/*
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */
package org.apache.hc.core5.pool;

import java.io.Closeable;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.ListIterator;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import org.apache.hc.core5.annotation.Contract;
import org.apache.hc.core5.annotation.ThreadingBehavior;
import org.apache.hc.core5.concurrent.BasicFuture;
import org.apache.hc.core5.concurrent.FutureCallback;
import org.apache.hc.core5.function.Callback;
import org.apache.hc.core5.util.Args;
import org.apache.hc.core5.util.Asserts;
import org.apache.hc.core5.util.LangUtils;

/**
 * Connection pool with strict max connection limit guarantees.
 *
 * @param <T> route
 * @param <C> connection object
 *
 * @since 4.2
 */
@Contract(threading = ThreadingBehavior.SAFE_CONDITIONAL)
public class StrictConnPool<T, C extends Closeable> implements ControlledConnPool<T, C> {

    private final long timeToLive;
    private final TimeUnit timeUnit;
    private final ConnPoolListener<T> connPoolListener;
    private final ConnPoolPolicy policy;
    private final Map<T, RoutePool<T, C>> routeToPool;
    private final LinkedList<LeaseRequest<T, C>> leasingRequests;
    private final Set<PoolEntry<T, C>> leased;
    private final LinkedList<PoolEntry<T, C>> available;
    private final ConcurrentLinkedQueue<LeaseRequest<T, C>> completedRequests;
    private final Map<T, Integer> maxPerRoute;
    private final Lock lock;
    private final AtomicBoolean isShutDown;

    private volatile int defaultMaxPerRoute;
    private volatile int maxTotal;

    /**
     * @since 5.0
     */
    public StrictConnPool(
            final int defaultMaxPerRoute,
            final int maxTotal,
            final long timeToLive,
            final TimeUnit timeUnit,
            final ConnPoolPolicy policy,
            final ConnPoolListener<T> connPoolListener) {
        super();
        Args.positive(defaultMaxPerRoute, "Max per route value");
        Args.positive(maxTotal, "Max total value");
        this.timeToLive = timeToLive;
        this.timeUnit = timeUnit != null ? timeUnit : TimeUnit.MILLISECONDS;
        this.connPoolListener = connPoolListener;
        this.policy = policy != null ? policy : ConnPoolPolicy.LIFO;
        this.routeToPool = new HashMap<>();
        this.leasingRequests = new LinkedList<>();
        this.leased = new HashSet<>();
        this.available = new LinkedList<>();
        this.completedRequests = new ConcurrentLinkedQueue<>();
        this.maxPerRoute = new HashMap<>();
        this.lock = new ReentrantLock();
        this.isShutDown = new AtomicBoolean(false);
        this.defaultMaxPerRoute = defaultMaxPerRoute;
        this.maxTotal = maxTotal;
    }

    public StrictConnPool(final int defaultMaxPerRoute, final int maxTotal) {
        this(defaultMaxPerRoute, maxTotal, 0, TimeUnit.MILLISECONDS, ConnPoolPolicy.LIFO, null);
    }

    public boolean isShutdown() {
        return this.isShutDown.get();
    }

    @Override
    public void shutdown() {
        if (this.isShutDown.compareAndSet(false, true)) {
            fireCallbacks();
            this.lock.lock();
            try {
                for (final RoutePool<T, C> pool: this.routeToPool.values()) {
                    pool.shutdown();
                }
                this.routeToPool.clear();
                this.leased.clear();
                this.available.clear();
                this.leasingRequests.clear();
            } finally {
                this.lock.unlock();
            }
        }
    }

    @Override
    public void close() throws Exception {
        shutdown();
    }

    private RoutePool<T, C> getPool(final T route) {
        RoutePool<T, C> pool = this.routeToPool.get(route);
        if (pool == null) {
            pool = new RoutePool<>(route);
            this.routeToPool.put(route, pool);
        }
        return pool;
    }

    public Future<PoolEntry<T, C>> lease(
            final T route, final Object state,
            final long leaseTimeout, final TimeUnit tunit,
            final FutureCallback<PoolEntry<T, C>> callback) {
        Args.notNull(route, "Route");
        Args.notNull(tunit, "Time unit");
        Asserts.check(!this.isShutDown.get(), "Connection pool shut down");
        final BasicFuture<PoolEntry<T, C>> future = new BasicFuture<>(callback);
        this.lock.lock();
        try {
            final LeaseRequest<T, C> request = new LeaseRequest<>(route, state, leaseTimeout, future);
            final boolean completed = processPendingRequest(request);
            if (!request.isDone() && !completed) {
                this.leasingRequests.add(request);
            }
            if (request.isDone()) {
                this.completedRequests.add(request);
            }
        } finally {
            this.lock.unlock();
        }
        fireCallbacks();
        return future;
    }

