직접 만드는 CRUD — 모든 개념을 하나의 서비스에

# Capstone scaffold — 뼈에 ~80 줄
import hashlib, json, secrets, time, uuid
from datetime import datetime, timezone
from fastapi import FastAPI, HTTPException, Response, Header, status, Depends
from fastapi.middleware.cors import CORSMiddleware
from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials
from pydantic import BaseModel, Field

app = FastAPI(title='Items API', version='1.0.0')
app.add_middleware(
    CORSMiddleware,
    allow_origins=['http://localhost:5173'],
    allow_credentials=True, allow_methods=['*'], allow_headers=['*'],
)
bearer = HTTPBearer()
TOKENS = {'tok_valid_xyz': 'u_42'}

class Item(BaseModel):
    id: str = Field(..., pattern='^itm_')
    name: str
    description: str | None = None
    version: int

_ITEMS: dict[str, dict] = {}
_JOBS: dict[str, dict] = {}

def compute_etag(d: dict) -> str:
    body = json.dumps(d, sort_keys=True, separators=(',', ':')).encode()
    return f'"{hashlib.sha256(body).hexdigest()[:12]}"'

async def current_user(creds: HTTPAuthorizationCredentials = Depends(bearer)):
    uid = TOKENS.get(creds.credentials)
    if not uid:
        raise HTTPException(401, detail='invalid token',
                            headers={'WWW-Authenticate': 'Bearer'})
    return uid

@app.post('/items', status_code=201)
async def create_item(payload: dict, response: Response, uid=Depends(current_user)):
    item_id = 'itm_' + secrets.token_urlsafe(8)
    item = {'id': item_id, 'version': 1, **payload}
    _ITEMS[item_id] = item
    response.headers['Location'] = f'/items/{item_id}'
    response.headers['ETag']     = compute_etag(item)
    return item

# ... GET / PUT / PATCH / DELETE / cursor pagination / action / async 계속
#     (full 빌드 위해 연습 봐)

# Optimistic update + conditional GET 조합 (더 어려운 절반)
from fastapi import Header

@app.get('/items/{item_id}')
async def read_item(item_id: str, response: Response,
                    if_none_match: str | None = Header(None, alias='If-None-Match'),
                    uid=Depends(current_user)):
    item = _ITEMS.get(item_id)
    if not item:
        raise HTTPException(404)
    etag = compute_etag(item)
    response.headers['ETag'] = etag
    response.headers['Cache-Control'] = 'private, max-age=60, must-revalidate'
    response.headers['Vary'] = 'Authorization'
    if if_none_match == etag:
        response.status_code = 304
        return None
    return item

@app.put('/items/{item_id}')
async def replace_item(item_id: str, payload: dict, response: Response,
                       if_match: str | None = Header(None, alias='If-Match'),
                       uid=Depends(current_user)):
    existing = _ITEMS.get(item_id)
    if not existing:
        raise HTTPException(404)
    current_etag = compute_etag(existing)
    if if_match and if_match != current_etag:
        raise HTTPException(412, detail='ETag 불일치; refetch 후 재시도')
    new = {**existing, **payload, 'version': existing['version'] + 1}
    _ITEMS[item_id] = new
    response.headers['ETag'] = compute_etag(new)
    return new

# 모든 요구사항에 대해 capstone 검증

# Create 가 201 + Location 돌려줌
curl -i -X POST http://localhost:8000/items -H 'Authorization: Bearer tok_valid_xyz' \
  -H 'Content-Type: application/json' -d '{"name":"first"}'

# Response 에서 ETag 저장
ETAG=$(curl -s -i http://localhost:8000/items/itm_xyz -H 'Authorization: Bearer tok_valid_xyz' | grep -i etag | awk '{print $2}' | tr -d '\r')

# Conditional GET — current ETag 면 304
curl -i http://localhost:8000/items/itm_xyz -H 'Authorization: Bearer tok_valid_xyz' -H "If-None-Match: $ETAG"

# Optimistic update — stale ETag 면 412
curl -i -X PUT http://localhost:8000/items/itm_xyz -H 'Authorization: Bearer tok_valid_xyz' \
  -H 'Content-Type: application/json' -H 'If-Match: "v99-stale"' -d '{"name":"updated"}'

# OpenAPI / Swagger UI 가용
open http://localhost:8000/docs