Configuration and Utilities

class Command(TraitType):
    """
    Traitlet for command-line commands with shell and string list support.
    
    Validates and processes command specifications for spawners and services.
    """
    
    def validate(self, obj, value):
        """
        Validate command specification.
        
        Args:
            obj: Object being configured
            value: Command value (string, list, or callable)
            
        Returns:
            Validated command as list of strings
            
        Raises:
            TraitError: If command format is invalid
        """

class URLPrefix(TraitType):
    """
    Traitlet for URL prefix validation and normalization.
    
    Ensures URL prefixes are properly formatted with leading/trailing slashes.
    """
    
    def validate(self, obj, value):
        """
        Validate and normalize URL prefix.
        
        Args:
            obj: Object being configured
            value: URL prefix string
            
        Returns:
            Normalized URL prefix with proper slash handling
        """

class ByteSpecification(TraitType):
    """
    Traitlet for memory/storage size specifications with unit support.
    
    Accepts values like '1G', '512M', '2048K' and converts to bytes.
    """
    
    UNIT_MAP = {
        'K': 1024,
        'M': 1024**2, 
        'G': 1024**3,
        'T': 1024**4
    }
    
    def validate(self, obj, value):
        """
        Validate and convert byte specification to integer bytes.
        
        Args:
            obj: Object being configured
            value: Size specification (int, string with units)
            
        Returns:
            Size in bytes as integer
        """

class Callable(TraitType):
    """
    Traitlet for callable objects with import string support.
    
    Accepts callable objects or import strings that resolve to callables.
    """
    
    def validate(self, obj, value):
        """
        Validate and resolve callable specification.
        
        Args:
            obj: Object being configured  
            value: Callable or import string
            
        Returns:
            Resolved callable object
        """

class EntryPointType(TraitType):
    """
    Traitlet for loading Python entry points for plugin systems.
    
    Supports authenticators, spawners, proxies, and other plugin types.
    """
    
    def __init__(self, entry_point_group, **kwargs):
        """
        Initialize entry point loader.
        
        Args:
            entry_point_group: Entry point group name (e.g., 'jupyterhub.authenticators')
            **kwargs: Additional traitlet options
        """
        self.entry_point_group = entry_point_group
        super().__init__(**kwargs)
    
    def validate(self, obj, value):
        """
        Load plugin from entry point specification.
        
        Args:
            obj: Object being configured
            value: Entry point name or class
            
        Returns:
            Loaded plugin class
        """

def new_token(length: int = 32, entropy: int = None) -> str:
    """
    Generate a new random API token.
    
    Args:
        length: Token length in characters (default: 32)
        entropy: Additional entropy source (optional)
        
    Returns:
        Random token string (URL-safe base64)
    """

def hash_token(token: str, salt: bytes = None, rounds: int = 16384) -> str:
    """
    Hash a token for secure storage using PBKDF2.
    
    Args:
        token: Token string to hash
        salt: Salt bytes (generated if None)
        rounds: PBKDF2 iteration count
        
    Returns:
        Base64-encoded hash suitable for database storage
    """

def compare_token(token: str, hashed: str) -> bool:
    """
    Compare a token against its stored hash.
    
    Args:
        token: Plain token string
        hashed: Stored hash from hash_token()
        
    Returns:
        True if token matches hash
    """

def token_authenticated(method):
    """
    Decorator for methods that require token authentication.
    
    Args:
        method: Method to protect with token auth
        
    Returns:
        Decorated method that checks for valid token
    """

def url_path_join(*pieces) -> str:
    """
    Join URL path components with proper slash handling.
    
    Args:
        *pieces: URL path components to join
        
    Returns:
        Properly joined URL path with normalized slashes
    """

def url_escape_path(path: str, safe: str = '@!:$&\'()*+,;=') -> str:
    """
    URL-encode path components while preserving safe characters.
    
    Args:
        path: Path string to encode
        safe: Characters to leave unencoded
        
    Returns:
        URL-encoded path string
    """

def url_unescape_path(path: str) -> str:
    """
    URL-decode path components.
    
    Args:
        path: URL-encoded path string
        
    Returns:
        Decoded path string
    """

def guess_base_url(url: str) -> str:
    """
    Guess the base URL from a full URL.
    
    Args:
        url: Full URL string
        
    Returns:
        Base URL (protocol + host + port)
    """

def maybe_future(value):
    """
    Convert value to Future if it's not already awaitable.
    
    Args:
        value: Value that may or may not be awaitable
        
    Returns:
        Future/coroutine that can be awaited
    """

def exponential_backoff(func, 
                       max_retries: int = 5,
                       initial_delay: float = 1.0,
                       max_delay: float = 60.0,
                       backoff_factor: float = 2.0):
    """
    Decorator for exponential backoff retry logic.
    
