path: root/docs/plugin-development.md

# LabUI Plugin Development Guide

Plugins live under `plugins/` as self-contained directories. The app discovers them automatically; the user enables or disables them in **Settings → Plugins**. A disabled plugin leaves zero trace in the UI.

---

## Table of Contents

1. [Directory structure](#1-directory-structure)
2. [manifest.json](#2-manifestjson)
3. [The LabPlugin class](#3-the-labplugin-class)
4. [PluginContext — accessing the app](#4-plugincontext--accessing-the-app)
5. [Integration hooks](#5-integration-hooks)
   - [Toolbar buttons](#51-toolbar-buttons)
   - [Devices — feeding data into the pipeline](#52-devices--feeding-data-into-the-pipeline)
   - [Custom signal filters](#53-custom-signal-filters)
   - [Settings widget](#54-settings-widget)
   - [Profile persistence](#55-profile-persistence)
6. [Writing a virtual device from scratch](#6-writing-a-virtual-device-from-scratch)
7. [Data flow reference](#7-data-flow-reference)
8. [Minimal end-to-end example](#8-minimal-end-to-end-example)
9. [Rules and gotchas](#9-rules-and-gotchas)

---

## 1. Directory structure

```
plugins/
  my_plugin/
    manifest.json     ← required
    plugin.py         ← required (entry point)
    my_device.py      ← any supporting files you need
    my_filter.py
    ui/
      my_window.py
```

The plugin directory is added to `sys.path` at load time, so internal imports work without path gymnastics:

```python
from my_device import MyDevice      # works inside plugin.py
from ui.my_window import MyWindow   # works too
```

---

## 2. manifest.json

```json
{
  "plugin_id":   "my_plugin",
  "name":        "My Plugin",
  "version":     "1.0.0",
  "description": "One-line description shown in Settings.",
  "author":      "Your Name",
  "entry_point": "plugin.MyPlugin"
}
```

| Field | Required | Notes |
|---|---|---|
| `plugin_id` | Yes | Unique `snake_case` identifier. Must match `LabPlugin.plugin_id`. |
| `name` | Yes | Display name shown in Settings → Plugins. |
| `version` | No | Defaults to `"1.0.0"`. |
| `description` | No | One sentence. Shown in Settings. |
| `author` | No | Shown in Settings. |
| `entry_point` | No | `"module.ClassName"` relative to the plugin dir. Defaults to `"plugin.Plugin"`. |

---

## 3. The LabPlugin class

```python
from plugins.base_plugin import LabPlugin, PluginAction, PluginContext

class MyPlugin(LabPlugin):

    @property
    def plugin_id(self) -> str:   # must match manifest
        return "my_plugin"

    @property
    def name(self) -> str:
        return "My Plugin"

    # version / description / author — optional overrides

    def on_load(self, context: PluginContext) -> None:
        self._ctx = context
        # initialise hardware, start threads, etc.

    def on_unload(self) -> None:
        # stop threads, close hardware, release memory
        pass
```

`plugin_id` and `name` are the only abstract properties — everything else is optional.

### Lifecycle

```
User enables plugin
      │
      ▼
  on_load(context)          ← store context, init hardware
      │
      ├── get_devices()     ← called once; devices added to registry + engine
      ├── get_filter_classes() ← registered in FILTER_CLASSES
      └── get_toolbar_actions() ← buttons added to main toolbar

User disables plugin  (or app closes)
      │
      ▼
  on_unload()               ← stop threads, close hardware
  (toolbar buttons removed, devices removed, filter classes unregistered)
```

---

## 4. PluginContext — accessing the app

`context` is passed to `on_load`. Store it as `self._ctx`.

```python
self._ctx.registry      # DeviceRegistry  — add/get/remove devices
self._ctx.engine        # AcquisitionEngine — start/stop, add/remove devices
self._ctx.processor     # SignalProcessor — add derived channels, set pipelines
self._ctx.main_window   # QMainWindow — parent for dialogs, geometry reference
```

### Common patterns

**Read a live channel value:**
```python
latest = self._ctx.processor._latest.get(("my_device", "ch0"))
if latest:
    timestamp, value = latest
```

