"""
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'


@dataclass
class EmailConfig:
    """Email service configuration."""
    smtp_host: str
    smtp_port: int
    smtp_username: str
    smtp_password: str
    smtp_use_tls: bool
    from_email: str
    from_name: str


@dataclass
class EmailConfig:
    """Email service configuration."""
    smtp_host: str
    smtp_port: int
    smtp_username: str
    smtp_password: str
    smtp_use_tls: bool
    from_email: str
    from_name: str


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

    def __init__(self):
        self.database = self._load_database_config()
        self.server = self._load_server_config()
        self.email = self._load_email_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 _load_email_config(self) -> EmailConfig:
        """Load email configuration from environment variables."""
        return EmailConfig(
            smtp_host=os.getenv('SMTP_HOST', 'smtp.gmail.com'),
            smtp_port=int(os.getenv('SMTP_PORT', '587')),
            smtp_username=os.getenv('SMTP_USERNAME', ''),
            smtp_password=os.getenv('SMTP_PASSWORD', ''),
            smtp_use_tls=os.getenv('SMTP_USE_TLS', 'true').lower() == 'true',
            from_email=os.getenv('SMTP_FROM_EMAIL', 'noreply@yourcompany.com'),
            from_name=os.getenv('SMTP_FROM_NAME', 'VPN Access Server')
        )

    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")

        # Validate email config
        if not self.email.smtp_username:
            errors.append("SMTP_USERNAME is required for email functionality")

        if not self.email.smtp_password:
            errors.append("SMTP_PASSWORD is required for email functionality")

        if self.email.smtp_port < 1 or self.email.smtp_port > 65535:
            errors.append("SMTP_PORT must be between 1 and 65535")

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

        return True


# Global configuration instance
config = Config()