# Unit 04 — Core Adapters

## Goal
Pluggable adapter pattern for Open5GS and free5gc. New cores can be added by subclassing `CoreAdapter`.

## Files
- `server/core_adapters/base.py`
- `server/core_adapters/open5gs.py`
- `server/core_adapters/free5gc.py`
- `server/core_adapters/__init__.py` (factory function)

---

## `server/core_adapters/base.py`

```python
from abc import ABC, abstractmethod
from typing import Optional

class CoreAdapter(ABC):
    @abstractmethod
    def add_subscriber(self, imsi: str, ki: str, opc: str) -> None:
        """Add a subscriber to the core network. ki and opc are hex strings."""

    @abstractmethod
    def remove_subscriber(self, imsi: str) -> None:
        """Remove a subscriber from the core network."""

    @abstractmethod
    def list_subscribers(self) -> list[dict]:
        """Return list of subscriber dicts from the core."""
```

---

## `server/core_adapters/open5gs.py`

Uses direct MongoDB insertion (same approach as Open5GS web UI).

```python
import logging
from pymongo import MongoClient
from .base import CoreAdapter

logger = logging.getLogger(__name__)

class Open5GSAdapter(CoreAdapter):
    def __init__(self, mongodb_uri: str, database_name: str = "open5gs"):
        self.client = MongoClient(mongodb_uri)
        self.db = self.client[database_name]

    def add_subscriber(self, imsi: str, ki: str, opc: str) -> None:
        doc = {
            "imsi": imsi,
            "security": {
                "k": ki,
                "opc": opc,
                "amf": "8000",
                "sqn": 0
            },
            "ambr": {
                "downlink": {"value": 1, "unit": 3},
                "uplink": {"value": 1, "unit": 3}
            },
            "slice": [{
                "sst": 1,
                "default_indicator": True,
                "session": [{
                    "name": "internet",
                    "type": 3,
                    "ambr": {
                        "downlink": {"value": 1, "unit": 3},
                        "uplink": {"value": 1, "unit": 3}
                    }
                }]
            }]
        }
        self.db.subscribers.replace_one({"imsi": imsi}, doc, upsert=True)
        logger.info(f"Added subscriber {imsi} to Open5GS")

    def remove_subscriber(self, imsi: str) -> None:
        self.db.subscribers.delete_one({"imsi": imsi})
        logger.info(f"Removed subscriber {imsi} from Open5GS")

    def list_subscribers(self) -> list[dict]:
        return list(self.db.subscribers.find({}, {"_id": 0}))
```

---

## `server/core_adapters/free5gc.py`

Stub — same document format, different DB name. Implement fully when free5gc is available.

```python
from .open5gs import Open5GSAdapter

class Free5GCAdapter(Open5GSAdapter):
    def __init__(self, mongodb_uri: str, database_name: str = "free5gc"):
        super().__init__(mongodb_uri, database_name)
```

---

## `server/core_adapters/__init__.py`

Factory function:
```python
from .base import CoreAdapter
from .open5gs import Open5GSAdapter
from .free5gc import Free5GCAdapter
from typing import Optional

def get_adapter(config: dict) -> Optional[CoreAdapter]:
    core_cfg = config.get("core", {})
    core_type = core_cfg.get("type", "none")
    uri = core_cfg.get("mongodb_uri", "mongodb://localhost:27017")
    db_name = core_cfg.get("database_name", "open5gs")

    if core_type == "open5gs":
        return Open5GSAdapter(uri, db_name)
    elif core_type == "free5gc":
        return Free5GCAdapter(uri, db_name)
    else:
        return None  # No core integration (export-only mode)
```

---

## Verification
```bash
# With no MongoDB running — verify import and factory
python -c "
from server.core_adapters import get_adapter
cfg = {'core': {'type': 'none'}}
adapter = get_adapter(cfg)
assert adapter is None
print('Factory returns None for type=none: OK')

# Test Open5GS adapter instantiation (no connection attempt until query)
cfg2 = {'core': {'type': 'open5gs', 'mongodb_uri': 'mongodb://localhost:27017', 'database_name': 'open5gs'}}
adapter2 = get_adapter(cfg2)
print(f'Open5GS adapter: {adapter2.__class__.__name__}')
"
```