#!/usr/bin/env python
"""Compute pretraining validation loss L(N,T) for pre2post-chess checkpoints.

The paper's Fig. 3a relates post-RL pass@1 to the *pretraining validation
loss* on held-out human games. The authors' val split is not released, so we
reconstruct a proxy: a held-out sample of Lichess standard rated games from
2023-01 (adjacent period to their 2022 corpus; same generator, properly held
out), filtered like their corpus (Elo 800-3000, >=10 plies, blitz/rapid-like
time controls). Games are scored with each checkpoint's own LAN tokenizer,
mean NLL per token over 1024-token windows.

Downloads only a partial slice of the public .pgn.zst dump via HTTP Range.
Uploads one JSON per checkpoint to the results repo.

No-arg invocation = sweep over the 20M/50M/200M/680M pretrain checkpoints.
"""
import argparse
import io
import json
import os
import re
import urllib.request

import torch
import chess
import chess.pgn
from huggingface_hub import HfApi, snapshot_download
from transformers import AutoModelForCausalLM, AutoTokenizer

URL = "https://database.lichess.org/standard/lichess_db_standard_rated_2023-01.pgn.zst"
RANGE_BYTES = 80 * 1024 * 1024
RESULTS_REPO = "ML-Intern-lab/pre2post-chess-replication"
PRETRAIN_REPO = "pavelslab-nyu/Chess-Pretrain-Models"
FAMILIES = ["20m", "50m", "200m", "680m"]


def fetch_partial_games(cache_path, range_bytes=RANGE_BYTES):
    if os.path.exists(cache_path):
        return open(cache_path).read()
    import zstandard
    req = urllib.request.Request(URL, headers={"Range": f"bytes=0-{range_bytes - 1}"})
    with urllib.request.urlopen(req, timeout=180) as resp:
        dctx = zstandard.ZstdDecompressor().stream_reader(resp)
        text = dctx.read().decode("utf-8", errors="ignore")
    starts = [m for m in range(len(text)) if text.startswith("[Event ", m)]
    text = text[: starts[4000]] if len(starts) > 4000 else text
    os.makedirs(os.path.dirname(cache_path), exist_ok=True)
    open(cache_path, "w").write(text)
    return text


def filter_games(raw, max_games=3000):
    out = []
    stream = io.StringIO(raw)
    while len(out) < max_games:
        game = chess.pgn.read_game(stream)
        if game is None:
            break
        tc = game.headers.get("TimeControl", "")
        base = tc.split("+")[0]
        if base and base.isdigit() and int(base) not in (60, 120, 180, 240, 300, 600):
            continue
        try:
            we, be = int(game.headers.get("WhiteElo", 0)), int(game.headers.get("BlackElo", 0))
        except ValueError:
            continue
        if not (800 <= we <= 3000 and 800 <= be <= 3000):
            continue
        b = game.board()
        sans = []
        for mv in game.mainline_moves():
            sans.append(b.san(mv))
            b.push(mv)
        if len(sans) < 10:
            continue
        out.append(" ".join(sans))
    return out


def windows_from_games(custom_tok, vocab, games, ctx=1024, min_tokens=64):
    ids_all = []
    for g in games:
        toks = custom_tok._pgn_to_tokens(g)
        if not toks:
            continue
        ids = [vocab[t] for t in toks if t in vocab]
        ids = [vocab["<bos>"]] + ids
        for i in range(0, len(ids) - 1 - min_tokens, ctx):
            w = ids[i:i + ctx]
            if len(w) > min_tokens:
                ids_all.append(w)
    return ids_all


