scripts/vpd.py

#!/usr/bin/env python3
"""Build, analyze, and sample a Vex Position Dataset (VPD1) database."""

from __future__ import annotations

import argparse
import hashlib
import io
import json
import math
import random
import sqlite3
import statistics
import sys
import tarfile
import time
from pathlib import Path

import chess
import chess.pgn


FORMAT_VERSION = "VPD1"
DEFAULT_TARGET = 1_500_000
PHASE_NAMES = {0: "opening", 1: "middlegame", 2: "endgame"}
PHASE_IDS = {name: value for value, name in PHASE_NAMES.items()}
PIECE_VALUES = {
    chess.PAWN: 1,
    chess.KNIGHT: 3,
    chess.BISHOP: 3,
    chess.ROOK: 5,
    chess.QUEEN: 9,
}


class NonSeekableReader(io.RawIOBase):
    """Adapt tarfile's streaming member object for TextIOWrapper on Python 3.14."""

    def __init__(self, source: object) -> None:
        self.source = source

    def readable(self) -> bool:
        return True

    def seekable(self) -> bool:
        return False

    def readinto(self, buffer: bytearray) -> int:
        chunk = self.source.read(len(buffer))
        if not chunk:
            return 0
        buffer[: len(chunk)] = chunk
        return len(chunk)


def connect(path: Path) -> sqlite3.Connection:
    db = sqlite3.connect(path)
    db.execute("PRAGMA journal_mode=WAL")
    db.execute("PRAGMA synchronous=NORMAL")
    db.execute("PRAGMA temp_store=MEMORY")
    db.execute("PRAGMA cache_size=-262144")
    db.execute("PRAGMA foreign_keys=ON")
    return db


def initialize(db: sqlite3.Connection) -> None:
    db.executescript(
        """
        CREATE TABLE IF NOT EXISTS metadata (
          key TEXT PRIMARY KEY,
          value TEXT NOT NULL
        ) WITHOUT ROWID;

        CREATE TABLE IF NOT EXISTS positions (
          id INTEGER PRIMARY KEY,
          random_key INTEGER NOT NULL UNIQUE,
          fen TEXT NOT NULL UNIQUE,
          source_split TEXT NOT NULL,
          source_member TEXT NOT NULL,
          game_number INTEGER NOT NULL,
          ply INTEGER NOT NULL,
          result TEXT NOT NULL,
          side_to_move INTEGER NOT NULL CHECK(side_to_move IN (0, 1)),
          phase INTEGER NOT NULL CHECK(phase BETWEEN 0 AND 2),
          piece_count INTEGER NOT NULL,
          non_pawn_material INTEGER NOT NULL,
          material_balance INTEGER NOT NULL,
          legal_moves INTEGER NOT NULL,
          in_check INTEGER NOT NULL CHECK(in_check IN (0, 1)),
          castling_mask INTEGER NOT NULL CHECK(castling_mask BETWEEN 0 AND 15),
          halfmove_clock INTEGER NOT NULL
        );

        CREATE INDEX IF NOT EXISTS positions_phase ON positions(phase);
        CREATE INDEX IF NOT EXISTS positions_result ON positions(result);
        CREATE INDEX IF NOT EXISTS positions_legal_moves ON positions(legal_moves);
        CREATE INDEX IF NOT EXISTS positions_piece_count ON positions(piece_count);
        CREATE INDEX IF NOT EXISTS positions_material_balance
          ON positions(material_balance);
        CREATE INDEX IF NOT EXISTS positions_split ON positions(source_split);
        """
    )
    set_metadata(db, "format", FORMAT_VERSION)
    set_metadata(db, "fen_fullmove_normalization", "1")


def set_metadata(db: sqlite3.Connection, key: str, value: object) -> None:
    db.execute(
        "INSERT INTO metadata(key, value) VALUES (?, ?) "
        "ON CONFLICT(key) DO UPDATE SET value=excluded.value",
        (key, str(value)),
    )


def normalized_fen(board: chess.Board) -> str:
    fields = board.fen(en_passant="fen").split()
    fields[5] = "1"
    return " ".join(fields)