**Subscribe to every processed sample:**
```python
# In on_load:
self._ctx.processor.processed_data.connect(self._on_data)

def _on_data(self, device_id, channel_id, timestamp, value):
    if device_id == "my_device":
        ...

# In on_unload:
self._ctx.processor.processed_data.disconnect(self._on_data)
```

**Add a derived channel programmatically:**
```python
from core.signal_processor import DerivedChannel

dc = DerivedChannel(
    channel_id = "my_computed",
    name       = "My Computed",
    unit       = "m/s",
    kind       = "expression",
    sources    = [("my_device", "ch0")],
    expression = "x[0] * 0.001",
)
self._ctx.processor.add_derived(dc)

# Clean up in on_unload:
self._ctx.processor.remove_derived("my_computed")
```

---

## 5. Integration hooks

All hooks are **optional** — return empty lists / `None` for anything your plugin doesn't use.

---

### 5.1 Toolbar buttons

```python
def get_toolbar_actions(self) -> list:
    return [
        PluginAction(
            label     = "Motion Capture",
            icon      = "🎥",            # emoji or empty string
            tooltip   = "Open motion capture window",
            checkable = True,            # button stays pressed
            callback  = self._open_window,
        )
    ]

def _open_window(self, checked: bool):
    if checked:
        self._win.show()
    else:
        self._win.hide()
```

Buttons appear between the **Plot** button and the clock. They are removed automatically when the plugin is disabled.

You can return multiple `PluginAction` objects for multiple buttons.

---

### 5.2 Devices — feeding data into the pipeline

Return `BaseDevice` instances from `get_devices()`. The app calls `device.connect()`, adds the device to the `DeviceRegistry` and `AcquisitionEngine`, and polls it at the configured rate (default 100 ms). The device's channels then appear everywhere — Signals window, Plot builder, derived channel expressions — exactly like hardware channels.

```python
def get_devices(self) -> list:
    self._device = MyCustomDevice(device_id="my_plugin_dev")
    return [self._device]
```

See [§6](#6-writing-a-virtual-device-from-scratch) for how to write a `BaseDevice`.

> **Important:** `get_devices()` is called once at load time. The list must be stable — don't return different objects each call.

---

### 5.3 Custom signal filters

Return a dict of `{type_name: FilterBase_subclass}`. These become available in the Signals → pipeline editor alongside built-ins like `low_pass`, `moving_average`, etc.

```python
def get_filter_classes(self) -> dict:
    from my_filter import PixelToMillimetreFilter
    return {"pixel_to_mm": PixelToMillimetreFilter}
```

**Writing a filter:**

```python
from core.signal_processor import FilterBase

class PixelToMillimetreFilter(FilterBase):
    name = "pixel_to_mm"

    def __init__(self, px_per_mm: float = 10.0):
        self.params = {"px_per_mm": px_per_mm}

    def __call__(self, value: float) -> float:
        return value / self.params["px_per_mm"]

    def reset(self):
        pass   # stateless filter — nothing to reset

    # to_dict() is inherited and uses self.name + self.params automatically
```

Rules:
- `name` must match the dict key returned from `get_filter_classes()`.
- `__init__` parameters must be JSON-serialisable (used in profiles).
- Stateful filters (ring buffers, IIR memory) must implement `reset()`.
- For filters that need the timestamp (derivatives, integrals), implement `process_with_t(value, timestamp) -> float` in addition to `__call__`.

---

### 5.4 Settings widget

Return any `QWidget` from `get_settings_widget()`. It is embedded inside **Settings → Plugins** below the plugin's name card, visible only when the plugin is enabled.

```python
def get_settings_widget(self) -> QWidget:
    from PyQt6.QtWidgets import QWidget, QFormLayout, QDoubleSpinBox

    w = QWidget()
    lay = QFormLayout(w)

    self._scale_spin = QDoubleSpinBox()
    self._scale_spin.setValue(self._scale)
    self._scale_spin.valueChanged.connect(self._on_scale_changed)
    lay.addRow("px / mm:", self._scale_spin)

    return w

def _on_scale_changed(self, value: float):
    self._scale = value
    # update whatever needs updating
```

The widget is created once when the plugin loads. Apply changes immediately (no Apply button required — the Settings window Apply button only applies the general settings, not plugin-specific widgets).

