# ADR-006: Plugin collector contract pattern

- **Status:** ACCEPTED
- **Date:** 2026-05-08
- **Deciders:** ShopDB maintainers
- **Supersedes:** none

## Context

PC inventory data was collected by PowerShell scripts pushing to `/api/collector/pc` (`shopdb/core/api/collector.py`, ~374 LOC). The endpoint is hardcoded for PCs: it accepts a fixed schema and writes to the legacy `Machine` model.

Per ADR-001, `Machine` is being retired in favor of `Asset`. Per the project shift to PXE-driven imaging, PC inventory is moving to a new collection pipeline (PXE / GE-Enforce / manifest engine produces JSON about each PC). Other asset classes may want similar collector pipelines (printers via Zabbix, network gear via SNMP scan).

This calls for a generalizable contract: any plugin that wants to accept external collector input declares a JSON schema, and the framework wires the endpoint, auth, and idempotency.

## Decision

`BasePlugin` gets two new hooks (added in __contract_version__ 0.2.x -> the surface is carried at 0.3.0):

```python
def get_collector_schema(self) -> Optional[dict]:
    """Return JSON Schema describing the collector payload for this plugin.
    Return None if the plugin does not accept collector input.

    The schema must include:
    - 'identityfield': name of the field that uniquely identifies an asset
      across submissions (e.g., 'hostname' for PCs, 'macaddress' for network
      devices). Used for idempotent upsert.
    - 'fields': JSON Schema definitions for the rest of the payload.
    """
    return None

def apply_collector_payload(self, payload: dict) -> dict:
    """Idempotently upsert an asset from a validated collector payload.

    Called by /api/collector/<pluginname> after identity validation.
    CONDITIONAL hook: required only when get_collector_schema returns
    non-None. Default raises NotImplementedError (the dispatcher returns
    500) so a schema-without-upsert fails loud. Returns a dict with at
    least 'action' ('created'|'updated'|'noop'), 'assetid', 'warnings'.
    """
    raise NotImplementedError
```

The pairing (schema present => apply implemented) is enforced by the
`test_schema_declaring_plugins_implement_apply` contract test.

A single dynamic dispatch route `/api/collector/<pluginname>` serves every
plugin that returns a schema (rather than registering a blueprint per plugin),
because Flask forbids `register_blueprint` after the first request and plugins
can be enabled at runtime. Auth is API-key, separate from JWT. Per-plugin keys via env vars:

- `COLLECTOR_API_KEY_<PLUGINNAME>` (preferred, plugin-specific)
- `COLLECTOR_API_KEY` (fallback, shared)

### Idempotent upsert

The endpoint uses the `identityfield` to find an existing `Asset` for the same identity. Found = update. Not found = insert. Existing relationships are preserved on update.

### Response contract

```json
{
  "status": "ok",
  "action": "created" | "updated" | "noop",
  "assetid": 12345,
  "identityvalue": "PC-1234",
  "warnings": []
}
```

### Audit logging

Every collector submission produces an audit log entry: `{action, plugin, identityvalue, before/after diff}`. Audit retention per site policy.

### Schema discovery

The framework exposes the registered schemas at `/api/collector/_schemas` (read-only, JWT-protected) so external collector authors can introspect what payloads are accepted by which plugins.

## Concrete first user: computers plugin

The `computers` plugin is the first to implement `get_collector_schema`. The PXE pipeline conforms.

Initial computers collector schema (sketch, finalized when plugin is built):

```json
{
  "identityfield": "hostname",
  "fields": {
    "hostname": "string, required",
    "macaddress": "string, optional, secondary identity",
    "osname": "string",
    "osversion": "string",
    "lastboottime": "datetime",
    "currentuser": "string",
    "ipaddress": "string",
    "memorygb": "number",
    "cputype": "string",
    "imagename": "string (PXE image deployed)",
    "imageappliedat": "datetime",
    "installedsoftware": "array of {name, version}"
  }
}
```

The PC re-image case is handled by the identity field: a freshly imaged PC keeps its hostname, so the existing `Asset` row is updated rather than duplicated. Existing `AssetRelationship` rows pointing at that PC (e.g., `controls` to a machine) are preserved across re-images.

## Migration of the existing endpoint

`shopdb/core/api/collector.py` (`/api/collector/pc`) is **deprecated** in v1 and **removed** before v1.0.

Migration path:

1. Implement `get_collector_schema` on the `computers` plugin. New endpoint `/api/collector/computers` is auto-registered.
2. Run both endpoints in parallel for one cycle of PXE imaging across the floor. PXE pipeline switches to `/api/collector/computers`.
3. Remove `shopdb/core/api/collector.py` and the legacy blueprint registration.

## Consequences

### Positive

- Generalizable across plugins. Sister sites adopting `printers`, `network`, etc. can wire their own collectors with no core change.
- Identity-based idempotency makes PC re-imaging safe by default.
- Audit logging is uniform across plugins.
- Schema discovery enables external tools to validate before submission.

### Negative

- Plugin authors must write a JSON schema. Slight learning curve, but JSON Schema is widely understood and the framework can ship a few examples.
- The `/api/collector/_schemas` endpoint plus per-plugin endpoints expand the public API surface; minor maintenance cost.

### Neutral

- API-key auth pattern stays as it is today (separate from JWT). Sites manage their own collector keys per plugin via env vars.

## Alternatives considered

1. **Keep `/api/collector/pc` and add new plugin-specific endpoints alongside.** Two ways to send PC data, plugin authors confused. Rejected.
2. **Use JWT for collectors instead of API key.** Collectors are headless processes (PXE pipeline, scripts), not interactive users. JWT lifecycle (refresh tokens, expiry) is the wrong tool. API key is simpler. Rejected.
3. **Plugins write directly to the database, no collector endpoint.** Skips audit logging and schema validation. Rejected.

## References

- `shopdb/core/api/collector.py` (legacy endpoint to be removed)
- `shopdb/plugins/base.py` (`get_collector_schema` + `apply_collector_payload` hooks)
- ADR-001 (asset model the collectors target)
- ADR-002 (collector schema is part of plugin contract; changes to the hook signature are major bumps)
- The PXE project (the PXE imaging project) which feeds the computers collector
