Task1

/* */
import re
import math

# Common weak passwords
common_passwords = [
    "123456", "password", "12345678", "qwerty", "12345", "123456789", 
    "letmein", "1234", "welcome", "password1", "abc123"
]

# Special character set
special_characters = "!@#$%^&*()-_=+[{]}|;:'\",<.>/?`~"


def password_entropy(password):
    """Calculate entropy based on password complexity."""
    pool_size = 0
    
    # Determine character pool size
    if re.search(r'[a-z]', password):
        pool_size += 26  # lowercase
    if re.search(r'[A-Z]', password):
        pool_size += 26  # uppercase
    if re.search(r'[0-9]', password):
        pool_size += 10  # digits
    if re.search(f"[{re.escape(special_characters)}]", password):
        pool_size += len(special_characters)  # special characters
    
    # Calculate entropy
    entropy = len(password) * math.log2(pool_size) if pool_size > 0 else 0
    return entropy


def is_common_password(password):
    """Check if the password is in the list of common passwords."""
    return password.lower() in common_passwords


def check_password_strength(password):
    """Evaluate the password strength and provide detailed feedback."""
    issues = []
    score = 0
    
    # Check length
    if len(password) < 8:
        issues.append("Password is too short (minimum 8 characters).")
    elif len(password) < 12:
        issues.append("Password is a bit short; 12+ characters recommended.")
        score += 1
    else:
        score += 2
    
    # Check character types
    if not re.search(r'[a-z]', password):
        issues.append("Add lowercase letters for a stronger password.")
    else:
        score += 1

    if not re.search(r'[A-Z]', password):
        issues.append("Add uppercase letters for a stronger password.")
    else:
        score += 1

    if not re.search(r'[0-9]', password):
        issues.append("Include numbers for better security.")
    else:
        score += 1

    if not re.search(f"[{re.escape(special_characters)}]", password):
        issues.append("Add special characters for improved security.")
    else:
        score += 1

    # Check common password list
    if is_common_password(password):
        issues.append("Password is too common; avoid easily guessed passwords.")
    else:
        score += 1

    # Calculate entropy and give feedback
    entropy = password_entropy(password)
    if entropy < 28:
        issues.append("Very weak password; try adding more varied characters.")
    elif entropy < 35:
        issues.append("Weak password; increase length and character variety.")
    elif entropy < 60:
        issues.append("Moderate strength; consider making it more complex.")
    else:
        score += 1
    
    # Final score-based feedback
    strength_level = ["Very Weak", "Weak", "Moderate", "Strong", "Very Strong"]
    strength_rating = strength_level[min(score, len(strength_level) - 1)]

    return {
        "password": password,
        "strength": strength_rating,
        "entropy": round(entropy, 2),
        "issues": issues
    }

# Main loop
while True:
    user_password = input("Enter a password to check its strength (or type 'exit' to quit): ")
    
    if user_password.lower() == 'exit':
        print("Exiting password checker. Goodbye!")
        break
    
    # Check password strength
    result = check_password_strength(user_password)
    
    # Display result
    print("\nPassword Strength Analysis:")
    print("Password:", result["password"])
    print("Strength Rating:", result["strength"])
    print("Entropy Score:", result["entropy"])
    print("Issues Found:")
    if result["issues"]:
        for issue in result["issues"]:
            print(" -", issue)
    else:
        print(" - No issues found. This is a strong password!")
    
    print("\n")  # Space before next prompt