/*
 * 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.reactive.result.condition;

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;

import org.springframework.http.HttpMethod;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.lang.Nullable;
import org.springframework.util.ObjectUtils;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.cors.reactive.CorsUtils;
import org.springframework.web.server.ServerWebExchange;

/**
 * A logical disjunction (' || ') request condition that matches a request
 * against a set of {@link RequestMethod RequestMethods}.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public final class RequestMethodsRequestCondition extends AbstractRequestCondition<RequestMethodsRequestCondition> {

        /** Per HTTP method cache to return ready instances from getMatchingCondition. */
        private static final Map<HttpMethod, RequestMethodsRequestCondition> requestMethodConditionCache;

        static {
                requestMethodConditionCache = new HashMap<>(RequestMethod.values().length);
                for (RequestMethod method : RequestMethod.values()) {
                        requestMethodConditionCache.put(
                                        HttpMethod.valueOf(method.name()), new RequestMethodsRequestCondition(method));
                }
        }


        private final Set<RequestMethod> methods;


        /**
         * Create a new instance with the given request methods.
         * @param requestMethods 0 or more HTTP request methods;
         * if, 0 the condition will match to every request
         */
        public RequestMethodsRequestCondition(RequestMethod... requestMethods) {
                this.methods = (ObjectUtils.isEmpty(requestMethods) ?
                                Collections.emptySet() : new LinkedHashSet<>(Arrays.asList(requestMethods)));
        }

        /**
         * Private constructor for internal use when combining conditions.
         */
        private RequestMethodsRequestCondition(Set<RequestMethod> requestMethods) {
                this.methods = requestMethods;
        }


        /**
         * Returns all {@link RequestMethod RequestMethods} contained in this condition.
         */
        public Set<RequestMethod> getMethods() {
                return this.methods;
        }

        @Override
        protected Collection<RequestMethod> getContent() {
                return this.methods;
        }

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

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

        /**
         * Check if any of the HTTP request methods match the given request and
         * return an instance that contains the matching HTTP request method only.
         * @param exchange the current exchange
         * @return the same instance if the condition is empty (unless the request
         * method is HTTP OPTIONS), a new condition with the matched request method,
         * or {@code null} if there is no match or the condition is empty and the
         * request method is OPTIONS.
         */
        @Override
        @Nullable
        public RequestMethodsRequestCondition getMatchingCondition(ServerWebExchange exchange) {
                if (CorsUtils.isPreFlightRequest(exchange.getRequest())) {
                        return matchPreFlight(exchange.getRequest());
                }
                if (getMethods().isEmpty()) {
                        if (RequestMethod.OPTIONS.name().equals(exchange.getRequest().getMethodValue())) {
                                return null; // We handle OPTIONS transparently, so don't match if no explicit declarations
                        }
                        return this;
                }
                return matchRequestMethod(exchange.getRequest().getMethod());
        }

        /**
         * On a pre-flight request match to the would-be, actual request.
         * Hence empty conditions is a match, otherwise try to match to the HTTP
         * method in the "Access-Control-Request-Method" header.
         */
        @Nullable
        private RequestMethodsRequestCondition matchPreFlight(ServerHttpRequest request) {
                if (getMethods().isEmpty()) {
                        return this;
                }
                HttpMethod expectedMethod = request.getHeaders().getAccessControlRequestMethod();
                return expectedMethod != null ? matchRequestMethod(expectedMethod) : null;
        }

        @Nullable
        private RequestMethodsRequestCondition matchRequestMethod(@Nullable HttpMethod httpMethod) {
                if (httpMethod == null) {
                        return null;
                }
                RequestMethod requestMethod = RequestMethod.valueOf(httpMethod.name());
                if (getMethods().contains(requestMethod)) {
                        return requestMethodConditionCache.get(httpMethod);
                }
                if (requestMethod.equals(RequestMethod.HEAD) && getMethods().contains(RequestMethod.GET)) {
                        return requestMethodConditionCache.get(HttpMethod.GET);
                }
                return null;
        }

        /**
         * Returns:
         * <ul>
         * <li>0 if the two conditions contain the same number of HTTP request methods
         * <li>Less than 0 if "this" instance has an HTTP request method but "other" doesn't
         * <li>Greater than 0 "other" has an HTTP request method but "this" doesn't
         * </ul>
         * <p>It is assumed that both instances have been obtained via
         * {@link #getMatchingCondition(ServerWebExchange)} and therefore each instance
         * contains the matching HTTP request method only or is otherwise empty.
         */
        @Override
        public int compareTo(RequestMethodsRequestCondition other, ServerWebExchange exchange) {
                if (other.methods.size() != this.methods.size()) {
                        return other.methods.size() - this.methods.size();
                }
                else if (this.methods.size() == 1) {
                        if (this.methods.contains(RequestMethod.HEAD) && other.methods.contains(RequestMethod.GET)) {
                                return -1;
                        }
                        else if (this.methods.contains(RequestMethod.GET) && other.methods.contains(RequestMethod.HEAD)) {
                                return 1;
                        }
                }
                return 0;
        }

}