"""
Configuration Loader - Load YAML config with environment variable substitution
Compatible with Python 3.6+
"""

import os
import re
import yaml
from dotenv import load_dotenv

def load_config(config_path='config/config.yaml'):
    """
    Load configuration from YAML file with environment variable substitution

    Supports:
    - ${VAR_NAME} - Required environment variable
    - ${VAR_NAME:-default} - Optional with default value
    """
    # Load environment variables from .env file
    # Check for custom .env file path or environment-specific file
    dotenv_path = os.getenv('DOTENV_PATH')
    if dotenv_path:
        # Use explicitly specified .env file
        load_dotenv(dotenv_path, override=True)
    else:
        # Check for ENV variable to determine which .env file to load
        env_name = os.getenv('ENV', 'dev')
        if env_name == 'prod' or env_name == 'production':
            # Load .env-prod for production
            if os.path.exists('.env-prod'):
                load_dotenv('.env-prod', override=True)
            else:
                load_dotenv()  # Fallback to default .env
        else:
            # Load default .env for dev/staging
            load_dotenv()

    # Read YAML file
    with open(config_path, 'r') as f:
        config_text = f.read()

    # Substitute environment variables
    config_text = substitute_env_vars(config_text)

    # Parse YAML
    config = yaml.safe_load(config_text)

    # Load environment-specific overrides if specified
    env = config.get('environment', 'staging')
    env_config_path = 'config/environments/{}.yaml'.format(env)

    if os.path.exists(env_config_path):
        with open(env_config_path, 'r') as f:
            env_config_text = f.read()
        env_config_text = substitute_env_vars(env_config_text)
        env_config = yaml.safe_load(env_config_text)

        # Merge environment-specific config
        config = deep_merge(config, env_config)

    return config

def substitute_env_vars(text):
    """
    Substitute ${VAR_NAME} and ${VAR_NAME:-default} patterns with environment variables
    """
    def replacer(match):
        var_expr = match.group(1)

        # Check for default value syntax: VAR:-default
        if ':-' in var_expr:
            var_name, default = var_expr.split(':-', 1)
            return os.getenv(var_name, default)
        else:
            # Required variable
            value = os.getenv(var_expr)
            if value is None:
                raise ValueError("Required environment variable not set: {}".format(var_expr))
            return value

    # Pattern: ${VAR_NAME} or ${VAR_NAME:-default}
    pattern = r'\$\{([^}]+)\}'
    return re.sub(pattern, replacer, text)

def deep_merge(base, override):
    """
    Deep merge two dictionaries
    """
    result = base.copy()

    for key, value in override.items():
        if key in result and isinstance(result[key], dict) and isinstance(value, dict):
            result[key] = deep_merge(result[key], value)
        else:
            result[key] = value

    return result

def load_field_mappings(config):
    """
    Load field mappings configuration
    Auto-detects environment (PPR or PROD) and loads appropriate file
    """
    # Detect environment based on DAM URL
    dam_url = config.get('dam', {}).get('base_url', '')

    # Determine which field mappings file to use
    if 'ppr' in dam_url.lower():
        # PPR environment
        mappings_file = 'config/field_mappings_ppr.yaml'
        env_name = 'PPR'
    else:
        # Production environment (default)
        mappings_file = 'config/field_mappings_prod.yaml'
        env_name = 'PROD'

    # Log which file is being loaded
    import logging
    logger = logging.getLogger('ConfigLoader')
    logger.info("Loading field mappings for {} environment: {}".format(env_name, mappings_file))

    with open(mappings_file, 'r') as f:
        return yaml.safe_load(f)

def load_country_code_mappings():
    """
    Load country code mappings: ISO 3166-1 Alpha-2 -> DAM Codes

    Returns:
        dict: ISO code -> DAM code mapping
        Example: {'BD': 'BG', 'DE': 'DE', 'IT': 'IT', ...}
    """
    mapping_path = 'config/country_code_mappings.yaml'

    try:
        with open(mapping_path, 'r') as f:
            mappings = yaml.safe_load(f)
        return mappings if mappings else {}
    except Exception as e:
        # If file doesn't exist or fails to load, return empty dict
        # This allows system to work without mapping (uses ISO codes as-is)
        return {}