let Some(score) = stop(self) {
-                break score;
-            }
-            self.next_turn(&[], rng);
-        }
-    }
-
-    pub fn next_turn(&mut self, actions: &[(u8, Direction)], rng: &mut impl RngCore) {
-        self.move_standard(actions, rng);
-        self.starvation_standard();
-        self.hazard_damage_standard();
-        self.feed_snakes_standard();
-        self.eliminate_snake_standard();
-        self.update_free_map();
-        self.spawn_food(rng);
-        self.turn += 1;
-    }
-
     fn id_to_index(&self, id: u8) -> Option<usize> {
         self.snakes.binary_search_by_key(&id, |snake| snake.id).ok()
     }
@@ -313,127 +342,6 @@ impl Board {
             .filter(move |direction| self.is_free(head.wrapping_apply(*direction)))
     }
 
-    fn move_standard(&mut self, actions: &[(u8, Direction)], rng: &mut impl RngCore) {
-        for i in 0..self.snakes.len() {
-            let snake = &self.snakes[i];
-            let action = actions.iter().find(|(id, _)| *id == snake.id).map_or_else(
-                || {
-                    self.valid_actions_index(i)
-                        .choose(rng)
-                        .unwrap_or(Direction::Up)
-                },
-                |(_, action)| *action,
-            );
-            let new_head = snake.head().wrapping_apply(action);
-            self.snakes[i].advance(new_head);
-        }
-    }
-
-    fn starvation_standard(&mut self) {
-        for snake in &mut self.snakes {
-            snake.health = snake.health.saturating_sub(1);
-        }
-    }
-
-    fn hazard_damage_standard(&mut self) {
-        let mut i = 0;
-        while i < self.snakes.len() {
-            let head = self.snakes[i].head();
-            if self.is_in_bounds(head) {
-                let head_index = self.coord_to_linear(head);
-                if self.hazard[head_index] && !self.food[head_index] {
-                    let health = &mut self.snakes[i].health;
-                    *health = health.saturating_sub(1);
-                    if *health == 0 {
-                        let snake = self.snakes.remove(i);
-                        for tile in snake.body {
-                            let index = self.coord_to_linear(tile);
-                            self.free.set(index, true);
-                        }
-                        continue;
-                    }
-                }
-            }
-            i += 1;
-        }
-    }
-
-    fn feed_snakes_standard(&mut self) {
-        if self.constrictor {
-            for snake in &mut self.snakes {
-                snake.feed();
-            }
-        } else {
-            let mut eaten_food = vec![];
-            for i in 0..self.snakes.len() {
-                let head = self.snakes[i].head();
-                if self.is_in_bounds(head) {
-                    let head_index = self.coord_to_linear(head);
-                    if self.food[head_index] {
-                        eaten_food.push(head_index);
-                        self.snakes[i].feed();
-                    }
-                }
-            }
-            for food_index in eaten_food {
-                self.food.set(food_index, false);
-            }
-        }
-    }
-
-    fn eliminate_snake_standard(&mut self) {
-        // eliminate out of health and out of bounds
-        let mut i = 0;
-        while i < self.snakes.len() {
-            let snake = &self.snakes[i];
-            if snake.health == 0 || !self.is_in_bounds(snake.head()) {
-                let snake = self.snakes.remove(i);
-                for tile in snake.body.iter().skip(1) {
-                    if self.is_in_bounds(*tile) {
-                        let index = self.coord_to_linear(*tile);
-                        self.free.set(index, true);
-                    }
-                }
-                continue;
-            }
-            i += 1;
-        }
-
-        // look for collisions
-        let mut collisions = vec![];
-        for snake in &self.snakes {
-            let head = snake.head();
-            let head_index = self.coord_to_linear(head);
-            if !self.free[head_index] {
-                collisions.push(snake.id);
-                continue;
-            }
-            for snake2 in &self.snakes {
-                if snake.id != snake2.id
-                    && snake.head() == snake2.head()
-                    && snake.body.len() <= snake2.body.len()
-                {
-                    collisions.push(snake.id);
-                    break;
-                }
-            }
-        }
-
-        // apply collisions
-        let mut i = 0;
-        while i < self.snakes.len() {
-            if collisions.contains(&self.snakes[i].id) {
-                let snake = self.snakes.remove(i);
-                for tile in snake.body {
-                    let index = self.coord_to_linear(tile);
-                    self.free.set(index, true);
-                }
-                continue;
-            }
-            i += 1;
-        }
-    }
-
     fn update_free_map(&mut self) {
         // free tails
         for snake in &self.snakes {
@@ -452,65 +360,49 @@ impl Board {
         }
     }
 
