undercooked/tests/unit/test_encoding_no_leak.py

"""Unit: the snapshot encoder keeps the sim's internals off the wire
(phase 06, task 04) — the recursive no-leak guard, the 2-decimal
quantization, the explicit event-payload map, the delta tombstones, and
`snapshot_size`'s UTF-8 accounting.

The no-leak rule (task 04): a frame contains no `token`, no
`display_name`, no `seed`, no station internal `id`, no `rng_state` —
checked recursively, on *values* as well as *keys* (a station's
internal id, `stove_1`, is a value, not a key). The sim's internal
identity is projected out by design: a station's wire identity is its
kind + coordinates (`k` + `x`/`y`), and an event's payload goes through
the explicit `EVENT_PAYLOAD_SHORT` map — a key that is not listed there
never leaves the server.
"""

from __future__ import annotations

import json
from collections.abc import Iterator
from dataclasses import replace
from typing import Any

import pytest

from undercooked.server.encoding import (
    EVENT_PAYLOAD_SHORT,
    encode_events,
    encode_snapshot,
    event_wire_dict,
    snapshot_size,
)
from undercooked.sim.grid import Grid
from undercooked.sim.model import (
    Event,
    EventKind,
    Facing,
    Hazard,
    HazardKind,
    Item,
    ItemForm,
    ItemKind,
    KitchenState,
    Order,
    Player,
    PlayerState,
    Station,
    StationKind,
    StationState,
    TileKind,
    Vec2,
)

pytestmark = pytest.mark.unit

#: The forbidden *key names* — the sim's internal fields, never on the
#: wire (task 04's no-leak list; `station` is the internal-id carrier
#: the explicit payload map exists to drop).
FORBIDDEN_KEYS: frozenset[str] = frozenset(
    {"token", "display_name", "seed", "rng_state", "station"}
)

#: The station/hazard internal ids (values — they must not appear
#: anywhere in a frame).
STOVE_ID = "stove_1"
CHOP_ID = "chop_board_1"
HARD_ID = "hz-fire-1"

A_DISPLAY_NAME = "A very unique cook name"
A_SEED = 0x0BADF00D
A_RNG_STATE = 0xCAFEBABE
A_PLAYER_ID = "tok-abcdef0123456789"  # the token value (allowed as `i`)


def make_state() -> KitchenState:
    """A hand-built state with every internal field set to a unique
    value: two stations (internal ids, contents, progress), one player
    (token id, display name, unquantized position, a carried item), one
    order, one hazard, a big `seed` and `rng_state`."""
    return KitchenState(
        level_id="01_first_kitchen",
        seed=A_SEED,
        grid=Grid(width=8, height=8, tiles=(TileKind.FLOOR,) * 64),
        tick=4821,
        stations=(
            Station(
                id=STOVE_ID,
                kind=StationKind.STOVE,
                x=3.23456,
                y=2.0,
                contents=(Item(ItemKind.ONION, ItemForm.RAW, quality=0.98765),),
                state=StationState.WORKING,
                progress=0.4242,
            ),
            Station(
                id=CHOP_ID,
                kind=StationKind.CHOP_BOARD,
                x=5.0,
                y=7.0,
                state=StationState.DIRTY,
                dirty=True,
            ),
        ),
        players=(
            Player(
                id=A_PLAYER_ID,
                pos=Vec2(1.23456, -2.34567),
                vel=Vec2(0.5, -0.5),
                facing=Facing.RIGHT,
                carrying=Item(ItemKind.TOMATO, ItemForm.CHOPPED, quality=0.98765),
                state=PlayerState.MOVING,
                seat=1,
                display_name=A_DISPLAY_NAME,
            ),
        ),
        orders=(
            Order(id=7, recipe_id="soup", time_left=30.0, deadline=1200, value=40),
        ),
        order_deadline=1200,
        hazards=(
            Hazard(
                id=HARD_ID,
                kind=HazardKind.FIRE,
                pos=Vec2(7.654321, 5.2),
                life=12.346,
            ),
        ),
        score=120,
        target_score=140,
        time_left=83.654,
        rng_state=A_RNG_STATE,
    )


