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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;

import io.jsonwebtoken.lang.Assert;

/**
 * Adapter pattern implementation for the {@link Locator} interface.  Subclasses can override any of the
 * {@link #doLocate(Header)}, {@link #locate(ProtectedHeader)}, {@link #locate(JwsHeader)}, or
 * {@link #locate(JweHeader)} methods for type-specific logic if desired when the encountered header is an
 * unprotected JWT, or an integrity-protected JWT (either a JWS or JWE).
 *
 * @param  the type of object to locate
 * @since 0.12.0
 */
public abstract class LocatorAdapter implements Locator {

    /**
     * Constructs a new instance, where all default method implementations return {@code null}.
     */
    public LocatorAdapter() {
    }

    /**
     * Inspects the specified header, and delegates to the {@link #locate(ProtectedHeader)} method if the header
     * is protected (either a {@link JwsHeader} or {@link JweHeader}), or the {@link #doLocate(Header)} method
     * if the header is not integrity protected.
     *
     * @param header the JWT header to inspect; may be an instance of {@link Header}, {@link JwsHeader}, or
     *               {@link JweHeader} depending on if the respective JWT is an unprotected JWT, JWS or JWE.
     * @return an object referenced in the specified header, or {@code null} if the referenced object cannot be found
     * or does not exist.
     */
    @Override
    public final T locate(Header header) {
        Assert.notNull(header, "Header cannot be null.");
        if (header instanceof ProtectedHeader) {
            ProtectedHeader protectedHeader = (ProtectedHeader) header;
            return locate(protectedHeader);
        }
        return doLocate(header);
    }

    /**
     * Returns an object referenced in the specified {@link ProtectedHeader}, or {@code null} if the referenced
     * object cannot be found or does not exist.  This is a convenience method that delegates to
     * {@link #locate(JwsHeader)} if the {@code header} is a {@link JwsHeader} or {@link #locate(JweHeader)} if the
     * {@code header} is a {@link JweHeader}.
     *
     * @param header the protected header of an encountered JWS or JWE.
     * @return an object referenced in the specified {@link ProtectedHeader}, or {@code null} if the referenced
     * object cannot be found or does not exist.
     */
    protected T locate(ProtectedHeader header) {
        if (header instanceof JwsHeader) {
            return locate((JwsHeader) header);
        } else {
            Assert.isInstanceOf(JweHeader.class, header, "Unrecognized ProtectedHeader type.");
            return locate((JweHeader) header);
        }
    }

    /**
     * Returns an object referenced in the specified JWE header, or {@code null} if the referenced
     * object cannot be found or does not exist.  Default implementation simply returns {@code null}.
     *
     * @param header the header of an encountered JWE.
     * @return an object referenced in the specified JWE header, or {@code null} if the referenced
     * object cannot be found or does not exist.
     */
    protected T locate(JweHeader header) {
        return null;
    }

    /**
     * Returns an object referenced in the specified JWS header, or {@code null} if the referenced
     * object cannot be found or does not exist. Default implementation simply returns {@code null}.
     *
     * @param header the header of an encountered JWS.
     * @return an object referenced in the specified JWS header, or {@code null} if the referenced
     * object cannot be found or does not exist.
     */
    protected T locate(JwsHeader header) {
        return null;
    }

    /**
     * Returns an object referenced in the specified unprotected JWT header, or {@code null} if the referenced
     * object cannot be found or does not exist. Default implementation simply returns {@code null}.
     *
     * @param header the header of an encountered JWT.
     * @return an object referenced in the specified unprotected JWT header, or {@code null} if the referenced
     * object cannot be found or does not exist.
     */
    @SuppressWarnings("unused")
    protected T doLocate(Header header) {
        return null;
    }
}