def phase_of(board: chess.Board, ply: int) -> int:
    non_pawn = sum(
        PIECE_VALUES[piece_type]
        * (
            len(board.pieces(piece_type, chess.WHITE))
            + len(board.pieces(piece_type, chess.BLACK))
        )
        for piece_type in (chess.KNIGHT, chess.BISHOP, chess.ROOK, chess.QUEEN)
    )
    piece_count = chess.popcount(board.occupied)
    if ply <= 20 and non_pawn >= 50:
        return PHASE_IDS["opening"]
    if non_pawn <= 20 or piece_count <= 12:
        return PHASE_IDS["endgame"]
    return PHASE_IDS["middlegame"]


def castling_mask(board: chess.Board) -> int:
    return (
        int(board.has_kingside_castling_rights(chess.WHITE))
        | (int(board.has_queenside_castling_rights(chess.WHITE)) << 1)
        | (int(board.has_kingside_castling_rights(chess.BLACK)) << 2)
        | (int(board.has_queenside_castling_rights(chess.BLACK)) << 3)
    )


def material(board: chess.Board) -> tuple[int, int]:
    white = sum(
        PIECE_VALUES[piece_type] * len(board.pieces(piece_type, chess.WHITE))
        for piece_type in PIECE_VALUES
    )
    black = sum(
        PIECE_VALUES[piece_type] * len(board.pieces(piece_type, chess.BLACK))
        for piece_type in PIECE_VALUES
    )
    non_pawn = sum(
        PIECE_VALUES[piece_type]
        * (
            len(board.pieces(piece_type, chess.WHITE))
            + len(board.pieces(piece_type, chess.BLACK))
        )
        for piece_type in (chess.KNIGHT, chess.BISHOP, chess.ROOK, chess.QUEEN)
    )
    return white - black, non_pawn


def random_key(fen: str) -> int:
    raw = hashlib.blake2b(fen.encode("ascii"), digest_size=8).digest()
    return int.from_bytes(raw, "big") & ((1 << 63) - 1)


def position_record(
    board: chess.Board,
    source_split: str,
    source_member: str,
    game_number: int,
    ply: int,
    result: str,
    phase: int,
) -> tuple[object, ...]:
    fen = normalized_fen(board)
    balance, non_pawn = material(board)
    return (
        random_key(fen),
        fen,
        source_split,
        source_member,
        game_number,
        ply,
        result,
        int(board.turn == chess.WHITE),
        phase,
        chess.popcount(board.occupied),
        non_pawn,
        balance,
        board.legal_moves.count(),
        int(board.is_check()),
        castling_mask(board),
        board.halfmove_clock,
    )


def split_for(member_name: str) -> str:
    lowered = member_name.lower()
    if "test" in lowered:
        return "test"
    if "train" in lowered:
        return "train"
    return "unspecified"


def make_quotas(target: int) -> dict[int, int]:
    opening = round(target * 0.15)
    endgame = round(target * 0.25)
    return {0: opening, 1: target - opening - endgame, 2: endgame}


def current_counts(db: sqlite3.Connection) -> dict[int, int]:
    counts = {phase: 0 for phase in PHASE_NAMES}
    counts.update(dict(db.execute("SELECT phase, COUNT(*) FROM positions GROUP BY phase")))
    return counts


def extract(args: argparse.Namespace) -> None:
    source = Path(args.source).resolve()
    output = Path(args.output).resolve()
    output.parent.mkdir(parents=True, exist_ok=True)
    db = connect(output)
    initialize(db)
    quotas = make_quotas(args.target)
    counts = current_counts(db)
    resume_row = db.execute(
        "SELECT source_member FROM positions ORDER BY id DESC LIMIT 1"
    ).fetchone()
    resume_member = resume_row[0] if resume_row else None
    games_seen = int(
        db.execute("SELECT COALESCE(value, '0') FROM metadata WHERE key='games_seen'")
        .fetchone()[0]
        if db.execute("SELECT 1 FROM metadata WHERE key='games_seen'").fetchone()
        else 0
    )
    candidates_attempted = int(
        db.execute(
            "SELECT COALESCE(value, '0') FROM metadata "
            "WHERE key='candidates_attempted'"
        ).fetchone()[0]
        if db.execute(
            "SELECT 1 FROM metadata WHERE key='candidates_attempted'"
        ).fetchone()
        else 0
    )
    parse_errors = 0
    inserted_since_commit = 0
    started = time.monotonic()

