# Process Package Specification

## Overview

The Process package provides a robust system process handling system that matches Laravel's process functionality. It supports process execution, input/output handling, process pools, and signal handling while integrating with our Event and Queue packages.

> **Related Documentation**
> - See [Laravel Compatibility Roadmap](laravel_compatibility_roadmap.md) for implementation status
> - See [Foundation Integration Guide](foundation_integration_guide.md) for integration patterns
> - See [Testing Guide](testing_guide.md) for testing approaches
> - See [Getting Started Guide](getting_started.md) for development setup
> - See [Events Package Specification](events_package_specification.md) for process events
> - See [Queue Package Specification](queue_package_specification.md) for background processing

## Core Features

### 1. Process Manager

```dart
/// Core process manager implementation
class ProcessManager implements ProcessContract {
  /// Container instance
  final Container _container;
  
  /// Active processes
  final Map<int, Process> _processes = {};
  
  /// Process event dispatcher
  final EventDispatcherContract _events;
  
  ProcessManager(this._container, this._events);
  
  /// Starts a process
  Future<Process> start(
    String command, [
    List<String>? arguments,
    ProcessOptions? options
  ]) async {
    options ??= ProcessOptions();
    
    var process = await Process.start(
      command,
      arguments ?? [],
      workingDirectory: options.workingDirectory,
      environment: options.environment,
      includeParentEnvironment: options.includeParentEnvironment,
      runInShell: options.runInShell
    );
    
    _processes[process.pid] = process;
    await _events.dispatch(ProcessStarted(process));
    
    return process;
  }
  
  /// Runs a process to completion
  Future<ProcessResult> run(
    String command, [
    List<String>? arguments,
    ProcessOptions? options
  ]) async {
    var process = await start(command, arguments, options);
    var result = await process.exitCode;
    
    await _events.dispatch(ProcessCompleted(
      process,
      result
    ));
    
    return ProcessResult(
      process.pid,
      result,
      await _readOutput(process.stdout),
      await _readOutput(process.stderr)
    );
  }
  
  /// Kills a process
  Future<void> kill(int pid, [ProcessSignal signal = ProcessSignal.sigterm]) async {
    var process = _processes[pid];
    if (process == null) return;
    
    process.kill(signal);
    await _events.dispatch(ProcessKilled(process));
    _processes.remove(pid);
  }
  
  /// Gets active processes
  List<Process> get activeProcesses => List.from(_processes.values);
  
  /// Reads process output
  Future<String> _readOutput(Stream<List<int>> stream) async {
    var buffer = StringBuffer();
    await for (var data in stream) {
      buffer.write(String.fromCharCodes(data));
    }
    return buffer.toString();
  }
}
```

### 2. Process Pool

```dart
/// Process pool for parallel execution
class ProcessPool {
  /// Maximum concurrent processes
  final int concurrency;
  
  /// Process manager
  final ProcessManager _manager;
  
  /// Active processes
  final Set<Process> _active = {};
  
  /// Pending commands
  final Queue<PendingCommand> _pending = Queue();
  
  ProcessPool(this._manager, {this.concurrency = 5});
  
  /// Starts a process in the pool
  Future<ProcessResult> start(
    String command, [
    List<String>? arguments,
    ProcessOptions? options
  ]) async {
    var pending = PendingCommand(
      command,
      arguments,
      options
    );
    
    _pending.add(pending);
    await _processQueue();
    
    return await pending.future;
  }
  
  /// Processes pending commands
  Future<void> _processQueue() async {
    while (_active.length < concurrency && _pending.isNotEmpty) {
      var command = _pending.removeFirst();
      await _startProcess(command);
    }
  }
  
  /// Starts a process
  Future<void> _startProcess(PendingCommand command) async {
    var process = await _manager.start(
      command.command,
      command.arguments,
      command.options
    );
    
    _active.add(process);
    
    process.exitCode.then((result) {
      _active.remove(process);
      command.complete(ProcessResult(
        process.pid,
        result,
        '',
        ''
      ));
      _processQueue();
    });
  }
}
```

### 3. Process Events

```dart
/// Process started event
class ProcessStarted {
  /// The started process
  final Process process;
  
  ProcessStarted(this.process);
}

/// Process completed event
class ProcessCompleted {
  /// The completed process
  final Process process;
  
  /// Exit code
  final int exitCode;
  
  ProcessCompleted(this.process, this.exitCode);
}

/// Process killed event
class ProcessKilled {
  /// The killed process
  final Process process;
  
  ProcessKilled(this.process);
}

/// Process failed event
class ProcessFailed {
  /// The failed process
  final Process process;
  
  /// Error details
  final Object error;
  
  ProcessFailed(this.process, this.error);
}
```

