sim/src/world.rs

use rune::termcolor::Buffer;
use rune::{Any, Context, Diagnostics, Module, Source, Sources, Vm};
use serde::{Deserialize, Serialize};
use std::fmt::Write;
use std::sync::Arc;

pub const W: usize = 96;
pub const H: usize = 64;
pub const DAY: u64 = 1800;

const WATER_DEEP: u8 = 0;
const WATER: u8 = 1;
const SAND: u8 = 2;
const GRASS: u8 = 3;
const FOREST: u8 = 4;
const HILLS: u8 = 5;
const MOUNTAIN: u8 = 6;

const TREE: u8 = 1;
const BERRY: u8 = 2;
const STONE: u8 = 3;

pub struct Rng(u64);

impl Rng {
    fn next(&mut self) -> u64 {
        let mut x = self.0;
        x ^= x >> 12;
        x ^= x << 25;
        x ^= x >> 27;
        self.0 = x;
        x.wrapping_mul(0x2545F4914F6CDD1D)
    }
    fn f(&mut self) -> f32 {
        (self.next() >> 40) as f32 / (1u64 << 24) as f32
    }
    fn chance(&mut self, p: f32) -> bool {
        self.f() < p
    }
    fn below(&mut self, n: usize) -> usize {
        (self.next() % n as u64) as usize
    }
}

fn hash(x: i32, y: i32, seed: u64) -> f32 {
    let mut h = (x as u64).wrapping_mul(0x9E3779B97F4A7C15)
        ^ (y as u64).wrapping_mul(0xC2B2AE3D27D4EB4F)
        ^ seed.wrapping_mul(0x165667B19E3779F9);
    h ^= h >> 33;
    h = h.wrapping_mul(0xFF51AFD7ED558CCD);
    h ^= h >> 33;
    (h >> 40) as f32 / (1u64 << 24) as f32
}

fn value_noise(x: f32, y: f32, seed: u64) -> f32 {
    let (xi, yi) = (x.floor() as i32, y.floor() as i32);
    let (fx, fy) = (x - xi as f32, y - yi as f32);
    let s = |t: f32| t * t * (3.0 - 2.0 * t);
    let (u, v) = (s(fx), s(fy));
    let a = hash(xi, yi, seed);
    let b = hash(xi + 1, yi, seed);
    let c = hash(xi, yi + 1, seed);
    let d = hash(xi + 1, yi + 1, seed);
    let top = a + (b - a) * u;
    let bot = c + (d - c) * u;
    top + (bot - top) * v
}

fn fbm(x: f32, y: f32, seed: u64) -> f32 {
    let (mut sum, mut amp, mut freq, mut norm) = (0.0, 1.0, 1.0 / 16.0, 0.0);
    for o in 0..4 {
        sum += amp * value_noise(x * freq, y * freq, seed + o);
        norm += amp;
        amp *= 0.5;
        freq *= 2.0;
    }
    sum / norm
}

/// What an entity senses this tick; passed to the Rune behaviour scripts.
#[derive(Any, Default, Clone)]
struct Ctx {
    #[rune(get)]
    night: bool,
    #[rune(get)]
    at_home: bool,
    #[rune(get)]
    hunger: f64,
    #[rune(get)]
    carry: i64,
    #[rune(get)]
    carried_food: i64,
    #[rune(get)]
    stock_food: i64,
    #[rune(get)]
    stock_wood: i64,
    #[rune(get)]
    stock_stone: i64,
    #[rune(get)]
    berry_near: bool,
    #[rune(get)]
    tree_near: bool,
    #[rune(get)]
    stone_near: bool,
    #[rune(get)]
    rabbit_near: bool,
    #[rune(get)]
    wolf_near: bool,
    #[rune(get)]
    prey_near: bool,
    #[rune(get)]
    roll: f64,
}

pub const DEFAULT_SCRIPT: &str = include_str!("behavior.rn");

