/*
 * 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;


import java.io.Serializable;
import java.text.ParseException;
import java.util.*;

import com.nimbusds.jose.util.Base64URL;
import com.nimbusds.jose.util.JSONObjectUtils;


/**
 * The base abstract class for unsecured ({@code alg=none}), JSON Web Signature
 * (JWS) and JSON Web Encryption (JWE) headers.
 *
 * <p>The header may also include {@link #getCustomParams custom
 * parameters}; these will be serialised and parsed along the registered ones.
 *
 * @author Vladimir Dzhuvinov
 * @version 2019-10-04
 */
public abstract class Header implements Serializable {


        private static final long serialVersionUID = 1L;


        /**
         * The algorithm ({@code alg}) parameter.
         */
        private final Algorithm alg;


        /**
         * The JOSE object type ({@code typ}) parameter.
         */
        private final JOSEObjectType typ;


        /**
         * The content type ({@code cty}) parameter.
         */
        private final String cty;


        /**
         * The critical headers ({@code crit}) parameter.
         */
        private final Set<String> crit;


        /**
         * Custom header parameters.
         */
        private final Map<String,Object> customParams;


        /**
         * Empty custom parameters constant.
         */
        private static final Map<String,Object> EMPTY_CUSTOM_PARAMS =
                Collections.unmodifiableMap(new HashMap<String,Object>());


        /**
         * The original parsed Base64URL, {@code null} if the header was 
         * created from scratch.
         */
        private final Base64URL parsedBase64URL;


        /**
         * Creates a new abstract header.
         *
         * @param alg             The algorithm ({@code alg}) parameter. Must
         *                        not be {@code null}.
         * @param typ             The type ({@code typ}) parameter,
         *                        {@code null} if not specified.
         * @param cty             The content type ({@code cty}) parameter,
         *                        {@code null} if not specified.
         * @param crit            The names of the critical header
         *                        ({@code crit}) parameters, empty set or
         *                        {@code null} if none.
         * @param customParams    The custom parameters, empty map or
         *                        {@code null} if none.
         * @param parsedBase64URL The parsed Base64URL, {@code null} if the
         *                        header is created from scratch.
         */
        protected Header(final Algorithm alg,
                         final JOSEObjectType typ,
                         final String cty, Set<String> crit,
                         final Map<String,Object> customParams,
                         final Base64URL parsedBase64URL) {

                if (alg == null) {
                        throw new IllegalArgumentException("The algorithm \"alg\" header parameter must not be null");
                }

                this.alg = alg;

                this.typ = typ;
                this.cty = cty;

                if (crit != null) {
                        // Copy and make unmodifiable
                        this.crit = Collections.unmodifiableSet(new HashSet<>(crit));
                } else {
                        this.crit = null;
                }

                if (customParams != null) {
                        // Copy and make unmodifiable
                        this.customParams = Collections.unmodifiableMap(new HashMap<>(customParams));
                } else {
                        this.customParams = EMPTY_CUSTOM_PARAMS;
                }

                this.parsedBase64URL = parsedBase64URL;
        }


        /**
         * Deep copy constructor.
         *
         * @param header The header to copy. Must not be {@code null}.
         */
        protected Header(final Header header) {

                this(
                        header.getAlgorithm(),
                        header.getType(),
                        header.getContentType(),
                        header.getCriticalParams(),
                        header.getCustomParams(),
                        header.getParsedBase64URL());
        }