### 4. Process Options

```dart
/// Process execution options
class ProcessOptions {
  /// Working directory
  final String? workingDirectory;
  
  /// Environment variables
  final Map<String, String>? environment;
  
  /// Include parent environment
  final bool includeParentEnvironment;
  
  /// Run in shell
  final bool runInShell;
  
  /// Process timeout
  final Duration? timeout;
  
  /// Idle timeout
  final Duration? idleTimeout;
  
  /// Retry attempts
  final int retryAttempts;
  
  /// Retry delay
  final Duration retryDelay;
  
  ProcessOptions({
    this.workingDirectory,
    this.environment,
    this.includeParentEnvironment = true,
    this.runInShell = false,
    this.timeout,
    this.idleTimeout,
    this.retryAttempts = 0,
    this.retryDelay = const Duration(seconds: 1)
  });
}
```

## Integration Examples

### 1. Basic Process Execution
```dart
// Run process
var result = await processManager.run('ls', ['-la']);
print('Output: ${result.stdout}');
print('Exit code: ${result.exitCode}');

// Start long-running process
var process = await processManager.start('server', ['--port=8080']);
await process.exitCode; // Wait for completion
```

### 2. Process Pool
```dart
// Create process pool
var pool = ProcessPool(processManager, concurrency: 3);

// Run multiple processes
await Future.wait([
  pool.start('task1'),
  pool.start('task2'),
  pool.start('task3'),
  pool.start('task4') // Queued until slot available
]);
```

### 3. Process Events
```dart
// Listen for process events
events.listen<ProcessStarted>((event) {
  print('Process ${event.process.pid} started');
});

events.listen<ProcessCompleted>((event) {
  print('Process ${event.process.pid} completed with code ${event.exitCode}');
});

// Start process
await processManager.start('long-task');
```

## Testing

```dart
void main() {
  group('Process Manager', () {
    test('runs processes', () async {
      var manager = ProcessManager(container, events);
      
      var result = await manager.run('echo', ['Hello']);
      
      expect(result.exitCode, equals(0));
      expect(result.stdout, contains('Hello'));
    });
    
    test('handles process failure', () async {
      var manager = ProcessManager(container, events);
      
      expect(
        () => manager.run('invalid-command'),
        throwsA(isA<ProcessException>())
      );
    });
  });
  
  group('Process Pool', () {
    test('limits concurrent processes', () async {
      var pool = ProcessPool(manager, concurrency: 2);
      var started = <String>[];
      
      events.listen<ProcessStarted>((event) {
        started.add(event.process.pid.toString());
      });
      
      await Future.wait([
        pool.start('task1'),
        pool.start('task2'),
        pool.start('task3')
      ]);
      
      expect(started.length, equals(3));
      expect(started.take(2).length, equals(2));
    });
  });
}
```

## Next Steps

1. Implement core process features
2. Add process pool
3. Add process events
4. Add retry handling
5. Write tests
6. Add benchmarks

## Development Guidelines

### 1. Getting Started
Before implementing process features:
1. Review [Getting Started Guide](getting_started.md)
2. Check [Laravel Compatibility Roadmap](laravel_compatibility_roadmap.md)
3. Follow [Testing Guide](testing_guide.md)
4. Use [Foundation Integration Guide](foundation_integration_guide.md)
5. Review [Events Package Specification](events_package_specification.md)
6. Review [Queue Package Specification](queue_package_specification.md)

### 2. Implementation Process
For each process feature:
1. Write tests following [Testing Guide](testing_guide.md)
2. Implement following Laravel patterns
3. Document following [Getting Started Guide](getting_started.md#documentation)
4. Integrate following [Foundation Integration Guide](foundation_integration_guide.md)

### 3. Quality Requirements
All implementations must:
1. Pass all tests (see [Testing Guide](testing_guide.md))
2. Meet Laravel compatibility requirements
3. Follow integration patterns (see [Foundation Integration Guide](foundation_integration_guide.md))
4. Support event integration (see [Events Package Specification](events_package_specification.md))
5. Support queue integration (see [Queue Package Specification](queue_package_specification.md))

### 4. Integration Considerations
When implementing process features:
1. Follow patterns in [Foundation Integration Guide](foundation_integration_guide.md)
2. Ensure Laravel compatibility per [Laravel Compatibility Roadmap](laravel_compatibility_roadmap.md)
3. Use testing approaches from [Testing Guide](testing_guide.md)
4. Follow development setup in [Getting Started Guide](getting_started.md)

### 5. Performance Guidelines
Process system must:
1. Handle concurrent processes efficiently
2. Manage system resources
3. Support process pooling
4. Scale with process count
5. Meet performance targets in [Laravel Compatibility Roadmap](laravel_compatibility_roadmap.md#performance-benchmarks)

### 6. Testing Requirements
Process tests must:
1. Cover all process operations
2. Test concurrent execution
3. Verify event handling
4. Check resource cleanup
5. Follow patterns in [Testing Guide](testing_guide.md)

### 7. Documentation Requirements
Process documentation must:
1. Explain process patterns
2. Show pool examples
3. Cover error handling
4. Include performance tips
5. Follow standards in [Getting Started Guide](getting_started.md#documentation)