/// Compiles the script and smoke-tests every entry point so errors surface at load time.
fn load_script(src: &str) -> Result<Vm, String> {
    let mut module = Module::new();
    module.ty::<Ctx>().map_err(|e| e.to_string())?;
    let mut context = Context::with_default_modules().map_err(|e| e.to_string())?;
    context.install(module).map_err(|e| e.to_string())?;
    let mut sources = Sources::new();
    sources
        .insert(Source::new("behavior", src).map_err(|e| e.to_string())?)
        .map_err(|e| e.to_string())?;
    let mut diagnostics = Diagnostics::new();
    let unit = rune::prepare(&mut sources)
        .with_context(&context)
        .with_diagnostics(&mut diagnostics)
        .build();
    let unit = match unit {
        Ok(u) => u,
        Err(_) => {
            let mut buf = Buffer::no_color();
            let _ = diagnostics.emit(&mut buf, &sources);
            return Err(String::from_utf8_lossy(buf.as_slice()).into_owned());
        }
    };
    let runtime = context.runtime().map_err(|e| e.to_string())?;
    let mut vm = Vm::new(Arc::new(runtime), Arc::new(unit));
    for f in ["person", "rabbit", "wolf"] {
        let v = vm
            .call([f], (Ctx::default(),))
            .map_err(|e| format!("{f}(): {e}"))?;
        rune::from_value::<String>(v).map_err(|_| format!("{f}() must return a string"))?;
    }
    Ok(vm)
}

#[derive(Clone, Serialize, Deserialize)]
pub struct Person {
    id: u32,
    x: usize,
    y: usize,
    hunger: f32,
    food: u32,
    wood: u32,
    stone: u32,
    action: String,
    dead: bool,
}

impl Person {
    fn carry(&self) -> u32 {
        self.food + self.wood + self.stone
    }
}

#[derive(Clone, Serialize, Deserialize)]
pub struct Animal {
    x: usize,
    y: usize,
    energy: f32,
    dead: bool,
}

pub struct World {
    tiles: Vec<u8>,
    res: Vec<(u8, u16)>,
    people: Vec<Person>,
    rabbits: Vec<Animal>,
    wolves: Vec<Animal>,
    houses: Vec<(usize, usize)>,
    home: (usize, usize),
    food: u32,
    wood: u32,
    stone: u32,
    tools: u32,
    rng: Rng,
    tick: u64,
    next_id: u32,
    log: Vec<String>,
    script: String,
    vm: Vm,
    pub paused: bool,
    pub speed: u32,
    pub terrain_rev: u32,
}

#[derive(Serialize, Deserialize)]
struct WorldSnapshot {
    version: u32,
    tiles: Vec<u8>,
    res: Vec<(u8, u16)>,
    people: Vec<Person>,
    rabbits: Vec<Animal>,
    wolves: Vec<Animal>,
    houses: Vec<(usize, usize)>,
    home: (usize, usize),
    food: u32,
    wood: u32,
    stone: u32,
    tools: u32,
    rng: u64,
    tick: u64,
    next_id: u32,
    log: Vec<String>,
    script: String,
    paused: bool,
    speed: u32,
    terrain_rev: u32,
}

fn cheb(a: (usize, usize), b: (usize, usize)) -> usize {
    a.0.abs_diff(b.0).max(a.1.abs_diff(b.1))
}

impl World {
    pub fn new(seed: u64) -> World {
        let mut tiles = vec![0u8; W * H];
        for y in 0..H {
            for x in 0..W {
                let dx = (x as f32 / W as f32 - 0.5) * 2.0;
                let dy = (y as f32 / H as f32 - 0.5) * 2.0;
                let d = (dx * dx + dy * dy).min(1.5);
                let h = fbm(x as f32, y as f32, seed) + 0.25 - 0.55 * d;
                let m = fbm(x as f32 + 500.0, y as f32 + 500.0, seed + 99);
                tiles[y * W + x] = if h < 0.28 {
                    WATER_DEEP
                } else if h < 0.36 {
                    WATER
                } else if h < 0.41 {
                    SAND
                } else if h < 0.68 {
                    if m > 0.52 { FOREST } else { GRASS }
                } else if h < 0.78 {
                    HILLS
                } else {
                    MOUNTAIN
                };
            }
        }
        let mut w = World {
            tiles,
            res: vec![(0, 0); W * H],
            people: vec![],
            rabbits: vec![],
            wolves: vec![],
            houses: vec![],
            home: (W / 2, H / 2),
            food: 4,
            wood: 0,
            stone: 0,
            tools: 0,
            rng: Rng(seed.wrapping_mul(0x9E3779B97F4A7C15) | 1),
            tick: DAY / 4,
            next_id: 1,
            log: vec![],
            script: DEFAULT_SCRIPT.to_string(),
            vm: load_script(DEFAULT_SCRIPT).expect("behavior.rn failed to load"),
            paused: false,
            speed: 1,
            terrain_rev: 0,
        };
        w.home = w
            .find_land(GRASS)
            .unwrap_or_else(|| w.find_land(SAND).unwrap_or((W / 2, H / 2)));
        for i in 0..W * H {
            let r = w.rng.f();
            w.res[i] = match w.tiles[i] {
                FOREST if r < 0.6 => (TREE, 5),
                GRASS if r < 0.04 => (BERRY, 4),
                HILLS if r < 0.15 => (STONE, 6),
                _ => (0, 0),
            };
        }
        let (hx, hy) = w.home;
        w.res[hy * W + hx] = (0, 0);
        for _ in 0..6 {
            w.spawn_person();
        }
        for _ in 0..60 {
            if let Some(p) = w.random_land() {
                w.rabbits.push(Animal {
                    x: p.0,
                    y: p.1,
                    energy: 70.0,
                    dead: false,
                });
            }
        }
        for _ in 0..4 {
            if let Some(p) = w.random_land() {
                if cheb(p, w.home) > 15 {
                    w.wolves.push(Animal {
                        x: p.0,
                        y: p.1,
                        energy: 70.0,
                        dead: false,
                    });
                }
            }
        }
        w
    }

