players.py

"""Players for the LM Tetris Arena: causal LMs scored zero-shot, plus two baselines."""
from __future__ import annotations

import json
import os
import re
import threading
from collections import OrderedDict

import torch
from huggingface_hub import HfApi, hf_hub_download
from huggingface_hub.utils import GatedRepoError, RepositoryNotFoundError

MAX_PARAMS = int(os.environ.get("MAX_PARAMS", 250_000_000))
ALLOW_REMOTE_CODE = os.environ.get("ALLOW_REMOTE_CODE", "1") == "1"
MAX_CACHED_MODELS = int(os.environ.get("MAX_CACHED_MODELS", 6))
BATCH_SIZE = 16

PROMPTS = {
    # The rules of the game are stated in the prompt: tests reading comprehension.
    "guided": (
        "In Tetris, the goal is to clear lines, avoid holes and keep the stack low.\n"
        "This move {desc}.\n"
        "It is a"
    ),
    # No rules: the model must already know from pre-training what is good in Tetris.
    "blind": (
        "Here is a move from a game of Tetris.\n"
        "This move {desc}.\n"
        "It is a"
    ),
}
GOOD, BAD = " good move", " bad move"

REPO_RE = re.compile(r"^[A-Za-z0-9][\w.\-]*/[\w.\-]+$")
WEIGHT_EXT = (".safetensors", ".bin", ".pt", ".pth")

RANDOM_ID = "baseline/random"
ORACLE_ID = "baseline/oracle-reader"
BASELINES = {
    RANDOM_ID: "🎲 Random (baseline)",
    ORACLE_ID: "📏 Oracle reader (baseline)",
}


class ModelRejected(Exception):
    """Raised with a user-facing message when a model can't enter the arena."""


def fmt_params(n: int | None) -> str:
    if not n:
        return "?"
    if n >= 1e9:
        return f"{n / 1e9:.2f}B"
    if n >= 1e6:
        return f"{n / 1e6:.1f}M"
    return f"{n / 1e3:.0f}K"


# ----------------------------------------------------------------------------
# Baselines
# ----------------------------------------------------------------------------
class RandomPlayer:
    model_id = RANDOM_ID
    display = BASELINES[RANDOM_ID]
    n_params = 0
    sha = None
    custom_code = False

    def values(self, protocol, cands):
        return [0.0] * len(cands)  # everything ties -> uniform random choice


def _buckets(c):
    holes = -1 if c.new_holes < 0 else 0 if c.new_holes == 0 else 1 if c.new_holes == 1 else 2
    mh = c.max_height
    height = 0 if mh <= 4 else 1 if mh <= 8 else 2 if mh <= 12 else 3 if mh <= 16 else 4
    bump = 0 if c.bump <= 4 else 1 if c.bump <= 10 else 2
    landing = 0 if c.landing <= 0 else 1 if c.landing <= 2 else 2
    return holes, c.lines, height, bump, landing


class OracleReaderPlayer:
    """Reads the exact same descriptions the LMs see and ranks them with fixed
    common-sense priorities (holes > lines > height > surface > landing).
    It is a reference point for 'a perfect reader of the text', not a strong bot."""

    model_id = ORACLE_ID
    display = BASELINES[ORACLE_ID]
    n_params = 0
    sha = None
    custom_code = False

    def values(self, protocol, cands):
        out = []
        for c in cands:
            holes, lines, height, bump, landing = _buckets(c)
            out.append(float(((-holes + 5) * 10 + lines + 5) * 1000 + (-height + 5) * 100 + (-bump + 5) * 10 + (-landing + 5)))
        return out


# ----------------------------------------------------------------------------
# Language-model player
# ----------------------------------------------------------------------------
class LMPlayer:
    def __init__(self, model_id, sha, model, tokenizer, n_params, custom_code):
        self.model_id = model_id
        self.display = model_id
        self.sha = sha
        self.model = model
        self.tok = tokenizer
        self.n_params = n_params
        self.custom_code = custom_code
        self._cache: dict[tuple[str, str], float] = {}
        self._lock = threading.Lock()
        self._fwd_kwargs = None  # discovered on first forward
        self.max_len = self._max_len()
        # Reproduce whatever the tokenizer prepends by default (e.g. <s>)
        with_special = self._ids("a", True)
        without = self._ids("a", False)
        n = len(with_special) - len(without)
        self.prefix = with_special[:n] if n > 0 and with_special[n:n + len(without)] == without else []
        pad = tokenizer.pad_token_id
        if pad is None:
            pad = tokenizer.eos_token_id if tokenizer.eos_token_id is not None else 0
        self.pad_id = int(pad)

