"""
merge_csv.py — combine sharded scraper outputs into one app_data.csv.

After PC #1 (shard 0) and PC #2 (shard 1) finish, copy both shard CSVs into the
same output folder and run this. It concatenates them and drops any duplicate
rows (same store + country + app_id).

Run:  python merge_csv.py
      python merge_csv.py --out output --pattern "app_data_shard*of*.csv"
"""

import argparse
import csv
from pathlib import Path


def main() -> None:
    parser = argparse.ArgumentParser(description="Merge sharded scraper CSVs")
    parser.add_argument("--out", default="output", help="folder holding the shard CSVs")
    parser.add_argument("--pattern", default="app_data_shard*of*.csv",
                        help="glob for the shard files")
    parser.add_argument("--dest", default="app_data.csv", help="merged filename")
    args = parser.parse_args()

    out_dir = Path(args.out)
    files = sorted(out_dir.glob(args.pattern))
    if not files:
        print(f"No shard files matching '{args.pattern}' in {out_dir}")
        return

    header = None
    seen = set()
    rows = []
    for f in files:
        with f.open(encoding="utf-8-sig", newline="") as fh:
            reader = csv.DictReader(fh)
            header = reader.fieldnames
            for row in reader:
                key = (row.get("store"), row.get("country"), row.get("app_id"))
                if key in seen:
                    continue
                seen.add(key)
                rows.append(row)
        print(f"  read {f.name}")

    dest = out_dir / args.dest
    with dest.open("w", encoding="utf-8-sig", newline="") as fh:
        writer = csv.DictWriter(fh, fieldnames=header)
        writer.writeheader()
        writer.writerows(rows)

    print(f"\nMerged {len(files)} files -> {dest}  ({len(rows)} unique rows)")


if __name__ == "__main__":
    main()