    fn find_land(&self, kind: u8) -> Option<(usize, usize)> {
        let c = (W / 2, H / 2);
        let mut best: Option<(usize, usize)> = None;
        for y in 0..H {
            for x in 0..W {
                if self.tiles[y * W + x] == kind
                    && best.is_none_or(|b| cheb((x, y), c) < cheb(b, c))
                {
                    best = Some((x, y));
                }
            }
        }
        best
    }

    fn random_land(&mut self) -> Option<(usize, usize)> {
        for _ in 0..50 {
            let (x, y) = (self.rng.below(W), self.rng.below(H));
            if self.walkable(x as i32, y as i32) {
                return Some((x, y));
            }
        }
        None
    }

    fn spawn_person(&mut self) {
        let (x, y) = self.home;
        self.people.push(Person {
            id: self.next_id,
            x,
            y,
            hunger: 10.0,
            food: 0,
            wood: 0,
            stone: 0,
            action: "idle".to_string(),
            dead: false,
        });
        self.next_id += 1;
    }

    fn say(&mut self, s: String) {
        self.log
            .push(format!("[day {}] {}", self.tick / DAY + 1, s));
        if self.log.len() > 8 {
            self.log.remove(0);
        }
    }

    pub fn daylight(&self) -> f32 {
        let phase = (self.tick % DAY) as f32 / DAY as f32;
        let v = -(phase * std::f32::consts::TAU).cos();
        (0.5 + v * 0.8).clamp(0.0, 1.0)
    }

    fn walkable(&self, x: i32, y: i32) -> bool {
        if x < 0 || y < 0 || x >= W as i32 || y >= H as i32 {
            return false;
        }
        matches!(
            self.tiles[y as usize * W + x as usize],
            SAND | GRASS | FOREST | HILLS
        )
    }

    fn move_dir(&mut self, x: usize, y: usize, dx: i32, dy: i32) -> (usize, usize) {
        for (a, b) in [(dx, dy), (dx, 0), (0, dy)] {
            if (a, b) != (0, 0) && self.walkable(x as i32 + a, y as i32 + b) {
                return ((x as i32 + a) as usize, (y as i32 + b) as usize);
            }
        }
        self.wander(x, y)
    }

    fn wander(&mut self, x: usize, y: usize) -> (usize, usize) {
        for _ in 0..4 {
            let (a, b) = (self.rng.below(3) as i32 - 1, self.rng.below(3) as i32 - 1);
            if (a, b) != (0, 0) && self.walkable(x as i32 + a, y as i32 + b) {
                return ((x as i32 + a) as usize, (y as i32 + b) as usize);
            }
        }
        (x, y)
    }

    fn move_toward(&mut self, from: (usize, usize), to: (usize, usize)) -> (usize, usize) {
        let dx = (to.0 as i32 - from.0 as i32).signum();
        let dy = (to.1 as i32 - from.1 as i32).signum();
        self.move_dir(from.0, from.1, dx, dy)
    }

    fn nearest_res(&self, from: (usize, usize), kind: u8, r: usize) -> Option<(usize, usize)> {
        let mut best: Option<(usize, usize)> = None;
        let (x0, x1) = (from.0.saturating_sub(r), (from.0 + r).min(W - 1));
        let (y0, y1) = (from.1.saturating_sub(r), (from.1 + r).min(H - 1));
        for y in y0..=y1 {
            for x in x0..=x1 {
                if self.res[y * W + x].0 == kind
                    && best.is_none_or(|b| cheb((x, y), from) < cheb(b, from))
                {
                    best = Some((x, y));
                }
            }
        }
        best
    }

