"""
Reservoir-sample random documents from FineWeb-Edu sample-100BT.

Usage:
    python sample_random.py --output audit_output/random_100k.csv --sample 100000
"""
import csv
import random
import argparse

from datasets import load_dataset

SEED = 42


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--output", default="audit_output/random_100k.csv")
    parser.add_argument("--sample", type=int, default=100_000)
    args = parser.parse_args()

    random.seed(SEED)

    ds = load_dataset("HuggingFaceFW/fineweb-edu", name="sample-100BT", split="train", streaming=True)

    reservoir = []
    n = 0

    for doc in ds:
        n += 1
        if n <= args.sample:
            reservoir.append(doc)
        else:
            j = random.randint(0, n - 1)
            if j < args.sample:
                reservoir[j] = doc
        if n % 1_000_000 == 0:
            print(f"{n:,} docs scanned...", flush=True)

    print(f"\nTotal docs: {n:,}")
    print(f"Sampled: {len(reservoir):,}")

    with open(args.output, "w", newline="") as f:
        writer = csv.DictWriter(f, fieldnames=["url", "score", "int_score", "dump", "full_text"])
        writer.writeheader()
        for doc in reservoir:
            writer.writerow({
                "url": doc["url"],
                "score": doc["score"],
                "int_score": doc["int_score"],
                "dump": doc["dump"],
                "full_text": doc["text"],
            })

    print(f"Written to {args.output}")


if __name__ == "__main__":
    main()