    set_metadata(db, "source", str(source))
    set_metadata(db, "target_positions", args.target)
    set_metadata(db, "seed", args.seed)
    set_metadata(db, "phase_quotas", json.dumps(quotas, sort_keys=True))
    db.commit()

    insert_sql = """
        INSERT OR IGNORE INTO positions(
          random_key, fen, source_split, source_member, game_number, ply,
          result, side_to_move, phase, piece_count, non_pawn_material,
          material_balance, legal_moves, in_check, castling_mask, halfmove_clock
        ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
    """

    with tarfile.open(source, mode="r|bz2") as archive:
        corpus_game_number = 0
        finished = False
        reached_resume_member = resume_member is None
        for member in archive:
            if finished:
                break
            if not member.isfile() or not member.name.lower().endswith(".pgn"):
                continue
            if not reached_resume_member:
                if member.name != resume_member:
                    continue
                reached_resume_member = True
            raw = archive.extractfile(member)
            if raw is None:
                continue
            split = split_for(member.name)
            buffered = io.BufferedReader(NonSeekableReader(raw))
            with io.TextIOWrapper(buffered, encoding="utf-8", errors="replace") as pgn:
                member_game_number = 0
                while True:
                    try:
                        game = chess.pgn.read_game(pgn)
                    except Exception as exc:  # Keep streaming past isolated bad games.
                        parse_errors += 1
                        print(f"PGN parse error in {member.name}: {exc}", file=sys.stderr)
                        continue
                    if game is None:
                        break
                    corpus_game_number += 1
                    member_game_number += 1
                    games_seen += 1
                    board = game.board()
                    result = game.headers.get("Result", "*")
                    reservoirs: dict[int, tuple[chess.Board, int]] = {}
                    phase_seen = {phase: 0 for phase in PHASE_NAMES}
                    game_seed = int.from_bytes(
                        hashlib.blake2b(
                            f"{args.seed}:{member.name}:{member_game_number}".encode(),
                            digest_size=8,
                        ).digest(),
                        "big",
                    )
                    game_rng = random.Random(game_seed)

                    try:
                        for ply, move in enumerate(game.mainline_moves(), start=1):
                            board.push(move)
                            phase = phase_of(board, ply)
                            if counts[phase] >= quotas[phase]:
                                continue
                            phase_seen[phase] += 1
                            if game_rng.randrange(phase_seen[phase]) == 0:
                                reservoirs[phase] = (board.copy(stack=False), ply)
                    except Exception:
                        parse_errors += 1
                        continue

                    for phase, (candidate, ply) in reservoirs.items():
                        if counts[phase] >= quotas[phase]:
                            continue
                        candidates_attempted += 1
                        cursor = db.execute(
                            insert_sql,
                            position_record(
                                candidate,
                                split,
                                member.name,
                                corpus_game_number,
                                ply,
                                result,
                                phase,
                            ),
                        )
                        if cursor.rowcount:
                            counts[phase] += 1
                            inserted_since_commit += 1

                    if inserted_since_commit >= args.commit_every:
                        set_metadata(db, "games_seen", games_seen)
                        set_metadata(db, "candidates_attempted", candidates_attempted)
                        set_metadata(db, "parse_errors", parse_errors)
                        db.commit()
                        inserted_since_commit = 0

                    if games_seen % args.progress_every == 0:
                        elapsed = max(time.monotonic() - started, 0.001)
                        total = sum(counts.values())
                        print(
                            f"games={games_seen:,} positions={total:,}/{args.target:,} "
                            f"opening={counts[0]:,} middle={counts[1]:,} "
                            f"endgame={counts[2]:,} rate={total / elapsed:,.0f} pos/s",
                            flush=True,
                        )

