package de.tavolio.realm.key;

import de.tavolio.realm.RealmEntity;
import jakarta.enterprise.context.ApplicationScoped;
import jakarta.inject.Inject;
import jakarta.transaction.Transactional;

import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.interfaces.ECPublicKey;
import java.security.spec.ECGenParameterSpec;
import java.util.Base64;
import java.util.NoSuchElementException;
import java.util.UUID;

@ApplicationScoped
public class KeypairService
{
    public static final String EC = "EC";
    public static final String P256 = "secp256r1";

    @Inject
    KeypairRepo keypairRepo;

    @Transactional
    public void create(RealmEntity realm, String type, String alg)
    {
        if ("EC".equals(type))
        {
            KeypairEntity keypair = getKeypair(realm);
            keypair.setRealm(realm);
            realm.getKeys().add(keypair);
            keypairRepo.persist(keypair);
            return;
        }
        throw new NoSuchElementException();
    }


    private KeypairEntity getKeypair(RealmEntity realm)
    {
        KeyPair pair = generate();
        ECPublicKey publicKey = (ECPublicKey) pair.getPublic();
        byte[] xBytes = toFixedLength(publicKey.getW().getAffineX().toByteArray());
        byte[] yBytes = toFixedLength(publicKey.getW().getAffineY().toByteArray());
        return new KeypairEntity()
            .setId(UUID.randomUUID().toString())
            .setRealm(realm)
            .setPrivateKey(pair.getPrivate().getEncoded())
            .setType("EC")
            .setUse("sig")
            .setAlg("ES256")
            .setCrv("P-256")
            .setX(Base64.getUrlEncoder().withoutPadding().encodeToString(xBytes))
            .setY(Base64.getUrlEncoder().withoutPadding().encodeToString(yBytes));
    }

    private KeyPair generate()
    {
        try
        {
            KeyPairGenerator generator = KeyPairGenerator.getInstance(EC);
            generator.initialize(new ECGenParameterSpec(P256));
            return generator.generateKeyPair();
        }
        catch (Exception e)
        {
            throw new RuntimeException();
        }
    }

    private byte[] toFixedLength(byte[] input)
    {
        if (input.length > 32)
        {
            byte[] result = new byte[32];
            System.arraycopy(input, input.length - 32, result, 0, 32);
            return result;
        }
        return input;
    }
}