import os
from pathlib import Path

PART_SIZE = 40 * 1024 * 1024 * 1024  # 40 GB
CHUNK_SIZE = 1024 * 1024 * 1024      # 1 GB


def split_gz_file(file_path: Path):
    file_size = file_path.stat().st_size
    print(f"\n[+] Processing: {file_path}")
    print(f"    Size: {file_size / (1024**3):.2f} GB")

    if file_size <= PART_SIZE:
        print("    File smaller than 40GB, skip.")
        return

    prefix = file_path.stem       # filename without .gz
    parent = file_path.parent     # original directory

    # For example: bigfile.gz.part001
    def part_name(n): 
        return parent / f"{prefix}.gz.part{n:03d}"

    part_num = 1
    written = 0
    out_file = None

    with open(file_path, "rb") as f:
        while True:
            chunk = f.read(CHUNK_SIZE)
            if not chunk:
                break

            # Open new part
            if written == 0:
                out_path = part_name(part_num)
                out_file = open(out_path, "wb")
                print(f"    [+] Creating {out_path.name}")

            out_file.write(chunk)
            written += len(chunk)

            # Close part when reaching 40GB
            if written >= PART_SIZE:
                out_file.close()
                print(f"    [✓] Finished part {part_num:03d}")
                part_num += 1
                written = 0

        if out_file:
            out_file.close()
            print(f"    [✓] Finished part {part_num:03d}")

    print(f"[OK] Finished splitting {file_path.name}\n")


def scan_and_split(root_dir: str):
    root = Path(root_dir)

    print(f"Scanning directory: {root.resolve()}\n")

    for path in root.rglob("*.gz"):
        try:
            if path.is_file():
                split_gz_file(path)
        except Exception as e:
            print(f"[ERROR] Failed on {path}: {e}")


if __name__ == "__main__":
    import sys
    if len(sys.argv) != 2:
        print("Usage: python split_gz_auto.py <directory>")
        exit(1)

    scan_and_split(sys.argv[1])