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/*
 * Copyright (C) 2021 jsonwebtoken.io
 *
 * 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 io.jsonwebtoken.impl.security;

import io.jsonwebtoken.lang.Classes;

import java.security.Provider;
import java.security.Security;
import java.util.concurrent.atomic.AtomicReference;

/**
 * @since 0.12.0
 */
final class Providers {

    private static final String BC_PROVIDER_CLASS_NAME = "org.bouncycastle.jce.provider.BouncyCastleProvider";
    static final boolean BOUNCY_CASTLE_AVAILABLE = Classes.isAvailable(BC_PROVIDER_CLASS_NAME);
    private static final AtomicReference BC_PROVIDER = new AtomicReference<>();

    private Providers() {
    }

    /**
     * Returns the BouncyCastle provider if and only if BouncyCastle is available, or {@code null} otherwise.
     *
     * If the JVM runtime already has BouncyCastle registered
     * (e.g. {@code Security.addProvider(bcProvider)}, that Provider instance will be found and returned.
     * If an existing BC provider is not found, a new BC instance will be created, cached for future reference,
     * and returned.
     *
     * If a new BC provider is created and returned, it is not registered in the JVM via
     * {@code Security.addProvider} to ensure JJWT doesn't interfere with the application security provider
     * configuration and/or expectations.
     *
     * @return any available BouncyCastle Provider, or {@code null} if BouncyCastle is not available.
     */
    public static Provider findBouncyCastle() {
        if (!BOUNCY_CASTLE_AVAILABLE) {
            return null;
        }
        Provider provider = BC_PROVIDER.get();
        if (provider == null) {

            Class clazz = Classes.forName(BC_PROVIDER_CLASS_NAME);

            //check to see if the user has already registered the BC provider:
            Provider[] providers = Security.getProviders();
            for (Provider aProvider : providers) {
                if (clazz.isInstance(aProvider)) {
                    BC_PROVIDER.set(aProvider);
                    return aProvider;
                }
            }

            //user hasn't created the BC provider, so we'll create one just for JJWT's needs:
            provider = Classes.newInstance(clazz);
            BC_PROVIDER.set(provider);
        }
        return provider;
    }
}