# Functional Specification — uopi

## 1. Purpose

uopi is a web-based HMI (Human-Machine Interface) for monitoring and controlling industrial/scientific systems, primarily EPICS-based control systems. It runs as a single server process and is accessed entirely through a web browser, making it suitable for SSH-tunnelled remote access.

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## 2. Users and Roles

| Role | Description |
|------|-------------|
| Operator | Uses interfaces in View mode; can interact with controls but cannot edit layouts |
| Engineer | Creates and edits interfaces in Edit mode; manages signal lists |
| Administrator | Manages server configuration, data sources, and saved interfaces |

In the initial version all users share the same access level. Role-based access control is deferred to a future release.

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## 3. System Modes

### 3.1 View Mode (default)

The default mode when opening the application.

**Interface list pane (left, collapsible)**
- Displays all interfaces saved on the server, grouped into a tree by folder.
- Right-click on an interface: options to open in Edit mode or clone it.
- "New interface" button opens Edit mode with a blank canvas.
- "Import" option loads an interface from a local XML file.

**HMI canvas (center)**
- Renders the selected interface as a live, interactive panel.
- Widgets display real-time data; controls (set-value, buttons) are active.
- No drag, resize, or layout operations are possible in this mode.
- Right-clicking any widget opens a context menu:
  - **Signal info** — floating window showing DS name, type, unit, range, current value and timestamp.
  - **Copy signal name** — copies the signal identifier to the clipboard.
  - **Export data to CSV** — downloads buffered/historical data for the signal(s) used by the widget.

**Top toolbar**
- Show/hide interface list pane.
- Time selector: navigate to a past timestamp (enabled only when the server has archive access for all signals on the canvas).
- "Live" button: return to real-time data after historical navigation.

### 3.2 Edit Mode

Activated via the "New interface" button or by right-clicking an existing interface.

**Signal tree pane (left, resizable and collapsible)**
- Shows all signals known to each connected data source.
- Sources are shown as top-level nodes; signals are nested within.
- User can add custom entries:
  - For EPICS: manually enter a PV name.
  - For Synthetic: define a new synthetic signal (see §5.2).
- User can load a CSV file with columns `NAME, DataSource, DS_PARAMETERS` to import a batch of signals.
- Filter/search box to narrow the list.

**Widget canvas (center)**
- Free-form canvas where widgets can be placed at arbitrary pixel positions.
- Background grid with optional snap-to-grid.

**Properties pane (right, collapsible)**
- Appears when one or more widgets are selected.
- Displays and edits all options for the selected widget (see §4).

**Top toolbar**
- Show/hide signal pane.
- Show/hide properties pane.
- Undo / Redo (also Ctrl+Z / Ctrl+Shift+Z).
- Save interface to server.
- Load interface from server.
- Export interface to local XML file.
- Import interface from local XML file.
- "Add text" tool — inserts a static text label.
- "Add image" tool — inserts a static image (uploaded to server or embedded as base64).
- "Add link" tool — inserts a button that opens another interface.

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## 4. Widgets

### 4.1 Creating Widgets

Drag a signal from the signal tree and drop it onto the canvas. A picker appears showing all widget types compatible with the signal's data type (iconised). The user selects one and the widget is placed at the drop location with default size.

### 4.2 Selecting Widgets

- Single click: select one widget (deselects others).
- Ctrl+click: add/remove a widget from the current selection.
- Click-drag on empty canvas area: rubber-band area select.

When a widget is selected, a bounding box appears with:
- 8 resize handles (corners + midpoints).
- A delete button (×) in the top-right corner.
- The widget can be moved by dragging its body.

### 4.3 Multi-selection Operations

When multiple widgets are selected:
- Drag any selected widget to move them all together.
- Del key deletes all selected widgets.
- An align/distribute toolbar appears above the canvas with:
  - Align left / center horizontal / right.
  - Align top / center vertical / bottom.
  - Distribute evenly — by center spacing (horizontal/vertical).
  - Distribute evenly — by gap size (horizontal/vertical).