        /**
         * Gets the algorithm ({@code alg}) parameter.
         *
         * @return The algorithm parameter.
         */
        public Algorithm getAlgorithm() {

                return alg;
        }


        /**
         * Gets the type ({@code typ}) parameter.
         *
         * @return The type parameter, {@code null} if not specified.
         */
        public JOSEObjectType getType() {

                return typ;
        }


        /**
         * Gets the content type ({@code cty}) parameter.
         *
         * @return The content type parameter, {@code null} if not specified.
         */
        public String getContentType() {

                return cty;
        }


        /**
         * Gets the critical header parameters ({@code crit}) parameter.
         *
         * @return The names of the critical header parameters, as a
         *         unmodifiable set, {@code null} if not specified.
         */
        public Set<String> getCriticalParams() {

                return crit;
        }


        /**
         * Gets a custom (non-registered) parameter.
         *
         * @param name The name of the custom parameter. Must not be
         *             {@code null}.
         *
         * @return The custom parameter, {@code null} if not specified.
         */
        public Object getCustomParam(final String name) {

                return customParams.get(name);
        }


        /**
         * Gets the custom (non-registered) parameters.
         *
         * @return The custom parameters, as a unmodifiable map, empty map if
         *         none.
         */
        public Map<String,Object> getCustomParams() {

                return customParams;
        }


        /**
         * Gets the original Base64URL used to create this header.
         *
         * @return The parsed Base64URL, {@code null} if the header was created
         *         from scratch.
         */
        public Base64URL getParsedBase64URL() {

                return parsedBase64URL;
        }


        /**
         * Gets the names of all included parameters (registered and custom) in
         * the header instance.
         *
         * @return The included parameters.
         */
        public Set<String> getIncludedParams() {

                Set<String> includedParameters =
                        new HashSet<>(getCustomParams().keySet());

                includedParameters.add("alg");

                if (getType() != null) {
                        includedParameters.add("typ");
                }

                if (getContentType() != null) {
                        includedParameters.add("cty");
                }

                if (getCriticalParams() != null && ! getCriticalParams().isEmpty()) {
                        includedParameters.add("crit");
                }

                return includedParameters;
        }


        /**
         * Returns a JSON object representation of the header. All custom
         * parameters are included if they serialise to a JSON entity and
         * their names don't conflict with the registered ones.
         *
         * @return The JSON object representation of the header.
         */
        public Map<String, Object> toJSONObject() {

                // Include custom parameters, they will be overwritten if their
                // names match specified registered ones
                Map<String, Object> o = JSONObjectUtils.newJSONObject();
                o.putAll(customParams);

                // Alg is always defined
                o.put("alg", alg.toString());

                if (typ != null) {
                        o.put("typ", typ.toString());
                }

                if (cty != null) {
                        o.put("cty", cty);
                }

                if (crit != null && ! crit.isEmpty()) {
                        o.put("crit", new ArrayList<>(crit));
                }

                return o;
        }


        /**
         * Returns a JSON string representation of the header. All custom
         * parameters will be included if they serialise to a JSON entity and
         * their names don't conflict with the registered ones.
         *
         * @return The JSON string representation of the header.
         */
        public String toString() {

                return JSONObjectUtils.toJSONString(toJSONObject());
        }


        /**
         * Returns a Base64URL representation of the header. If the header was
         * parsed always returns the original Base64URL (required for JWS
         * validation and authenticated JWE decryption).
         *
         * @return The original parsed Base64URL representation of the header,
         *         or a new Base64URL representation if the header was created
         *         from scratch.
         */
        public Base64URL toBase64URL() {

                if (parsedBase64URL == null) {

                        // Header was created from scratch, return new Base64URL
                        return Base64URL.encode(toString());

                } else {

                        // Header was parsed, return original Base64URL
                        return parsedBase64URL;
                }
        }


        /**
         * Parses an algorithm ({@code alg}) parameter from the specified 
         * header JSON object. Intended for initial parsing of unsecured
         * (plain), JWS and JWE headers.
         *
         * <p>The algorithm type (none, JWS or JWE) is determined by inspecting
         * the algorithm name for "none" and the presence of an "enc"
         * parameter.
         *
         * @param json The JSON object to parse. Must not be {@code null}.
         *
         * @return The algorithm, an instance of {@link Algorithm#NONE},
         *         {@link JWSAlgorithm} or {@link JWEAlgorithm}. {@code null}
         *         if not found.
         *
         * @throws ParseException If the {@code alg} parameter couldn't be 
         *                        parsed.
         */
        public static Algorithm parseAlgorithm(final Map<String, Object> json)
                throws ParseException {

