/*
 * Copyright 2013-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.cloudfoundry.reactor.uaa;

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.JwsHeader;
import io.jsonwebtoken.SigningKeyResolver;
import io.jsonwebtoken.impl.Base64Codec;
import org.cloudfoundry.uaa.tokens.ListTokenKeysRequest;
import org.cloudfoundry.uaa.tokens.ListTokenKeysResponse;
import org.cloudfoundry.uaa.tokens.TokenKey;
import org.cloudfoundry.uaa.tokens.Tokens;
import reactor.core.Exceptions;

import java.security.Key;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.X509EncodedKeySpec;
import java.time.Duration;
import java.util.HashMap;
import java.util.Map;

final class UaaSigningKeyResolver implements SigningKeyResolver {

    private static final Base64Codec BASE64 = new Base64Codec();

    private static final String BEGIN = "-----BEGIN PUBLIC KEY-----";

    private static final String END = "-----END PUBLIC KEY-----";

    private final Object monitor = new Object();

    private final Map<String, Key> signingKeys = new HashMap<>();

    private final Tokens tokens;

    UaaSigningKeyResolver(Tokens tokens) {
        this.tokens = tokens;
    }

    @Override
    @SuppressWarnings("rawtypes")
    public Key resolveSigningKey(JwsHeader header, Claims claims) {
        return getKey(header.getKeyId());
    }

    @Override
    @SuppressWarnings("rawtypes")
    public Key resolveSigningKey(JwsHeader header, String plaintext) {
        return getKey(header.getKeyId());
    }

    private static byte[] decode(TokenKey tokenKey) {
        return BASE64.decode(tokenKey.getValue().replace(BEGIN, "").replace(END, "").trim());
    }

    private static Key generateKey(TokenKey tokenKey) {
        try {
            return KeyFactory
                .getInstance(tokenKey.getKeyType().toString())
                .generatePublic(new X509EncodedKeySpec(decode(tokenKey)));
        } catch (InvalidKeySpecException | NoSuchAlgorithmException e) {
            throw Exceptions.propagate(e);
        }
    }

    private Key getKey(String keyId) {
        synchronized (this.monitor) {
            Key key = this.signingKeys.get(keyId);
            if (key != null) {
                return key;
            }

            refreshKeys();

            key = this.signingKeys.get(keyId);
            if (key != null) {
                return key;
            }

            throw new IllegalStateException(String.format("Unable to retrieve signing key %s", keyId));
        }
    }

    private void refreshKeys() {
        this.signingKeys.clear();
        this.signingKeys.putAll(this.tokens
            .listKeys(ListTokenKeysRequest.builder()
                .build())
            .flatMapIterable(ListTokenKeysResponse::getKeys)
            .collectMap(TokenKey::getId, UaaSigningKeyResolver::generateKey)
            .block(Duration.ofMinutes(5)));
    }

}