Grovewright/core/tests/host_guest.rs

//! Host and guest driven by hand, message by message. These tests produce
//! what the in-memory network of `session.rs` never does, because it lets
//! every guest run each tick before the next one arrives: a guest that lags
//! behind, a tick that gets lost, and joins that wait at the limits.

use grovewright_core::command::Command;
use grovewright_core::guest::{Arrival, Guest};
use grovewright_core::host::{Host, Peer, MAX_ACTIONS_PER_TICK};
use grovewright_core::map::Pos;
use grovewright_core::mapgen::outcrop_origin;
use grovewright_core::player::{PlayerId, PlayerKey};
use grovewright_core::protocol::{Action, Refusal, ToGuest, ToHost, CHECK_INTERVAL_TICKS};
use grovewright_core::world::{Event, World, DIG_COOLDOWN_TICKS};

const HOST_KEY: PlayerKey = [100; 16];

/// A host whose own player is in a new world.
fn started_host() -> Host {
    let mut host = Host::new(World::new(5));
    host.join_local(HOST_KEY, "Host");
    host.step();
    host
}

/// Connects a guest with a key made of `key` as `peer` and hands its
/// greeting to the host.
fn greet(host: &mut Host, peer: Peer, key: u8) -> Guest {
    host.connect(peer);
    let mut guest = Guest::new([key; 16], "Guest");
    for bytes in guest.take_outbox() {
        host.receive(peer, &bytes);
    }
    guest
}

/// Takes the host's whole outbox and keeps what is for `peer`.
fn messages_for(host: &mut Host, peer: Peer) -> Vec<Vec<u8>> {
    host.take_outbox()
        .into_iter()
        .filter(|(to, _)| *to == peer)
        .map(|(_, bytes)| bytes)
        .collect()
}

/// The host's answer to a greeting from `peer`: `None` for its world, or
/// the reason it turned the guest away.
fn answer_to(host: &mut Host, peer: Peer) -> Option<Refusal> {
    let messages = messages_for(host, peer);
    match ToGuest::decode(&messages[0]) {
        Ok(ToGuest::World { .. }) => None,
        Ok(ToGuest::Refused(refusal)) => Some(refusal),
        other => panic!("unexpected answer {other:?}"),
    }
}

/// A host and the guest Ada at peer 2, in the same state.
fn host_with_ada() -> (Host, Guest) {
    let mut host = started_host();
    let mut ada = greet(&mut host, 2, 1);
    for bytes in messages_for(&mut host, 2) {
        ada.receive(&bytes).unwrap();
    }
    host.step();
    for bytes in messages_for(&mut host, 2) {
        ada.receive(&bytes).unwrap();
    }
    while ada.step().is_some() {}
    assert!(ada.local_player().is_some());
    assert_eq!(
        ada.world().map(World::state_hash),
        Some(host.world().state_hash())
    );
    (host, ada)
}

/// A world that knows players with keys made of 1 to `count`, all offline.
fn world_with_offline_players(count: u8) -> World {
    let mut world = World::new(5);
    for key in 1..=count {
        world.step(&[Command::Join {
            key: [key; 16],
            name: "Visitor".to_owned(),
        }]);
        world.step(&[Command::Leave {
            player: PlayerId(key - 1),
        }]);
    }
    world
}

#[test]
fn the_hosts_own_queued_join_counts_for_the_online_limit() {
    let mut host = Host::new(World::new(5));
    host.join_local(HOST_KEY, "Host");
    // No tick has run: the host's join is still queued.
    let mut answers = Vec::new();
    for key in 1..=4 {
        let peer = Peer::from(key) + 1;
        greet(&mut host, peer, key);
        answers.push(answer_to(&mut host, peer));
    }
    assert_eq!(answers, [None, None, None, Some(Refusal::WorldFull)]);
}

#[test]
fn queued_new_keys_count_for_the_limit_of_known_players_but_known_ones_do_not() {
    let mut host = Host::new(world_with_offline_players(15));
    greet(&mut host, 2, 3);
    assert_eq!(answer_to(&mut host, 2), None, "a returning player");
    greet(&mut host, 3, 200);
    assert_eq!(
        answer_to(&mut host, 3),
        None,
        "a new player fits as the 16th"
    );
    greet(&mut host, 4, 201);
    assert_eq!(
        answer_to(&mut host, 4),
        Some(Refusal::TooManyPlayers),
        "a second new player does not"
    );

    let events = host.step();
    assert!(!events
        .iter()
        .any(|event| matches!(event, Event::JoinRefused { .. })));
    assert_eq!(host.world().players().len(), 16);
}

