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DatTT127
363
AGENT_SKILL/design_pattern_compliance/EXAMPLES.md
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363
AGENT_SKILL/design_pattern_compliance/EXAMPLES.md
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# Examples: design_pattern_compliance
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## Correct Examples
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### Layered Architecture (Python/FastAPI)
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```python
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# GOOD: Proper layer separation
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# presentation layer (api/patients.py)
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from fastapi import APIRouter, Depends, HTTPException
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from services.patient_service import PatientService
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from models.patient import PatientResponse
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router = APIRouter(prefix="/patients", tags=["patients"])
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def get_patient_service() -> PatientService:
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# Dependency injection - could come from a DI container
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return PatientService(
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repository=PatientRepository() # In practice, this would be injected
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)
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@router.get("/{patient_id}", response_model=PatientResponse)
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def get_patient(
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patient_id: str,
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service: PatientService = Depends(get_patient_service)
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):
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"""Controller handles only HTTP concerns."""
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patient = service.get_patient_by_id(patient_id)
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if not patient:
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raise HTTPException(status_code=404, detail="Patient not found")
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return patient
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# service layer (services/patient_service.py)
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from repositories.patient_repository import PatientRepository
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from models.patient import PatientModel
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class PatientService:
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def __init__(self, repository: PatientRepository):
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self.repository = repository # Dependency injected
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def get_patient_by_id(self, patient_id: str) -> Optional[PatientModel]:
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# Business logic lives here
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return self.repository.get_by_id(patient_id)
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# data access layer (repositories/patient_repository.py)
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from models.patient import PatientModel
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class PatientRepository:
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def get_by_id(self, patient_id: str) -> Optional[PatientModel]:
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# Data access concerns only
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# In real implementation, this would query a database
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pass
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```
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### Dependency Injection with Interfaces
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```python
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# GOOD: Interface-based dependencies
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from abc import ABC, abstractmethod
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from typing import Protocol
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# Define interface (protocol)
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class PatientRepository(Protocol):
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def get_by_id(self, patient_id: str) -> Optional[PatientModel]: ...
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def save(self, patient: PatientModel) -> bool: ...
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# Concrete implementation
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class PostgreSQLPatientRepository:
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def __init__(self, connection_string: str):
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self.connection_string = connection_string
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def get_by_id(self, patient_id: str) -> Optional[PatientModel]:
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# Implementation details
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pass
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# Service depends on interface, not concrete class
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class PatientService:
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def __init__(self, repository: PatientRepository): # Accepts any implementation
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self.repository = repository
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def get_patient(self, patient_id: str) -> Optional[PatientModel]:
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return self.repository.get_by_id(patient_id)
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# Usage with dependency injection
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def get_patient_service() -> PatientService:
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repo = PostgreSQLPatientRepository(os.getenv("DB_CONNECTION"))
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return PatientService(repository)
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```
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### Frontend Zustand Store
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```javascript
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// GOOD: Proper Zustand store usage
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import { create } from 'zustand';
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// Patient store slice
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const usePatientStore = create((set, get) => ({
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// State
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patients: [],
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loading: false,
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error: null,
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// Actions
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setPatients: (patients) => set({ patients }),
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fetchPatients: async () => {
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set({ loading: true, error: null });
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try {
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const response = await api.getPatients();
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set({ patients: response.data, loading: false });
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} catch (err) {
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set({ error: err.message, loading: false });
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}
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},
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addPatient: (patient) => set((state) => ({
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patients: [...state.patients, patient],
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loading: false,
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error: null
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})),
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}));
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// Component using store - ONLY for UI state
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import { useState } from 'react';
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import { usePatientStore } from '../store/patientStore';
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export const PatientForm: React.FC = () => {
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// LOCAL UI state only - correct use of useState
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const [name, setName] = useState('');
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const [dob, setDob] = useState('');
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const [submitting, setSubmitting] = useState(false);
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// GLOBAL state from store
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const { patients, loading, error, addPatient } = usePatientStore();
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const handleSubmit = async (e) => {
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e.preventDefault();
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setSubmitting(true);
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try {
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await addPatient({ id: Date.now(), name, dob });
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setName('');
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setDob('');
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} finally {
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setSubmitting(false);
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}
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};
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return (
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<form onSubmit={handleSubmit}>
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{/* Form fields using local state */}
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<input value={name} onChange={(e) => setName(e.target.value)} placeholder="Name" />
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<input value={dob} onChange={(e) => setDob(e.target.value)} placeholder="Date of Birth" />
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<button type="submit" disabled={submitting}>
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{submitting ? 'Adding...' : 'Add Patient'}
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</button>
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{/* Displaying global state */}
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{loading && <p>Saving...</p>}
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{error && <p>Error: {error}</p>}
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</form>
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);
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};
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```
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### Infrastructure as Code (Terraform)
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```hcl
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# GOOD: Proper Terraform practices
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terraform {
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# REQUIRED: Remote backend
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backend "gcs" {
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bucket = "vkist-terraform-state"
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prefix = "env/${var.environment}"
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}
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# REQUIRED: Versioned providers
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required_providers {
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google = {
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source = "hashicorp/google"
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version = "~> 4.0"
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}
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}
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}
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variable "environment" {
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description = "Deployment environment"
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type = string
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validation {
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condition = ["dev", "staging", "prod"].contains(var.upper)
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error_message = "Environment must be either dev, staging, or prod."
