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Server-side library used by applications created with the JHipster generator, see https://www.jhipster.tech/ for more information on JHipster
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/*
 * Copyright 2016-2020 the original author or authors from the JHipster project.
 *
 * This file is part of the JHipster project, see https://www.jhipster.tech/
 * for more information.
 *
 * 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
 *
 *      http://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 io.github.jhipster.security;

import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Simple time-limited cache for login tokens, necessary to avoid concurrent
 * requests invalidating one another. It uses a {@link java.util.LinkedHashMap}
 * to keep the tokens in order of expiration. During access any entries which
 * have expired are automatically purged.
 */
public class PersistentTokenCache {

    private final long expireMillis;

    private final Map map;
    private long latestWriteTime;

    /**
     * Construct a new TokenCache.
     *
     * @param expireMillis Delay until tokens expire, in millis.
     * @throws java.lang.IllegalArgumentException if expireMillis is non-positive.
     */
    public PersistentTokenCache(long expireMillis) {
        if (expireMillis <= 0l) {
            throw new IllegalArgumentException();
        }
        this.expireMillis = expireMillis;

        map = new LinkedHashMap<>(64, 0.75f);
        latestWriteTime = System.currentTimeMillis();
    }

    /**
     * Get a token from the cache.
     *
     * @param key The key to look for.
     * @return The token, if present and not yet expired, or null otherwise.
     */
    public T get(String key) {
        purge();
        final Value val = map.get(key);
        final long time = System.currentTimeMillis();
        return val != null && time < val.expire ? val.token : null;
    }

    /**
     * Put a token in the cache.
     * If a token already exists for the given key, it is replaced.
     *
     * @param key   The key to insert for.
     * @param token The token to insert.
     */
    public void put(String key, T token) {
        purge();
        if (map.containsKey(key)) {
            map.remove(key);
        }
        final long time = System.currentTimeMillis();
        map.put(key, new Value(token, time + expireMillis));
        latestWriteTime = time;
    }

    /**
     * Get the number of tokens in the cache. Note, this may include expired
     * tokens, unless {@link #purge()} is invoked first.
     *
     * @return The size of the cache.
     */
    public int size() {
        return map.size();
    }

    /**
     * Remove expired entries from the map. This will be called automatically
     * before read/write access, but could be manually invoked if desired.
     */
    public void purge() {
        long time = System.currentTimeMillis();
        if (time - latestWriteTime > expireMillis) {
            // Everything in the map is expired, clear all at once
            map.clear();
        } else {
            // Iterate and remove until the first non-expired token
            Iterator values = map.values().iterator();
            while (values.hasNext()) {
                if (time >= values.next().expire) {
                    values.remove();
                } else {
                    break;
                }
            }
        }
    }


    private class Value {

        private final T token;
        private final long expire;

        Value(T token, long expire) {
            this.token = token;
            this.expire = expire;
        }
    }

}