---

### 5.5 Profile persistence

`.labui` profiles save the **enabled plugin list** automatically — loading a profile enables/disables plugins to match the saved state. Per-plugin configuration state is also saved if you implement these two methods.

```python
def get_save_state(self) -> dict:
    # Must be JSON-serialisable
    return {
        "scale":      self._scale,
        "track_point": list(self._track_point),
    }

def apply_save_state(self, state: dict) -> None:
    self._scale       = state.get("scale", 10.0)
    self._track_point = tuple(state.get("track_point", [0, 0]))
    # update UI if it exists
```

`apply_save_state` is called after `on_load`, so `self._ctx` is available. The plugin must already be enabled in `enabled.json` for state to be restored — profiles do not enable plugins automatically.

---

## 6. Writing a virtual device from scratch

A plugin device is a normal `BaseDevice` subclass. The polling loop in `AcquisitionEngine` calls `read_channels()` every 100 ms (configurable) and routes the returned values through the signal processor to the strip chart.

```python
import time
import threading
from devices.base_device import BaseDevice, DeviceInfo, DeviceStatus, ChannelConfig

class MyVirtualDevice(BaseDevice):

    def __init__(self, device_id: str = "my_virtual"):
        super().__init__(DeviceInfo(
            device_id   = device_id,
            name        = "My Virtual Device",
            device_type = "virtual",
            description = "Produces synthetic data.",
            channels    = [
                ChannelConfig("ch0", "X Position", unit="px",
                              min_value=-1000, max_value=1000),
                ChannelConfig("ch1", "Y Position", unit="px",
                              min_value=-1000, max_value=1000),
            ],
        ))
        self._value = {"ch0": 0.0, "ch1": 0.0}
        self._lock  = threading.Lock()

    # ── Required interface ────────────────────────────────────────────────

    def connect(self) -> bool:
        # Open camera / serial port / socket here.
        # Return False and set status to ERROR if it fails.
        self.status = DeviceStatus.SIMULATED
        return True

    def disconnect(self) -> None:
        self.status = DeviceStatus.DISCONNECTED

    def read_channels(self) -> dict:
        # Called every poll interval from AcquisitionEngine's background thread.
        # Must return quickly — no blocking I/O here.
        # If your hardware is slow, read in a background thread and cache here.
        with self._lock:
            return dict(self._value)

    def write_channel(self, channel_id: str, value) -> bool:
        return False   # read-only device

    def get_config_widget(self):
        from PyQt6.QtWidgets import QLabel
        return QLabel("No configuration available.")

    # ── Plugin-specific: push data from your own thread ───────────────────

    def push(self, ch0: float, ch1: float):
        """Call this from your background thread to update the cached value."""
        with self._lock:
            self._value["ch0"] = ch0
            self._value["ch1"] = ch1
```

### Background thread pattern

If your hardware delivers data asynchronously (camera callback, serial stream), use a background thread that writes to the cache, and let the polling loop read from it:

```python
def connect(self) -> bool:
    self._running = True
    self._thread  = threading.Thread(target=self._reader, daemon=True)
    self._thread.start()
    self.status = DeviceStatus.CONNECTED
    return True

def disconnect(self) -> None:
    self._running = False
    self._thread.join(timeout=2)
    self.status = DeviceStatus.DISCONNECTED

def _reader(self):
    while self._running:
        x, y = self._capture_frame()   # your hardware call
        with self._lock:
            self._value["ch0"] = x
            self._value["ch1"] = y
```

---

## 7. Data flow reference

```
Your hardware / background thread
        │
        ▼
  MyVirtualDevice.read_channels()      ← polled every 100 ms
        │
        ▼
  AcquisitionEngine                    ← engine.new_data signal emitted
        │
        ▼
  SignalProcessor.on_raw_data()        ← applies filter pipelines
        │                              ← evaluates derived channels
        ▼
  SignalProcessor.processed_data       ← (device_id, channel_id, t, value)
        │
        ├─→ StripChartWidget           ← plotted in real time
        └─→ your plugin callback       ← if you connected to processed_data
```

Your plugin channels participate in every stage:
- **Signals window** — can rename, set color, enable/disable
- **Signal pipeline** — user can attach built-in or custom filters
- **Derived channels** — can reference your channel in expressions (`x[0]`)
- **Plot builder** — appears in channel picker like any physical channel
- **CSV logging** — logged automatically when LOG is active

---

## 8. Minimal end-to-end example

This plugin adds a sine-wave virtual channel and a toolbar button to toggle a display window.

