cannaiq/backend/docs/WORKER_TASK_ARCHITECTURE.md

# Worker Task Architecture

This document describes the unified task-based worker system that replaces the legacy fragmented job systems.

## Overview

The task worker architecture provides a single, unified system for managing all background work in CannaiQ:

- **Store discovery** - Find new dispensaries on platforms
- **Entry point discovery** - Resolve platform IDs from menu URLs
- **Product discovery** - Initial product fetch for new stores
- **Product resync** - Regular price/stock updates for existing stores
- **Analytics refresh** - Refresh materialized views and analytics

## Architecture

### Database Tables

**`worker_tasks`** - Central task queue
```sql
CREATE TABLE worker_tasks (
  id SERIAL PRIMARY KEY,
  role task_role NOT NULL,           -- What type of work
  dispensary_id INTEGER,              -- Which store (if applicable)
  platform VARCHAR(50),               -- Which platform (dutchie, etc.)
  status task_status DEFAULT 'pending',
  priority INTEGER DEFAULT 0,         -- Higher = process first
  scheduled_for TIMESTAMP,            -- Don't process before this time
  worker_id VARCHAR(100),             -- Which worker claimed it
  claimed_at TIMESTAMP,
  started_at TIMESTAMP,
  completed_at TIMESTAMP,
  last_heartbeat_at TIMESTAMP,        -- For stale detection
  result JSONB,                       -- Output from handler
  error_message TEXT,
  retry_count INTEGER DEFAULT 0,
  max_retries INTEGER DEFAULT 3,
  created_at TIMESTAMP DEFAULT NOW(),
  updated_at TIMESTAMP DEFAULT NOW()
);
```

**Key indexes:**
- `idx_worker_tasks_pending_priority` - For efficient task claiming
- `idx_worker_tasks_active_dispensary` - Prevents concurrent tasks per store (partial unique index)

### Task Roles

| Role | Purpose | Per-Store | Scheduled |
|------|---------|-----------|-----------|
| `store_discovery` | Find new stores on a platform | No | Daily |
| `entry_point_discovery` | Resolve platform IDs | Yes | On-demand |
| `product_discovery` | Initial product fetch | Yes | After entry_point |
| `product_resync` | Price/stock updates | Yes | Every 4 hours |
| `analytics_refresh` | Refresh MVs | No | Daily |

### Task Lifecycle

```
pending → claimed → running → completed
                  ↓
                failed
```

1. **pending** - Task is waiting to be picked up
2. **claimed** - Worker has claimed it (atomic via SELECT FOR UPDATE SKIP LOCKED)
3. **running** - Worker is actively processing
4. **completed** - Task finished successfully
5. **failed** - Task encountered an error
6. **stale** - Task lost its worker (recovered automatically)

## Files

### Core Files

| File | Purpose |
|------|---------|
| `src/tasks/task-service.ts` | TaskService - CRUD, claiming, capacity metrics |
| `src/tasks/task-worker.ts` | TaskWorker - Main worker loop |
| `src/tasks/index.ts` | Module exports |
| `src/routes/tasks.ts` | API endpoints |
| `migrations/074_worker_task_queue.sql` | Database schema |

### Task Handlers

| File | Role |
|------|------|
| `src/tasks/handlers/store-discovery.ts` | `store_discovery` |
| `src/tasks/handlers/entry-point-discovery.ts` | `entry_point_discovery` |
| `src/tasks/handlers/product-discovery.ts` | `product_discovery` |
| `src/tasks/handlers/product-resync.ts` | `product_resync` |
| `src/tasks/handlers/analytics-refresh.ts` | `analytics_refresh` |

## Running Workers

### Environment Variables

| Variable | Default | Description |
|----------|---------|-------------|
| `WORKER_ROLE` | (required) | Which task role to process |
| `WORKER_ID` | auto-generated | Custom worker identifier |
| `POLL_INTERVAL_MS` | 5000 | How often to check for tasks |
| `HEARTBEAT_INTERVAL_MS` | 30000 | How often to update heartbeat |

