"""
Configuration management for VPN Access Server.

Handles loading database credentials and system constants from environment variables
and configuration files with secure defaults.
"""

import os
from typing import Optional
from dataclasses import dataclass


@dataclass
class DatabaseConfig:
    """Database connection configuration."""
    host: str
    port: int
    database: str
    username: str
    password: str
    charset: str = 'utf8mb4'
    autocommit: bool = False
    pool_size: int = 5
    max_overflow: int = 10


@dataclass
class ServerConfig:
    """VPN Access Server configuration."""
    log_level: str = 'INFO'
    log_file: Optional[str] = '/var/log/openvpn/access-server.log'
    default_session_limit: int = 28800  # 8 hours in seconds
    max_session_limit: int = 86400  # 24 hours in seconds
    timezone: str = 'UTC'


class Config:
    """Main configuration loader for VPN Access Server."""

    def __init__(self):
        self.database = self._load_database_config()
        self.server = self._load_server_config()

    def _load_database_config(self) -> DatabaseConfig:
        """Load database configuration from environment variables."""
        return DatabaseConfig(
            host=os.getenv('DB_HOST', 'localhost'),
            port=int(os.getenv('DB_PORT', '3306')),
            database=os.getenv('DB_NAME', 'vpn_access'),
            username=os.getenv('DB_USER', 'vpn_user'),
            password=os.getenv('DB_PASSWORD', ''),
            charset=os.getenv('DB_CHARSET', 'utf8mb4'),
            autocommit=os.getenv('DB_AUTOCOMMIT', 'false').lower() == 'true',
            pool_size=int(os.getenv('DB_POOL_SIZE', '5')),
            max_overflow=int(os.getenv('DB_MAX_OVERFLOW', '10'))
        )

    def _load_server_config(self) -> ServerConfig:
        """Load server configuration from environment variables."""
        return ServerConfig(
            log_level=os.getenv('LOG_LEVEL', 'INFO').upper(),
            log_file=os.getenv('LOG_FILE', '/var/log/openvpn/access-server.log'),
            default_session_limit=int(os.getenv('DEFAULT_SESSION_LIMIT', '28800')),
            max_session_limit=int(os.getenv('MAX_SESSION_LIMIT', '86400')),
            timezone=os.getenv('TIMEZONE', 'UTC')
        )

    def validate(self) -> bool:
        """Validate configuration values."""
        errors = []

        # Validate database config
        if not self.database.password:
            errors.append("DB_PASSWORD is required")

        if self.database.port < 1 or self.database.port > 65535:
            errors.append("DB_PORT must be between 1 and 65535")

        # Validate server config
        if self.server.log_level not in ['DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL']:
            errors.append("LOG_LEVEL must be one of: DEBUG, INFO, WARNING, ERROR, CRITICAL")

        if self.server.default_session_limit > self.server.max_session_limit:
            errors.append("DEFAULT_SESSION_LIMIT cannot exceed MAX_SESSION_LIMIT")

        if errors:
            for error in errors:
                print(f"Configuration Error: {error}")
            return False

        return True


# Global configuration instance
config = Config()