/*
 * Copyright 2002-2017 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.messaging.handler;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

import org.springframework.messaging.Message;
import org.springframework.util.AntPathMatcher;
import org.springframework.util.PathMatcher;
import org.springframework.util.StringUtils;

/**
 * A {@link MessageCondition} for matching the destination of a Message against one or
 * more destination patterns using a {@link PathMatcher}.
 *
 * @author Rossen Stoyanchev
 * @since 4.0
 */
public class DestinationPatternsMessageCondition extends AbstractMessageCondition<DestinationPatternsMessageCondition> {

        public static final String LOOKUP_DESTINATION_HEADER = "lookupDestination";


        private final Set<String> patterns;

        private final PathMatcher pathMatcher;


        /**
         * Creates a new instance with the given destination patterns.
         * Each pattern that is not empty and does not start with "/" is prepended with "/".
         * @param patterns 0 or more URL patterns; if 0 the condition will match to every request.
         */
        public DestinationPatternsMessageCondition(String... patterns) {
                this(patterns, null);
        }

        /**
         * Alternative constructor accepting a custom PathMatcher.
         * @param patterns the URL patterns to use; if 0, the condition will match to every request.
         * @param pathMatcher the PathMatcher to use
         */
        public DestinationPatternsMessageCondition(String[] patterns, PathMatcher pathMatcher) {
                this(asList(patterns), pathMatcher);
        }

        private DestinationPatternsMessageCondition(Collection<String> patterns, PathMatcher pathMatcher) {
                this.pathMatcher = (pathMatcher != null ? pathMatcher : new AntPathMatcher());
                this.patterns = Collections.unmodifiableSet(prependLeadingSlash(patterns, this.pathMatcher));
        }


        private static List<String> asList(String... patterns) {
                return (patterns != null ? Arrays.asList(patterns) : Collections.<String>emptyList());
        }

        private static Set<String> prependLeadingSlash(Collection<String> patterns, PathMatcher pathMatcher) {
                if (patterns == null) {
                        return Collections.emptySet();
                }
                boolean slashSeparator = pathMatcher.combine("a", "a").equals("a/a");
                Set<String> result = new LinkedHashSet<String>(patterns.size());
                for (String pattern : patterns) {
                        if (slashSeparator) {
                                if (StringUtils.hasLength(pattern) && !pattern.startsWith("/")) {
                                        pattern = "/" + pattern;
                                }
                        }
                        result.add(pattern);
                }
                return result;
        }


        public Set<String> getPatterns() {
                return this.patterns;
        }

        @Override
        protected Collection<String> getContent() {
                return this.patterns;
        }

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


        /**
         * Returns a new instance with URL patterns from the current instance ("this") and
         * the "other" instance as follows:
         * <ul>
         * <li>If there are patterns in both instances, combine the patterns in "this" with
         * the patterns in "other" using {@link org.springframework.util.PathMatcher#combine(String, String)}.
         * <li>If only one instance has patterns, use them.
         * <li>If neither instance has patterns, use an empty String (i.e. "").
         * </ul>
         */
        @Override
        public DestinationPatternsMessageCondition combine(DestinationPatternsMessageCondition other) {
                Set<String> result = new LinkedHashSet<String>();
                if (!this.patterns.isEmpty() && !other.patterns.isEmpty()) {
                        for (String pattern1 : this.patterns) {
                                for (String pattern2 : other.patterns) {
                                        result.add(this.pathMatcher.combine(pattern1, pattern2));
                                }
                        }
                }
                else if (!this.patterns.isEmpty()) {
                        result.addAll(this.patterns);
                }
                else if (!other.patterns.isEmpty()) {
                        result.addAll(other.patterns);
                }
                else {
                        result.add("");
                }
                return new DestinationPatternsMessageCondition(result, this.pathMatcher);
        }

        /**
         * Check if any of the patterns match the given Message destination and return an instance
         * that is guaranteed to contain matching patterns, sorted via
         * {@link org.springframework.util.PathMatcher#getPatternComparator(String)}.
         * @param message the message to match to
         * @return the same instance if the condition contains no patterns;
         * or a new condition with sorted matching patterns;
         * or {@code null} either if a destination can not be extracted or there is no match
         */
        @Override
        public DestinationPatternsMessageCondition getMatchingCondition(Message<?> message) {
                String destination = (String) message.getHeaders().get(LOOKUP_DESTINATION_HEADER);
                if (destination == null) {
                        return null;
                }

                if (this.patterns.isEmpty()) {
                        return this;
                }

                List<String> matches = new ArrayList<String>();
                for (String pattern : this.patterns) {
                        if (pattern.equals(destination) || this.pathMatcher.match(pattern, destination)) {
                                matches.add(pattern);
                        }
                }

                if (matches.isEmpty()) {
                        return null;
                }

                Collections.sort(matches, this.pathMatcher.getPatternComparator(destination));
                return new DestinationPatternsMessageCondition(matches, this.pathMatcher);
        }

        /**
         * Compare the two conditions based on the destination patterns they contain.
         * Patterns are compared one at a time, from top to bottom via
         * {@link org.springframework.util.PathMatcher#getPatternComparator(String)}.
         * If all compared patterns match equally, but one instance has more patterns,
         * it is considered a closer match.
         * <p>It is assumed that both instances have been obtained via
         * {@link #getMatchingCondition(Message)} to ensure they
         * contain only patterns that match the request and are sorted with
         * the best matches on top.
         */
        @Override
        public int compareTo(DestinationPatternsMessageCondition other, Message<?> message) {
                String destination = (String) message.getHeaders().get(LOOKUP_DESTINATION_HEADER);
                if (destination == null) {
                        return 0;
                }
                Comparator<String> patternComparator = this.pathMatcher.getPatternComparator(destination);

                Iterator<String> iterator = patterns.iterator();
                Iterator<String> iteratorOther = other.patterns.iterator();
                while (iterator.hasNext() && iteratorOther.hasNext()) {
                        int result = patternComparator.compare(iterator.next(), iteratorOther.next());
                        if (result != 0) {
                                return result;
                        }
                }
                if (iterator.hasNext()) {
                        return -1;
                }
                else if (iteratorOther.hasNext()) {
                        return 1;
                }
                else {
                        return 0;
                }
        }

}