lmxopcua/docs/HistoricalDataAccess.md

# Historical Data Access

`LmxNodeManager` exposes OPC UA historical data access (HDA) through an abstract `IHistorianDataSource` interface (`Historian/IHistorianDataSource.cs`). The Wonderware Historian implementation lives in a separate assembly, `ZB.MOM.WW.LmxOpcUa.Historian.Aveva`, which is loaded at runtime only when `Historian.Enabled=true`. This keeps the `aahClientManaged` SDK out of the core Host so deployments that do not need history do not need the SDK installed.

## Plugin Architecture

The historian surface is split across two assemblies:

- **`ZB.MOM.WW.LmxOpcUa.Host`** (core) owns only OPC UA / BCL types:
    - `IHistorianDataSource` -- the interface `LmxNodeManager` depends on
    - `HistorianEventDto` -- SDK-free representation of a historian event record
    - `HistorianAggregateMap` -- maps OPC UA aggregate NodeIds to AnalogSummary column names
    - `HistorianPluginLoader` -- loads the plugin via `Assembly.LoadFrom` at startup
    - `HistoryContinuationPointManager` -- paginates HistoryRead results
- **`ZB.MOM.WW.LmxOpcUa.Historian.Aveva`** (plugin) owns everything SDK-bound:
    - `HistorianDataSource` -- implements `IHistorianDataSource`, wraps `aahClientManaged`
    - `IHistorianConnectionFactory` / `SdkHistorianConnectionFactory` -- opens and polls `ArchestrA.HistorianAccess` connections
    - `AvevaHistorianPluginEntry.Create(HistorianConfiguration)` -- the static factory invoked by the loader

The plugin assembly and its SDK dependencies (`aahClientManaged.dll`, `aahClient.dll`, `aahClientCommon.dll`, `Historian.CBE.dll`, `Historian.DPAPI.dll`, `ArchestrA.CloudHistorian.Contract.dll`) deploy to a `Historian/` subfolder next to `ZB.MOM.WW.LmxOpcUa.Host.exe`. See [Service Hosting](ServiceHosting.md#required-runtime-assemblies) for the full layout and deployment matrix.

## Plugin Loading

When the service starts with `Historian.Enabled=true`, `OpcUaService` calls `HistorianPluginLoader.TryLoad(config)`. The loader:

1. Probes `AppDomain.CurrentDomain.BaseDirectory\Historian\ZB.MOM.WW.LmxOpcUa.Historian.Aveva.dll`.
2. Installs a one-shot `AppDomain.AssemblyResolve` handler that redirects any `aahClientManaged`/`aahClientCommon`/`Historian.*` lookups to the same subfolder, so the CLR can resolve SDK dependencies when the plugin first JITs.
3. Calls the plugin's `AvevaHistorianPluginEntry.Create(HistorianConfiguration)` via reflection and returns the resulting `IHistorianDataSource`.
4. On any failure (plugin missing, entry type not found, SDK assembly unresolvable, bad image), logs a warning with the expected plugin path and returns `null`. The server starts normally and `LmxNodeManager` returns `BadHistoryOperationUnsupported` for every history call.

## Wonderware Historian SDK

The plugin uses the AVEVA Historian managed SDK (`aahClientManaged.dll`) to query historical data. The SDK provides a cursor-based query API through `ArchestrA.HistorianAccess`, replacing direct SQL queries against the Historian Runtime database. Two query types are used:

- **`HistoryQuery`** -- Raw historical samples with timestamp, value (numeric or string), and OPC quality.
- **`AnalogSummaryQuery`** -- Pre-computed aggregates with properties for Average, Minimum, Maximum, ValueCount, First, Last, StdDev, and more.

The SDK DLLs are located in `lib/` and originate from `C:\Program Files (x86)\Wonderware\Historian\`. Only the plugin project (`src/ZB.MOM.WW.LmxOpcUa.Historian.Aveva/`) references them at build time; the core Host project does not.

## Configuration

`HistorianConfiguration` controls the SDK connection:

```csharp
public class HistorianConfiguration
{
    public bool Enabled { get; set; } = false;
    public string ServerName { get; set; } = "localhost";
    public bool IntegratedSecurity { get; set; } = true;
    public string? UserName { get; set; }
    public string? Password { get; set; }
    public int Port { get; set; } = 32568;
    public int CommandTimeoutSeconds { get; set; } = 30;
    public int MaxValuesPerRead { get; set; } = 10000;
}
```

When `Enabled` is `false`, `HistorianPluginLoader.TryLoad` is not called, no plugin is loaded, and the node manager returns `BadHistoryOperationUnsupported` for history read requests. When `Enabled` is `true` but the plugin cannot be loaded (missing `Historian/` subfolder, SDK assembly resolve failure, etc.), the server still starts and returns the same `BadHistoryOperationUnsupported` status with a warning in the log.

### Connection Properties

| Property | Default | Description |
|---|---|---|
| `ServerName` | `localhost` | Historian server hostname |
| `IntegratedSecurity` | `true` | Use Windows authentication |
| `UserName` | `null` | Username when `IntegratedSecurity` is false |
| `Password` | `null` | Password when `IntegratedSecurity` is false |
| `Port` | `32568` | Historian TCP port |
| `CommandTimeoutSeconds` | `30` | SDK packet timeout in seconds |
| `MaxValuesPerRead` | `10000` | Maximum values per history read request |

## Connection Lifecycle

`HistorianDataSource` (in the plugin assembly) maintains a persistent connection to the Historian server via `ArchestrA.HistorianAccess`:

1. **Lazy connect** -- The connection is established on the first query via `EnsureConnected()`.
2. **Connection reuse** -- Subsequent queries reuse the same connection.
3. **Auto-reconnect** -- On connection failure, the connection is disposed and re-established on the next query.
4. **Clean shutdown** -- `Dispose()` closes the connection when the service stops.

