# SignalR DataSource

Change-tracked real-time collection built on top of the SignalR transport layer. Source: `AyCode.Services.Server/SignalRs/AcSignalRDataSource.cs`.

> For the underlying transport (tag system, wire protocol, dispatch) see [`SIGNALR.md`](SIGNALR.md).

## Overview

`AcSignalRDataSource` is a generic `IList<T>` that synchronizes with the server via CRUD tags. It handles change tracking, rollback, sync state, and binary deserialization — so consuming code works with a regular list while the DataSource manages communication.

```csharp
AcSignalRDataSource<TDataItem, TId, TIList>
    where TDataItem : class, IId<TId>     // entity with ID
    where TId : struct                     // Guid, int, etc.
    where TIList : class, IList<TDataItem> // List<T> or AcObservableCollection<T>
```

Implements `IList<TDataItem>`, `IList`, `IReadOnlyList<TDataItem>`.

**Constructor:**

```csharp
new AcSignalRDataSource<T, TId, TIList>(
    AcSignalRClientBase signalRClient,   // transport client
    SignalRCrudTags crudTags,            // 5 tags for CRUD operations
    object[]? contextIds = null          // optional server-side filter context
)
```

## SignalRCrudTags

A `sealed class` that bundles **5 independent tag integers** — one per CRUD operation. Tags are NOT sequential offsets; each tag is independently assigned:

```csharp
public sealed class SignalRCrudTags(
    int getAllTag,
    int getItemTag,
    int addTag,
    int updateTag,
    int removeTag)
```

**Usage (consuming project):**

```csharp
// Tags are defined as independent constants in the project's tag class
public abstract class MyProjectTags : AcSignalRTags
{
    public const int OrderGetAll  = 300;
    public const int OrderGetItem = 301;
    public const int OrderAdd     = 302;
    public const int OrderUpdate  = 303;
    public const int OrderRemove  = 304;
    // Tags don't have to be sequential — they just happen to be here
}

// Construct with 5 explicit tags
var crudTags = new SignalRCrudTags(
    MyProjectTags.OrderGetAll,
    MyProjectTags.OrderGetItem,
    MyProjectTags.OrderAdd,
    MyProjectTags.OrderUpdate,
    MyProjectTags.OrderRemove
);
```

**Tag lookup:** `GetMessageTagByTrackingState(TrackingState)` maps tracking state to the corresponding tag via switch expression.

## Data Loading

```csharp
// Awaits full response via sync-wait transport pattern (polls up to 60s)
await dataSource.LoadDataSource();

// Async callback — requests SignalResponseDataMessage directly to avoid double deserialization
await dataSource.LoadDataSourceAsync();

// Load from raw response bytes (public — usable when response is already available)
await dataSource.LoadDataSourceFromResponseData(responseData, serializerType);

// Single item by ID — updates or adds to InnerList
await dataSource.LoadItem(id);
```

All load methods are `async Task`. `LoadDataSource` uses the sync-wait transport pattern (`GetAllAsync<T>` → polls for response), while `LoadDataSourceAsync` uses the async callback path (avoids deserializing `ResponseData` into a typed object — works directly with `byte[]`).

**Binary deserialization paths:**
- `AcObservableCollection<T>`: `BeginUpdate()` → `BinaryToMerge()` → `EndUpdate()` — single batched UI notification.
- `List<T>`: `BinaryTo(InnerList)` — direct populate.

**Context/Filtering:** `ContextIds` (object[]) and `FilterText` (string) are sent with every GetAll request for server-side filtering.

## Change Tracking

Each modified item is wrapped in `TrackingItem<TDataItem, TId>`:

| Field | Purpose |
|-------|---------|
| `TrackingState` | Add, Update, Remove |
| `CurrentValue` | Current item reference |
| `OriginalValue` | Clone for rollback (`JsonClone` or `ReflectionClone`) |

The `ChangeTracking<TDataItem, TId>` class manages the list of tracked items.

### CRUD Operations

```
Add(item):            → TrackingState.Add + InnerList.Add(item)
AddOrUpdate(item):    → exists? Update : Add (determines TrackingState automatically)
Insert(index, item):  → TrackingState.Add + InnerList.Insert(index, item)
Update(i, item):      → TrackingState.Update + clone original + InnerList[i] = item
Remove(id):           → TrackingState.Remove + clone original + InnerList.RemoveAt(index)
```

Each operation has an optional `autoSave` parameter — if true, immediately calls `SaveItem()` for that single change.