    Args:
        func: Function to wrap with retry logic
        max_retries: Maximum number of retry attempts
        initial_delay: Initial delay between retries (seconds)
        max_delay: Maximum delay between retries (seconds)
        backoff_factor: Multiplier for delay on each retry
        
    Returns:
        Decorated function with retry logic
    """

async def cancel_tasks(tasks):
    """
    Cancel a collection of asyncio tasks gracefully.
    
    Args:
        tasks: Iterable of asyncio tasks to cancel
    """

def run_sync(async_func):
    """
    Run an async function synchronously.
    
    Args:
        async_func: Async function to run
        
    Returns:
        Result of the async function
    """

def make_ssl_context(keyfile: str = None, 
                    certfile: str = None,
                    cafile: str = None,
                    verify_mode: ssl.VerifyMode = None,
                    check_hostname: bool = None,
                    **kwargs) -> ssl.SSLContext:
    """
    Create SSL context with common JupyterHub defaults.
    
    Args:
        keyfile: Path to SSL private key file
        certfile: Path to SSL certificate file  
        cafile: Path to CA certificate file
        verify_mode: SSL verification mode
        check_hostname: Whether to verify hostname
        **kwargs: Additional SSL context options
        
    Returns:
        Configured SSL context
    """

def random_port() -> int:
    """
    Find a random available port.
    
    Returns:
        Available port number
    """

def is_valid_ip(ip: str) -> bool:
    """
    Check if string is a valid IP address.
    
    Args:
        ip: IP address string to validate
        
    Returns:
        True if valid IPv4 or IPv6 address
    """

def get_server_info(url: str) -> Dict[str, Any]:
    """
    Get server information from URL.
    
    Args:
        url: Server URL to analyze
        
    Returns:
        Dictionary with host, port, protocol info
    """

def mysql_large_prefix_check():
    """
    Check MySQL configuration for large index prefix support.
    
    Raises:
        DatabaseError: If MySQL doesn't support required index sizes
    """

def upgrade_if_needed(db_url: str, log=None):
    """
    Upgrade database schema if needed.
    
    Args:
        db_url: Database connection URL
        log: Logger instance for output
    """

def get_schema_version(db_url: str) -> str:
    """
    Get current database schema version.
    
    Args:
        db_url: Database connection URL
        
    Returns:
        Schema version string
    """

# jupyterhub_config.py using custom traitlets
c = get_config()

# Memory limits using ByteSpecification
c.Spawner.mem_limit = '2G'  # Converted to 2147483648 bytes
c.Spawner.mem_guarantee = '512M'  # Converted to 536870912 bytes

# URL prefix configuration
c.JupyterHub.base_url = '/hub/'  # Normalized to '/hub/'

# Command configuration
c.Spawner.cmd = ['jupyterhub-singleuser']  # Validated as command list
c.LocalProcessSpawner.shell_cmd = ['/bin/bash', '-l', '-c']

# Plugin loading via entry points
c.JupyterHub.authenticator_class = 'pam'  # Loads PAMAuthenticator
c.JupyterHub.spawner_class = 'localprocess'  # Loads LocalProcessSpawner

from jupyterhub.utils import new_token, hash_token, compare_token
from jupyterhub.orm import APIToken

# Generate API token for user
user = db.query(User).filter(User.name == 'alice').first()
token = new_token(length=32)
hashed = hash_token(token)

# Store in database
api_token = APIToken(
    user=user,
    hashed=hashed,
    prefix=token[:4],  # Store prefix for identification
    note='CLI access token'
)
db.add(api_token)
db.commit()

# Validate token later
def validate_api_token(provided_token):
    """Validate API token against database"""
    prefix = provided_token[:4]
    token_record = db.query(APIToken).filter(
        APIToken.prefix == prefix
    ).first()
    
    if token_record and compare_token(provided_token, token_record.hashed):
        return token_record.user
    return None

from jupyterhub.utils import url_path_join, url_escape_path

# Safe URL path joining
base_url = '/hub'
user_name = 'alice@example.com'
server_name = 'my-server'

# Build user server URL safely
server_url = url_path_join(
    base_url,
    'user',
    url_escape_path(user_name),
    url_escape_path(server_name)
)
# Result: '/hub/user/alice%40example.com/my-server'

# Build API endpoint URLs
api_url = url_path_join(base_url, 'api', 'users', url_escape_path(user_name))
# Result: '/hub/api/users/alice%40example.com'

from jupyterhub.utils import maybe_future, exponential_backoff
import asyncio

# Convert sync/async values consistently
async def handle_result(result):
    """Handle potentially async result"""
    # maybe_future ensures we can always await
    final_result = await maybe_future(result)
    return final_result