    fn nearest_animal(list: &[Animal], from: (usize, usize), r: usize) -> Option<usize> {
        let mut best: Option<(usize, usize)> = None;
        for (i, a) in list.iter().enumerate() {
            let d = cheb((a.x, a.y), from);
            if !a.dead && d <= r && best.is_none_or(|(_, bd)| d < bd) {
                best = Some((i, d));
            }
        }
        best.map(|b| b.0)
    }

    pub fn step(&mut self) {
        self.tick += 1;
        self.regrow();
        if self.tick % 2 == 0 {
            for i in 0..self.people.len() {
                self.tick_person(i);
            }
            for i in 0..self.rabbits.len() {
                self.tick_rabbit(i);
            }
        } else {
            for i in 0..self.wolves.len() {
                self.tick_wolf(i);
            }
        }
        self.people.retain(|p| !p.dead);
        self.rabbits.retain(|a| !a.dead);
        self.wolves.retain(|a| !a.dead);
        self.population();
    }

    fn regrow(&mut self) {
        for _ in 0..20 {
            let i = self.rng.below(W * H);
            if self.res[i].0 != 0 {
                continue;
            }
            let p = self.rng.f();
            match self.tiles[i] {
                FOREST if p < 0.02 => self.res[i] = (TREE, 5),
                GRASS if p < 0.02 => self.res[i] = (BERRY, 4),
                HILLS if p < 0.004 => self.res[i] = (STONE, 6),
                _ => {}
            }
        }
    }

    fn population(&mut self) {
        if self.tick % 400 == 0 && self.food >= 10 && self.people.len() < 8 + self.houses.len() * 3
        {
            self.food -= 6;
            self.spawn_person();
            self.say("A child was born".into());
        }
        if self.tick % 50 == 0 {
            if self.rabbits.len() < 15 {
                if let Some(p) = self.random_land() {
                    self.rabbits.push(Animal {
                        x: p.0,
                        y: p.1,
                        energy: 70.0,
                        dead: false,
                    });
                }
            }
            if self.wolves.len() < 2 && self.rabbits.len() > 40 {
                if let Some(p) = self.random_land() {
                    if cheb(p, self.home) > 15 {
                        self.wolves.push(Animal {
                            x: p.0,
                            y: p.1,
                            energy: 70.0,
                            dead: false,
                        });
                    }
                }
            }
        }
    }

    fn decide(&mut self, func: &str, c: Ctx) -> String {
        match self.vm.call([func], (c,)) {
            Ok(v) => rune::from_value::<String>(v).unwrap_or_else(|_| "wander".into()),
            Err(e) => {
                eprintln!("script error in {func}: {e}");
                "wander".into()
            }
        }
    }

    fn tick_person(&mut self, i: usize) {
        let mut p = self.people[i].clone();
        let night = self.daylight() < 0.2;
        let pos = (p.x, p.y);
        let home = self.home;
        let at_home = cheb(pos, home) <= 1;
        p.hunger += if night && at_home { 0.04 } else { 0.1 };
        if p.hunger >= 100.0 {
            p.dead = true;
            self.say(format!("Person #{} starved", p.id));
            self.people[i] = p;
            return;
        }
        if at_home {
            self.food += p.food;
            self.wood += p.wood;
            self.stone += p.stone;
            p.food = 0;
            p.wood = 0;
            p.stone = 0;
            if p.hunger > 40.0 && self.food > 0 {
                self.food -= 1;
                p.hunger = (p.hunger - 25.0).max(0.0);
            }
            self.craft_and_build();
        }
        if p.hunger > 50.0 && p.food > 0 {
            p.food -= 1;
            p.hunger = (p.hunger - 25.0).max(0.0);
        }

        let berry = self.nearest_res(pos, BERRY, 25);
        let tree = self.nearest_res(pos, TREE, 25);
        let stone = self.nearest_res(pos, STONE, 25);
        let rabbit = Self::nearest_animal(&self.rabbits, pos, 25);
        let c = Ctx {
            night,
            at_home,
            hunger: p.hunger as f64,
            carry: p.carry() as i64,
            carried_food: p.food as i64,
            stock_food: self.food as i64,
            stock_wood: self.wood as i64,
            stock_stone: self.stone as i64,
            berry_near: berry.is_some(),
            tree_near: tree.is_some(),
            stone_near: stone.is_some(),
            rabbit_near: rabbit.is_some(),
            roll: self.rng.f() as f64,
            ..Default::default()
        };
        let choice = self.decide("person", c);