-    fn spawn_food(&mut self, rng: &mut impl RngCore) {
-        let food_needed = self.check_food_needing_placement(rng);
-
-        if food_needed > 0 {
-            self.place_food_randomly(food_needed, rng);
-        }
-    }
-
-    fn check_food_needing_placement(&self, rng: &mut impl RngCore) -> u16 {
-        let min_food = self.min_food;
-        let food_spawn_chance = self.food_spawn_chance;
-        let num_current_food = u16::try_from(self.food.count_ones()).unwrap_or(u16::MAX);
-
-        if num_current_food < min_food {
-            return min_food - num_current_food;
-        }
-        if food_spawn_chance > 0 && (100 - rng.random_range(0..100)) < food_spawn_chance {
-            return 1;
-        }
-
-        0
-    }
-
-    fn place_food_randomly(&mut self, amount: u16, rng: &mut impl RngCore) {
-        let tails: Vec<_> = self
-            .snakes
+    fn get_unoccupied_points(
+        &self,
+        include_possible_moves: bool,
+        include_hazards: bool,
+    ) -> impl Iterator<Item = Coord> + use<'_> {
+        let possible_moves: Vec<_> = if include_possible_moves {
+            Vec::new()
+        } else {
+            self.snakes
+                .iter()
+                .flat_map(|snake| {
+                    let head = snake.head();
+                    enum_iterator::all::<Direction>()
+                        .map(move |direction| head.wrapping_apply(direction))
+                        .filter(|tile| self.is_in_bounds(*tile))
+                        .map(|tile| self.coord_to_linear(tile))
+                })
+                .collect()
+        };
+        self.free
             .iter()
-            .map(|snake| self.coord_to_linear(snake.tail()))
-            .collect();
-        let possible_moves: Vec<_> = self
-            .snakes
-            .iter()
-            .flat_map(|snake| {
-                let head = snake.head();
-                enum_iterator::all::<Direction>()
-                    .map(move |direction| head.wrapping_apply(direction))
-                    .filter(|tile| self.is_in_bounds(*tile))
-                    .map(|tile| self.coord_to_linear(tile))
-            })
-            .collect();
-        let unoccupied_points = self
-            .free
-            .iter()
-            .by_vals()
+            .zip(self.food.iter())
+            .zip(self.hazard.iter())
             .enumerate()
-            .zip(self.hazard.iter().by_vals())
-            .filter_map(|((i, free), hazard)| (!hazard && free).then_some(i))
-            .filter(|i| !tails.contains(i))
-            .filter(|i| !possible_moves.contains(i));
-
-        for food_spot in unoccupied_points.choose_multiple(rng, usize::from(amount)) {
-            self.food.set(food_spot, true);
-        }
+            .filter(move |(i, ((free, food), hazard))| {
+                **free
+                    && !**food
+                    && (include_hazards || !**hazard)
+                    && (include_possible_moves || !possible_moves.contains(i))
+            })
+            .map(|(i, _)| self.linear_to_coord(i))
     }
 
     fn coord_to_linear(&self, coord: Coord) -> usize {
         usize::from(coord.x) + usize::from(coord.y) * usize::from(self.width)
     }
 
