# Enhanced Signal Handling for Scheduled Operations

## Overview

The enhanced signal handling system provides intelligent cancellation support for scheduled price update operations. It distinguishes between different phases of execution and responds appropriately to interrupt signals (SIGINT/SIGTERM).

## Features

### 1. Phase-Aware Cancellation

The system recognizes three distinct phases:

- **Scheduling Wait Period**: Cancellation is allowed and encouraged
- **Price Update Operations**: Cancellation is prevented to avoid data corruption
- **Normal Operations**: Standard graceful shutdown behavior

### 2. Clear User Feedback

When users press Ctrl+C during different phases, they receive clear, contextual messages:

#### During Scheduling Wait Period

```
🛑 Received SIGINT during scheduled wait period.
📋 Cancelling scheduled operation...
✅ Scheduled operation cancelled successfully. No price updates were performed.
```

#### During Price Update Operations

```
⚠️  Received SIGINT during active price update operations.
🔒 Cannot cancel while price updates are in progress to prevent data corruption.
⏳ Please wait for current operations to complete...
💡 Tip: You can cancel during the countdown period before operations begin.
```

### 3. State Coordination

The system uses state management to coordinate between the main application and the ScheduleService:

- `schedulingActive`: Indicates if the system is in the scheduling wait period
- `operationInProgress`: Indicates if price update operations are running

## Implementation Details

### Main Application Signal Handlers

Located in `src/index.js`, the enhanced signal handlers:

1. Check the current phase (scheduling vs. operations)
2. Provide appropriate user feedback
3. Coordinate with the ScheduleService for cleanup
4. Prevent interruption during critical operations

### ScheduleService Integration

The `ScheduleService` (`src/services/schedule.js`) has been updated to:

1. Remove its own signal handling (delegated to main application)
2. Support external cancellation through the `cleanup()` method
3. Provide proper resource cleanup and state management

### State Management Functions

The main application provides state management functions to the ShopifyPriceUpdater instance:

- `setSchedulingActive(boolean)`: Updates scheduling phase state
- `setOperationInProgress(boolean)`: Updates operation phase state

## Usage Examples

### Scheduled Operation with Cancellation

```bash
# Set scheduled execution time
export SCHEDULED_EXECUTION_TIME="2025-08-07T15:30:00"

# Run the application
npm start

# During countdown, press Ctrl+C to cancel
# Result: Clean cancellation with confirmation message
```

### Scheduled Operation During Updates

```bash
# Same setup, but let the countdown complete
# Once price updates begin, press Ctrl+C
# Result: Cancellation is prevented with explanation
```

## Testing

The enhanced signal handling is thoroughly tested in:

- `tests/services/schedule-signal-handling.test.js`: Unit tests for all requirements
- Tests cover all three requirements:
  - 3.1: Cancellation during wait period
  - 3.2: Clear cancellation confirmation messages
  - 3.3: No interruption once operations begin

## Requirements Compliance

### Requirement 3.1: Cancellation Support

✅ **IMPLEMENTED**: System responds to SIGINT and SIGTERM during wait period

### Requirement 3.2: Clear Confirmation Messages

✅ **IMPLEMENTED**: Contextual messages inform users about cancellation status

### Requirement 3.3: Operation Protection

✅ **IMPLEMENTED**: Price updates cannot be interrupted to prevent data corruption

## Benefits

1. **Data Integrity**: Prevents partial updates that could corrupt pricing data
2. **User Experience**: Clear feedback about what's happening and what's possible
3. **Flexibility**: Users can cancel during planning phase but not during execution
4. **Reliability**: Proper resource cleanup and state management