**`plugins/sine_demo/manifest.json`**
```json
{
  "plugin_id":   "sine_demo",
  "name":        "Sine Demo",
  "version":     "1.0.0",
  "description": "Virtual sine-wave channel for testing.",
  "author":      "LabUI",
  "entry_point": "plugin.SineDemoPlugin"
}
```

**`plugins/sine_demo/plugin.py`**
```python
import math, time, threading
from devices.base_device import BaseDevice, DeviceInfo, DeviceStatus, ChannelConfig
from plugins.base_plugin import LabPlugin, PluginAction, PluginContext


class SineDevice(BaseDevice):
    def __init__(self):
        super().__init__(DeviceInfo(
            device_id   = "sine_demo_dev",
            name        = "Sine Generator",
            device_type = "virtual",
            channels    = [ChannelConfig("sine", "Sine Wave", unit="V",
                                         min_value=-1, max_value=1)],
        ))
        self._t0 = time.monotonic()

    def connect(self):
        self.status = DeviceStatus.SIMULATED; return True
    def disconnect(self):
        self.status = DeviceStatus.DISCONNECTED
    def read_channels(self):
        return {"sine": math.sin(2 * math.pi * (time.monotonic() - self._t0))}
    def write_channel(self, ch, v): return False
    def get_config_widget(self):
        from PyQt6.QtWidgets import QLabel
        return QLabel("No config.")


class SineDemoPlugin(LabPlugin):

    @property
    def plugin_id(self): return "sine_demo"

    @property
    def name(self): return "Sine Demo"

    def on_load(self, context: PluginContext):
        self._ctx = context
        self._dev = SineDevice()
        self._win = None

    def on_unload(self):
        if self._win:
            self._win.close()

    def get_devices(self):
        return [self._dev]

    def get_toolbar_actions(self):
        return [PluginAction(
            label="Sine Demo", icon="〜",
            tooltip="Open sine demo window",
            checkable=True,
            callback=self._toggle_window,
        )]

    def _toggle_window(self, checked: bool):
        from PyQt6.QtWidgets import QLabel, QWidget, QVBoxLayout
        if self._win is None:
            self._win = QWidget(None)
            self._win.setWindowTitle("Sine Demo")
            lay = QVBoxLayout(self._win)
            lay.addWidget(QLabel(
                "Sine wave channel 'sine_demo_dev / sine' is now live.\n"
                "Add it to a plot via Plot → channel picker."
            ))
        if checked:
            self._win.show()
        else:
            self._win.hide()
```

Enable it in **Settings → Plugins**, then open **Plot** and add the `sine_demo_dev / sine` channel.

---

## 9. Rules and gotchas

**`plugin_id` must be globally unique and match the manifest.**
The manager keys everything by this string. Collision = second plugin silently ignored.

**`get_devices()` is called once.**
Return a stable list. Don't construct new device objects on repeated calls.

**`read_channels()` runs on the acquisition thread.**
Keep it fast. Do not block. Cache hardware values from a separate thread if needed.

**Don't import Qt in module scope inside a plugin.**
Import Qt widgets inside methods or inside `on_load`. This avoids import errors if the plugin directory is scanned before the `QApplication` is created.

**`on_unload()` must clean up everything.**
Stop background threads (`_running = False; _thread.join()`), disconnect signals, close windows. The app calls `on_unload()` both on user disable and on application close.

**Filter `__init__` params must be JSON-serialisable.**
They are written into `.labui` profiles via `to_dict()` and reconstructed via `filter_from_dict()`. Stick to `int`, `float`, `str`, `bool`.

**Profiles enable and disable plugins.**
Loading a `.labui` profile reconciles plugin state: plugins not in the profile's enabled list are disabled, plugins in the list are enabled. `apply_save_state` is called after the plugin is loaded. `plugins/enabled.json` is updated to match.

**Enabled state persists across restarts.**
`plugins/enabled.json` is written every time a toggle changes. Delete it to reset all plugins to disabled.