def walk(node: Any) -> Iterator[tuple[Any, Any]]:
    """Every `(key, value)` pair in the JSON tree (keys only on objects)."""
    if isinstance(node, dict):
        for key, value in node.items():
            yield key, value
            yield from walk(value)
    elif isinstance(node, list):
        for item in node:
            yield from walk(item)


def assert_no_leak(frame: dict[str, Any]) -> None:
    """The recursive no-leak check: no forbidden key, and no internal
    value (a station/hazard id, the display name, the seed, the
    rng_state) anywhere in the tree."""
    values: list[Any] = []
    for key, value in walk(frame):
        assert key not in FORBIDDEN_KEYS, f"forbidden key on the wire: {key!r}"
        values.append(value)
    for forbidden in (STOVE_ID, CHOP_ID, HARD_ID, A_DISPLAY_NAME):
        assert forbidden not in values, f"internal value on the wire: {forbidden!r}"
    assert A_SEED not in values, "the round seed leaked onto the wire"
    assert A_RNG_STATE not in values, "the rng_state leaked onto the wire"


# ------------------------------------------------------------- the no-leak guard


def test_no_forbidden_key_or_internal_value_reaches_the_wire() -> None:
    assert_no_leak(encode_snapshot(make_state()))


def test_the_delta_frame_is_no_leakier_than_the_full() -> None:
    state = make_state()
    full = encode_snapshot(state)
    moved = state.with_players(
        (replace(state.players[0], pos=Vec2(4.321, 2.765), state=PlayerState.IDLE),)
    )
    assert_no_leak(encode_snapshot(moved, full))


def test_the_event_entries_carry_only_the_mapped_keys() -> None:
    """An event whose payload carries the internal keys (`station`,
    `tick`, an unknown one) is projected through the explicit map — the
    unlisted keys (and the internal id they carry) never reach the
    wire."""
    events = [
        Event(
            kind=EventKind.RESYNC,
            payload={"player_id": A_PLAYER_ID, "seq": 41},
        ),
        Event(
            kind=EventKind.DENIED,
            x=3.23456,
            y=2.0,
            payload={
                "player_id": A_PLAYER_ID,
                "reason": "contested",
                "station": STOVE_ID,  # the internal id: must not survive
                "tick": 4821,  # the frame's `t` is the tick: dropped
                "mystery": "no-such-mapping",
            },
        ),
    ]
    encoded = encode_events(events)
    assert len(encoded) == 2
    allowed = {"k", "x", "y", *EVENT_PAYLOAD_SHORT.values()}
    for entry in encoded:
        for key, _ in walk(entry):
            assert key in allowed, f"an unlisted event key reached the wire: {key!r}"
    (denied,) = [entry for entry in encoded if entry["k"] == "denied"]
    assert denied == {"k": "denied", "x": 3.23, "y": 2.0, "i": A_PLAYER_ID, "r": "contested"}
    assert STOVE_ID not in [value for _, value in walk(encoded)]


def test_the_event_wire_dict_drops_unlisted_keys_the_same_way() -> None:
    event = Event(
        kind=EventKind.BURNT,
        x=3.23456,
        y=2.0,
        payload={
            "station": STOVE_ID,
            "item": "onion",
            "form": "burnt",
            "tick": 4821,
            "mystery": 1,
        },
    )
    wire = event_wire_dict(event)
    assert wire["kind"] == "burnt"
    assert wire["x"] == 3.23
    assert wire["payload"] == {"it": "onion", "fm": "burnt"}


