import os
import json
import glob
import argparse


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--input-dir", type=str, required=True)
    parser.add_argument("--pattern", type=str, required=True)
    parser.add_argument("--output-path", type=str, required=True)
    args = parser.parse_args()

    input_pattern = os.path.join(args.input_dir, args.pattern)
    input_paths = sorted(glob.glob(input_pattern))
    if not input_paths:
        raise FileNotFoundError(f"No files matched pattern: {input_pattern}")

    merged = []
    for path in input_paths:
        with open(path, "r", encoding="utf-8") as f:
            data = json.load(f)
        if not isinstance(data, list):
            raise ValueError(f"{path} is not a JSON list, got {type(data)}")
        merged.extend(data)

    output_dir = os.path.dirname(args.output_path)
    if output_dir:
        os.makedirs(output_dir, exist_ok=True)

    with open(args.output_path, "w", encoding="utf-8") as f:
        json.dump(merged, f, ensure_ascii=False, indent=2)

    print(f"Merged {len(input_paths)} files into {args.output_path}")
    print(f"Total items: {len(merged)}")


if __name__ == "__main__":
    main()