package civitas.crypto.keyshare;
   
   import org.springframework.beans.factory.annotation.Autowired;
   import org.springframework.stereotype.Controller;
   
   import civitas.crypto.Constants;
   import civitas.crypto.CryptoException;
   import civitas.crypto.parameters.ElGamalParameters;
   import civitas.crypto.publickey.ElGamalPublicKey;
  import civitas.util.CivitasBigInteger;
  
  @Controller
  public class CombineKeyShares implements Constants {
  	@Autowired
  	VerifyElGamalKeyShare verifyElGamalKeyShare;
  
  	public ElGamalPublicKey apply(final ElGamalKeyShare... shares) throws CryptoException {
  		if (shares == null || shares.length == 0) {
  			return null;
  		}
  		CivitasBigInteger product = ONE;
  		ElGamalParameters params = null;
  		for (ElGamalKeyShare share : shares) {
  			if (share == null) {
  				throw new CryptoException("Share is null");
  			}
  			// Check the proofs that this is a valid share
  			if (params == null) {
  				params = share.pubKey().params;
  			}
  			if (!verifyElGamalKeyShare.apply(share)) {
  				throw new CryptoException("Invalid share");
  			}
  			// accumulate the keys...
  			product = product.multiply(share.pubKey().y);
  		}
  		return new ElGamalPublicKey(product, params);
  	}
  }