+    fn linear_to_coord(&self, linear: usize) -> Coord {
+        let x = (linear % usize::from(self.width)).saturating_as();
+        let y = (linear / usize::from(self.width)).saturating_as();
+        Coord { x, y }
+    }
+
     const fn is_in_bounds(&self, coord: Coord) -> bool {
         coord.x < self.width && coord.y < self.height
     }

battlesnake/src/types/simulation/rules/constrictor.rs

@@ -0,0 +1,38 @@
+use crate::types::{Direction, simulation::Board, wire};
+
+use super::{
+    Ruleset,
+    standard::{DamageHazards, eliminate_snakes, game_over, move_snakes, reduce_snake_health},
+};
+
+#[derive(Debug, Clone, Copy)]
+pub struct Constrictor {
+    damage_hazards: DamageHazards,
+}
+
+impl From<&wire::Ruleset> for Constrictor {
+    fn from(value: &wire::Ruleset) -> Self {
+        Self {
+            damage_hazards: (&value.settings).into(),
+        }
+    }
+}
+
+impl Ruleset for Constrictor {
+    fn execute(&self, board: &mut Board, actions: &[(u8, Direction)]) -> bool {
+        let game_over = game_over(board);
+        move_snakes(board, actions);
+        reduce_snake_health(board);
+        self.damage_hazards.execute(board);
+        eliminate_snakes(board);
+        grow_snakes(board);
+        board.update_free_map();
+        game_over
+    }
+}
+
+fn grow_snakes(board: &mut Board) {
+    for snake in &mut board.snakes {
+        snake.feed();
+    }
+}

battlesnake/src/types/simulation/rules/mod.rs

@@ -0,0 +1,37 @@
+mod constrictor;
+mod solo;
+mod standard;
+
+use constrictor::Constrictor;
+use enum_dispatch::enum_dispatch;
+use solo::Solo;
+use standard::Standard;
+
+use crate::types::{Direction, wire};
+
+use super::Board;
+
+#[enum_dispatch]
+pub trait Ruleset {
+    /// executes one turn of the ruleset.
+    /// Returns true if the game is over
+    fn execute(&self, board: &mut Board, actions: &[(u8, Direction)]) -> bool;
+}
+
+#[enum_dispatch(Ruleset)]
+#[derive(Debug, Clone, Copy)]
+pub enum Rulesets {
+    Standard,
+    Constrictor,
+    Solo,
+}
+
+impl From<&wire::Ruleset> for Rulesets {
+    fn from(value: &wire::Ruleset) -> Self {
+        match value.name.as_ref() {
+            "solo" => Solo::from(value).into(),
+            "constrictor" => Constrictor::from(value).into(),
+            _ => Standard::from(value).into(),
+        }
+    }
+}

battlesnake/src/types/simulation/rules/solo.rs

@@ -0,0 +1,36 @@
+use crate::types::{Direction, simulation::Board, wire};
+
+use super::{
+    Ruleset,
+    standard::{DamageHazards, eliminate_snakes, feed_snakes, move_snakes, reduce_snake_health},
+};
+
+#[derive(Debug, Clone, Copy)]
+pub struct Solo {
+    damage_hazards: DamageHazards,
+}
+
+impl From<&wire::Ruleset> for Solo {
+    fn from(value: &wire::Ruleset) -> Self {
+        Self {
+            damage_hazards: (&value.settings).into(),
+        }
+    }
+}
+
+impl Ruleset for Solo {
+    fn execute(&self, board: &mut Board, actions: &[(u8, Direction)]) -> bool {
+        let game_over = game_over(board);
+        move_snakes(board, actions);
+        reduce_snake_health(board);
+        self.damage_hazards.execute(board);
+        feed_snakes(board);
+        eliminate_snakes(board);
+        board.update_free_map();
+        game_over
+    }
+}
+
+pub fn game_over(board: &Board) -> bool {
+    board.num_snakes() == 0
+}