### 4.4 Widget Catalogue

| Widget | Compatible signal types | Description |
|--------|-------------------------|-------------|
| Text view | any scalar | Displays `name: value unit` |
| Gauge | numeric scalar | Circular or arc gauge with configurable range |
| Vertical bar | numeric scalar | Vertical level indicator |
| Horizontal bar | numeric scalar | Horizontal level indicator |
| Set value | numeric or string, writable | Shows `name: [input field] current_value unit` + Set button |
| LED | boolean / numeric | Coloured indicator with configurable condition and label |
| Multi-LED | integer (bitset) | One LED per bit with individual labels and conditions |
| Button | writable | Sends a fixed value or command on click |
| Plot | numeric scalar or array | Multi-signal plot; sub-types below |
| Text label | — | Static text annotation |
| Image | — | Static image |
| Link | — | Button navigating to another interface |

**Plot sub-types:**

| Sub-type | Signal requirement |
|----------|--------------------|
| Time series | numeric scalar(s) |
| FFT | 1-D numeric array |
| Waterfall | 1-D numeric array (repeated) |
| Histogram | numeric scalar(s) |
| Bar chart | numeric scalar(s) |
| Logic analyser | boolean / integer (bitset) |

### 4.5 Widget Properties (Properties Pane)

Common to all:
- Label text, font size, text colour.
- Position (X, Y) and size (W, H) — editable numerically.
- Data source and signal name (read-only after creation; reassignable via drag).

Per type:
- **Gauge / Bar**: min value, max value, alert thresholds with colours, unit label.
- **LED / Multi-LED**: condition expression (e.g. `value > 0`), colours for true/false states.
- **Plot**: plot sub-type selector, Y-axis range (auto or manual), time window duration, legend position, colour per signal, line style.
- **Set value**: input type (numeric / string / enum), confirmation prompt toggle.
- **Link**: target interface name.

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## 5. Data Sources

### 5.1 EPICS

- Connects to an EPICS environment via Channel Access (CA) or PVAccess (PVA).
- On connect, retrieves full metadata from the PV name: data type, engineering units, display range (DRVL/DRVH, LOPR/HOPR), alarm limits, enum strings (for mbbi/mbbo records), read/write mode, acquisition mode.
- Prefers monitor/subscription over polling. Falls back to polling only when monitors are unavailable.
- Attempts to enumerate available PV names from the IOC (e.g. via PV lists or Channel Finder). Unknown PVs can still be manually added by the user.
- When an EPICS Archive Appliance or Channel Archiver is configured, the server can satisfy historical data requests.

### 5.2 Synthetic

A signal defined by composing one or more input signals (from any data source) through a chain of processing functions.

**Built-in processing functions (non-exhaustive):**
- Arithmetic: gain, offset, add, subtract, multiply, divide.
- Signal processing: moving average (N samples or time window), RMS, bandpass filter (IIR/FIR), lowpass / highpass filter, derivative, integral.
- FFT, inverse FFT.
- Peak detection, threshold crossing.
- Custom formula: inline expression (`a * sin(b) + c`).
- Lua script block: arbitrary Lua code with access to input values and state.

**User workflow:**
1. Click "New synthetic signal" in the signal tree.
2. Name the signal and choose input signals.
3. Build a processing pipeline by chaining function blocks (UI similar to a node graph or an ordered list).
4. Optionally write a Lua snippet for custom logic.
5. The synthetic signal appears in the tree and can be used like any other signal.

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## 6. Interface Persistence

- Interfaces are saved to the server in XML format and are available to all connected clients.
- Export/Import allows local file exchange of XML files.
- The XML schema records: widget type, position, size, signal bindings, and all property values.

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## 7. Historical Data Navigation

When the server has archive access for all signals on the current canvas:
- The top toolbar shows a date/time picker.
- Selecting a past time replays data from the archive into all widgets.
- The "Live" button resumes real-time streaming.
- Widgets that support time-axis (plots) show the historical range; point-value widgets show the value at the selected time.

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## 8. Non-functional Requirements

| Requirement | Target |
|-------------|--------|
| Server binary | Single statically-linked executable; no runtime dependencies |
| Target platform | Linux x86-64; also aarch64 optional |
| Minimum server OS | RHEL/CentOS 7 (glibc 2.17) or equivalent |
| Concurrent clients | ≥ 20 simultaneous browser clients |
| Data fan-out latency | < 5 ms added latency vs. raw EPICS update rate |
| Frontend responsiveness | 60 fps canvas rendering during live updates |
| Screen DPI | Frontend adapts to device pixel ratio |