The connection is opened with `ReadOnly = true` and `ConnectionType = Process`.

## Raw Reads

`IHistorianDataSource.ReadRawAsync` (plugin implementation) uses a `HistoryQuery` to retrieve individual samples within a time range:

1. Create a `HistoryQuery` via `_connection.CreateHistoryQuery()`
2. Configure `HistoryQueryArgs` with `TagNames`, `StartDateTime`, `EndDateTime`, and `RetrievalMode = Full`
3. Iterate: `StartQuery` -> `MoveNext` loop -> `EndQuery`

Each result row is converted to an OPC UA `DataValue`:

- `QueryResult.Value` (double) takes priority; `QueryResult.StringValue` is used as fallback for string-typed tags.
- `SourceTimestamp` and `ServerTimestamp` are both set to `QueryResult.StartDateTime`.
- `StatusCode` is mapped from the `QueryResult.OpcQuality` (UInt16) via `QualityMapper` (the same OPC DA quality byte mapping used for live MXAccess data).

## Aggregate Reads

`IHistorianDataSource.ReadAggregateAsync` (plugin implementation) uses an `AnalogSummaryQuery` to retrieve pre-computed aggregates:

1. Create an `AnalogSummaryQuery` via `_connection.CreateAnalogSummaryQuery()`
2. Configure `AnalogSummaryQueryArgs` with `TagNames`, `StartDateTime`, `EndDateTime`, and `Resolution` (milliseconds)
3. Iterate the same `StartQuery` -> `MoveNext` -> `EndQuery` pattern
4. Extract the requested aggregate from named properties on `AnalogSummaryQueryResult`

Null aggregate values return `BadNoData` status rather than `Good` with a null variant.

## Quality Mapping

The Historian SDK returns standard OPC DA quality values in `QueryResult.OpcQuality` (UInt16). The low byte is passed through the shared `QualityMapper` pipeline (`MapFromMxAccessQuality` -> `MapToOpcUaStatusCode`), which maps the OPC DA quality families to OPC UA status codes:

| OPC Quality Byte | OPC DA Family | OPC UA StatusCode |
|---|---|---|
| 0-63 | Bad | `Bad` (with sub-code when an exact enum match exists) |
| 64-191 | Uncertain | `Uncertain` (with sub-code when an exact enum match exists) |
| 192+ | Good | `Good` (with sub-code when an exact enum match exists) |

See `Domain/QualityMapper.cs` and `Domain/Quality.cs` for the full mapping table and sub-code definitions.

## Aggregate Function Mapping

`HistorianAggregateMap.MapAggregateToColumn` (in the core Host assembly, so the node manager can validate aggregate support without requiring the plugin to be loaded) translates OPC UA aggregate NodeIds to `AnalogSummaryQueryResult` property names:

| OPC UA Aggregate | Result Property |
|---|---|
| `AggregateFunction_Average` | `Average` |
| `AggregateFunction_Minimum` | `Minimum` |
| `AggregateFunction_Maximum` | `Maximum` |
| `AggregateFunction_Count` | `ValueCount` |
| `AggregateFunction_Start` | `First` |
| `AggregateFunction_End` | `Last` |
| `AggregateFunction_StandardDeviationPopulation` | `StdDev` |

Unsupported aggregates return `null`, which causes the node manager to return `BadAggregateNotSupported`.

## HistoryReadRawModified Override

`LmxNodeManager` overrides `HistoryReadRawModified` to handle raw history read requests:

1. Resolve the `NodeHandle` to a tag reference via `_nodeIdToTagReference`. Return `BadNodeIdUnknown` if not found.
2. Check that `_historianDataSource` is not null. Return `BadHistoryOperationUnsupported` if historian is disabled.
3. Call `ReadRawAsync` with the time range and `NumValuesPerNode` from the `ReadRawModifiedDetails`.
4. Pack the resulting `DataValue` list into a `HistoryData` object and wrap it in an `ExtensionObject` for the `HistoryReadResult`.

## HistoryReadProcessed Override

`HistoryReadProcessed` handles aggregate history requests with additional validation:

1. Resolve the node and check historian availability (same as raw).
2. Validate that `AggregateType` is present in the `ReadProcessedDetails`. Return `BadAggregateListMismatch` if empty.
3. Map the requested aggregate to a result property via `MapAggregateToColumn`. Return `BadAggregateNotSupported` if unmapped.
4. Call `ReadAggregateAsync` with the time range, `ProcessingInterval`, and property name.
5. Return results in the same `HistoryData` / `ExtensionObject` format.

## Historizing Flag and AccessLevel

During variable node creation in `CreateAttributeVariable`, attributes with `IsHistorized == true` receive two additional settings:

```csharp
if (attr.IsHistorized)
    accessLevel |= AccessLevels.HistoryRead;
variable.Historizing = attr.IsHistorized;
```

- **`Historizing = true`** -- Tells OPC UA clients that this node has historical data available.
- **`AccessLevels.HistoryRead`** -- Enables the `HistoryRead` access bit on the node, which the OPC UA stack checks before routing history requests to the node manager override. Nodes without this bit set will be rejected by the framework before reaching `HistoryReadRawModified` or `HistoryReadProcessed`.

The `IsHistorized` flag originates from the Galaxy repository database query, which checks whether the attribute has Historian logging configured.