package com.nimbusds.jwt.proc;


import java.security.Key;
import java.text.ParseException;
import java.util.List;
import java.util.ListIterator;

import com.nimbusds.jose.JOSEException;
import com.nimbusds.jose.JWEDecrypter;
import com.nimbusds.jose.JWSVerifier;
import com.nimbusds.jose.crypto.factories.DefaultJWEDecrypterFactory;
import com.nimbusds.jose.crypto.factories.DefaultJWSVerifierFactory;
import com.nimbusds.jose.proc.*;
import com.nimbusds.jwt.*;


/**
 * Default processor of {@link com.nimbusds.jwt.PlainJWT unsecured} (plain),
 * {@link com.nimbusds.jwt.SignedJWT signed} and
 * {@link com.nimbusds.jwt.EncryptedJWT encrypted} JSON Web Tokens (JWTs).
 *
 * <p>Must be configured with the following:
 *
 * <ol>
 *     <li>To process signed JWTs: A {@link JWSKeySelector JWS key selector}
 *     to determine the key candidate(s) for the signature verification. The
 *     key selection procedure is application-specific and may involve key ID
 *     lookup, a certificate check and / or other information supplied in the
 *     message {@link SecurityContext context}.</li>
 *
 *     <li>To process encrypted JWTs: A {@link JWEKeySelector JWE key selector}
 *     to determine the key candidate(s) for decryption. The key selection
 *     procedure is application-specific and may involve key ID lookup, a
 *     certificate check and / or other information supplied in the message
 *     {@link SecurityContext context}.</li>
 * </ol>
 *
 * <p>See sections 6 of RFC 7515 (JWS) and RFC 7516 (JWE) for guidelines on key
 * selection.
 *
 * <p>This processor comes with the default {@link DefaultJWSVerifierFactory
 * JWS verifier factory} and the default {@link DefaultJWEDecrypterFactory
 * JWE decrypter factory}; they can construct verifiers / decrypters for all
 * standard JOSE algorithms implemented by the library.
 *
 * <p>Note that for security reasons this processor is hardwired to reject
 * unsecured (plain) JWTs. Override the {@link #process(PlainJWT, SecurityContext)}
 * if you need to handle plain JWTs as well.
 *
 * <p>A {@link DefaultJWTClaimsVerifier default JWT claims verifier} is
 * provided, to perform a minimal check of the claims after a successful JWS
 * verification / JWE decryption. It checks the token expiration (exp) and
 * not-before (nbf) timestamps if these are present. The default JWT claims
 * verifier may be extended to perform additional checks, such as issuer and
 * subject acceptance.
 *
 * <p>To process generic JOSE objects (with arbitrary payloads) use the
 * {@link com.nimbusds.jose.proc.DefaultJOSEProcessor} class.
 *
 * @author Vladimir Dzhuvinov
 * @version 2015-10-20
 */
public class DefaultJWTProcessor<C extends SecurityContext>
        implements ConfigurableJWTProcessor<C> {

        // Cache exceptions
        private static final BadJOSEException PLAIN_JWT_REJECTED_EXCEPTION =
                new BadJOSEException("Unsecured (plain) JWTs are rejected, extend class to handle");
        private static final BadJOSEException NO_JWS_KEY_SELECTOR_EXCEPTION =
                new BadJOSEException("Signed JWT rejected: No JWS key selector is configured");
        private static final BadJOSEException NO_JWE_KEY_SELECTOR_EXCEPTION =
                new BadJOSEException("Encrypted JWT rejected: No JWE key selector is configured");
        private static final JOSEException NO_JWS_VERIFIER_FACTORY_EXCEPTION =
                new JOSEException("No JWS verifier is configured");
        private static final JOSEException NO_JWE_DECRYPTER_FACTORY_EXCEPTION =
                new JOSEException("No JWE decrypter is configured");
        private static final BadJOSEException NO_JWS_KEY_CANDIDATES_EXCEPTION =
                new BadJOSEException("Signed JWT rejected: No matching key(s) found");
        private static final BadJOSEException NO_JWE_KEY_CANDIDATES_EXCEPTION =
                new BadJOSEException("Encrypted JWT rejected: No matching key(s) found");
        private static final BadJOSEException INVALID_SIGNATURE =
                new BadJWSException("Signed JWT rejected: Invalid signature");
        private static final BadJWTException INVALID_NESTED_JWT_EXCEPTION =
                new BadJWTException("The payload is not a nested JWT");
        private static final BadJOSEException NO_MATCHING_VERIFIERS_EXCEPTION =
                new BadJOSEException("JWS object rejected: No matching verifier(s) found");
        private static final BadJOSEException NO_MATCHING_DECRYPTERS_EXCEPTION =
                new BadJOSEException("Encrypted JWT rejected: No matching decrypter(s) found");