# ----------------------------------------------------------- quantization


def test_quantization_is_to_two_decimals() -> None:
    frame = encode_snapshot(make_state())
    (player,) = frame["p"]
    (station,) = (
        entry for entry in frame["st"] if entry["k"] == "chop_board"
    )
    (stove,) = (entry for entry in frame["st"] if entry["k"] == "stove")
    (order,) = frame["o"]
    (hazard,) = frame["hz"]
    # The player's position (Vec2.quantized(2)).
    assert (player["x"], player["y"]) == (1.23, -2.35)
    # The station's position, progress and the content's quality.
    assert (stove["x"], stove["y"]) == (3.23, 2.0)
    assert stove["p"] == 0.42
    assert stove["q"] == 0.99  # round(0.98765, 2)
    # The order's deadline share (30 s of a 60 s window) and the clock.
    assert order["l"] == 0.5
    assert frame["tl"] == 83.65  # round(83.654, 2)
    # The hazard's position and life (seconds, 2 decimals).
    assert (hazard["x"], hazard["y"]) == (7.65, 5.2)
    assert hazard["l"] == 12.35
    # The carried item's short form (the `h` field) and the station's
    # first content (`g`).
    assert player["h"] == "tomato_chopped"
    assert stove["g"] == "onion_raw"
    assert station["g"] is None
    assert station["q"] == 1.0  # an empty station's quality


def test_facing_is_an_index_of_zero_to_three() -> None:
    frame = encode_snapshot(make_state())
    (player,) = frame["p"]
    assert player["f"] == 1  # Facing.RIGHT
    for entry in frame["p"]:
        assert entry["f"] in (0, 1, 2, 3)


def test_snapshot_size_is_the_utf8_length_of_the_frame_json() -> None:
    frame = encode_snapshot(make_state())
    assert snapshot_size(frame) == len(json.dumps(frame).encode("utf-8"))


# ---------------------------------------------------------------- the delta


def test_removed_orders_and_hazards_are_tombstoned() -> None:
    state = make_state()
    full = encode_snapshot(state)
    without = state.with_orders(()).with_hazards(())
    delta = encode_snapshot(without, full)
    assert delta["full"] is False
    (order_tombstone,) = [
        entry for entry in delta["d"]["o"] if entry.get("gone") is True
    ]
    assert order_tombstone == {"id": 7, "gone": True}
    (hazard_tombstone,) = [
        entry for entry in delta["d"]["hz"] if entry.get("gone") is True
    ]
    assert hazard_tombstone == {"t": "fire", "x": 7.65, "y": 5.2, "gone": True}


def test_removed_players_and_stations_are_tombstoned_too() -> None:
    """Every collection tombstones a vanished entity: a player (a cook
    that left the round) and a station (a fixture that is gone) carry
    their identity keys under `gone` so the client can drop them."""
    state = make_state()
    full = encode_snapshot(state)
    without = state.with_players(()).with_stations(())
    delta = encode_snapshot(without, full)
    (player_tombstone,) = [
        entry for entry in delta["d"]["p"] if entry.get("gone") is True
    ]
    assert player_tombstone == {"i": A_PLAYER_ID, "gone": True}
    station_tombstones = [
        entry for entry in delta["d"]["st"] if entry.get("gone") is True
    ]
    assert len(station_tombstones) == 2
    assert {
        (entry["k"], entry["x"], entry["y"])
        for entry in station_tombstones
    } == {("stove", 3.23, 2.0), ("chop_board", 5.0, 7.0)}


def test_a_malformed_prev_degrades_to_an_empty_prev() -> None:
    """A `prev` whose entity collection is not a list (a client bug in
    the stream, not a sim state) degrades to an empty previous: every
    current entity is in, and no tombstone is invented."""
    state = make_state()
    delta = encode_snapshot(state, prev={"p": {}, "st": "nope"})
    expected_player = {
        "i": A_PLAYER_ID,
        "x": 1.23,
        "y": -2.35,
        "f": 1,
        "h": "tomato_chopped",
        "s": "moving",
        "pi": 1,
    }
    assert delta["d"]["p"] == [expected_player]
    assert len(delta["d"]["st"]) == 2
    assert not any(entry.get("gone") for entry in delta["d"]["st"])


