# Plugin System Overview

Plugins extend Steward with new data sources, UI pages, scheduled tasks, and dashboard widgets. Only enabled plugins are imported — disabled or unlisted plugins have zero runtime overhead.

---

## How Plugins Are Loaded

Plugin loading happens in step 9 of `create_app()`, after all core blueprints and tasks are registered. The entrypoint is `load_plugins(app)` in `steward/core/plugin_manager.py`.

For each plugin listed as `enabled: true` in the `PLUGINS` config:

1. **Directory check** — `plugins/<name>/` must exist
2. **`plugin.yaml` check** — file must exist and be valid YAML
3. **Name validation** — `plugin.yaml` `name` field must match the directory name exactly
4. **Version check** — if `min_app_version` is set, the running app version must be >= that value (uses SemVer comparison)
5. **Config merge** — `plugin.yaml` `config` defaults are merged with user overrides from app settings; result stored in `app.config["PLUGINS"][name]`
6. **Import** — `importlib.import_module(name)` imports the plugin package (the plugins directory is prepended to `sys.path`)
7. **Export validation** — plugin must export `setup` and `get_scheduled_tasks`
8. **`setup(app)`** called
9. **Blueprint registration** — if plugin exports `get_blueprint()`, the returned blueprint is registered at `/plugins/<name>/`
10. **Task registration** — `get_scheduled_tasks()` results are appended to `app._task_registry`

If any step fails, the plugin is skipped with an error log and startup continues.

---

## Plugin Directory Structure

```
plugins/
└── myplugin/
    ├── __init__.py           # Required: setup(), get_scheduled_tasks(), optionally get_blueprint()
    ├── plugin.yaml           # Required: name, version, description
    ├── models.py             # SQLAlchemy models (optional if plugin has no DB tables)
    ├── routes.py             # Quart Blueprint (optional if plugin has no UI)
    ├── scheduler.py          # Task logic (optional if plugin has no background tasks)
    ├── migrations/           # Alembic migrations for plugin DB tables
    │   ├── env.py
    │   ├── script.py.mako
    │   └── versions/
    └── templates/
        └── myplugin/         # Jinja2 templates (namespaced under plugin name)
            ├── index.html
            └── widget.html
```

---

## plugin.yaml Schema

```yaml
# Required
name: myplugin              # Must match directory name exactly
version: "1.0.0"            # SemVer
description: "Does a thing"

# Optional
author: "Your Name"
min_app_version: "0.1.0"   # Minimum Steward version required

# Default config — merged with user overrides at runtime
# Access at runtime via: app.config["PLUGINS"]["myplugin"]["my_setting"]
config:
  my_setting: "default_value"
  poll_interval_seconds: 60
```

---

## Required Python Exports

Every plugin's `__init__.py` must export:

### `setup(app: Quart) -> None`

Called once during app startup. Use it to store the `app` reference for use in scheduled tasks, and to import models so they register with SQLAlchemy metadata.

```python
_app = None

def setup(app):
    global _app
    _app = app
    from .models import MyModel  # noqa: registers model with Base.metadata
```

### `get_scheduled_tasks() -> list[ScheduledTask]`

Returns a list of `ScheduledTask` objects. Return `[]` if the plugin has no background tasks. Called after `setup()`, so any app references set in `setup()` are available.

```python
from steward.core.scheduler import ScheduledTask

def get_scheduled_tasks():
    app = _app

    async def my_task():
        async with app.db_sessionmaker() as session:
            async with session.begin():
                # do work
                pass

    return [
        ScheduledTask(
            name="myplugin_task",
            coro_factory=my_task,
            interval_seconds=app.config["PLUGINS"]["myplugin"]["poll_interval_seconds"],
            run_on_startup=True,
        )
    ]
```

### `get_blueprint() -> Blueprint` (optional)

Return a Quart `Blueprint`. The plugin manager mounts it automatically at `/plugins/<name>/`. Do not set `url_prefix` on the blueprint itself.

```python
def get_blueprint():
    from .routes import my_bp
    return my_bp
```

---

## Plugin Migrations

Plugins manage their own Alembic migrations in `migrations/versions/`. Plugin migrations run after core migrations, so the core schema (including `app_settings`) is always available.

Each plugin's initial revision declares a dependency on the core migration head using `depends_on` (not `down_revision`), keeping the plugin on a separate migration branch:

```python
# In the plugin's first migration file:
depends_on = ("0004_core_head_revision_id",)
down_revision = None
branch_labels = ("myplugin",)
```

Revision IDs should be prefixed with the plugin name to avoid collisions:

```
myplugin_001_initial.py
myplugin_002_add_column.py
```

If a plugin is disabled after its migrations have been applied, its tables remain in the database. Re-enabling it skips already-applied migrations and resumes normally.

---

## Dashboard Widgets

A plugin can contribute a dashboard widget by:

1. Adding a `GET /widget` route to its blueprint that returns an HTMX HTML fragment
2. The dashboard template polling that endpoint with HTMX

The dashboard (`steward/templates/dashboard/index.html`) currently includes the Traefik widget conditionally based on `traefik_enabled`. To add a new plugin widget, the dashboard route and template both need to be updated to detect and render the new widget. See the Traefik widget implementation as a reference.

---

## Available Context in Plugins

Inside scheduled tasks and request handlers, the following is available via `app` or `current_app`:

| Attribute | Type | Description |
|---|---|---|
| `app.config["PLUGINS"]["myplugin"]` | dict | Merged plugin config (defaults + user overrides) |
| `app.db_sessionmaker` | async_sessionmaker | Open DB sessions |
| `app.logger` | Logger | Standard Python logger |
| `app.config["SMTP"]` | dict | Email config |
| `app.config["WEBHOOK"]` | dict | Webhook config |

During `setup(app)`, do not open DB sessions — the event loop is not yet running. Store the `app` reference and open sessions inside coroutines only.