/*
 * 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.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;

import javax.servlet.DispatcherType;
import javax.servlet.http.HttpServletRequest;

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.lang.Nullable;
import org.springframework.util.CollectionUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.cors.CorsUtils;

A logical disjunction (' || ') request condition that matches a request against a set of RequestMethods. 
Author:
Arjen Poutsma, Rossen Stoyanchev
Since:
3.1/**
 * A logical disjunction (' || ') request condition that matches a request
 * against a set of {@link RequestMethod RequestMethods}.
 *
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @since 3.1
 */
public final class RequestMethodsRequestCondition extends AbstractRequestCondition<RequestMethodsRequestCondition> {

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

	static {
		requestMethodConditionCache = CollectionUtils.newHashMap(RequestMethod.values().length);
		for (RequestMethod method : RequestMethod.values()) {
			requestMethodConditionCache.put(method.name(), new RequestMethodsRequestCondition(method));
		}
	}


	private final Set<RequestMethod> methods;


	
Create a new instance with the given request methods.
Params:
requestMethods – 0 or more HTTP request methods;
if, 0 the condition will match to every request/**
	 * 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 constructor for internal use when combining conditions.
	 */
	private RequestMethodsRequestCondition(Set<RequestMethod> methods) {
		this.methods = methods;
	}


	
Returns all RequestMethods contained in this condition. /**
	 * 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.
/**
	 * 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.
Params:
request – the current request
Returns:
the same instance if the condition is empty (unless the request method is HTTP OPTIONS), a new condition with the matched request method, or null if there is no match or the condition is empty and the request method is OPTIONS./**
	 * 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 request the current request
	 * @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(HttpServletRequest request) {
		if (CorsUtils.isPreFlightRequest(request)) {
			return matchPreFlight(request);
		}

		if (getMethods().isEmpty()) {
			if (RequestMethod.OPTIONS.name().equals(request.getMethod()) &&
					!DispatcherType.ERROR.equals(request.getDispatcherType())) {

				return null; // We handle OPTIONS transparently, so don't match if no explicit declarations
			}
			return this;
		}

		return matchRequestMethod(request.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.
/**
	 * 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(HttpServletRequest request) {
		if (getMethods().isEmpty()) {
			return this;
		}
		String expectedMethod = request.getHeader(HttpHeaders.ACCESS_CONTROL_REQUEST_METHOD);
		return matchRequestMethod(expectedMethod);
	}

	@Nullable
	private RequestMethodsRequestCondition matchRequestMethod(String httpMethodValue) {
		RequestMethod requestMethod;
		try {
			requestMethod = RequestMethod.valueOf(httpMethodValue);
			if (getMethods().contains(requestMethod)) {
				return requestMethodConditionCache.get(httpMethodValue);
			}
			if (requestMethod.equals(RequestMethod.HEAD) && getMethods().contains(RequestMethod.GET)) {
				return requestMethodConditionCache.get(HttpMethod.GET.name());
			}
		}
		catch (IllegalArgumentException ex) {
			// Custom request method
		}
		return null;
	}

	
Returns:

0 if the two conditions contain the same number of HTTP request methods
Less than 0 if "this" instance has an HTTP request method but "other" doesn't
Greater than 0 "other" has an HTTP request method but "this" doesn't

It is assumed that both instances have been obtained via getMatchingCondition(HttpServletRequest) and therefore each instance contains the matching HTTP request method only or is otherwise empty. /**
	 * 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(HttpServletRequest)} and therefore each instance
	 * contains the matching HTTP request method only or is otherwise empty.
	 */
	@Override
	public int compareTo(RequestMethodsRequestCondition other, HttpServletRequest request) {
		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;
	}

}