                    if all(counts[p] >= quotas[p] for p in quotas):
                        finished = True
                        break

    set_metadata(db, "games_seen", games_seen)
    set_metadata(db, "candidates_attempted", candidates_attempted)
    set_metadata(db, "parse_errors", parse_errors)
    set_metadata(db, "completed_unix", int(time.time()))
    set_metadata(db, "position_count", sum(counts.values()))
    db.commit()
    db.execute("PRAGMA optimize")
    db.execute("PRAGMA wal_checkpoint(TRUNCATE)")
    db.close()
    print(json.dumps(analyze_database(output), indent=2, sort_keys=True))


def grouped(db: sqlite3.Connection, column: str) -> dict[str, int]:
    return {
        str(key): count
        for key, count in db.execute(
            f"SELECT {column}, COUNT(*) FROM positions GROUP BY {column}"
        )
    }


def quantile(db: sqlite3.Connection, column: str, q: float, total: int) -> int:
    offset = max(0, min(total - 1, round((total - 1) * q)))
    return db.execute(
        f"SELECT {column} FROM positions ORDER BY {column} LIMIT 1 OFFSET ?",
        (offset,),
    ).fetchone()[0]


def numeric_stats(db: sqlite3.Connection, column: str, total: int) -> dict[str, float]:
    mean, mean_square, minimum, maximum = db.execute(
        f"SELECT AVG({column}), AVG({column} * {column}), "
        f"MIN({column}), MAX({column}) FROM positions"
    ).fetchone()
    variance = max(0.0, mean_square - mean * mean)
    return {
        "min": minimum,
        "p10": quantile(db, column, 0.10, total),
        "median": quantile(db, column, 0.50, total),
        "p90": quantile(db, column, 0.90, total),
        "max": maximum,
        "mean": round(mean, 4),
        "stdev": round(math.sqrt(variance), 4),
    }


def normalized_entropy(counts: list[int]) -> float:
    total = sum(counts)
    probabilities = [count / total for count in counts if count]
    entropy = -sum(value * math.log(value) for value in probabilities)
    return entropy / math.log(len(counts))


def analyze_database(path: Path) -> dict[str, object]:
    db = sqlite3.connect(f"file:{path}?mode=ro&immutable=1", uri=True)
    total = db.execute("SELECT COUNT(*) FROM positions").fetchone()[0]
    if total == 0:
        raise RuntimeError("dataset is empty")
    phases_raw = grouped(db, "phase")
    phases = {PHASE_NAMES[int(key)]: value for key, value in phases_raw.items()}
    results = grouped(db, "result")
    sides = grouped(db, "side_to_move")
    splits = grouped(db, "source_split")
    legal = numeric_stats(db, "legal_moves", total)
    pieces = numeric_stats(db, "piece_count", total)
    balance = numeric_stats(db, "material_balance", total)
    no_castling = db.execute(
        "SELECT COUNT(*) FROM positions WHERE castling_mask=0"
    ).fetchone()[0]
    with_castling = total - no_castling
    checks = db.execute("SELECT COUNT(*) FROM positions WHERE in_check=1").fetchone()[0]
    imbalanced = db.execute(
        "SELECT COUNT(*) FROM positions WHERE ABS(material_balance)>=3"
    ).fetchone()[0]
    min_phase_share = min(phases.values()) / total
    known_results = [results.get(key, 0) for key in ("1-0", "1/2-1/2", "0-1")]
    min_result_share = min(known_results) / max(1, sum(known_results))
    white_share = int(sides.get("1", 0)) / total