battlesnake/src/types/simulation/rules/standard.rs

@@ -0,0 +1,180 @@
+use crate::types::{
+    Direction,
+    simulation::Board,
+    wire::{self, Settings},
+};
+
+use super::Ruleset;
+
+#[derive(Debug, Clone, Copy)]
+pub struct Standard {
+    damage_hazards: DamageHazards,
+}
+
+impl From<&wire::Ruleset> for Standard {
+    fn from(value: &wire::Ruleset) -> Self {
+        Self {
+            damage_hazards: (&value.settings).into(),
+        }
+    }
+}
+
+impl Ruleset for Standard {
+    fn execute(&self, board: &mut Board, actions: &[(u8, Direction)]) -> bool {
+        let game_over = game_over(board);
+        move_snakes(board, actions);
+        reduce_snake_health(board);
+        self.damage_hazards.execute(board);
+        feed_snakes(board);
+        eliminate_snakes(board);
+        board.update_free_map();
+        game_over
+    }
+}
+
+pub fn move_snakes(board: &mut Board, actions: &[(u8, Direction)]) {
+    for i in 0..board.snakes.len() {
+        let snake = &board.snakes[i];
+        let action = actions.iter().find(|(id, _)| *id == snake.id).map_or_else(
+            || {
+                let head = snake.body[0];
+                let previous_head = snake.body[1];
+                let delta_x = i16::from(head.x) - i16::from(previous_head.x);
+                let delta_y = i16::from(head.y) - i16::from(previous_head.y);
+                if delta_x == 0 && delta_y == 0 {
+                    Direction::Up
+                } else if delta_x.abs() > delta_y.abs() {
+                    if delta_x < 0 {
+                        Direction::Left
+                    } else {
+                        Direction::Right
+                    }
+                } else if delta_y < 0 {
+                    Direction::Down
+                } else {
+                    Direction::Up
+                }
+            },
+            |(_, action)| *action,
+        );
+        let new_head = snake.head().wrapping_apply(action);
+        board.snakes[i].advance(new_head);
+    }
+}
+
+pub fn reduce_snake_health(board: &mut Board) {
+    for snake in &mut board.snakes {
+        snake.health = snake.health.saturating_sub(1);
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct DamageHazards {
+    damage: u8,
+}
+
+impl DamageHazards {
+    pub fn execute(self, board: &mut Board) {
+        let mut i = 0;
+        while i < board.snakes.len() {
+            let head = board.snakes[i].head();
+            if board.is_in_bounds(head) {
+                let head_index = board.coord_to_linear(head);
+                if board.hazard[head_index] && !board.food[head_index] {
+                    let health = &mut board.snakes[i].health;
+                    *health = health.saturating_sub(self.damage);
+                    if *health == 0 {
+                        let snake = board.snakes.remove(i);
+                        for tile in snake.body {
+                            let index = board.coord_to_linear(tile);
+                            board.free.set(index, true);
+                        }
+                        continue;
+                    }
+                }
+            }
+            i += 1;
+        }
+    }
+}
+
+impl From<&Settings> for DamageHazards {
+    fn from(value: &Settings) -> Self {
+        let damage = value.hazard_damage_per_turn;
+        Self { damage }
+    }
+}
+
+pub fn eliminate_snakes(board: &mut Board) {
+    // eliminate out of health and out of bounds
+    let mut i = 0;
+    while i < board.snakes.len() {
+        let snake = &board.snakes[i];
+        if snake.health == 0 || !board.is_in_bounds(snake.head()) {
+            let snake = board.snakes.remove(i);
+            for tile in snake.body.iter().skip(1) {
+                if board.is_in_bounds(*tile) {
+                    let index = board.coord_to_linear(*tile);
+                    board.free.set(index, true);
+                }
+            }
+            continue;
+        }
+        i += 1;
+    }
+
+    // look for collisions
+    let mut collisions = vec![];
+    for snake in &board.snakes {
+        let head = snake.head();
+        let head_index = board.coord_to_linear(head);
+        if !board.free[head_index] {
+            collisions.push(snake.id);
+            continue;
+        }
+        for snake2 in &board.snakes {
+            if snake.id != snake2.id
+                && snake.head() == snake2.head()
+                && snake.body.len() <= snake2.body.len()
+            {
+                collisions.push(snake.id);
+                break;
+            }
+        }
+    }
+
+    // apply collisions
+    let mut i = 0;
+    while i < board.snakes.len() {
+        if collisions.contains(&board.snakes[i].id) {
+            let snake = board.snakes.remove(i);
+            for tile in snake.body {
+                let index = board.coord_to_linear(tile);
+                board.free.set(index, true);
+            }
+            continue;
+        }
+        i += 1;
+    }
+}
+
+pub fn feed_snakes(board: &mut Board) {
+    let mut eaten_food = vec![];
+    for i in 0..board.snakes.len() {
+        let head = board.snakes[i].head();
+        if board.is_in_bounds(head) {
+            let head_index = board.coord_to_linear(head);
+            if board.food[head_index] {
+                eaten_food.push(head_index);
+                board.snakes[i].feed();
+            }
+        }
+    }
+    for food_index in eaten_food {
+        board.food.set(food_index, false);
+    }
+}
+
+pub fn game_over(board: &Board) -> bool {
+    board.num_snakes() <= 1
+}

