Grovewright/core/tests/determinism.rs

//! The central promise of the core: the same commands always produce the
//! same world.

use grovewright_core::codec::{Reader, Writer};
use grovewright_core::command::Command;
use grovewright_core::inventory::ITEM_STONE;
use grovewright_core::map::Pos;
use grovewright_core::mapgen::TEST_MAP_SIZE;
use grovewright_core::player::PlayerId;
use grovewright_core::replay::Recording;
use grovewright_core::rng::Rng;
use grovewright_core::world::World;

/// Edge length of the square around the map centre in which the script digs.
const DIG_AREA: u32 = 24;

/// Builds a busy, repeatable command stream: four players join, dig at
/// random places near the centre, and now and then leave and return.
fn script(seed: u64, ticks: usize) -> Vec<Vec<Command>> {
    let mut rng = Rng::new(seed);
    let first = (TEST_MAP_SIZE - DIG_AREA) / 2;
    let mut out = Vec::with_capacity(ticks);
    for tick in 0..ticks {
        let mut commands = Vec::new();
        if tick < 4 {
            commands.push(Command::Join {
                key: [tick as u8 + 1; 16],
                name: format!("P{tick}"),
            });
        }
        for player in 0..4 {
            if rng.below(3) == 0 {
                let x = first + rng.below(DIG_AREA);
                let y = first + rng.below(DIG_AREA);
                commands.push(Command::Dig {
                    player: PlayerId(player),
                    pos: Pos::new(x as i32, y as i32),
                });
            }
        }
        if rng.below(200) == 0 {
            commands.push(Command::Leave {
                player: PlayerId(rng.below(4) as u8),
            });
        }
        if rng.below(200) == 0 {
            let n = rng.below(4) as u8;
            commands.push(Command::Join {
                key: [n + 1; 16],
                name: format!("P{n}"),
            });
        }
        out.push(commands);
    }
    out
}

fn stones(world: &World) -> u32 {
    world
        .players()
        .iter()
        .map(|player| player.inventory.count(ITEM_STONE))
        .sum()
}

#[test]
fn the_same_commands_give_the_same_world() {
    let script = script(2026, 3_000);
    let mut a = World::new(99);
    let mut b = World::new(99);
    for (tick, commands) in script.iter().enumerate() {
        assert_eq!(
            a.step(commands),
            b.step(commands),
            "events differ at tick {tick}"
        );
        if tick.is_multiple_of(100) {
            assert_eq!(
                a.state_hash(),
                b.state_hash(),
                "state differs at tick {tick}"
            );
        }
    }
    assert_eq!(a, b);
    assert!(
        stones(&a) > 50,
        "the script should break plenty of rock, broke {}",
        stones(&a)
    );
}

#[test]
fn a_different_seed_gives_a_different_world() {
    let script = script(2026, 200);
    let mut a = World::new(1);
    let mut b = World::new(2);
    assert_ne!(a.map(), b.map(), "the seed must shape the map");
    for commands in &script {
        a.step(commands);
        b.step(commands);
    }
    assert_ne!(a.state_hash(), b.state_hash());
}

#[test]
fn a_world_restored_in_the_middle_of_a_session_stays_in_step() {
    let script = script(7, 2_000);
    let mut original = World::new(5);
    for commands in &script[..1_000] {
        original.step(commands);
    }
    let mut restored = World::from_snapshot(&original.to_snapshot()).unwrap();
    for commands in &script[1_000..] {
        assert_eq!(original.step(commands), restored.step(commands));
    }
    assert_eq!(original.state_hash(), restored.state_hash());
}

#[test]
fn a_recorded_session_replays_to_the_same_hash() {
    let script = script(31, 2_000);
    let mut world = World::new(8);
    let mut recording = Recording::start(&world);
    for commands in &script {
        recording.step(&mut world, commands);
    }
    let bytes = recording.to_bytes(&world);
    let replayed = Recording::verify(&bytes).expect("the recording replays cleanly");
    assert_eq!(replayed.state_hash(), world.state_hash());
}

#[test]
fn commands_sent_as_bytes_give_the_same_world() {
    let script = script(3, 1_500);
    let mut local = World::new(21);
    let mut remote = World::new(21);
    for commands in &script {
        let mut w = Writer::new();
        for command in commands {
            command.encode(&mut w);
        }
        let bytes = w.into_bytes();
        let mut r = Reader::new(&bytes);
        let mut received = Vec::new();
        while r.remaining() > 0 {
            received.push(Command::decode(&mut r).expect("command decodes"));
        }
        local.step(commands);
        remote.step(&received);
    }
    assert_eq!(local.state_hash(), remote.state_hash());
}