                String algName = JSONObjectUtils.getString(json, "alg");
                
                if (algName == null) {
                        throw new ParseException("Missing \"alg\" in header JSON object", 0);
                }

                // Infer algorithm type
                if (algName.equals(Algorithm.NONE.getName())) {
                        // Plain
                        return Algorithm.NONE;
                } else if (json.containsKey("enc")) {
                        // JWE
                        return JWEAlgorithm.parse(algName);
                } else {
                        // JWS
                        return JWSAlgorithm.parse(algName);
                }
        }


        /**
         * Parses a {@link PlainHeader}, {@link JWSHeader} or {@link JWEHeader}
         * from the specified JSON object.
         *
         * @param jsonObject      The JSON object to parse. Must not be
         *                        {@code null}.
         *
         * @return The header.
         *
         * @throws ParseException If the specified JSON object doesn't
         *                        represent a valid header.
         */
        public static Header parse(final Map<String, Object> jsonObject)
                throws ParseException {

                return parse(jsonObject, null);
        }


        /**
         * Parses a {@link PlainHeader}, {@link JWSHeader} or {@link JWEHeader} 
         * from the specified JSON object.
         *
         * @param jsonObject      The JSON object to parse. Must not be
         *                        {@code null}.
         * @param parsedBase64URL The original parsed Base64URL, {@code null}
         *                        if not applicable.
         *
         * @return The header.
         *
         * @throws ParseException If the specified JSON object doesn't 
         *                        represent a valid header.
         */
        public static Header parse(final Map<String, Object> jsonObject,
                                   final Base64URL parsedBase64URL)
                throws ParseException {

                Algorithm alg = parseAlgorithm(jsonObject);

                if (alg.equals(Algorithm.NONE)) {

                        return PlainHeader.parse(jsonObject, parsedBase64URL);

                } else if (alg instanceof JWSAlgorithm) {

                        return JWSHeader.parse(jsonObject, parsedBase64URL);

                } else if (alg instanceof JWEAlgorithm) {

                        return JWEHeader.parse(jsonObject, parsedBase64URL);

                } else {

                        throw new AssertionError("Unexpected algorithm type: " + alg);
                }
        }


        /**
         * Parses a {@link PlainHeader}, {@link JWSHeader} or {@link JWEHeader}
         * from the specified JSON object string.
         *
         * @param jsonString      The JSON object string to parse. Must not be
         *                        {@code null}.
         *
         * @return The header.
         *
         * @throws ParseException If the specified JSON object string doesn't
         *                        represent a valid header.
         */
        public static Header parse(final String jsonString)
                throws ParseException {

                return parse(jsonString, null);
        }


        /**
         * Parses a {@link PlainHeader}, {@link JWSHeader} or {@link JWEHeader}
         * from the specified JSON object string.
         *
         * @param jsonString      The JSON object string to parse. Must not be
         *                        {@code null}.
         * @param parsedBase64URL The original parsed Base64URL, {@code null}
         *                        if not applicable.
         *
         * @return The header.
         *
         * @throws ParseException If the specified JSON object string doesn't
         *                        represent a valid header.
         */
        public static Header parse(final String jsonString,
                                   final Base64URL parsedBase64URL)
                throws ParseException {

                Map<String, Object> jsonObject = JSONObjectUtils.parse(jsonString);

                return parse(jsonObject, parsedBase64URL);
        }


        /**
         * Parses a {@link PlainHeader}, {@link JWSHeader} or {@link JWEHeader}
         * from the specified Base64URL.
         *
         * @param base64URL The Base64URL to parse. Must not be {@code null}.
         *
         * @return The header.
         *
         * @throws ParseException If the specified Base64URL doesn't represent
         *                        a valid header.
         */
        public static Header parse(final Base64URL base64URL)
                throws ParseException {

                return parse(base64URL.decodeToString(), base64URL);
        }
}