    checks_map = {
        "at_least_1_5m_positions": total >= 1_500_000,
        "phase_min_share_at_least_15pct": min_phase_share >= 0.15,
        "phase_entropy_at_least_0_85": normalized_entropy(list(phases.values())) >= 0.85,
        "result_min_share_at_least_20pct": min_result_share >= 0.20,
        "side_to_move_between_47_and_53pct_white": 0.47 <= white_share <= 0.53,
        "legal_move_stdev_at_least_8": legal["stdev"] >= 8,
        "legal_move_p10_at_most_22": legal["p10"] <= 22,
        "legal_move_p90_at_least_38": legal["p90"] >= 38,
        "piece_count_stdev_at_least_5": pieces["stdev"] >= 5,
        "material_imbalance_at_least_15pct": imbalanced / total >= 0.15,
        "both_castling_states_at_least_10pct": min(no_castling, with_castling) / total
        >= 0.10,
        "checks_at_least_1pct": checks / total >= 0.01,
    }
    metadata = dict(db.execute("SELECT key, value FROM metadata"))
    report = {
        "format": metadata.get("format"),
        "database": str(path),
        "positions": total,
        "database_bytes": path.stat().st_size,
        "distributions": {
            "phase": phases,
            "result": results,
            "side_to_move": {"black": sides.get("0", 0), "white": sides.get("1", 0)},
            "source_split": splits,
            "with_castling_rights": with_castling,
            "without_castling_rights": no_castling,
            "in_check": checks,
            "material_imbalance_abs_ge_3": imbalanced,
        },
        "numeric": {
            "legal_moves": legal,
            "piece_count": pieces,
            "material_balance_white_minus_black": balance,
        },
        "normalized_phase_entropy": round(
            normalized_entropy(list(phases.values())), 6
        ),
        "thresholds": checks_map,
        "high_variance": all(checks_map.values()),
        "metadata": metadata,
    }
    db.close()
    return report


def analyze(args: argparse.Namespace) -> None:
    report = analyze_database(Path(args.database).resolve())
    rendered = json.dumps(report, indent=2, sort_keys=True)
    print(rendered)
    if args.report:
        Path(args.report).write_text(rendered + "\n", encoding="utf-8")


def sample(args: argparse.Namespace) -> None:
    path = Path(args.database).resolve()
    db = sqlite3.connect(f"file:{path}?mode=ro&immutable=1", uri=True)
    if args.id is not None:
        row = db.execute(
            "SELECT id, fen, phase, result FROM positions WHERE id=?", (args.id,)
        ).fetchone()
    else:
        key = random.SystemRandom().randrange(1 << 63)
        row = db.execute(
            "SELECT id, fen, phase, result FROM positions "
            "WHERE random_key>=? ORDER BY random_key LIMIT 1",
            (key,),
        ).fetchone()
        if row is None:
            row = db.execute(
                "SELECT id, fen, phase, result FROM positions ORDER BY random_key LIMIT 1"
            ).fetchone()
    db.close()
    if row is None:
        raise RuntimeError("position not found")
    print(
        json.dumps(
            {"id": row[0], "fen": row[1], "phase": PHASE_NAMES[row[2]], "result": row[3]},
            separators=(",", ":"),
        )
    )


def parser() -> argparse.ArgumentParser:
    root = argparse.ArgumentParser(description=__doc__)
    commands = root.add_subparsers(dest="command", required=True)

    extract_cmd = commands.add_parser("extract", help="stream PGNs into VPD1")
    extract_cmd.add_argument("--source", required=True)
    extract_cmd.add_argument("--output", required=True)
    extract_cmd.add_argument("--target", type=int, default=DEFAULT_TARGET)
    extract_cmd.add_argument("--seed", type=int, default=91)
    extract_cmd.add_argument("--commit-every", type=int, default=10_000)
    extract_cmd.add_argument("--progress-every", type=int, default=10_000)
    extract_cmd.set_defaults(func=extract)

    analyze_cmd = commands.add_parser("analyze", help="calculate variance")
    analyze_cmd.add_argument("database")
    analyze_cmd.add_argument("--report")
    analyze_cmd.set_defaults(func=analyze)

    sample_cmd = commands.add_parser("sample", help="return one board immediately")
    sample_cmd.add_argument("database")
    sample_cmd.add_argument("--id", type=int)
    sample_cmd.set_defaults(func=sample)
    return root


if __name__ == "__main__":
    arguments = parser().parse_args()
    arguments.func(arguments)