/*
 * 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;

import java.util.HashMap;

import org.springframework.lang.Nullable;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.util.ObjectUtils;
import org.springframework.util.StringUtils;

/**
 * A FlashMap provides a way for one request to store attributes intended for
 * use in another. This is most commonly needed when redirecting from one URL
 * to another -- e.g. the Post/Redirect/Get pattern. A FlashMap is saved before
 * the redirect (typically in the session) and is made available after the
 * redirect and removed immediately.
 *
 * <p>A FlashMap can be set up with a request path and request parameters to
 * help identify the target request. Without this information, a FlashMap is
 * made available to the next request, which may or may not be the intended
 * recipient. On a redirect, the target URL is known and a FlashMap can be
 * updated with that information. This is done automatically when the
 * {@code org.springframework.web.servlet.view.RedirectView} is used.
 *
 * <p>Note: annotated controllers will usually not use FlashMap directly.
 * See {@code org.springframework.web.servlet.mvc.support.RedirectAttributes}
 * for an overview of using flash attributes in annotated controllers.
 *
 * @author Rossen Stoyanchev
 * @since 3.1
 * @see FlashMapManager
 */
@SuppressWarnings("serial")
public final class FlashMap extends HashMap<String, Object> implements Comparable<FlashMap> {

        @Nullable
        private String targetRequestPath;

        private final MultiValueMap<String, String> targetRequestParams = new LinkedMultiValueMap<>(4);

        private long expirationTime = -1;


        /**
         * Provide a URL path to help identify the target request for this FlashMap.
         * <p>The path may be absolute (e.g. "/application/resource") or relative to the
         * current request (e.g. "../resource").
         */
        public void setTargetRequestPath(@Nullable String path) {
                this.targetRequestPath = path;
        }

        /**
         * Return the target URL path (or {@code null} if none specified).
         */
        @Nullable
        public String getTargetRequestPath() {
                return this.targetRequestPath;
        }

        /**
         * Provide request parameters identifying the request for this FlashMap.
         * @param params a Map with the names and values of expected parameters
         */
        public FlashMap addTargetRequestParams(@Nullable MultiValueMap<String, String> params) {
                if (params != null) {
                        params.forEach((key, values) -> {
                                for (String value : values) {
                                        addTargetRequestParam(key, value);
                                }
                        });
                }
                return this;
        }

        /**
         * Provide a request parameter identifying the request for this FlashMap.
         * @param name the expected parameter name (skipped if empty)
         * @param value the expected value (skipped if empty)
         */
        public FlashMap addTargetRequestParam(String name, String value) {
                if (StringUtils.hasText(name) && StringUtils.hasText(value)) {
                        this.targetRequestParams.add(name, value);
                }
                return this;
        }

        /**
         * Return the parameters identifying the target request, or an empty map.
         */
        public MultiValueMap<String, String> getTargetRequestParams() {
                return this.targetRequestParams;
        }

        /**
         * Start the expiration period for this instance.
         * @param timeToLive the number of seconds before expiration
         */
        public void startExpirationPeriod(int timeToLive) {
                this.expirationTime = System.currentTimeMillis() + timeToLive * 1000;
        }

        /**
         * Set the expiration time for the FlashMap. This is provided for serialization
         * purposes but can also be used instead {@link #startExpirationPeriod(int)}.
         * @since 4.2
         */
        public void setExpirationTime(long expirationTime) {
                this.expirationTime = expirationTime;
        }

        /**
         * Return the expiration time for the FlashMap or -1 if the expiration
         * period has not started.
         * @since 4.2
         */
        public long getExpirationTime() {
                return this.expirationTime;
        }

        /**
         * Return whether this instance has expired depending on the amount of
         * elapsed time since the call to {@link #startExpirationPeriod}.
         */
        public boolean isExpired() {
                return (this.expirationTime != -1 && System.currentTimeMillis() > this.expirationTime);
        }


        /**
         * Compare two FlashMaps and prefer the one that specifies a target URL
         * path or has more target URL parameters. Before comparing FlashMap
         * instances ensure that they match a given request.
         */
        @Override
        public int compareTo(FlashMap other) {
                int thisUrlPath = (this.targetRequestPath != null ? 1 : 0);
                int otherUrlPath = (other.targetRequestPath != null ? 1 : 0);
                if (thisUrlPath != otherUrlPath) {
                        return otherUrlPath - thisUrlPath;
                }
                else {
                        return other.targetRequestParams.size() - this.targetRequestParams.size();
                }
        }

        @Override
        public boolean equals(@Nullable Object other) {
                if (this == other) {
                        return true;
                }
                if (!(other instanceof FlashMap)) {
                        return false;
                }
                FlashMap otherFlashMap = (FlashMap) other;
                return (super.equals(otherFlashMap) &&
                                ObjectUtils.nullSafeEquals(this.targetRequestPath, otherFlashMap.targetRequestPath) &&
                                this.targetRequestParams.equals(otherFlashMap.targetRequestParams));
        }

        @Override
        public int hashCode() {
                int result = super.hashCode();
                result = 31 * result + ObjectUtils.nullSafeHashCode(this.targetRequestPath);
                result = 31 * result + this.targetRequestParams.hashCode();
                return result;
        }

        @Override
        public String toString() {
                return "FlashMap [attributes=" + super.toString() + ", targetRequestPath=" +
                                this.targetRequestPath + ", targetRequestParams=" + this.targetRequestParams + "]";
        }

}