    def _max_len(self):
        cfg = self.model.config
        for k in ("max_position_embeddings", "n_positions", "max_seq_len", "seq_length", "block_size", "n_ctx"):
            v = getattr(cfg, k, None)
            if isinstance(v, int) and v > 0:
                return v
        return 2048

    def _ids(self, text, special):
        return list(self.tok(text, add_special_tokens=special)["input_ids"])

    def _build(self, context, continuation):
        ctx = self._ids(context, False)
        full = self._ids(context + continuation, False)
        if len(full) > len(ctx) and full[: len(ctx)] == ctx:
            cont = full[len(ctx):]
        else:  # tokenizer merged across the boundary: encode separately
            cont = self._ids(continuation, False)
        ids = self.prefix + ctx + cont
        return ids, len(self.prefix) + len(ctx)

    def _forward(self, input_ids, attention_mask):
        attempts = (
            [self._fwd_kwargs]
            if self._fwd_kwargs is not None
            else [{"attention_mask": True, "use_cache": False}, {"attention_mask": True}, {}]
        )
        last_err = None
        for kw in attempts:
            call = {}
            if kw.get("attention_mask"):
                call["attention_mask"] = attention_mask
            if "use_cache" in kw:
                call["use_cache"] = False
            try:
                out = self.model(input_ids=input_ids, **call)
                self._fwd_kwargs = kw
                break
            except TypeError as e:  # custom forward() without these kwargs
                last_err = e
        else:
            raise last_err
        if isinstance(out, dict) and "logits" in out:
            return out["logits"]
        if hasattr(out, "logits"):
            return out.logits
        if isinstance(out, (tuple, list)):
            return out[0]
        return out

    @torch.inference_mode()
    def _logprob_batch(self, items):
        """items: list of (ids, start). Returns sum log p(ids[start:] | ids[:start])."""
        L = max(len(ids) for ids, _ in items)
        inp = torch.full((len(items), L), self.pad_id, dtype=torch.long)
        mask = torch.zeros((len(items), L), dtype=torch.long)
        for i, (ids, _) in enumerate(items):
            inp[i, : len(ids)] = torch.tensor(ids)
            mask[i, : len(ids)] = 1
        logits = self._forward(inp, mask)
        out = []
        for i, (ids, start) in enumerate(items):
            pos = torch.arange(start - 1, len(ids) - 1)
            lp = torch.log_softmax(logits[i, pos].float(), dim=-1)
            tgt = torch.tensor(ids[start:])
            out.append(lp.gather(1, tgt[:, None]).sum().item())
        return out

    def score_descriptions(self, protocol, descs):
        template = PROMPTS[protocol]
        with self._lock:
            todo = [d for d in dict.fromkeys(descs) if (protocol, d) not in self._cache]
            items = []
            for d in todo:
                ctx = template.format(desc=d)
                for cont in (GOOD, BAD):
                    ids, start = self._build(ctx, cont)
                    if len(ids) > self.max_len:
                        raise ModelRejected(f"{self.model_id}: prompt ({len(ids)} tokens) exceeds context ({self.max_len}).")
                    items.append((ids, start))
            scores = []
            for i in range(0, len(items), BATCH_SIZE):
                scores.extend(self._logprob_batch(items[i : i + BATCH_SIZE]))
            for k, d in enumerate(todo):
                self._cache[(protocol, d)] = scores[2 * k] - scores[2 * k + 1]  # log P(good) - log P(bad)
            return {d: self._cache[(protocol, d)] for d in descs}

    def values(self, protocol, cands):
        table = self.score_descriptions(protocol, [c.description for c in cands])
        return [table[c.description] for c in cands]