**Manual tracking:** `SetTrackingStateToUpdate(item)` marks an existing item as modified without replacing it — useful when properties are mutated in-place.

### Events

| Event | Signature | Fires when |
|-------|-----------|------------|
| `OnDataSourceItemChanged` | `Func<ItemChangedEventArgs<T>, Task>?` | After each item is saved or loaded (carries item + TrackingState) |
| `OnDataSourceLoaded` | `Func<Task>?` | After `LoadDataSource` / `LoadDataSourceAsync` completes |
| `OnSyncingStateChanged` | `Action<bool>?` | On 0→1 (true) and 1→0 (false) sync transitions |

## SaveChanges

Two variants with different transport patterns:

| Method | Returns | Transport pattern | Use case |
|--------|---------|-------------------|----------|
| `SaveChanges()` | `List<TrackingItem>` (remaining failures) | Sync-wait (`ContinueWith`) | When caller needs to know what failed |
| `SaveChangesAsync()` | `Task` (void) | Fire-and-forget callback (`Action`) | Background save, no result inspection |

```
Both follow the same flow:
  BeginSync()
  for each tracked item:
    tag = CrudTags.GetMessageTagByTrackingState(state)
    response = SignalRClient.PostDataAsync(tag, item)
    on success: remove from tracking, CopyTo InnerList item with server response
    on failure: TryRollbackItem() → restore OriginalValue
  EndSync()
```

**SaveItem(item, trackingState):** saves a single item (same flow). **SaveItem(id):** looks up tracking item by ID, then saves.

**Rollback:** `TryRollbackItem(id)` restores `OriginalValue` to `InnerList`. For `TrackingState.Add`: removes item entirely. For `Remove`: re-adds `OriginalValue`. Manual `Rollback()` reverts all tracked changes at once.

## Sync State

```csharp
private int _activeSyncOperations;  // Interlocked counter

BeginSync(): Interlocked.Increment → fires OnSyncingStateChanged(true) on 0→1
EndSync():   Interlocked.Decrement → fires OnSyncingStateChanged(false) on 1→0
IsSyncing:   _activeSyncOperations > 0
```

UI binds to `IsSyncing` to show loading indicators. The counter supports nested sync operations.

## Working Reference List

Allows an external list to become the DataSource's inner storage:

```csharp
dataSource.SetWorkingReferenceList(externalList);
// Now dataSource operates directly on externalList — same reference, no copy

// Read back the current inner list reference
TIList innerList = dataSource.GetReferenceInnerList();
```

This is useful when the UI already has a bound collection and you want the DataSource to manage it in-place. `HasWorkingReferenceList` indicates whether an external list has been set.

## Locking Strategy

| Lock | Scope | Used by |
|------|-------|---------|
| `object _syncRoot` | Synchronous | Count, Contains, IndexOf, GetEnumerator |
| `SemaphoreSlim _asyncLock` | Asynchronous | Add/Update/Remove with save, LoadDataSource |

`GetEnumerator()` returns `InnerList.ToList().GetEnumerator()` — safe copy to avoid mutation during iteration.

## Relationship to Transport

The DataSource is a **consumer** of the SignalR transport, not part of it. The flow:

```
DataSource.SaveChanges()
  → CrudTags.GetMessageTagByTrackingState(state) → tag
  → AcSignalRClientBase.PostDataAsync(tag, item)     ← transport layer
  → OnReceiveMessage(tag, bytes, requestId)           ← wire protocol
  → Server method with [SignalR(tag)]                 ← tag dispatch
```

Projects can also call the transport directly without DataSource — see [`SIGNALR.md` § How Projects Use Tags](SIGNALR.md#how-projects-use-tags).

## Key Source Files

| Component | Path |
|-----------|------|
| DataSource | `AyCode.Services.Server/SignalRs/AcSignalRDataSource.cs` |
| CRUD tags | `AyCode.Services/SignalRs/SignalRCrudTags.cs` |
| Tracking helpers | `AyCode.Services.Server/SignalRs/TrackingItemHelpers.cs` |
| Transport client | `AyCode.Services/SignalRs/AcSignalRClientBase.cs` |
| Transport doc | [`docs/SIGNALR.md`](SIGNALR.md) |