#[test]
fn a_queued_join_of_a_player_who_is_online_already_counts_once() {
    let mut world = World::new(5);
    let joins = [HOST_KEY, [1; 16], [2; 16]].map(|key| Command::Join {
        key,
        name: "Online".to_owned(),
    });
    world.step(&joins);
    let mut host = Host::new(world);
    // The host's player is online already; its queued join changes nothing.
    host.join_local(HOST_KEY, "Host");
    greet(&mut host, 2, 3);
    assert_eq!(answer_to(&mut host, 2), None, "the fourth player fits");
}

#[test]
fn the_count_of_a_guests_actions_starts_again_in_every_tick() {
    let (mut host, mut ada) = host_with_ada();
    for tick in 0..3 {
        for x in 0..10 {
            ada.act(Action::Dig {
                pos: Pos::new(x, 1),
            });
        }
        for bytes in ada.take_outbox() {
            host.receive(2, &bytes);
        }
        host.step();
        let counts: Vec<usize> = messages_for(&mut host, 2)
            .iter()
            .filter_map(|bytes| match ToGuest::decode(bytes) {
                Ok(ToGuest::Tick { commands, .. }) => Some(commands.len()),
                _ => None,
            })
            .collect();
        assert_eq!(counts, [MAX_ACTIONS_PER_TICK as usize], "tick {tick}");
    }
}

#[test]
fn a_tick_carries_the_number_of_the_tick_before_it_runs() {
    let (mut host, mut ada) = host_with_ada();
    let before = host.world().tick();
    host.step();
    let messages = messages_for(&mut host, 2);
    let Ok(ToGuest::Tick { tick, .. }) = ToGuest::decode(&messages[0]) else {
        panic!("not a tick");
    };
    assert_eq!(tick, before);
    for bytes in messages {
        ada.receive(&bytes).unwrap();
    }
    ada.step().unwrap();
    assert_eq!(ada.world().map(World::tick), Some(before + 1));
}

#[test]
fn a_lagging_guest_that_diverges_runs_nothing_until_the_world_comes_and_drops_older_ticks() {
    let (mut host, mut ada) = host_with_ada();

    // The host's player hits the rock, but Ada's copy of that tick loses the
    // command, as if her machine had run it differently.
    host.act_local(Action::Dig {
        pos: outcrop_origin(host.world().map()),
    });
    host.step();
    for bytes in messages_for(&mut host, 2) {
        let bytes = match ToGuest::decode(&bytes) {
            Ok(ToGuest::Tick { tick, check, .. }) => ToGuest::Tick {
                tick,
                commands: vec![],
                check,
            }
            .encode(),
            _ => bytes,
        };
        ada.receive(&bytes).unwrap();
    }
    while ada.step().is_some() {}
    assert!(!ada.has_diverged());

    // Thirty more ticks arrive before Ada runs any of them.
    for _ in 0..30 {
        host.step();
        for bytes in messages_for(&mut host, 2) {
            ada.receive(&bytes).unwrap();
        }
    }
    assert!(ada.pending_ticks() >= 30);

    // She catches up and trips over the next checksum.
    while ada.step().is_some() && !ada.has_diverged() {}
    assert!(ada.has_diverged());
    let waiting = ada.pending_ticks();
    assert!(waiting > 0, "newer ticks are still waiting");
    assert!(ada.step().is_none(), "no tick runs after a divergence");
    assert_eq!(ada.pending_ticks(), waiting, "and none is used up");

    // Her report names her tick after the step that showed the divergence.
    let reports = ada.take_outbox();
    assert_eq!(reports.len(), 1);
    let Ok(ToHost::Diverged { tick, hash }) = ToHost::decode(&reports[0]) else {
        panic!("not a divergence report");
    };
    assert_eq!(Some(tick), ada.world().map(World::tick));
    assert_eq!(tick % CHECK_INTERVAL_TICKS, 0);
    host.receive(2, &reports[0]);
    let divergences = host.take_divergences();
    assert_eq!(divergences.len(), 1);
    assert_eq!((divergences[0].tick, divergences[0].hash), (tick, hash));

