"""
Deduplicate flagged_documents.csv.gz by URL.
=============================================
Same page can appear multiple times from different Common Crawl snapshots.
Keeps the first occurrence of each URL.

Usage:
    python deduplicate_flagged.py \
        --input audit_output/flagged_documents.csv.gz \
        --output audit_output/flagged_documents_deduped.csv.gz
"""

import csv
import gzip
import argparse

csv.field_size_limit(10_000_000)


def deduplicate(input_path, output_path):
    seen = set()
    kept = 0
    total = 0

    with gzip.open(input_path, "rt") as fin, \
         gzip.open(output_path, "wt") as fout:
        reader = csv.DictReader(fin)
        writer = csv.DictWriter(fout, fieldnames=reader.fieldnames)
        writer.writeheader()
        for row in reader:
            total += 1
            url = row.get("url", "")
            if url and url not in seen:
                seen.add(url)
                writer.writerow(row)
                kept += 1
            if total % 100000 == 0:
                print(f"  {total:,} processed, {kept:,} kept", flush=True)

    print(f"\nDone: {total:,} total → {kept:,} unique ({total - kept:,} duplicates removed)")


if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("--input", default="audit_output/flagged_documents.csv.gz")
    parser.add_argument("--output", default="audit_output/flagged_documents_deduped.csv.gz")
    args = parser.parse_args()

    deduplicate(args.input, args.output)