/*
 * 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));
		}
	}

}