battlesnake/src/types/wire.rs

@@ -4,7 +4,7 @@ use serde::{Deserialize, Serialize};
 
 use super::{Coord, Direction};
 
-#[derive(Debug, PartialEq, Eq, Clone, Deserialize)]
+#[derive(Debug, PartialEq, Eq, Clone, Deserialize, Serialize)]
 pub struct Request {
     /// Game object describing the game being played.
     pub game: Game,
@@ -16,7 +16,7 @@ pub struct Request {
     pub you: Battlesnake,
 }
 
-#[derive(Debug, PartialEq, Eq, Clone, Deserialize)]
+#[derive(Debug, PartialEq, Eq, Clone, Deserialize, Serialize)]
 pub struct Game {
     /// A unique identifier for this Game.
     pub id: Arc<str>,
@@ -36,7 +36,7 @@ pub struct Game {
     pub source: Arc<str>,
 }
 
-#[derive(Debug, PartialEq, Eq, Clone, Deserialize)]
+#[derive(Debug, PartialEq, Eq, Clone, Deserialize, Serialize)]
 pub struct Ruleset {
     /// Name of the ruleset being used to run this game.
     pub name: Arc<str>,
@@ -47,7 +47,7 @@ pub struct Ruleset {
     pub settings: Settings,
 }
 
-#[derive(Debug, PartialEq, Eq, Clone, Copy, Deserialize)]
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Deserialize, Serialize)]
 #[serde(rename_all = "camelCase")]
 pub struct Settings {
     /// Percentage chance of spawning a new food every round.
@@ -61,14 +61,14 @@ pub struct Settings {
     pub royale: RoyaleSettings,
 }
 
-#[derive(Debug, PartialEq, Eq, Clone, Copy, Deserialize)]
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Deserialize, Serialize)]
 #[serde(rename_all = "camelCase")]
 pub struct RoyaleSettings {
     /// The number of turns between generating new hazards (shrinking the safe board space).
     pub shrink_every_n_turns: u8,
 }
 
-#[derive(Debug, PartialEq, Eq, Clone, Deserialize)]
+#[derive(Debug, PartialEq, Eq, Clone, Deserialize, Serialize)]
 pub struct Board {
     /// The number of rows in the y-axis of the game board.
     pub height: u8,
@@ -83,7 +83,7 @@ pub struct Board {
     pub snakes: Vec<Battlesnake>,
 }
 
-#[derive(Debug, PartialEq, Eq, Clone, Deserialize)]
+#[derive(Debug, PartialEq, Eq, Clone, Deserialize, Serialize)]
 pub struct Battlesnake {
     /// Unique identifier for this Battlesnake in the context of the current Game.
     pub id: Arc<str>,