import sys
import glob
from mcap.reader import make_reader

class LargeRecordWrapper:
    def __init__(self, fp):
        self.fp = fp

    def read(self, size=-1):
        return self.fp.read(size)

    def seek(self, pos, whence=0):
        return self.fp.seek(pos, whence)

    def tell(self):
        return self.fp.tell()

    def seekable(self):
        return True

def inspect(bag_dir: str):
    files = sorted(glob.glob(f"{bag_dir}/*.mcap"))
    if not files:
        print(f"No MCAP files in {bag_dir}")
        return
    topics: dict[str, dict] = {}
    for path in files:
        try:
            with open(path, "rb") as fp:
                wrapped = LargeRecordWrapper(fp)
                reader = make_reader(wrapped)
                for schema, channel, message in reader.iter_messages():
                    t = channel.topic
                    if t not in topics:
                        topics[t] = {"type": schema.name if schema else "?", "count": 0, "encoding": channel.message_encoding}
                    topics[t]["count"] += 1
        except Exception as e:
            print(f"Warning: error reading {path}: {e}", file=sys.stderr)
            continue

    print(f"\n{'Topic':<50} {'Type':<45} {'Msgs':>6}")
    print("-" * 105)
    for t, info in sorted(topics.items()):
        print(f"{t:<50} {info['type']:<45} {info['count']:>6}")

if __name__ == "__main__":
    inspect(sys.argv[1] if len(sys.argv) > 1 else "data/bags")