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}
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}
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# RESOURCE NAMING with environment
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resource "google_compute_instance" "vm" {
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name = "vkist-${var.environment}-backend"
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machine_type = "e2-medium"
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# ... other configuration
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}
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# LEAST PRIVILEGE IAM
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resource "google_service_account" "backend" {
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account_id = "vkist-backend-${var.environment}"
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display_name = "VKIST Backend Service Account"
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}
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# Grant only necessary roles
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resource "google_project_iam_member" "storage_reader" {
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role = "roles/storage.objectViewer"
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member = "serviceAccount:${google_service_account.backend.email}"
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}
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# VERSIONED MODULES
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module "network" {
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source = "terraform-google-modules/network/google"
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version = "~> 5.0"
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project_id = var.project_id
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network_name = "vkist-${var.environment}-net"
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# ... other parameters
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}
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```
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### Dependency Pinning
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```txt
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# GOOD: requirements.txt with exact versions
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fastapi==0.104.1
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uvicorn[standard]==0.24.0
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pydantic==2.5.0
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sqlalchemy==2.0.23
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alembic==1.13.1
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python-multipart==0.0.6
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```
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```json
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// GOOD: package.json with package-lock.json
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{
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"name": "vkist-frontend",
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"version": "1.0.0",
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"dependencies": {
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"react": "^18.2.0",
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"react-dom": "^18.2.0",
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"zustand": "^4.4.1",
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"axios": "^1.6.2"
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}
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}
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// package-lock.json ensures exact versions are installed
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```
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## Incorrect Examples (to avoid)
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### Layer Violation
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```python
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# BAD: Controller directly accessing repository (skipping service layer)
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from fastapi import APIRouter, Depends
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from repositories.patient_repository import PatientRepository
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router = APIRouter()
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@router.get("/patients/{id}")
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def get_patient(patient_id: str, repo: PatientRepository = Depends()):
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# VIOLATION: Presentation layer accessing data layer directly
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return repo.get_by_id(patient_id)
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```
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### Direct Infrastructure Instantiation
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```python
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# BAD: Service creating its own database connection
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import psycopg2
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import os
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class PatientService:
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def __init__(self):
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# VIOLATION: Direct instantiation of infrastructure
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self.conn = psycopg2.connect(
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host=os.getenv("DB_HOST"),
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database=os.getenv("DB_NAME"),
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user=os.getenv("DB_USER"),
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password=os.getenv("DB_PASSWORD")
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)
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def get_patient(self, patient_id: str):
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cursor = self.conn.cursor()
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cursor.execute("SELECT * FROM patients WHERE id = %s", (patient_id,))
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return cursor.fetchone()
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```
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### Frontend Anti-pattern: State in Components
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```javascript
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// BAD: Using useState for shared data that should be in store
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import { useState, useEffect } from 'react';
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import { fetchPatients } from '../api/patientApi';
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export const PatientList: React.FC = () => {
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// WRONG: This state is shared and should be in a store
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const [patients, setPatients] = useState([]);
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const [loading, setLoading] = useState(false);
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useEffect(() => {
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const loadPatients = async () => {
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setLoading(true);
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try {
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const data = await fetchPatients();
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setPatients(data); // This state might be needed by other components
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setLoading(false);
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} catch (err) {
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setError(err.message);
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setLoading(false);
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}
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};
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loadPatients();
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}, []);
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// ... render logic
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};
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// If another component needs patients data, it would have to fetch again
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// or receive it via props - inefficient and not scalable
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```
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### Infrastructure Mistakes
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```hcl
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# BAD: Local state storage (should be remote)
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terraform {
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# MISSING: backend configuration
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# state will be stored locally - VIOLATION
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}
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# BAD: Hard-coded environment (should be variable)
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resource "google_compute_network" "vpc" {
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name = "vkist-prod-network" # What if we want to deploy to staging?
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}
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# BAD: Overly permissive IAM
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resource "google_project_iam_member" "admin" {
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role = "roles/editor" # Too permissive - VIOLATION of least privilege
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member = "user:admin@example.com"
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}
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# BAD: Unpinned module version
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module "network" {
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source = "terraform-google-modules/network/google"
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# MISSING: version parameter - could get breaking changes on next run
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}
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```
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### Dependency Issues
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```txt
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# BAD: Unpinned dependencies in requirements.txt
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fastapi
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uvicorn
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pydantic
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# Any of these could break on next pip install
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```
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```json
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// BAD: Missing or outdated lock file
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{
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"name": "my-app",
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"dependencies": {
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"lodash": "^4.17.21"
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// No package-lock.json - versions not locked
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}
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}
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```
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