def test_a_non_finite_or_null_payload_value_never_reaches_the_wire() -> None:
    """`_short_value`'s guard: a `None` (and a `NaN`/`inf`) payload
    value is dropped — a null or a `NaN` in a JSON frame is noise, not
    information; a finite float is quantized to 2 decimals."""
    event = Event(
        kind=EventKind.SERVED,
        payload={
            "order_id": 7,
            "points": float("nan"),
            "quality": None,
            "streak": float("inf"),
            "delta": 12.346,
        },
    )
    (entry,) = encode_events([event])
    assert entry == {"k": "served", "x": 0.0, "y": 0.0, "oi": 7, "d": 12.35}
    (wire,) = [event_wire_dict(event)]
    assert wire["payload"] == {"oi": 7, "d": 12.35}


def test_an_unchanged_entity_is_out_of_the_delta() -> None:
    """The diff is against the *previous* frame (not the last full): an
    entity unchanged since `prev` is out, and one that moved *back* to
    its original values is in (the client holds the previous values —
    the move back is a change it must hear about). Decoding the chain
    (full → delta1) must land on `moved`'s full frame."""
    state = make_state()
    full = encode_snapshot(state)
    moved = state.with_players(
        (replace(state.players[0], pos=Vec2(4.321, 2.765)),)
    )
    delta1 = encode_snapshot(moved, full)
    assert delta1["d"]["p"][0]["x"] == 4.32  # the move is in
    # Unchanged since the previous frame: out.
    delta2 = encode_snapshot(moved, delta1)
    assert delta2["d"]["p"] == []
    # Back at the original values: in (a change since the previous frame).
    delta3 = encode_snapshot(state, delta2)
    (player,) = delta3["d"]["p"]
    assert player["x"] == 1.23 and player["y"] == -2.35
    # And the chain decodes: applying delta1 to the full lands on
    # `moved`'s full frame.
    assert _apply_delta(full, delta1) == encode_snapshot(moved)


def _apply_delta(base: dict[str, Any], delta: dict[str, Any]) -> dict[str, Any]:
    """The client's merge: upsert by identity key (preserving the base's
    order, new entities appended — the encoder's own semantics), drop
    the `gone` tombstones, take the scalars and `e` from the delta."""
    # The scalars (`t`, `s`, `tgt`, `tl`) and `e` ride the delta; the
    # entity arrays merge onto the base.
    decoded = {
        key: value
        for key, value in delta.items()
        if key not in ("d", "full")
    }
    identity: dict[str, Any] = {
        "p": lambda e: (e["i"],),
        "st": lambda e: (e["k"], e["x"], e["y"]),
        "o": lambda e: (e["id"],),
        "hz": lambda e: (e["t"], e["x"], e["y"]),
    }
    for key in ("p", "st", "o", "hz"):
        base_entries: list[dict[str, Any]] = base.get(key, [])
        delta_entries: list[dict[str, Any]] = delta["d"][key]
        by_identity = {identity[key](entry): dict(entry) for entry in delta_entries}
        merged: list[dict[str, Any]] = []
        seen: set[tuple[Any, ...]] = set()
        for entry in base_entries:
            key_ = identity[key](entry)
            if by_identity.get(key_, {}).get("gone") is True:
                continue  # tombstoned
            merged.append(by_identity.get(key_, dict(entry)))
            seen.add(key_)
        for entry in delta_entries:
            key_ = identity[key](entry)
            if key_ not in seen and entry.get("gone") is not True:
                merged.append(dict(entry))
        decoded[key] = merged
    decoded["full"] = True  # a decoded chain is a full state
    return decoded


def test_the_delta_against_a_delta_prev_reads_the_prev_from_d() -> None:
    """A delta frame's entities live under `d` — the next delta must
    diff against *that* (a prev that is itself a delta)."""
    state = make_state()
    full = encode_snapshot(state)
    moved = state.with_players(
        (replace(state.players[0], pos=Vec2(4.321, 2.765)),)
    )
    delta1 = encode_snapshot(moved, full)
    moved_again = state.with_players(
        (replace(state.players[0], pos=Vec2(4.5, 2.765)),)
    )
    delta2 = encode_snapshot(moved_again, delta1)
    (player,) = delta2["d"]["p"]
    assert player["x"] == 4.5  # the change since delta1, not since the full
    # `y` is unchanged since delta1, but the whole entry is in (it is a
    # whole-entry diff): the entry carries both values.
    assert player["y"] == 2.77