import pandas as pd

def analyze_weakness(csv_file):
    """
    Analyzes a CSV file with student scores to identify weak topics.
    
    Parameters:
        csv_file (file): Uploaded CSV file (must contain 'Topic' and 'Score' columns).
    
    Returns:
        str: Analysis report of weak and strong topics.
    """
    try:
        df = pd.read_csv(csv_file)

        if 'Topic' not in df.columns or 'Score' not in df.columns:
            return "❌ CSV must contain 'Topic' and 'Score' columns."

        avg_score = df['Score'].mean()
        weak_topics = df[df['Score'] < avg_score]
        strong_topics = df[df['Score'] >= avg_score]

        report = f"📊 Average Score: {round(avg_score, 2)}\n\n"
        report += "❌ Weak Topics:\n"
        if not weak_topics.empty:
            report += "\n".join(
                [f"- {row['Topic']} ({row['Score']})" for index, row in weak_topics.iterrows()]
            )
        else:
            report += "None 🎉"

        report += "\n\n✅ Strong Topics:\n"
        if not strong_topics.empty:
            report += "\n".join(
                [f"- {row['Topic']} ({row['Score']})" for index, row in strong_topics.iterrows()]
            )
        else:
            report += "None"

        return report

    except Exception as e:
        return f"Error analyzing file: {str(e)}"