# Background Tasks (Task Manager)

## Principle

**All long-running operations use the Task Manager. SSE (Server-Sent Events) must not be used.**

---

## Flow

```
1. Client sends POST request
         │
         ▼
2. Handler creates task: taskManager.Submit(...)
         │
         ▼
3. Handler returns { "task_id": "uuid" }
         │
         ▼
4. Client polls GET /api/tasks/:id every 500ms
         │
         ▼
5. On completed/error — show toast notification
```

---

## Task Types

| Constant | Purpose |
|----------|---------|
| `TaskTypeRecalculate` | Recalculate all component prices |
| `TaskTypeStockImport` | Import stock file (.mxl/.xlsx) |
| `TaskTypePricelistCreate` | Create pricelist (estimate/warehouse/competitor) |

---

## Task Structure

```go
type Task struct {
    ID        string                 // Task UUID
    Type      TaskType               // Task type
    Status    TaskStatus             // running | completed | error
    Progress  int                    // 0-100
    Message   string                 // Current UI message
    Result    map[string]interface{} // Result when completed
    Error     string                 // Error text when error
    CreatedAt time.Time
    DoneAt    *time.Time
}
```

---

## Usage Example (Backend)

```go
taskID := h.taskManager.Submit(tasks.TaskTypeStockImport,
    func(ctx context.Context, progressCb func(int, string)) (map[string]interface{}, error) {
        progressCb(25, "Reading file")
        // ... work ...
        progressCb(75, "Saving to DB")
        return map[string]interface{}{
            "rows_total": 100,
            "inserted":   95,
        }, nil
    },
)
c.JSON(http.StatusOK, gin.H{"task_id": taskID})
```

---

## API

| Method | URL | Description |
|--------|-----|-------------|
| GET | `/api/tasks/:id` | Task status and result |

---

## Implementation

`internal/tasks/` — Task Manager: Submit, track, poll.