import csv
from io import StringIO


def summarize_inventory(csv_text):
    reader = csv.DictReader(StringIO(csv_text))
    if reader.fieldnames != ["item_id", "item", "available"]:
        raise ValueError("Expected item_id,item,available columns")

    seen = set()
    available_ids = []
    total_units = 0
    for row in reader:
        if None in row or any(value is None for value in row.values()):
            raise ValueError("A row has missing or extra fields")
        item_id = row["item_id"].strip()
        item = row["item"].strip()
        quantity_text = row["available"].strip()
        if not item_id or not item or item_id in seen:
            raise ValueError("Item IDs must be unique; names are required")
        if not (quantity_text.isascii() and quantity_text.isdigit()):
            raise ValueError("Available quantity must contain digits 0-9")
        quantity = int(quantity_text)
        if quantity > 999:
            raise ValueError("Available quantity must be between 0 and 999")
        seen.add(item_id)
        total_units += quantity
        if quantity > 0:
            available_ids.append(item_id)
    return {
        "item_types": len(seen),
        "available_units": total_units,
        "available_ids": available_ids,
    }


SAMPLE = """item_id,item,available
T1,spade,3
T2,rake,0
T3,watering can,2
T4,hand fork,1
"""

if __name__ == "__main__":
    result = summarize_inventory(SAMPLE)
    print("Item types:", result["item_types"])
    print("Available units:", result["available_units"])
    print("Available IDs:", ", ".join(result["available_ids"]))