#!/usr/bin/env python3
"""Download the public TinyStories parquet shard used for corpus holdouts.

Derived from Andrej Karpathy's nanochat project.

MIT License

Copyright (c) 2025 Andrej Karpathy

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
"""

from __future__ import annotations

import argparse
import hashlib
from pathlib import Path
from urllib.request import urlretrieve


TINYSTORIES_TRAIN_URL = (
    "https://huggingface.co/datasets/roneneldan/TinyStories/resolve/"
    "f54c09fd23315a6f9c86f9dc80f725de7d8f9c64/"
    "data/train-00000-of-00004-2d5a1467fff1081b.parquet?download=true"
)
EXPECTED_BYTES = 248_731_111
EXPECTED_SHA256 = "77cf780cebe52b6e83e3a2ac84bc56d8059363113e41d17a023f1d8b2ed0fc0b"


def sha256(path: Path) -> str:
    digest = hashlib.sha256()
    with path.open("rb") as handle:
        for chunk in iter(lambda: handle.read(1024 * 1024), b""):
            digest.update(chunk)
    return digest.hexdigest()


def verify_file(path: Path) -> None:
    size = path.stat().st_size
    if size != EXPECTED_BYTES:
        raise SystemExit(f"{path} has {size:,} bytes; expected {EXPECTED_BYTES:,}.")
    actual = sha256(path)
    if actual != EXPECTED_SHA256:
        raise SystemExit(f"{path} has sha256 {actual}; expected {EXPECTED_SHA256}.")


def parse_args() -> argparse.Namespace:
    parser = argparse.ArgumentParser(
        description="Prepare the TinyStories public corpus holdout."
    )
    parser.add_argument(
        "--output-dir",
        type=Path,
        default=Path("data/tinystories"),
        help="Directory where the parquet file should be stored.",
    )
    parser.add_argument(
        "--force",
        action="store_true",
        help="Download again even if the target file already exists.",
    )
    return parser.parse_args()


def main() -> None:
    args = parse_args()
    args.output_dir.mkdir(parents=True, exist_ok=True)
    target = args.output_dir / "train-00000-of-00004.parquet"
    if target.exists() and not args.force:
        verify_file(target)
        print(target)
        return

    print(f"Downloading TinyStories train parquet shard to {target}")
    urlretrieve(TINYSTORIES_TRAIN_URL, target)
    verify_file(target)
    print(target)


if __name__ == "__main__":
    main()