/*
 * 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.web.servlet.mvc.condition;

import java.util.Collection;
import java.util.Collections;

import javax.servlet.http.HttpServletRequest;

import org.springframework.lang.Nullable;

A holder for a RequestCondition useful when the type of the request condition is not known ahead of time, e.g. custom condition. Since this class is also an implementation of RequestCondition, effectively it decorates the held request condition and allows it to be combined and compared with other request conditions in a type and null safe way. 
When two RequestConditionHolder instances are combined or compared with each other, it is expected the conditions they hold are of the same type. If they are not, a ClassCastException is raised. 
Author:
Rossen Stoyanchev
Since:
3.1/**
 * A holder for a {@link RequestCondition} useful when the type of the request
 * condition is not known ahead of time, e.g. custom condition. Since this
 * class is also an implementation of {@code RequestCondition}, effectively it
 * decorates the held request condition and allows it to be combined and compared
 * with other request conditions in a type and null safe way.
 *
 * <p>When two {@code RequestConditionHolder} instances are combined or compared
 * with each other, it is expected the conditions they hold are of the same type.
 * If they are not, a {@link ClassCastException} is raised.
 *
 * @author Rossen Stoyanchev
 * @since 3.1
 */
public final class RequestConditionHolder extends AbstractRequestCondition<RequestConditionHolder> {

	@Nullable
	private final RequestCondition<Object> condition;


	
Create a new holder to wrap the given request condition.
Params:
requestCondition – the condition to hold, may be null/**
	 * Create a new holder to wrap the given request condition.
	 * @param requestCondition the condition to hold, may be {@code null}
	 */
	@SuppressWarnings("unchecked")
	public RequestConditionHolder(@Nullable RequestCondition<?> requestCondition) {
		this.condition = (RequestCondition<Object>) requestCondition;
	}


	
Return the held request condition, or null if not holding one. /**
	 * Return the held request condition, or {@code null} if not holding one.
	 */
	@Nullable
	public RequestCondition<?> getCondition() {
		return this.condition;
	}

	@Override
	protected Collection<?> getContent() {
		return (this.condition != null ? Collections.singleton(this.condition) : Collections.emptyList());
	}

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

	
Combine the request conditions held by the two RequestConditionHolder
instances after making sure the conditions are of the same type.
Or if one holder is empty, the other holder is returned.
/**
	 * Combine the request conditions held by the two RequestConditionHolder
	 * instances after making sure the conditions are of the same type.
	 * Or if one holder is empty, the other holder is returned.
	 */
	@Override
	public RequestConditionHolder combine(RequestConditionHolder other) {
		if (this.condition == null && other.condition == null) {
			return this;
		}
		else if (this.condition == null) {
			return other;
		}
		else if (other.condition == null) {
			return this;
		}
		else {
			assertEqualConditionTypes(this.condition, other.condition);
			RequestCondition<?> combined = (RequestCondition<?>) this.condition.combine(other.condition);
			return new RequestConditionHolder(combined);
		}
	}

	
Ensure the held request conditions are of the same type.
/**
	 * Ensure the held request conditions are of the same type.
	 */
	private void assertEqualConditionTypes(RequestCondition<?> thisCondition, RequestCondition<?> otherCondition) {
		Class<?> clazz = thisCondition.getClass();
		Class<?> otherClazz = otherCondition.getClass();
		if (!clazz.equals(otherClazz)) {
			throw new ClassCastException("Incompatible request conditions: " + clazz + " and " + otherClazz);
		}
	}

	
Get the matching condition for the held request condition wrap it in a
new RequestConditionHolder instance. Or otherwise if this is an empty
holder, return the same holder instance.
/**
	 * Get the matching condition for the held request condition wrap it in a
	 * new RequestConditionHolder instance. Or otherwise if this is an empty
	 * holder, return the same holder instance.
	 */
	@Override
	@Nullable
	public RequestConditionHolder getMatchingCondition(HttpServletRequest request) {
		if (this.condition == null) {
			return this;
		}
		RequestCondition<?> match = (RequestCondition<?>) this.condition.getMatchingCondition(request);
		return (match != null ? new RequestConditionHolder(match) : null);
	}

	
Compare the request conditions held by the two RequestConditionHolder
instances after making sure the conditions are of the same type.
Or if one holder is empty, the other holder is preferred.
/**
	 * Compare the request conditions held by the two RequestConditionHolder
	 * instances after making sure the conditions are of the same type.
	 * Or if one holder is empty, the other holder is preferred.
	 */
	@Override
	public int compareTo(RequestConditionHolder other, HttpServletRequest request) {
		if (this.condition == null && other.condition == null) {
			return 0;
		}
		else if (this.condition == null) {
			return 1;
		}
		else if (other.condition == null) {
			return -1;
		}
		else {
			assertEqualConditionTypes(this.condition, other.condition);
			return this.condition.compareTo(other.condition, request);
		}
	}

}