# ----------------------------------------------------------------------------
# Validation + loading
# ----------------------------------------------------------------------------
_api = HfApi()
_models: "OrderedDict[tuple[str, str], LMPlayer]" = OrderedDict()
_models_lock = threading.Lock()


def precheck(model_id: str) -> dict:
    """Cheap checks before downloading any weights."""
    model_id = model_id.strip()
    if not REPO_RE.match(model_id):
        raise ModelRejected(f"`{model_id}` is not a valid repo id (expected `owner/name`).")
    try:
        info = _api.model_info(model_id, files_metadata=True)
    except (RepositoryNotFoundError, GatedRepoError):
        raise ModelRejected(f"`{model_id}` was not found, is private or gated.")
    except Exception as e:  # network etc.
        raise ModelRejected(f"`{model_id}`: could not read repo info ({type(e).__name__}).")
    if getattr(info, "gated", False):
        raise ModelRejected(f"`{model_id}` is gated; only public models can play.")
    files = {s.rfilename: (s.size or 0) for s in (info.siblings or [])}
    if "config.json" not in files:
        raise ModelRejected(f"`{model_id}` has no config.json (GGUF/ONNX-only repos are not supported).")
    try:
        cfg = json.load(open(hf_hub_download(model_id, "config.json", revision=info.sha)))
    except Exception:
        raise ModelRejected(f"`{model_id}`: config.json could not be read.")
    if cfg.get("is_encoder_decoder"):
        raise ModelRejected(f"`{model_id}` is an encoder-decoder model; only decoder-only models can play.")
    weights = {f: s for f, s in files.items() if f.endswith(WEIGHT_EXT) and "/" not in f.strip("./")}
    st = {f: s for f, s in weights.items() if f.endswith(".safetensors")}
    use = st or weights
    if not use:
        raise ModelRejected(f"`{model_id}` has no PyTorch/safetensors weights at the repo root.")
    est = None
    if getattr(info, "safetensors", None) and getattr(info.safetensors, "total", None):
        est = int(info.safetensors.total)
    else:
        dtype = str(cfg.get("dtype") or cfg.get("torch_dtype") or "float32")
        est = int(sum(use.values()) / (2 if ("16" in dtype) else 4))
    # generous margin: tied embeddings are often stored twice on disk; the exact
    # count after loading is what decides
    if est > MAX_PARAMS * 1.5:
        raise ModelRejected(f"`{model_id}` has ~{fmt_params(est)} parameters; the limit is {fmt_params(MAX_PARAMS)}.")
    # canonical id (fixes casing) so the leaderboard has one entry per repo
    return {"id": info.id or model_id, "sha": info.sha, "custom_code": "auto_map" in cfg, "est_params": est}


def load_player(model_id: str, meta: dict) -> LMPlayer:
    from transformers import AutoModelForCausalLM, AutoTokenizer

    key = (model_id, meta["sha"])
    with _models_lock:
        if key in _models:
            _models.move_to_end(key)
            return _models[key]
    if meta["custom_code"] and not ALLOW_REMOTE_CODE:
        raise ModelRejected(f"`{model_id}` needs custom code, which is disabled on this Space.")
    kw = dict(revision=meta["sha"], trust_remote_code=ALLOW_REMOTE_CODE)
    try:
        tok = AutoTokenizer.from_pretrained(model_id, **kw)
    except Exception as e:
        raise ModelRejected(f"`{model_id}`: tokenizer failed to load ({type(e).__name__}: {str(e)[:200]}).")
    try:
        model = AutoModelForCausalLM.from_pretrained(model_id, dtype=torch.float32, **kw)
    except Exception as e:
        raise ModelRejected(f"`{model_id}`: could not load as a causal LM ({type(e).__name__}: {str(e)[:200]}).")
    if getattr(model.config, "is_encoder_decoder", False):
        raise ModelRejected(f"`{model_id}` is an encoder-decoder model.")
    model.eval()
    n_params = sum(p.numel() for p in model.parameters())  # tied weights counted once
    if n_params > MAX_PARAMS:
        del model
        raise ModelRejected(f"`{model_id}` has {fmt_params(n_params)} parameters; the limit is {fmt_params(MAX_PARAMS)}.")
    player = LMPlayer(model_id, meta["sha"], model, tok, n_params, meta["custom_code"])
    # smoke test: one forward pass on a real prompt
    try:
        player.score_descriptions("guided", ["drops the piece into the lowest part of the board, clears one line, creates no new holes, keeps the stack very low and leaves the surface flat"])
    except ModelRejected:
        raise
    except Exception as e:
        raise ModelRejected(f"`{model_id}`: forward pass failed ({type(e).__name__}: {str(e)[:200]}).")
    with _models_lock:
        _models[key] = player
        while len(_models) > MAX_CACHED_MODELS:
            _models.popitem(last=False)
    return player