# Server API Package

This package contains the HTTP API server implementation for the Query Orchestration system, including REST endpoints, request handlers, and background processing workers.

## Overview

The `internal/server/api` package provides:
- HTTP server setup and configuration
- REST API endpoint handlers for document management
- Batch upload processing capabilities
- Background task processing for asynchronous operations
- Integration with AWS services (S3, SQS)
- Document lifecycle management

## Key Components

### 1. Server Setup (`listener.go`)
- Initializes the Echo HTTP server with middleware
- Configures authentication and authorization
- Sets up route handlers for API endpoints
- Initializes background task runners
- Manages server lifecycle and graceful shutdown

### 2. Document Handlers (`document_handler.go`)
- Handles individual document upload requests
- Validates document metadata
- Manages S3 storage operations
- Triggers document processing pipeline

### 3. Batch Processing (`batch_handler.go`)
- Manages ZIP file uploads containing multiple documents
- Creates batch records for tracking
- Queues batches for background processing
- Provides batch status and progress endpoints

### 4. Background Batch Worker (`batch_worker.go`)
The batch worker is a background task processor that handles asynchronous batch document processing.

## Batch Worker Architecture

### Purpose
The batch worker processes ZIP archives containing multiple documents that were uploaded through the batch upload API. It runs as a background task to avoid blocking the API response and to handle potentially long-running batch operations.

### How It Works

#### 1. **Task Scheduling**
- Runs periodically (configurable interval, default 30 seconds)
- Queries the database for unprocessed batches (status = "processing")
- Processes batches sequentially to manage resource usage

#### 2. **Batch Processing Flow**

```
ZIP Upload → S3 Storage → Batch Record → Background Worker → Document Processing
```

Detailed steps:

1. **Batch Discovery**
   - Worker queries `batch_uploads` table for batches with status "processing"
   - Retrieves batch metadata including S3 location of ZIP file

2. **ZIP Download**
   - Downloads the ZIP archive from S3 using batch's `archive_key`
   - Loads entire ZIP into memory for processing

3. **File Extraction & Processing**
   - Iterates through each file in the ZIP archive
   - For each file:
     - Skips directories and system files (`.DS_Store`, `__MACOSX/`)
     - Sanitizes filename to prevent path traversal attacks
     - Extracts file content
     - Uploads extracted file to S3 temporary directory
     - Validates file type (currently only PDFs supported)
     - Calls document upload handler to create document record
     - Document enters standard processing pipeline

4. **Progress Tracking**
   - Maintains counters for:
     - `processedCount`: Successfully processed documents
     - `failedCount`: Documents that failed processing
     - `invalidCount`: Documents with invalid file types
   - Updates batch progress in database after processing all files
   - Records failed filenames for troubleshooting

5. **Status Management**
   - Batch starts with "processing" status when created
   - Updates to "completed" if at least one document processed successfully
   - Updates to "failed" if no documents processed successfully
   - Can be "canceled" by user intervention

#### 3. **Configuration**
The worker receives configuration through a map containing:
- `ConfigKeyBatchService`: Service for batch database operations
- `ConfigKeyS3Client`: AWS S3 client for file operations
- `ConfigKeyBucket`: S3 bucket name for storage
- `ConfigKeyUploadHandler`: Function to handle individual document uploads

#### 4. **Error Handling**
- Individual file failures don't stop batch processing
- Failed files are logged and recorded in `failed_filenames`
- Batch marked as "failed" only if ZIP can't be downloaded or opened
- All errors logged with context for debugging

#### 5. **Security Considerations**
- Filename sanitization using `path.Base()` to prevent directory traversal
- File type validation (PDF only)
- Proper resource cleanup (file readers closed after use)
- Safe integer conversion with bounds checking

### Batch States

| Status | Description |
|--------|-------------|
| `processing` | Default state when batch created, being processed by worker |
| `completed` | At least one document processed successfully |
| `failed` | No documents processed successfully or critical error |
| `canceled` | Manually canceled by user |

### Integration Points

1. **Database**: 
   - Reads from `batch_uploads` table
   - Updates batch progress and status
   - Creates document records

2. **S3 Storage**:
   - Downloads ZIP archives
   - Uploads extracted files to temporary directories
   - Files organized by batch ID for traceability

3. **Document Pipeline**:
   - Processed documents enter standard pipeline
   - Associated with batch via `batch_id` foreign key
   - Follows normal document lifecycle (init → sync → clean → text extraction)

### Performance Considerations

- Processes one batch at a time to control resource usage
- ZIP files loaded entirely into memory (consider streaming for large files)
- Background processing prevents API blocking
- Configurable processing interval for load management

### Monitoring

The worker logs:
- Number of unprocessed batches found
- Processing start/completion for each batch
- Individual file processing results
- Error details for troubleshooting
- Final counts (processed/failed/invalid)

## API Endpoints

### Document Management
- `POST /clients/:clientId/documents` - Upload single document
- `GET /clients/:clientId/documents` - List client documents
- `GET /documents/:documentId` - Get document details

### Batch Operations
- `POST /clients/:clientId/documents/batches` - Upload ZIP batch
- `GET /clients/:clientId/documents/batches` - List client batches
- `GET /clients/:clientId/documents/batches/:batchId` - Get batch status
- `DELETE /clients/:clientId/documents/batches/:batchId` - Cancel batch

## Testing

The package includes comprehensive tests:
- Unit tests for individual handlers
- Integration tests with test containers
- Batch worker processing tests
- S3 operation mocking for isolated testing

## Dependencies

- Echo framework for HTTP server
- AWS SDK v2 for S3 operations
- PostgreSQL for data persistence
- Background task runner for async processing