🎉 Initial commit: QQuiz - 智能刷题与题库管理平台

## 功能特性

✅ **核心功能**
- 多文件上传与智能去重（基于 content_hash）
- 异步文档解析（支持 TXT/PDF/DOCX/XLSX）
- AI 智能题目提取与评分（OpenAI/Anthropic/Qwen）
- 断点续做与进度管理
- 自动错题本收集

✅ **技术栈**
- Backend: FastAPI + SQLAlchemy 2.0 + PostgreSQL
- Frontend: React 18 + Vite + Tailwind CSS
- Deployment: Docker Compose

✅ **项目结构**
- 53 个文件
- 完整的前后端分离架构
- Docker/源码双模部署支持

🚀 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/utils.py

@@ -0,0 +1,83 @@
+"""
+Utility functions
+"""
+import hashlib
+import re
+from datetime import datetime, timedelta
+from typing import Optional
+from jose import JWTError, jwt
+from passlib.context import CryptContext
+import os
+
+# Password hashing
+pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+
+# JWT settings
+SECRET_KEY = os.getenv("SECRET_KEY", "your-secret-key-change-this")
+ALGORITHM = "HS256"
+ACCESS_TOKEN_EXPIRE_MINUTES = 60 * 24 * 7  # 7 days
+
+
+def hash_password(password: str) -> str:
+    """Hash a password"""
+    return pwd_context.hash(password)
+
+
+def verify_password(plain_password: str, hashed_password: str) -> bool:
+    """Verify a password against a hash"""
+    return pwd_context.verify(plain_password, hashed_password)
+
+
+def create_access_token(data: dict, expires_delta: Optional[timedelta] = None) -> str:
+    """Create a JWT access token"""
+    to_encode = data.copy()
+    if expires_delta:
+        expire = datetime.utcnow() + expires_delta
+    else:
+        expire = datetime.utcnow() + timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES)
+
+    to_encode.update({"exp": expire})
+    encoded_jwt = jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)
+    return encoded_jwt
+
+
+def decode_access_token(token: str) -> Optional[dict]:
+    """Decode a JWT access token"""
+    try:
+        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
+        return payload
+    except JWTError:
+        return None
+
+
+def normalize_content(content: str) -> str:
+    """
+    Normalize content for deduplication.
+    Removes whitespace, punctuation, and converts to lowercase.
+    """
+    # Remove all whitespace
+    normalized = re.sub(r'\s+', '', content)
+    # Remove punctuation
+    normalized = re.sub(r'[^\w\u4e00-\u9fff]', '', normalized)
+    # Convert to lowercase
+    normalized = normalized.lower()
+    return normalized
+
+
+def calculate_content_hash(content: str) -> str:
+    """
+    Calculate MD5 hash of normalized content for deduplication.
+    """
+    normalized = normalize_content(content)
+    return hashlib.md5(normalized.encode('utf-8')).hexdigest()
+
+
+def get_file_extension(filename: str) -> str:
+    """Get file extension from filename"""
+    return filename.rsplit('.', 1)[-1].lower() if '.' in filename else ''
+
+
+def is_allowed_file(filename: str) -> bool:
+    """Check if file extension is allowed"""
+    allowed_extensions = {'txt', 'pdf', 'doc', 'docx', 'xlsx', 'xls'}
+    return get_file_extension(filename) in allowed_extensions