import re
import nltk
from nltk.corpus import stopwords
from nltk.stem import WordNetLemmatizer

# Ensure nltk resources are downloaded
try:
    nltk.data.find('corpora/stopwords')
except LookupError:
    nltk.download('stopwords')
try:
    nltk.data.find('corpora/wordnet')
except LookupError:
    nltk.download('wordnet')

stop_words = set(stopwords.words('english'))
lemmatizer = WordNetLemmatizer()

def preprocess_text(text):
    if not isinstance(text, str):
        return ""
    
    # Lowercase
    text = text.lower()
    
    # Remove special characters, numbers, and urls
    text = re.sub(r'http\S+', '', text)
    text = re.sub(r'[^a-zA-Z\s]', '', text)
    
    # Tokenize and remove stopwords & lemmatize
    words = text.split()
    clean_words = [lemmatizer.lemmatize(w) for w in words if w not in stop_words]
    
    return " ".join(clean_words)