Added JobRepository and JobServices

Readme.md

@@ -342,6 +342,71 @@ class ProcessingJob(BaseModel):
 4. TODO : Watchdog file monitoring implementation
 5. TODO : FastAPI integration and startup coordination
 
+## Job Management Layer
+
+### Repository Pattern Implementation
+
+The job management system follows the repository pattern for clean separation between data access and business logic.
+
+#### JobRepository
+
+Handles direct MongoDB operations for processing jobs:
+
+**CRUD Operations:**
+- `create_job()` - Create new processing job with automatic `created_at` timestamp
+- `get_job_by_id()` - Retrieve job by ObjectId
+- `update_job_status()` - Update job status with automatic timestamp management
+- `delete_job()` - Remove job from database
+- `get_jobs_by_file_id()` - Get all jobs for specific file
+- `get_jobs_by_status()` - Get jobs filtered by processing status
+
+**Automatic Timestamp Management:**
+- `created_at`: Set automatically during job creation
+- `started_at`: Set automatically when status changes to PROCESSING  
+- `completed_at`: Set automatically when status changes to COMPLETED or FAILED
+
+#### JobService
+
+Provides business logic layer with strict status transition validation:
+
+**Status Transition Methods:**
+- `mark_job_as_started()` - PENDING → PROCESSING
+- `mark_job_as_completed()` - PROCESSING → COMPLETED
+- `mark_job_as_failed()` - PROCESSING → FAILED
+
+**Validation Rules:**
+- Strict status transitions (invalid transitions raise exceptions)
+- Job existence verification before any operation
+- Automatic timestamp management through repository layer
+
+#### Custom Exceptions
+
+**JobNotFoundError**: Raised when job ID doesn't exist
+**InvalidStatusTransitionError**: Raised for invalid status transitions  
+**JobRepositoryError**: Raised for MongoDB operation failures
+
+#### Valid Status Transitions
+
+```
+PENDING → PROCESSING    (via mark_job_as_started)
+PROCESSING → COMPLETED  (via mark_job_as_completed)
+PROCESSING → FAILED     (via mark_job_as_failed)
+```
+
+All other transitions are forbidden and will raise `InvalidStatusTransitionError`.
+
+### File Structure
+
+```
+src/file-processor/app/
+├── database/repositories/
+│   └── job_repository.py           # JobRepository class
+├── services/  
+│   └── job_service.py             # JobService class
+└── exceptions/
+    └── job_exceptions.py          # Custom exceptions
+```
+
 ### Processing Pipeline Features
 
 - **Duplicate Detection**: SHA256 hashing prevents reprocessing same files