### Starting a Worker

```bash
# Start a product resync worker
WORKER_ROLE=product_resync npx tsx src/tasks/task-worker.ts

# Start with custom ID
WORKER_ROLE=product_resync WORKER_ID=resync-1 npx tsx src/tasks/task-worker.ts

# Start multiple workers for different roles
WORKER_ROLE=store_discovery npx tsx src/tasks/task-worker.ts &
WORKER_ROLE=product_resync npx tsx src/tasks/task-worker.ts &
```

### Kubernetes Deployment

```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: task-worker-resync
spec:
  replicas: 3
  template:
    spec:
      containers:
      - name: worker
        image: code.cannabrands.app/creationshop/dispensary-scraper:latest
        command: ["npx", "tsx", "src/tasks/task-worker.ts"]
        env:
        - name: WORKER_ROLE
          value: "product_resync"
```

## API Endpoints

### Task Management

| Endpoint | Method | Description |
|----------|--------|-------------|
| `/api/tasks` | GET | List tasks with filters |
| `/api/tasks` | POST | Create a new task |
| `/api/tasks/:id` | GET | Get task by ID |
| `/api/tasks/counts` | GET | Get counts by status |
| `/api/tasks/capacity` | GET | Get capacity metrics |
| `/api/tasks/capacity/:role` | GET | Get role-specific capacity |
| `/api/tasks/recover-stale` | POST | Recover tasks from dead workers |

### Task Generation

| Endpoint | Method | Description |
|----------|--------|-------------|
| `/api/tasks/generate/resync` | POST | Generate daily resync tasks |
| `/api/tasks/generate/discovery` | POST | Create store discovery task |

### Migration (from legacy systems)

| Endpoint | Method | Description |
|----------|--------|-------------|
| `/api/tasks/migration/status` | GET | Compare old vs new systems |
| `/api/tasks/migration/disable-old-schedules` | POST | Disable job_schedules |
| `/api/tasks/migration/cancel-pending-crawl-jobs` | POST | Cancel old crawl jobs |
| `/api/tasks/migration/create-resync-tasks` | POST | Create tasks for all stores |
| `/api/tasks/migration/full-migrate` | POST | One-click migration |

### Role-Specific Endpoints

| Endpoint | Method | Description |
|----------|--------|-------------|
| `/api/tasks/role/:role/last-completion` | GET | Last completion time |
| `/api/tasks/role/:role/recent` | GET | Recent completions |
| `/api/tasks/store/:id/active` | GET | Check if store has active task |

## Capacity Planning

The `v_worker_capacity` view provides real-time metrics:

```sql
SELECT * FROM v_worker_capacity;
```

Returns:
- `pending_tasks` - Tasks waiting to be claimed
- `ready_tasks` - Tasks ready now (scheduled_for is null or past)
- `claimed_tasks` - Tasks claimed but not started
- `running_tasks` - Tasks actively processing
- `completed_last_hour` - Recent completions
- `failed_last_hour` - Recent failures
- `active_workers` - Workers with recent heartbeats
- `avg_duration_sec` - Average task duration
- `tasks_per_worker_hour` - Throughput estimate
- `estimated_hours_to_drain` - Time to clear queue

### Scaling Recommendations

```javascript
// API: GET /api/tasks/capacity/:role
{
  "role": "product_resync",
  "pending_tasks": 500,
  "active_workers": 3,
  "workers_needed": {
    "for_1_hour": 10,
    "for_4_hours": 3,
    "for_8_hours": 2
  }
}
```

## Task Chaining

Tasks can automatically create follow-up tasks:

```
store_discovery → entry_point_discovery → product_discovery
                              ↓
                     (store has platform_dispensary_id)
                              ↓
                     Daily resync tasks
```

The `chainNextTask()` method handles this automatically.