        let yield_n: u16 = if self.tools >= self.people.len() as u32 {
            2
        } else {
            1
        };
        let gather = match choice.as_str() {
            "forage" => Some((BERRY, berry, "foraging")),
            "chop" => Some((TREE, tree, "chopping wood")),
            "mine" => Some((STONE, stone, "mining stone")),
            _ => None,
        };
        match (choice.as_str(), gather, rabbit) {
            ("sleep", ..) => p.action = "sleeping".to_string(),
            ("go_home" | "haul" | "eat", ..) => {
                p.action = match choice.as_str() {
                    "go_home" => "going home",
                    "haul" => "hauling goods",
                    _ => "going to eat",
                }
                .to_string();
                if !at_home {
                    (p.x, p.y) = self.move_toward(pos, home);
                }
            }
            ("hunt", _, Some(r)) => {
                p.action = "hunting".to_string();
                let t = (self.rabbits[r].x, self.rabbits[r].y);
                if cheb(pos, t) <= 1 {
                    if self.rng.chance(0.5) {
                        self.rabbits[r].dead = true;
                        p.food += 3;
                    }
                } else {
                    (p.x, p.y) = self.move_toward(pos, t);
                }
            }
            (_, Some((kind, Some(t), label)), _) => {
                p.action = label.to_string();
                let idx = pos.1 * W + pos.0;
                if pos == t && self.res[idx].0 == kind {
                    let take = yield_n.min(self.res[idx].1);
                    self.res[idx].1 -= take;
                    if self.res[idx].1 == 0 {
                        self.res[idx].0 = 0;
                    }
                    match kind {
                        BERRY => p.food += take as u32,
                        TREE => p.wood += take as u32,
                        _ => p.stone += take as u32,
                    }
                } else {
                    (p.x, p.y) = self.move_toward(pos, t);
                }
            }
            _ => {
                p.action = "wandering".to_string();
                (p.x, p.y) = self.wander(p.x, p.y);
            }
        }
        self.people[i] = p;
    }

    fn craft_and_build(&mut self) {
        if self.wood >= 3 && self.stone >= 1 && self.tools < self.people.len() as u32 {
            self.wood -= 3;
            self.stone -= 1;
            self.tools += 1;
        }
        if self.wood >= 12 && self.stone >= 4 && self.houses.len() < 10 {
            let (hx, hy) = self.home;
            let x = (hx as i32 + self.rng.below(13) as i32 - 6).clamp(0, W as i32 - 1);
            let y = (hy as i32 + self.rng.below(13) as i32 - 6).clamp(0, H as i32 - 1);
            if self.walkable(x, y)
                && self.res[y as usize * W + x as usize].0 == 0
                && !self.houses.contains(&(x as usize, y as usize))
            {
                self.wood -= 12;
                self.stone -= 4;
                self.houses.push((x as usize, y as usize));
                self.say("A new house was built".into());
            }
        }
    }

    fn tick_rabbit(&mut self, i: usize) {
        let mut a = self.rabbits[i].clone();
        a.energy -= 0.05;
        if matches!(self.tiles[a.y * W + a.x], GRASS | FOREST) {
            a.energy = (a.energy + 0.2).min(100.0);
        }
        let pos = (a.x, a.y);
        let wolf = Self::nearest_animal(&self.wolves, pos, 4);
        let c = Ctx {
            wolf_near: wolf.is_some(),
            roll: self.rng.f() as f64,
            ..Default::default()
        };
        match (self.decide("rabbit", c).as_str(), wolf) {
            ("flee", Some(w)) => {
                let dx = (a.x as i32 - self.wolves[w].x as i32).signum();
                let dy = (a.y as i32 - self.wolves[w].y as i32).signum();
                (a.x, a.y) = self.move_dir(a.x, a.y, dx, dy);
            }
            ("wander", _) => (a.x, a.y) = self.wander(a.x, a.y),
            _ => {}
        }
        if a.energy > 80.0 && self.rabbits.len() < 120 && self.rng.chance(0.01) {
            a.energy -= 30.0;
            self.rabbits.push(Animal {
                x: a.x,
                y: a.y,
                energy: 50.0,
                dead: false,
            });
        }
        if a.energy <= 0.0 {
            a.dead = true;
        }
        self.rabbits[i] = a;
    }

