import re
from typing import Dict, Any, Optional
from urllib.parse import urlparse

EMAIL_REGEX = re.compile(r"^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$")
COMMON_PREFIXES = ["info", "contact", "sales", "hello", "support", "inquiries"]

def is_valid_email(email: str) -> bool:
    """Check if the provided string is a valid email format."""
    if not email:
        return False
    return bool(EMAIL_REGEX.match(email))

def extract_domain(url: str) -> Optional[str]:
    """Extract domain from a URL to use for email guessing."""
    if not url:
        return None
    
    if not url.startswith(('http://', 'https://')):
        url = 'http://' + url
        
    try:
        parsed = urlparse(url)
        domain = parsed.netloc
        if domain.startswith('www.'):
            domain = domain[4:]
        return domain
    except Exception:
        return None

def guess_fallback_email(url: str) -> Optional[str]:
    """Generate a potential contact email based on the website domain."""
    domain = extract_domain(url)
    if not domain:
        return None
    # Lightweight pattern matching routine: returns the first common corporate format
    # In a real-world scenario, you might ping these to check validity via SMTP, 
    # but here we just return the most likely fallback.
    return f"{COMMON_PREFIXES[0]}@{domain}" 

def validate_and_enrich_lead(lead: Dict[str, Any]) -> Optional[Dict[str, Any]]:
    """
    Applies the Data Completeness Rule:
    A lead is dropped unless it contains a company name, city, and a valid email address.
    Also attempts Email Validation Fallback.
    """
    company_name = lead.get("company_name")
    city = lead.get("city")
    email = lead.get("contact_email")
    website = lead.get("website_url")

    # Check for basic required fields
    if not company_name or not str(company_name).strip():
        return None
    
    if not city or not str(city).strip():
        return None

    # Validate email or attempt fallback
    if not is_valid_email(email):
        if website:
            fallback = guess_fallback_email(website)
            if fallback:
                lead["contact_email"] = fallback
            else:
                return None # No valid email and couldn't generate fallback
        else:
            return None # No valid email and no website for fallback
            
    return lead