import os
import sys
import yaml
from loguru import logger
from typing import Optional

# Define a custom exception for configuration errors
class AppConfigError(Exception):
    pass

class Settings:
    def __init__(self, config_path: str = "config/application.yml"):
        """
        Loads configuration from a YAML file and overrides with environment variables.
        """
        # --- Load from YAML file ---
        try:
            with open(config_path, 'r') as f:
                config = yaml.safe_load(f)
        except FileNotFoundError:
            raise AppConfigError(f"Configuration file not found at '{config_path}'.")
        except yaml.YAMLError as e:
            raise AppConfigError(f"Error parsing YAML file: {e}")

        # --- Read and Combine Settings (Environment variables take precedence) ---
        llm_config = config.get('llm', {})

        # General settings
        self.llm_mode: str = os.getenv("LLM_MODE", llm_config.get('mode', 'openai')).lower()

        # OpenAI settings
        openai_config = llm_config.get('openai', {})
        self.openai_api_key: Optional[str] = os.getenv("OPENAI_API_KEY", openai_config.get('api_key'))
        self.openai_api_base_url: Optional[str] = os.getenv("OPENAI_API_BASE_URL", openai_config.get('api_base_url'))
        self.openai_model: Optional[str] = os.getenv("OPENAI_MODEL", openai_config.get('model'))

        # Ollama settings
        ollama_config = llm_config.get('ollama', {})
        self.ollama_base_url: Optional[str] = os.getenv("OLLAMA_BASE_URL", ollama_config.get('base_url'))
        self.ollama_model: Optional[str] = os.getenv("OLLAMA_MODEL", ollama_config.get('model'))

        self._validate()

    def _validate(self):
        """
        Validates that required configuration variables are set.
        """
        logger.info(f"LLM mode set to: '{self.llm_mode}'")

        if self.llm_mode == 'openai':
            if not self.openai_api_key:
                raise AppConfigError("LLM mode is 'openai', but OPENAI_API_KEY is not set.")
            if not self.openai_api_base_url:
                raise AppConfigError("LLM mode is 'openai', but OPENAI_API_BASE_URL is not set.")
            if not self.openai_model:
                 raise AppConfigError("LLM mode is 'openai', but OPENAI_MODEL is not set.")

        elif self.llm_mode == 'ollama':
            if not self.ollama_base_url:
                raise AppConfigError("LLM mode is 'ollama', but OLLAMA_BASE_URL is not set.")
            if not self.ollama_model:
                raise AppConfigError("LLM mode is 'ollama', but OLLAMA_MODEL is not set.")

        else:
            raise AppConfigError(f"Invalid LLM_MODE: '{self.llm_mode}'. Must be 'openai' or 'ollama'.")

        logger.info("Configuration validated successfully.")

# Create a single, validated instance of the settings to be imported by other modules.
try:
    settings = Settings()
except AppConfigError as e:
    logger.error(f"FATAL: {e}")
    logger.error("Application shutting down due to configuration error.")
    sys.exit(1) # Exit the application if configuration is invalid