    fn tick_wolf(&mut self, i: usize) {
        let mut a = self.wolves[i].clone();
        a.energy -= 0.15;
        let pos = (a.x, a.y);
        let prey = Self::nearest_animal(&self.rabbits, pos, 10);
        let c = Ctx {
            prey_near: prey.is_some(),
            ..Default::default()
        };
        match (self.decide("wolf", c).as_str(), prey) {
            ("hunt", Some(r)) => {
                let t = (self.rabbits[r].x, self.rabbits[r].y);
                if cheb(pos, t) <= 1 {
                    if self.rng.chance(0.4) {
                        self.rabbits[r].dead = true;
                        a.energy = (a.energy + 50.0).min(100.0);
                    }
                } else {
                    (a.x, a.y) = self.move_toward(pos, t);
                }
            }
            _ => (a.x, a.y) = self.wander(a.x, a.y),
        }
        if a.energy > 90.0 && self.wolves.len() < 10 && self.rng.chance(0.02) {
            a.energy -= 40.0;
            self.wolves.push(Animal {
                x: a.x,
                y: a.y,
                energy: 50.0,
                dead: false,
            });
        }
        if a.energy <= 0.0 {
            a.dead = true;
        }
        self.wolves[i] = a;
    }

    pub fn set_script(&mut self, src: &str) -> Result<(), String> {
        let vm = load_script(src)?;
        self.vm = vm;
        self.script = src.to_string();
        Ok(())
    }

    pub fn snapshot_json(&self) -> Result<String, serde_json::Error> {
        serde_json::to_string(&WorldSnapshot {
            version: 1,
            tiles: self.tiles.clone(),
            res: self.res.clone(),
            people: self.people.clone(),
            rabbits: self.rabbits.clone(),
            wolves: self.wolves.clone(),
            houses: self.houses.clone(),
            home: self.home,
            food: self.food,
            wood: self.wood,
            stone: self.stone,
            tools: self.tools,
            rng: self.rng.0,
            tick: self.tick,
            next_id: self.next_id,
            log: self.log.clone(),
            script: self.script.clone(),
            paused: self.paused,
            speed: self.speed,
            terrain_rev: self.terrain_rev,
        })
    }

    pub fn script(&self) -> &str {
        &self.script
    }

    pub fn from_snapshot(snapshot: &str) -> Result<Self, String> {
        let saved: WorldSnapshot = serde_json::from_str(snapshot).map_err(|e| e.to_string())?;
        if saved.version != 1 {
            return Err(format!(
                "unsupported world snapshot version {}",
                saved.version
            ));
        }
        if saved.tiles.len() != W * H || saved.res.len() != W * H {
            return Err("world snapshot has invalid terrain dimensions".into());
        }
        let vm = load_script(&saved.script)?;
        Ok(Self {
            tiles: saved.tiles,
            res: saved.res,
            people: saved.people,
            rabbits: saved.rabbits,
            wolves: saved.wolves,
            houses: saved.houses,
            home: saved.home,
            food: saved.food,
            wood: saved.wood,
            stone: saved.stone,
            tools: saved.tools,
            rng: Rng(saved.rng),
            tick: saved.tick,
            next_id: saved.next_id,
            log: saved.log,
            script: saved.script,
            vm,
            paused: saved.paused,
            speed: saved.speed,
            terrain_rev: saved.terrain_rev,
        })
    }

    fn rect(t: &[&str], i: usize) -> Option<(usize, usize, usize, usize)> {
        let n: Vec<i64> = (i..i + 4).filter_map(|k| t.get(k)?.parse().ok()).collect();
        if n.len() != 4 {
            return None;
        }
        let c = |v: i64, max: usize| v.clamp(0, max as i64 - 1) as usize;
        let (x0, x1) = (c(n[0].min(n[2]), W), c(n[0].max(n[2]), W));
        let (y0, y1) = (c(n[1].min(n[3]), H), c(n[1].max(n[3]), H));
        Some((x0, y0, x1, y1))
    }