    // The host has gone on meanwhile. Its world comes first, then later ticks.
    let world_tick = host.world().tick();
    let answer = messages_for(&mut host, 2);
    assert_eq!(answer.len(), 1);
    host.step();
    host.step();
    let later = messages_for(&mut host, 2);
    assert_eq!(later.len(), 2);

    assert_eq!(
        ada.receive(&answer[0]),
        Ok(Arrival::World { replaced: true })
    );
    assert_eq!(ada.pending_ticks(), 0, "the older ticks are dropped");
    assert_eq!(ada.world().map(World::tick), Some(world_tick));
    assert!(!ada.has_diverged());
    for bytes in later {
        ada.receive(&bytes).unwrap();
    }
    while ada.step().is_some() {}
    assert_eq!(
        ada.world().map(World::state_hash),
        Some(host.world().state_hash())
    );
    assert!(ada.take_diverged_recording().is_some());
}

#[test]
fn a_missing_tick_makes_the_guest_ask_for_the_world() {
    let (mut host, mut ada) = host_with_ada();
    host.step();
    // This tick never arrives.
    messages_for(&mut host, 2);
    host.step();
    for bytes in messages_for(&mut host, 2) {
        ada.receive(&bytes).unwrap();
    }
    assert!(ada.step().is_none());
    assert!(ada.has_diverged());
    let reports = ada.take_outbox();
    assert_eq!(reports.len(), 1);

    host.receive(2, &reports[0]);
    for bytes in messages_for(&mut host, 2) {
        assert_eq!(ada.receive(&bytes), Ok(Arrival::World { replaced: true }));
    }
    host.step();
    for bytes in messages_for(&mut host, 2) {
        ada.receive(&bytes).unwrap();
    }
    while ada.step().is_some() {}
    assert_eq!(
        ada.world().map(World::state_hash),
        Some(host.world().state_hash())
    );
}

/// Hands a pickaxe hit of `guest` at `pos` to the host as from `peer`.
fn dig(host: &mut Host, peer: Peer, guest: &mut Guest, pos: Pos) {
    guest.act(Action::Dig { pos });
    for bytes in guest.take_outbox() {
        host.receive(peer, &bytes);
    }
}

/// The tiles that pickaxe hits landed on, without breaking them.
fn hits(events: &[Event]) -> Vec<Pos> {
    events
        .iter()
        .filter_map(|event| match event {
            Event::TileHit { pos, .. } => Some(*pos),
            _ => None,
        })
        .collect()
}

#[test]
fn a_guests_hit_that_comes_during_the_cooldown_waits_for_it() {
    let (mut host, mut ada) = host_with_ada();
    let rock = outcrop_origin(host.world().map());
    let next = Pos::new(rock.x + 1, rock.y);
    dig(&mut host, 2, &mut ada, rock);
    let first = host.world().tick();
    assert_eq!(hits(&host.step()), [rock], "the first hit lands at once");

    // Two more hits come during the cooldown, as if the round trip had
    // become shorter. The newer one waits for the end of the cooldown.
    dig(&mut host, 2, &mut ada, rock);
    dig(&mut host, 2, &mut ada, next);
    let mut landed = Vec::new();
    for _ in 0..DIG_COOLDOWN_TICKS {
        let tick = host.world().tick();
        for pos in hits(&host.step()) {
            landed.push((tick, pos));
        }
    }
    assert_eq!(landed, [(first + DIG_COOLDOWN_TICKS, next)]);
}

#[test]
fn a_waiting_hit_is_dropped_when_its_guest_leaves() {
    let (mut host, mut ada) = host_with_ada();
    let rock = outcrop_origin(host.world().map());
    dig(&mut host, 2, &mut ada, rock);
    host.step();
    dig(&mut host, 2, &mut ada, rock);
    host.disconnect(2);
    for _ in 0..DIG_COOLDOWN_TICKS {
        assert_eq!(hits(&host.step()), [], "nobody hits");
    }
}