## Stale Task Recovery

Tasks are considered stale if `last_heartbeat_at` is older than the threshold (default 10 minutes).

```sql
SELECT recover_stale_tasks(10); -- 10 minute threshold
```

Or via API:
```bash
curl -X POST /api/tasks/recover-stale \
  -H 'Content-Type: application/json' \
  -d '{"threshold_minutes": 10}'
```

## Migration from Legacy Systems

### Legacy Systems Replaced

1. **job_schedules + job_run_logs** - Scheduled job definitions
2. **dispensary_crawl_jobs** - Per-dispensary crawl queue
3. **SyncOrchestrator + HydrationWorker** - Raw payload processing

### Migration Steps

**Option 1: One-Click Migration**
```bash
curl -X POST /api/tasks/migration/full-migrate
```

This will:
1. Disable all job_schedules
2. Cancel pending dispensary_crawl_jobs
3. Generate resync tasks for all stores
4. Create discovery and analytics tasks

**Option 2: Manual Migration**
```bash
# 1. Check current status
curl /api/tasks/migration/status

# 2. Disable old schedules
curl -X POST /api/tasks/migration/disable-old-schedules

# 3. Cancel pending crawl jobs
curl -X POST /api/tasks/migration/cancel-pending-crawl-jobs

# 4. Create resync tasks
curl -X POST /api/tasks/migration/create-resync-tasks \
  -H 'Content-Type: application/json' \
  -d '{"state_code": "AZ"}'

# 5. Generate daily resync schedule
curl -X POST /api/tasks/generate/resync \
  -H 'Content-Type: application/json' \
  -d '{"batches_per_day": 6}'
```

## Per-Store Locking

The system prevents concurrent tasks for the same store using a partial unique index:

```sql
CREATE UNIQUE INDEX idx_worker_tasks_active_dispensary
ON worker_tasks (dispensary_id)
WHERE dispensary_id IS NOT NULL
AND status IN ('claimed', 'running');
```

This ensures only one task can be active per store at any time.

## Task Priority

Tasks are claimed in priority order (higher first), then by creation time:

```sql
ORDER BY priority DESC, created_at ASC
```

Default priorities:
- `store_discovery`: 0
- `entry_point_discovery`: 10 (high - new stores)
- `product_discovery`: 10 (high - new stores)
- `product_resync`: 0
- `analytics_refresh`: 0

## Scheduled Tasks

Tasks can be scheduled for future execution:

```javascript
await taskService.createTask({
  role: 'product_resync',
  dispensary_id: 123,
  scheduled_for: new Date('2025-01-10T06:00:00Z'),
});
```

The `generate_resync_tasks()` function creates staggered tasks throughout the day:

```sql
SELECT generate_resync_tasks(6, '2025-01-10'); -- 6 batches = every 4 hours
```

## Dashboard Integration

The admin dashboard shows task queue status in the main overview:

```
Task Queue Summary
------------------
Pending:   45
Running:   3
Completed: 1,234
Failed:    12
```

Full task management is available at `/admin/tasks`.

## Error Handling

Failed tasks include the error message in `error_message` and can be retried:

```sql
-- View failed tasks
SELECT id, role, dispensary_id, error_message, retry_count
FROM worker_tasks
WHERE status = 'failed'
ORDER BY completed_at DESC
LIMIT 20;

-- Retry failed tasks
UPDATE worker_tasks
SET status = 'pending', retry_count = retry_count + 1
WHERE status = 'failed' AND retry_count < max_retries;
```

## Monitoring

### Logs

Workers log to stdout:
```
[TaskWorker] Starting worker worker-product_resync-a1b2c3d4 for role: product_resync
[TaskWorker] Claimed task 123 (product_resync) for dispensary 456
[TaskWorker] Task 123 completed successfully
```

### Health Check

Check if workers are active:
```sql
SELECT worker_id, role, COUNT(*), MAX(last_heartbeat_at)
FROM worker_tasks
WHERE last_heartbeat_at > NOW() - INTERVAL '5 minutes'
GROUP BY worker_id, role;
```

### Metrics

```sql
-- Tasks by status
SELECT status, COUNT(*) FROM worker_tasks GROUP BY status;

-- Tasks by role
SELECT role, status, COUNT(*) FROM worker_tasks GROUP BY role, status;

-- Average duration by role
SELECT role, AVG(EXTRACT(EPOCH FROM (completed_at - started_at))) as avg_seconds
FROM worker_tasks
WHERE status = 'completed' AND completed_at > NOW() - INTERVAL '24 hours'
GROUP BY role;
```