    /// Applies one whitespace-separated edit command; malformed commands are ignored.
    pub fn apply(&mut self, cmd: &str) {
        let t: Vec<&str> = cmd.split_whitespace().collect();
        let num = |i: usize| t.get(i).and_then(|s| s.parse::<i64>().ok());
        match t.first().copied() {
            Some("pause") => self.paused = num(1) != Some(0),
            Some("speed") => {
                if let Some(n) = num(1) {
                    self.speed = n.clamp(1, 8) as u32;
                }
            }
            Some("stock") => {
                if let (Some(name), Some(v)) = (t.get(1), num(2)) {
                    let v = v.clamp(0, 9999) as u32;
                    match *name {
                        "food" => self.food = v,
                        "wood" => self.wood = v,
                        "stone" => self.stone = v,
                        "tools" => self.tools = v,
                        _ => {}
                    }
                }
            }
            Some("person") => {
                if let (Some(id), Some(field), Some(v)) = (num(1), t.get(2), num(3)) {
                    if let Some(p) = self.people.iter_mut().find(|p| p.id as i64 == id) {
                        let u = v.clamp(0, 99) as u32;
                        match *field {
                            "hunger" => p.hunger = v.clamp(0, 99) as f32,
                            "food" => p.food = u,
                            "wood" => p.wood = u,
                            "stone" => p.stone = u,
                            _ => {}
                        }
                    }
                }
            }
            Some("energy") => {
                if let (Some((x0, y0, x1, y1)), Some(v)) = (Self::rect(&t, 1), num(5)) {
                    let v = v.clamp(1, 100) as f32;
                    let inside = |a: &Animal| a.x >= x0 && a.x <= x1 && a.y >= y0 && a.y <= y1;
                    for a in self.rabbits.iter_mut().chain(self.wolves.iter_mut()) {
                        if inside(a) {
                            a.energy = v;
                        }
                    }
                }
            }
            Some("terrain") => {
                if let (Some((x0, y0, x1, y1)), Some(kind)) = (Self::rect(&t, 1), num(5)) {
                    if (0..=6).contains(&kind) {
                        self.paint_terrain(x0, y0, x1, y1, kind as u8);
                    }
                }
            }
            Some("res") => {
                if let (Some((x0, y0, x1, y1)), Some(kind), Some(amt)) =
                    (Self::rect(&t, 1), num(5), num(6))
                {
                    if (0..=3).contains(&kind) {
                        let amt = amt.clamp(1, 50) as u16;
                        for y in y0..=y1 {
                            for x in x0..=x1 {
                                let i = y * W + x;
                                let free = self.walkable(x as i32, y as i32)
                                    && (x, y) != self.home
                                    && !self.houses.contains(&(x, y));
                                if kind == 0 {
                                    self.res[i] = (0, 0);
                                } else if free {
                                    self.res[i] = (kind as u8, amt);
                                }
                            }
                        }
                    }
                }
            }
            Some("spawn") => {
                if let (Some(what), Some((x0, y0, x1, y1))) = (t.get(1), Self::rect(&t, 2)) {
                    let mut left = 25;
                    for y in y0..=y1 {
                        for x in x0..=x1 {
                            if left == 0 || !self.walkable(x as i32, y as i32) {
                                continue;
                            }
                            left -= 1;
                            let a = Animal {
                                x,
                                y,
                                energy: 70.0,
                                dead: false,
                            };
                            match *what {
                                "person" => {
                                    self.spawn_person();
                                    let p = self.people.last_mut().unwrap();
                                    (p.x, p.y) = (x, y);
                                }
                                "rabbit" => self.rabbits.push(a),
                                "wolf" => self.wolves.push(a),
                                _ => left += 1,
                            }
                        }
                    }
                }
            }
            Some("house") => {
                if let Some((x0, y0, x1, y1)) = Self::rect(&t, 1) {
                    for y in y0..=y1 {
                        for x in x0..=x1 {
                            if self.houses.len() < 30
                                && self.walkable(x as i32, y as i32)
                                && self.res[y * W + x].0 == 0
                                && (x, y) != self.home
                                && !self.houses.contains(&(x, y))
                            {
                                self.houses.push((x, y));
                            }
                        }
                    }
                }
            }
            Some("remove") => {
                if let (Some((x0, y0, x1, y1)), Some(what)) = (Self::rect(&t, 1), t.get(5)) {
                    let inside = |x: usize, y: usize| x >= x0 && x <= x1 && y >= y0 && y <= y1;
                    let all = *what == "all";
                    if all || *what == "people" {
                        self.people.retain(|p| !inside(p.x, p.y));
                    }
                    if all || *what == "rabbits" {
                        self.rabbits.retain(|a| !inside(a.x, a.y));
                    }
                    if all || *what == "wolves" {
                        self.wolves.retain(|a| !inside(a.x, a.y));
                    }
                    if all || *what == "houses" {
                        self.houses.retain(|h| !inside(h.0, h.1));
                    }
                    if all || *what == "res" {
                        for y in y0..=y1 {
                            for x in x0..=x1 {
                                self.res[y * W + x] = (0, 0);
                            }
                        }
                    }
                }
            }
            _ => {}
        }
    }

