import os
import shutil

def get_and_prepare_campaign_descriptor(num=1, initials='LI'):
    """
    Prepares a campaign descriptor for use.
    
    Args:
        num (int): Campaign number. Options: 1, 2, 3
        initials (str): Campaign initials. Options: 'LI', 'TBR', 'NG'
    
    Returns:
        str: Path to the prepared descriptor file
    """
    # Define available options
    options = {
        1: 'LI',
        2: 'TBR',
        3: 'NG'
    }
    
    if num not in options or initials != options[num]:
        raise ValueError(f"Invalid combination. Available options: {options}")
    
    # Determine paths
    descriptor_src = f'../dima/input_files/campaignDescriptor{num}_{initials}.yaml'
    descriptor_dst = f'../data/campaignDescriptor{num}_{initials}.yaml'
    
    # Copy descriptor to local folder
    shutil.copyfile(descriptor_src, descriptor_dst)
    
    # Decide network mount path
    mount_path = '/mnt/network_mount' if os.path.exists('/mnt/network_mount') else '../data'
    
    # Replace placeholder in descriptor
    with open(descriptor_dst, 'r') as f:
        content = f.read()
    content = content.replace('${NETWORK_MOUNT}', mount_path)
    with open(descriptor_dst, 'w') as f:
        f.write(content)
    
    print(f"Descriptor ready at {descriptor_dst} using mount {mount_path}")
    return descriptor_dst

# Example usage:
# prepare_campaign_descriptor(1, 'LI')