        /**
         * The JWS key selector.
         */
        private JWSKeySelector<C> jwsKeySelector;


        /**
         * The JWE key selector.
         */
        private JWEKeySelector<C> jweKeySelector;


        /**
         * The JWS verifier factory.
         */
        private JWSVerifierFactory jwsVerifierFactory = new DefaultJWSVerifierFactory();


        /**
         * The JWE decrypter factory.
         */
        private JWEDecrypterFactory jweDecrypterFactory = new DefaultJWEDecrypterFactory();


        /**
         * The claims verifier.
         */
        private JWTClaimsVerifier claimsVerifier = new DefaultJWTClaimsVerifier();


        @Override
        public JWSKeySelector<C> getJWSKeySelector() {

                return jwsKeySelector;
        }


        @Override
        public void setJWSKeySelector(final JWSKeySelector<C> jwsKeySelector) {

                this.jwsKeySelector = jwsKeySelector;
        }


        @Override
        public JWEKeySelector<C> getJWEKeySelector() {

                return jweKeySelector;
        }


        @Override
        public void setJWEKeySelector(final JWEKeySelector<C> jweKeySelector) {

                this.jweKeySelector = jweKeySelector;
        }


        @Override
        public JWSVerifierFactory getJWSVerifierFactory() {

                return jwsVerifierFactory;
        }


        @Override
        public void setJWSVerifierFactory(final JWSVerifierFactory factory) {

                jwsVerifierFactory = factory;
        }


        @Override
        public JWEDecrypterFactory getJWEDecrypterFactory() {

                return jweDecrypterFactory;
        }


        @Override
        public void setJWEDecrypterFactory(final JWEDecrypterFactory factory) {

                jweDecrypterFactory = factory;
        }


        @Override
        public JWTClaimsVerifier getJWTClaimsVerifier() {

                return claimsVerifier;
        }


        @Override
        public void setJWTClaimsVerifier(final JWTClaimsVerifier claimsVerifier) {

                this.claimsVerifier = claimsVerifier;
        }


        /**
         * Verifies the claims of the specified JWT.
         *
         * @param jwt The JWT. Must be in a state which allows the claims to
         *            be extracted.
         *
         * @return The JWT claims set.
         *
         * @throws BadJWTException If the JWT claims are invalid or rejected.
         */
        private JWTClaimsSet verifyAndReturnClaims(final JWT jwt)
                throws BadJWTException {

                JWTClaimsSet claimsSet;

                try {
                        claimsSet = jwt.getJWTClaimsSet();

                } catch (ParseException e) {
                        // Payload not a JSON object
                        throw new BadJWTException(e.getMessage(), e);
                }

                if (getJWTClaimsVerifier() != null) {
                        getJWTClaimsVerifier().verify(claimsSet);
                }

                return claimsSet;
        }


        @Override
        public JWTClaimsSet process(final String jwtString, final C context)
                throws ParseException, BadJOSEException, JOSEException {

                return process(JWTParser.parse(jwtString), context);
        }


        @Override
        public JWTClaimsSet process(final JWT jwt, final C context)
                throws BadJOSEException, JOSEException {

                if (jwt instanceof SignedJWT) {
                        return process((SignedJWT)jwt, context);
                }

                if (jwt instanceof EncryptedJWT) {
                        return process((EncryptedJWT)jwt, context);
                }

                if (jwt instanceof PlainJWT) {
                        return process((PlainJWT)jwt, context);
                }