    fn paint_terrain(&mut self, x0: usize, y0: usize, x1: usize, y1: usize, kind: u8) {
        let land = matches!(kind, SAND | GRASS | FOREST | HILLS);
        for y in y0..=y1 {
            for x in x0..=x1 {
                if !land && (x, y) == self.home {
                    continue;
                }
                self.tiles[y * W + x] = kind;
                if !land {
                    self.res[y * W + x] = (0, 0);
                    self.houses.retain(|h| *h != (x, y));
                }
            }
        }
        if !land {
            let ok = |tiles: &[u8], x: usize, y: usize| {
                matches!(tiles[y * W + x], SAND | GRASS | FOREST | HILLS)
            };
            let tiles = self.tiles.clone();
            self.rabbits.retain(|a| ok(&tiles, a.x, a.y));
            self.wolves.retain(|a| ok(&tiles, a.x, a.y));
            let home = self.home;
            for p in self.people.iter_mut().filter(|p| !ok(&tiles, p.x, p.y)) {
                (p.x, p.y) = home;
            }
        }
        self.terrain_rev += 1;
    }

    pub fn terrain_json(&self) -> String {
        let tiles: String = self.tiles.iter().map(|t| (b'0' + t) as char).collect();
        format!("{{\"w\":{},\"h\":{},\"tiles\":\"{}\"}}", W, H, tiles)
    }

    pub fn state_json(&self) -> String {
        let mut s = String::new();
        let _ = write!(
            s,
            "{{\"paused\":{},\"speed\":{},\"rev\":{},\"tick\":{},\"day\":{},\"hour\":{:.2},\"daylight\":{:.3},\"stock\":{{\"food\":{},\"wood\":{},\"stone\":{},\"tools\":{}}},\"home\":[{},{}],",
            self.paused,
            self.speed,
            self.terrain_rev,
            self.tick,
            self.tick / DAY + 1,
            (self.tick % DAY) as f32 / DAY as f32 * 24.0,
            self.daylight(),
            self.food,
            self.wood,
            self.stone,
            self.tools,
            self.home.0,
            self.home.1
        );
        s.push_str("\"houses\":[");
        let j: Vec<String> = self
            .houses
            .iter()
            .map(|h| format!("[{},{}]", h.0, h.1))
            .collect();
        s.push_str(&j.join(","));
        s.push_str("],\"people\":[");
        let j: Vec<String> = self
            .people
            .iter()
            .map(|p| {
                format!(
                    "[{},{},{},\"{}\",{:.0},{},{},{}]",
                    p.id, p.x, p.y, p.action, p.hunger, p.food, p.wood, p.stone
                )
            })
            .collect();
        s.push_str(&j.join(","));
        s.push_str("],\"rabbits\":[");
        let j: Vec<String> = self
            .rabbits
            .iter()
            .map(|a| format!("[{},{},{:.0}]", a.x, a.y, a.energy))
            .collect();
        s.push_str(&j.join(","));
        s.push_str("],\"wolves\":[");
        let j: Vec<String> = self
            .wolves
            .iter()
            .map(|a| format!("[{},{},{:.0}]", a.x, a.y, a.energy))
            .collect();
        s.push_str(&j.join(","));
        s.push_str("],\"res\":[");
        let mut first = true;
        for (i, r) in self.res.iter().enumerate() {
            if r.0 != 0 {
                if !first {
                    s.push(',');
                }
                first = false;
                let _ = write!(s, "[{},{},{},{}]", i % W, i / W, r.0, r.1);
            }
        }
        s.push_str("],\"log\":[");
        let j: Vec<String> = self.log.iter().map(|l| format!("\"{}\"", l)).collect();
        s.push_str(&j.join(","));
        s.push_str("]}");
        s
    }
}

#[cfg(test)]
mod tests {
    use super::World;

    #[test]
    fn snapshot_restores_state_and_rng() {
        let mut original = World::new(42);
        for _ in 0..10 {
            original.step();
        }
        original.paused = true;
        original.speed = 4;

        let snapshot = original.snapshot_json().unwrap();
        let mut restored = World::from_snapshot(&snapshot).unwrap();
        assert_eq!(original.state_json(), restored.state_json());

        original.step();
        restored.step();
        assert_eq!(original.state_json(), restored.state_json());
    }
}