/*
 * nimbus-jose-jwt
 *
 * Copyright 2012-2016, Connect2id Ltd.
 *
 * 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 com.nimbusds.jose.jwk;


import java.io.Serializable;
import java.security.cert.X509Certificate;
import java.text.ParseException;
import java.util.Objects;


/**
 * Enumeration of public key uses. Represents the {@code use} parameter in a
 * JSON Web Key (JWK).
 *
 * <p>Public JWK use values:
 *
 * <ul>
 *     <li>{@link #SIGNATURE sig}
 *     <li>{@link #ENCRYPTION enc}
 * </ul>
 *
 * @author Vladimir Dzhuvinov
 * @version 2019-10-03
 */
public final class KeyUse implements Serializable {
        
        
        private static final long serialVersionUID = 1L;


        /**
         * Signature.
         */
        public static final KeyUse SIGNATURE = new KeyUse("sig");


        /**
         * Encryption.
         */
        public static final KeyUse ENCRYPTION = new KeyUse("enc");


        /**
         * The public key use identifier.
         */
        private final String identifier;


        /**
         * Creates a new public key use with the specified identifier.
         *
         * @param identifier The public key use identifier. Must not be
         *                   {@code null}.
         */
        public KeyUse(final String identifier) {

                if (identifier == null)
                        throw new IllegalArgumentException("The key use identifier must not be null");

                this.identifier = identifier;
        }


        /**
         * Returns the identifier of this public key use.
         *
         * @return The identifier.
         */
        public String identifier() {

                return identifier;
        }
        
        
        /**
         * @see #identifier()
         */
        public String getValue() {
                
                return identifier();
        }


        /**
         * @see #identifier()
         */
        @Override
        public String toString() {

                return identifier();
        }
        
        
        @Override
        public boolean equals(Object o) {
                if (this == o) return true;
                if (!(o instanceof KeyUse)) return false;
                KeyUse keyUse = (KeyUse) o;
                return Objects.equals(identifier, keyUse.identifier);
        }
        
        
        @Override
        public int hashCode() {
                return Objects.hash(identifier);
        }
        
        
        /**
         * Parses a public key use from the specified JWK {@code use} parameter
         * value.
         *
         * @param s The string to parse. May be {@code null}.
         *
         * @return The public key use, {@code null} if none.
         *
         * @throws ParseException If the string couldn't be parsed to a valid
         *                        public key use.
         */
        public static KeyUse parse(final String s)
                throws ParseException {

                if (s == null) {
                        return null;
                }
                
                if (s.equals(SIGNATURE.identifier())) {
                        return SIGNATURE;
                }
                
                if (s.equals(ENCRYPTION.identifier())) {
                        return ENCRYPTION;
                }
                
                if (s.trim().isEmpty()) {
                        throw new ParseException("JWK use value must not be empty or blank", 0);
                }
                
                return new KeyUse(s);
        }
        
        
        /**
         * Infers the public key use of the specified X.509 certificate. Note
         * that there is no standard algorithm for mapping PKIX key usage to
         * JWK use. See RFC 2459, section 4.2.1.3, as well as the underlying
         * code for the chosen algorithm to infer JWK use.
         *
         * @param cert The X.509 certificate. Must not be {@code null}.
         *
         * @return The public key use, {@code null} if the key use couldn't be
         *         reliably determined.
         */
        public static KeyUse from(final X509Certificate cert) {
                
                if (cert.getKeyUsage() == null) {
                        return null;
                }
                
                // nonRepudiation
                if (cert.getKeyUsage()[1]) {
                        return SIGNATURE;
                }
                
                // digitalSignature && keyEncipherment
                // (e.g. RSA TLS certificate for authenticated encryption)
                if (cert.getKeyUsage()[0] && cert.getKeyUsage()[2]) {
                        return KeyUse.ENCRYPTION;
                }
                
                // digitalSignature && keyAgreement
                // (e.g. EC TLS certificate for authenticated encryption)
                if (cert.getKeyUsage()[0] && cert.getKeyUsage()[4]) {
                        return KeyUse.ENCRYPTION;
                }
                
                // keyEncipherment || dataEncipherment || keyAgreement
                if (cert.getKeyUsage()[2] || cert.getKeyUsage()[3] || cert.getKeyUsage()[4]) {
                        return ENCRYPTION;
                }
                
                // keyCertSign || cRLSign
                if (cert.getKeyUsage()[5] || cert.getKeyUsage()[6]) {
                        return SIGNATURE;
                }
                
                return null;
        }
}