@torch.no_grad()
def eval_loss(model, vocab, windows, device, batch_size=16):
    pad = vocab["<bos>"]
    total, ntok = 0.0, 0
    for i in range(0, len(windows), batch_size):
        batch = windows[i:i + batch_size]
        maxlen = max(len(w) for w in batch)
        input_ids = torch.full((len(batch), maxlen), pad, dtype=torch.long)
        attn = torch.zeros((len(batch), maxlen), dtype=torch.long)
        for j, w in enumerate(batch):
            input_ids[j, :len(w)] = torch.tensor(w)
            attn[j, :len(w)] = 1
        input_ids, attn = input_ids.to(device), attn.to(device)
        logits = model(input_ids=input_ids, attention_mask=attn).logits
        targets = input_ids[:, 1:]
        mask = attn[:, 1:].bool()
        ll = torch.nn.functional.cross_entropy(
            logits[:, :-1].reshape(-1, logits[:, :-1].size(-1)).float(),
            targets.reshape(-1), reduction="none").view(targets.shape)
        sel = ll[mask]
        total += sel.sum().item()
        ntok += int(mask.sum().item())
    return total / ntok, ntok


def main():
    ap = argparse.ArgumentParser()
    ap.add_argument("--n-games", type=int, default=3000)
    ap.add_argument("--max-windows", type=int, default=2048)
    ap.add_argument("--cache", default="/work/data/lichess_2023_01_head.pgn")
    ap.add_argument("--families", nargs="+", default=FAMILIES)
    ap.add_argument("--out-dir", default="/work/results/loss")
    args = ap.parse_args()

    raw = fetch_partial_games(args.cache)
    games = filter_games(raw, args.n_games)
    print(f"held-out games: {len(games)}", flush=True)

    api = HfApi()
    files = api.list_repo_files(PRETRAIN_REPO, repo_type="model")
    runs = sorted(set(f.split("/")[0] for f in files
                      if f.startswith("model_") and "/" in f))
    runs = [r for r in runs if any(r.startswith(f"model_{fam}_") for fam in args.families)]
    print(f"{len(runs)} checkpoints: {runs}", flush=True)

    for run in runs:
        out_path = os.path.join(args.out_dir, f"loss_{run}.json")
        if os.path.exists(out_path):
            print(f"[skip] {run} done", flush=True)
            continue
        try:
            local = snapshot_download(PRETRAIN_REPO, allow_patterns=f"{run}/*")
            path = os.path.join(local, run)
            device = "cuda" if torch.cuda.is_available() else "cpu"
            model = AutoModelForCausalLM.from_pretrained(path, trust_remote_code=True).to(device).eval()
            tok = AutoTokenizer.from_pretrained(path, trust_remote_code=True)
            custom, vocab = tok.custom_tokenizer, tok.custom_tokenizer._tok2id
            windows = windows_from_games(custom, vocab, games)[: args.max_windows]
            loss, ntok = eval_loss(model, vocab, windows, device)
            # parse size and tokens from the run name, e.g. model_20m_5.3B
            m = re.match(r"model_(\d+)m_([\d.]+)B", run)
            size_m, tokens_b = (m.group(1), m.group(2)) if m else ("?", "?")
            rec = {"run": run, "val_loss": loss, "n_tokens": ntok,
                   "n_windows": len(windows), "n_games": len(games),
                   "size_millions": int(size_m) if size_m != "?" else None,
                   "pretrain_tokens": float(tokens_b) * 1e9 if tokens_b != "?" else None}
            os.makedirs(args.out_dir, exist_ok=True)
            with open(out_path, "w") as f:
                json.dump(rec, f)
            del model
            torch.cuda.empty_cache()
            print(f"[loss] {run}: {loss:.4f} ({ntok} tokens)", flush=True)
            try:
                api.upload_file(path_or_fileobj=out_path,
                                path_in_repo=f"results/loss/loss_{run}.json",
                                repo_id=RESULTS_REPO, repo_type="dataset")
                print(f"[upload] loss_{run}", flush=True)
            except Exception as e:
                print(f"[upload] FAILED {run}: {e}", flush=True)
        except Exception as e:
            print(f"[loss] {run} FAILED: {e}", flush=True)


if __name__ == "__main__":
    main()