import hmac
import hashlib
import json
from datetime import datetime, timedelta

# This is your master key. NEVER share this or put it in public code.
SECRET_KEY = b"mxPIC_Super_Secret_Master_Key_2026!"

def generate_license(mac_address: str, days_valid: int, output_file: str = "mxpic.lic"):
    """Generates a cryptographically signed license file."""
    
    # Calculate the expiration date
    expiration = (datetime.now() + timedelta(days=days_valid)).strftime("%Y-%m-%d")
    
    # Create the payload message we want to sign
    message = f"{mac_address}|{expiration}".encode('utf-8')
    
    # Generate the unforgeable signature using HMAC + SHA256
    signature = hmac.new(SECRET_KEY, message, hashlib.sha256).hexdigest()
    
    # Create the license dictionary
    license_data = {
        "mac_address": mac_address,
        "expiration": expiration,
        "signature": signature
    }
    
    # Save to file
    with open(output_file, "w") as f:
        json.dump(license_data, f, indent=4)
    
    # 
    print(f"✅ License generated for MAC {mac_address}")
    print(f"✅ Expires on {expiration}")
    print(f"✅ Saved to {output_file}")

if __name__ == "__main__":
    # Example: Customer sends MAC "A1:B2:C3:D4:E5:F6", they bought a 1-year license
    generate_license("D4:54:8B:F1:46:49", days_valid=365,output_file="mxpic.lic")