                // Should never happen
                throw new JOSEException("Unexpected JWT object type: " + jwt.getClass());
        }


        @Override
        public JWTClaimsSet process(final PlainJWT plainJWT, final C context)
                throws BadJOSEException, JOSEException {

                verifyAndReturnClaims(plainJWT); // just check claims, no return

                throw PLAIN_JWT_REJECTED_EXCEPTION;
        }


        @Override
        public JWTClaimsSet process(final SignedJWT signedJWT, final C context)
                throws BadJOSEException, JOSEException {

                if (getJWSKeySelector() == null) {
                        // JWS key selector may have been deliberately omitted
                        throw NO_JWS_KEY_SELECTOR_EXCEPTION;
                }

                if (getJWSVerifierFactory() == null) {
                        throw NO_JWS_VERIFIER_FACTORY_EXCEPTION;
                }

                List<? extends Key> keyCandidates = getJWSKeySelector().selectJWSKeys(signedJWT.getHeader(), context);

                if (keyCandidates == null || keyCandidates.isEmpty()) {
                        throw NO_JWS_KEY_CANDIDATES_EXCEPTION;
                }

                ListIterator<? extends Key> it = keyCandidates.listIterator();

                while (it.hasNext()) {

                        JWSVerifier verifier = getJWSVerifierFactory().createJWSVerifier(signedJWT.getHeader(), it.next());

                        if (verifier == null) {
                                continue;
                        }

                        final boolean validSignature = signedJWT.verify(verifier);

                        if (validSignature) {
                                return verifyAndReturnClaims(signedJWT);
                        }

                        if (! it.hasNext()) {
                                // No more keys to try out
                                throw INVALID_SIGNATURE;
                        }
                }

                throw NO_MATCHING_VERIFIERS_EXCEPTION;
        }


        @Override
        public JWTClaimsSet process(final EncryptedJWT encryptedJWT, final C context)
                throws BadJOSEException, JOSEException {

                if (getJWEKeySelector() == null) {
                        // JWE key selector may have been deliberately omitted
                        throw NO_JWE_KEY_SELECTOR_EXCEPTION;
                }

                if (getJWEDecrypterFactory() == null) {
                        throw NO_JWE_DECRYPTER_FACTORY_EXCEPTION;
                }

                List<? extends Key> keyCandidates = getJWEKeySelector().selectJWEKeys(encryptedJWT.getHeader(), context);

                if (keyCandidates == null || keyCandidates.isEmpty()) {
                        throw NO_JWE_KEY_CANDIDATES_EXCEPTION;
                }

                ListIterator<? extends Key> it = keyCandidates.listIterator();

                while (it.hasNext()) {

                        JWEDecrypter decrypter = getJWEDecrypterFactory().createJWEDecrypter(encryptedJWT.getHeader(), it.next());

                        if (decrypter == null) {
                                continue;
                        }

                        try {
                                encryptedJWT.decrypt(decrypter);

                        } catch (JOSEException e) {

                                if (it.hasNext()) {
                                        // Try next key
                                        continue;
                                }

                                // No more keys to try
                                throw new BadJWEException("Encrypted JWT rejected: " + e.getMessage(), e);
                        }

                        if ("JWT".equalsIgnoreCase(encryptedJWT.getHeader().getContentType())) {

                                // Handle nested signed JWT, see http://tools.ietf.org/html/rfc7519#section-5.2
                                SignedJWT nestedJWT = encryptedJWT.getPayload().toSignedJWT();

                                if (nestedJWT == null) {
                                        // Cannot parse payload to signed JWT
                                        throw INVALID_NESTED_JWT_EXCEPTION;
                                }

                                return process(nestedJWT, context);
                        }

                        return verifyAndReturnClaims(encryptedJWT);
                }

                throw NO_MATCHING_DECRYPTERS_EXCEPTION;
        }
}