import pandas as pd

def _build_docs_index(docs_df):
    index = {}
    rows = docs_df.to_dict(orient="records") if hasattr(docs_df, 'to_dict') else []
    for row in rows:
        title = row.get("Título", "")
        authors_raw = row.get("Autores", "")
        year = str(row.get("Año", ""))
        
        if isinstance(authors_raw, list):
            surnames = [a.split()[-1] for a in authors_raw[:3] if a]
        elif isinstance(authors_raw, str) and authors_raw:
            parts = [a.strip() for a in authors_raw.split(",")]
            surnames = [p.split()[-1] for p in parts[:3] if p]
        else:
            surnames = []
            
        print("Surnames:", surnames, "Year:", year)
        for s in surnames:
            key = f"{s.lower()}_{year}"
            index[key] = title

    return index

df = pd.DataFrame([
    {"Título": "Paper 1", "Autores": "Nguyen, T. P.", "Año": "2020"},
    {"Título": "Paper 2", "Autores": "Raj, A., Kumar, B.", "Año": "2021"}
])

print(_build_docs_index(df))