# Retry with exponential backoff
@exponential_backoff(max_retries=3, initial_delay=1.0)
async def unreliable_operation():
    """Operation that might fail temporarily"""
    # Simulate operation that might fail
    if random.random() < 0.5:
        raise Exception("Temporary failure")
    return "Success"

# Usage
try:
    result = await unreliable_operation()
    print(f"Operation succeeded: {result}")
except Exception as e:
    print(f"Operation failed after retries: {e}")

from jupyterhub.utils import make_ssl_context

# Create SSL context for HTTPS
ssl_context = make_ssl_context(
    keyfile='/path/to/private.key',
    certfile='/path/to/certificate.crt',
    cafile='/path/to/ca-bundle.crt'
)

# Use in JupyterHub configuration
c.JupyterHub.ssl_key = '/path/to/private.key'
c.JupyterHub.ssl_cert = '/path/to/certificate.crt'

# Or programmatically
app = JupyterHub()
app.ssl_context = ssl_context

from traitlets import Unicode, Integer, Bool
from traitlets.config import Configurable
from jupyterhub.traitlets import ByteSpecification, Command

class CustomSpawner(Spawner):
    """Custom spawner with additional configuration"""
    
    # Memory configuration using ByteSpecification
    memory_limit = ByteSpecification(
        config=True,
        help="""
        Memory limit for user servers.
        Specify with units like '1G', '512M', etc.
        """
    )
    
    # Custom command configuration
    setup_command = Command(
        config=True,
        help="""
        Command to run before starting notebook server.
        Can be string or list of strings.
        """
    )
    
    # Container image with validation
    image = Unicode(
        'jupyter/base-notebook',
        config=True,
        help="Docker image to use for user servers"
    )
    
    # Advanced configuration
    privileged = Bool(
        False,
        config=True,
        help="Whether to run containers in privileged mode"
    )
    
    async def start(self):
        """Start server with custom configuration"""
        # Use configured values
        print(f"Memory limit: {self.memory_limit} bytes")
        print(f"Setup command: {self.setup_command}")
        print(f"Image: {self.image}")
        
        # Custom startup logic here
        return await super().start()

# Usage in config
c.JupyterHub.spawner_class = CustomSpawner
c.CustomSpawner.memory_limit = '4G'
c.CustomSpawner.setup_command = ['conda', 'activate', 'myenv']
c.CustomSpawner.image = 'myregistry/custom-notebook:latest'

from jupyterhub.dbutil import upgrade_if_needed

# Automatic database upgrades
def initialize_database(db_url):
    """Initialize database with schema upgrades"""
    try:
        upgrade_if_needed(db_url, log=app.log)
        app.log.info("Database schema is up to date")
    except Exception as e:
        app.log.error(f"Database upgrade failed: {e}")
        raise

# Use in application startup
app = JupyterHub()
initialize_database(app.db_url)
app.start()

import os
from jupyterhub.utils import url_path_join

# Environment-aware configuration
def get_config():
    """Get configuration based on environment"""
    c = super().get_config()
    
    # Database URL from environment
    c.JupyterHub.db_url = os.environ.get(
        'JUPYTERHUB_DB_URL',
        'sqlite:///jupyterhub.sqlite'
    )
    
    # Base URL handling
    base_url = os.environ.get('JUPYTERHUB_BASE_URL', '/')
    c.JupyterHub.base_url = base_url
    
    # SSL in production
    if os.environ.get('JUPYTERHUB_ENV') == 'production':
        c.JupyterHub.ssl_key = os.environ['SSL_KEY_PATH']
        c.JupyterHub.ssl_cert = os.environ['SSL_CERT_PATH']
        c.JupyterHub.port = 443
    else:
        c.JupyterHub.port = 8000
    
    return c

class DynamicConfig(Configurable):
    """Configuration that can be updated at runtime"""
    
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.config_watchers = []
    
    def watch_config_changes(self, callback):
        """Register callback for configuration changes"""
        self.config_watchers.append(callback)
    
    def update_config(self, **kwargs):
        """Update configuration and notify watchers"""
        for key, value in kwargs.items():
            if hasattr(self, key):
                setattr(self, key, value)
        
        # Notify watchers
        for callback in self.config_watchers:
            callback(kwargs)

# Usage
config = DynamicConfig()
config.watch_config_changes(lambda changes: print(f"Config updated: {changes}"))
config.update_config(memory_limit='8G', image='new-image:latest')