package com.nimbusds.jose.crypto;


import java.util.HashSet;
import java.util.Set;
import javax.crypto.SecretKey;

import com.nimbusds.jose.EncryptionMethod;
import com.nimbusds.jose.JOSEException;
import com.nimbusds.jose.JWEAlgorithm;
import com.nimbusds.jose.JWEDecrypter;
import com.nimbusds.jose.JWEHeader;
import com.nimbusds.jose.util.Base64URL;
import com.nimbusds.jose.util.StringUtils;
import net.jcip.annotations.ThreadSafe;


/**
 * Direct decrypter of {@link com.nimbusds.jose.JWEObject JWE objects} with a
 * shared symmetric key. This class is thread-safe.
 *
 * <p>Supports the following JWE algorithms:
 *
 * <ul>
 *     <li>{@link com.nimbusds.jose.JWEAlgorithm#DIR}
 * </ul>
 *
 * <p>Supports the following encryption methods:
 *
 * <ul>
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A128CBC_HS256}
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A192CBC_HS384}
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A256CBC_HS512}
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A128GCM}
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A192GCM}
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A256GCM}
 * </ul>
 *
 * <p>Accepts all {@link com.nimbusds.jose.JWEHeader#getRegisteredParameterNames
 * registered JWE header parameters}. Use {@link #setAcceptedAlgorithms} and
 * {@link #setAcceptedEncryptionMethods} to restrict the acceptable JWE
 * algorithms and encryption methods.
 * 
 * @author Vladimir Dzhuvinov
 * @version $version$ (2014-07-08)
 */
@ThreadSafe
public class DirectDecrypter extends DirectCryptoProvider implements JWEDecrypter {


        /**
         * The accepted JWE algorithms.
         */
        private Set<JWEAlgorithm> acceptedAlgs =
                new HashSet<>(supportedAlgorithms());


        /**
         * The accepted encryption methods.
         */
        private Set<EncryptionMethod> acceptedEncs =
                new HashSet<>(supportedEncryptionMethods());


        /**
         * The critical header parameter checker.
         */
        private final CriticalHeaderParameterChecker critParamChecker =
                new CriticalHeaderParameterChecker();


        /**
         * Creates a new direct decrypter.
         *
         * @param key The shared symmetric key. Its algorithm must be "AES".
         *            Must be 128 bits (16 bytes), 192 bits (24 bytes), 256
         *            bits (32 bytes), 384 bits (48 bytes) or 512 bits
         *            (64 bytes) long. Must not be {@code null}.
         *
         * @throws JOSEException If the key length is unexpected.
         */
        public DirectDecrypter(final SecretKey key)
                throws JOSEException {

                super(key);
        }


        /**
         * Creates a new direct decrypter.
         *
         * @param keyBytes The shared symmetric key, as a byte array. Must be 
         *                 128 bits (16 bytes), 192 bits (24 bytes), 256 bits
         *                 (32 bytes), 384 bits (48 bytes) or 512 bits (64
         *                 bytes) long. Must not be {@code null}.
         *
         * @throws JOSEException If the key length is unexpected.
         */
        public DirectDecrypter(final byte[] keyBytes)
                throws JOSEException {

                super(keyBytes);
        }


        @Override
        public Set<JWEAlgorithm> getAcceptedAlgorithms() {

                return acceptedAlgs;
        }


        @Override
        public void setAcceptedAlgorithms(final Set<JWEAlgorithm> acceptedAlgs) {

                if (acceptedAlgs == null) {
                        throw new IllegalArgumentException("The accepted JWE algorithms must not be null");
                }

                if (! supportedAlgorithms().containsAll(acceptedAlgs)) {
                        throw new IllegalArgumentException("Unsupported JWE algorithm(s)");
                }

                this.acceptedAlgs = acceptedAlgs;
        }


        @Override
        public Set<EncryptionMethod> getAcceptedEncryptionMethods() {

                return acceptedEncs;
        }


        @Override
        public void setAcceptedEncryptionMethods(final Set<EncryptionMethod> acceptedEncs) {

                if (acceptedEncs == null)
                        throw new IllegalArgumentException("The accepted encryption methods must not be null");

                if (!supportedEncryptionMethods().containsAll(acceptedEncs)) {
                        throw new IllegalArgumentException("Unsupported encryption method(s)");
                }

                this.acceptedEncs = acceptedEncs;
        }


        @Override
        public Set<String> getIgnoredCriticalHeaderParameters() {

                return critParamChecker.getIgnoredCriticalHeaders();
        }


        @Override
        public void setIgnoredCriticalHeaderParameters(final Set<String> headers) {

                critParamChecker.setIgnoredCriticalHeaders(headers);
        }


        @Override
        public byte[] decrypt(final JWEHeader header,
                              final Base64URL encryptedKey,
                              final Base64URL iv,
                              final Base64URL cipherText,
                              final Base64URL authTag) 
                throws JOSEException {

                // Validate required JWE parts
                if (encryptedKey != null) {

                        throw new JOSEException("Unexpected encrypted key, must be omitted");
                }       

                if (iv == null) {

                        throw new JOSEException("The initialization vector (IV) must not be null");
                }

                if (authTag == null) {

                        throw new JOSEException("The authentication tag must not be null");
                }
                

                JWEAlgorithm alg = header.getAlgorithm();

                if (! alg.equals(JWEAlgorithm.DIR)) {

                        throw new JOSEException("Unsupported algorithm, must be \"dir\"");
                }

                if (! critParamChecker.headerPasses(header)) {

                        throw new JOSEException("Unsupported critical header parameter");
                }

                // Compose the AAD
                byte[] aad = StringUtils.toByteArray(header.toBase64URL().toString());

                // Decrypt the cipher text according to the JWE enc
                EncryptionMethod enc = header.getEncryptionMethod();

                byte[] plainText;

                if (enc.equals(EncryptionMethod.A128CBC_HS256) || enc.equals(EncryptionMethod.A192CBC_HS384) || enc.equals(EncryptionMethod.A256CBC_HS512)) {

                        plainText = AESCBC.decryptAuthenticated(getKey(), iv.decode(), cipherText.decode(), aad, authTag.decode(), contentEncryptionProvider, macProvider);

                } else if (enc.equals(EncryptionMethod.A128GCM) || enc.equals(EncryptionMethod.A192GCM) || enc.equals(EncryptionMethod.A256GCM)) {

                        plainText = AESGCM.decrypt(getKey(), iv.decode(), cipherText.decode(), aad, authTag.decode(), contentEncryptionProvider);

                } else {

                        throw new JOSEException("Unsupported encryption method, must be A128CBC_HS256, A192CBC_HS384, A256CBC_HS512, A128GCM, A192GCM or A128GCM");
                }


                // Apply decompression if requested
                return DeflateHelper.applyDecompression(header, plainText);
        }
}