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/*
 * Copyright 2023 Greptime Team
 *
 * 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.greptime.common.util;

import java.util.IdentityHashMap;
import java.util.Map;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Resource holder with ref count.
 */
public class RcResourceHolder {

    private static final Logger LOG = LoggerFactory.getLogger(RcResourceHolder.class);

    private final Map, Instance> instances = new IdentityHashMap<>();

    public synchronized T get(ObjectPool.Resource resource) {
        Instance ins = this.instances.get(resource);
        if (ins == null) {
            ins = new Instance<>(resource.create());
            this.instances.put(resource, ins);
            LOG.info("[RcResourceHolder] create instance: {}.", ins);
        }
        ins.inc();
        return ins.payload();
    }

    public synchronized void release(ObjectPool.Resource resource, T returned) {
        Instance cached = this.instances.get(resource);
        Ensures.ensureNonNull(cached, "No cached instance found for " + resource);
        Ensures.ensure(
                returned == cached.payload(),
                "Releasing the wrong instance, expected=%s, actual=%s",
                cached.payload(),
                returned);
        Ensures.ensure(cached.rc() > 0, "RefCount has already reached zero");
        if (cached.decAndGet() == 0) {
            LOG.info("[RcResourceHolder] close instance: {}.", cached);
            resource.close(cached.payload());
            this.instances.remove(resource);
        }
    }

    private static class Instance {
        final T payload;
        int refCount;
        int maxRefCount;

        Instance(T payload) {
            this.payload = payload;
        }

        void inc() {
            this.refCount++;
            this.maxRefCount = Math.max(this.maxRefCount, this.refCount);
        }

        int decAndGet() {
            return --this.refCount;
        }

        int rc() {
            return this.refCount;
        }

        T payload() {
            return this.payload;
        }

        @Override
        public String toString() {
            return "Instance{" + "payload=" + payload + ", refCount=" + refCount + ", maxRefCount=" + maxRefCount + '}';
        }
    }
}