/*
 * Copyright 2002-2020 the original author or authors.
 *
 * 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
 *
 *      https://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 org.springframework.web.servlet.mvc.condition;

import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.Set;

import javax.servlet.http.HttpServletRequest;

import org.springframework.lang.Nullable;
import org.springframework.util.ObjectUtils;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.cors.CorsUtils;

/**
 * A logical conjunction (' && ') request condition that matches a request against
 * a set of header expressions with syntax defined in {@link RequestMapping#headers()}.
 *
 * <p>Expressions passed to the constructor with header names 'Accept' or
 * 'Content-Type' are ignored. See {@link ConsumesRequestCondition} and
 * {@link ProducesRequestCondition} for those.
 *
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @since 3.1
 */
public final class HeadersRequestCondition extends AbstractRequestCondition<HeadersRequestCondition> {

        private static final HeadersRequestCondition PRE_FLIGHT_MATCH = new HeadersRequestCondition();


        private final Set<HeaderExpression> expressions;


        /**
         * Create a new instance from the given header expressions. Expressions with
         * header names 'Accept' or 'Content-Type' are ignored. See {@link ConsumesRequestCondition}
         * and {@link ProducesRequestCondition} for those.
         * @param headers media type expressions with syntax defined in {@link RequestMapping#headers()};
         * if 0, the condition will match to every request
         */
        public HeadersRequestCondition(String... headers) {
                this.expressions = parseExpressions(headers);
        }

        private static Set<HeaderExpression> parseExpressions(String... headers) {
                Set<HeaderExpression> result = null;
                if (!ObjectUtils.isEmpty(headers)) {
                        for (String header : headers) {
                                HeaderExpression expr = new HeaderExpression(header);
                                if ("Accept".equalsIgnoreCase(expr.name) || "Content-Type".equalsIgnoreCase(expr.name)) {
                                        continue;
                                }
                                result = (result != null ? result : new LinkedHashSet<>(headers.length));
                                result.add(expr);
                        }
                }
                return (result != null ? result : Collections.emptySet());
        }

        private HeadersRequestCondition(Set<HeaderExpression> conditions) {
                this.expressions = conditions;
        }


        /**
         * Return the contained request header expressions.
         */
        public Set<NameValueExpression<String>> getExpressions() {
                return new LinkedHashSet<>(this.expressions);
        }

        @Override
        protected Collection<HeaderExpression> getContent() {
                return this.expressions;
        }

        @Override
        protected String getToStringInfix() {
                return " && ";
        }

        /**
         * Returns a new instance with the union of the header expressions
         * from "this" and the "other" instance.
         */
        @Override
        public HeadersRequestCondition combine(HeadersRequestCondition other) {
                if (isEmpty() && other.isEmpty()) {
                        return this;
                }
                else if (other.isEmpty()) {
                        return this;
                }
                else if (isEmpty()) {
                        return other;
                }
                Set<HeaderExpression> set = new LinkedHashSet<>(this.expressions);
                set.addAll(other.expressions);
                return new HeadersRequestCondition(set);
        }

        /**
         * Returns "this" instance if the request matches all expressions;
         * or {@code null} otherwise.
         */
        @Override
        @Nullable
        public HeadersRequestCondition getMatchingCondition(HttpServletRequest request) {
                if (CorsUtils.isPreFlightRequest(request)) {
                        return PRE_FLIGHT_MATCH;
                }
                for (HeaderExpression expression : this.expressions) {
                        if (!expression.match(request)) {
                                return null;
                        }
                }
                return this;
        }

        /**
         * Compare to another condition based on header expressions. A condition
         * is considered to be a more specific match, if it has:
         * <ol>
         * <li>A greater number of expressions.
         * <li>A greater number of non-negated expressions with a concrete value.
         * </ol>
         * <p>It is assumed that both instances have been obtained via
         * {@link #getMatchingCondition(HttpServletRequest)} and each instance
         * contains the matching header expression only or is otherwise empty.
         */
        @Override
        public int compareTo(HeadersRequestCondition other, HttpServletRequest request) {
                int result = other.expressions.size() - this.expressions.size();
                if (result != 0) {
                        return result;
                }
                return (int) (getValueMatchCount(other.expressions) - getValueMatchCount(this.expressions));
        }

        private long getValueMatchCount(Set<HeaderExpression> expressions) {
                long count = 0;
                for (HeaderExpression e : expressions) {
                        if (e.getValue() != null && !e.isNegated()) {
                                count++;
                        }
                }
                return count;
        }


        /**
         * Parses and matches a single header expression to a request.
         */
        static class HeaderExpression extends AbstractNameValueExpression<String> {

                HeaderExpression(String expression) {
                        super(expression);
                }

                @Override
                protected boolean isCaseSensitiveName() {
                        return false;
                }

                @Override
                protected String parseValue(String valueExpression) {
                        return valueExpression;
                }

                @Override
                protected boolean matchName(HttpServletRequest request) {
                        return (request.getHeader(this.name) != null);
                }

                @Override
                protected boolean matchValue(HttpServletRequest request) {
                        return ObjectUtils.nullSafeEquals(this.value, request.getHeader(this.name));
                }
        }

}