"""
Configuration management for Telegram Archiver.
Uses pydantic-settings for .env file parsing and validation.
"""

from pydantic_settings import BaseSettings, SettingsConfigDict
from pydantic import Field
from pathlib import Path
from typing import Optional


class Settings(BaseSettings):
    """Application settings loaded from environment variables and .env file."""

    model_config = SettingsConfigDict(
        env_file=".env",
        env_file_encoding="utf-8",
        case_sensitive=False,
        extra="ignore",
    )

    # Telegram API credentials
    api_id: int = Field(..., description="Telegram API ID from my.telegram.org")
    api_hash: str = Field(..., description="Telegram API Hash from my.telegram.org")
    phone: str = Field(..., description="Phone number for Telegram account")

    # Session configuration
    session_name: str = Field(
        default="telegram-archiver",
        description="Session name for Telethon (creates .session file)"
    )

    # File download limits
    max_file_size: int = Field(
        default=209715200,  # 200 MB
        description="Maximum file size to download in bytes"
    )

    # Output configuration
    output_dir: Path = Field(
        default=Path("./archives"),
        description="Directory to store archived channels"
    )

    # Logging configuration
    log_level: str = Field(
        default="INFO",
        description="Logging level: DEBUG, INFO, WARNING, ERROR"
    )

    # OpenTelemetry (optional, for future)
    otel_service_name: str = Field(
        default="telegram-archiver",
        description="Service name for OpenTelemetry traces"
    )
    otel_enabled: bool = Field(
        default=False,
        description="Enable OpenTelemetry tracing"
    )

    @property
    def session_path(self) -> Path:
        """Return full path to session file."""
        return Path(__file__).parent / f"{self.session_name}.session"

    def validate_credentials(self) -> bool:
        """Validate that required credentials are present."""
        if self.api_id <= 0:
            raise ValueError("API_ID must be a positive integer")
        if len(self.api_hash) < 10:
            raise ValueError("API_HASH seems too short")
        if not self.phone.startswith("+"):
            raise ValueError("PHONE must start with +")
        return True


# Global settings instance
settings: Optional[Settings] = None


def get_settings() -> Settings:
    """Get or create settings instance."""
    global settings
    if settings is None:
        settings = Settings()
        settings.validate_credentials()
    return settings