    @Override
    public Future<PoolEntry<T, C>> lease(final T route, final Object state, final FutureCallback<PoolEntry<T, C>> callback) {
        return lease(route, state, -1, TimeUnit.MICROSECONDS, callback);
    }

    public Future<PoolEntry<T, C>> lease(final T route, final Object state) {
        return lease(route, state, -1, TimeUnit.MICROSECONDS, null);
    }

    @Override
    public void release(final PoolEntry<T, C> entry, final boolean reusable) {
        if (entry == null) {
            return;
        }
        if (this.isShutDown.get()) {
            return;
        }
        if (!reusable) {
            entry.discardConnection();
        }
        this.lock.lock();
        try {
            if (this.leased.remove(entry)) {
                final RoutePool<T, C> pool = getPool(entry.getRoute());
                final boolean keepAlive = entry.hasConnection() && reusable;
                pool.free(entry, keepAlive);
                if (keepAlive) {
                    switch (policy) {
                        case LIFO:
                            this.available.addFirst(entry);
                            break;
                        case FIFO:
                            this.available.addLast(entry);
                            break;
                        default:
                            throw new IllegalStateException("Unexpected ConnPoolPolicy value: " + policy);
                    }
                    if (this.connPoolListener != null) {
                        this.connPoolListener.onRelease(entry.getRoute(), this);
                    }
                } else {
                    entry.discardConnection();
                }
                processNextPendingRequest();
            }
        } finally {
            this.lock.unlock();
        }
        fireCallbacks();
    }

    private void processPendingRequests() {
        final ListIterator<LeaseRequest<T, C>> it = this.leasingRequests.listIterator();
        while (it.hasNext()) {
            final LeaseRequest<T, C> request = it.next();
            final BasicFuture<PoolEntry<T, C>> future = request.getFuture();
            if (future.isCancelled()) {
                it.remove();
                continue;
            }
            final boolean completed = processPendingRequest(request);
            if (request.isDone() || completed) {
                it.remove();
            }
            if (request.isDone()) {
                this.completedRequests.add(request);
            }
        }
    }

    private void processNextPendingRequest() {
        final ListIterator<LeaseRequest<T, C>> it = this.leasingRequests.listIterator();
        while (it.hasNext()) {
            final LeaseRequest<T, C> request = it.next();
            final BasicFuture<PoolEntry<T, C>> future = request.getFuture();
            if (future.isCancelled()) {
                it.remove();
                continue;
            }
            final boolean completed = processPendingRequest(request);
            if (request.isDone() || completed) {
                it.remove();
            }
            if (request.isDone()) {
                this.completedRequests.add(request);
            }
            if (completed) {
                return;
            }
        }
    }

    private boolean processPendingRequest(final LeaseRequest<T, C> request) {
        final T route = request.getRoute();
        final Object state = request.getState();
        final long deadline = request.getDeadline();

        final long now = System.currentTimeMillis();
        if (now > deadline) {
            request.failed(new TimeoutException());
            return false;
        }

        final RoutePool<T, C> pool = getPool(route);
        PoolEntry<T, C> entry;
        for (;;) {
            entry = pool.getFree(state);
            if (entry == null) {
                break;
            }
            if (entry.getExpiry() < System.currentTimeMillis()) {
                entry.discardConnection();
                this.available.remove(entry);
                pool.free(entry, false);
            } else {
                break;
            }
        }
        if (entry != null) {
            this.available.remove(entry);
            this.leased.add(entry);
            request.completed(entry);
            if (this.connPoolListener != null) {
                this.connPoolListener.onLease(entry.getRoute(), this);
            }
            return true;
        }

        // New connection is needed
        final int maxPerRoute = getMax(route);
        // Shrink the pool prior to allocating a new connection
        final int excess = Math.max(0, pool.getAllocatedCount() + 1 - maxPerRoute);
        if (excess > 0) {
            for (int i = 0; i < excess; i++) {
                final PoolEntry<T, C> lastUsed = pool.getLastUsed();
                if (lastUsed == null) {
                    break;
                }
                lastUsed.discardConnection();
                this.available.remove(lastUsed);
                pool.remove(lastUsed);
            }
        }

        if (pool.getAllocatedCount() < maxPerRoute) {
            final int freeCapacity = Math.max(this.maxTotal - this.leased.size(), 0);
            if (freeCapacity == 0) {
                return false;
            }
            final int totalAvailable = this.available.size();
            if (totalAvailable > freeCapacity - 1) {
                if (!this.available.isEmpty()) {
                    final PoolEntry<T, C> lastUsed = this.available.removeLast();
                    lastUsed.discardConnection();
                    final RoutePool<T, C> otherpool = getPool(lastUsed.getRoute());
                    otherpool.remove(lastUsed);
                }
            }

            entry = pool.createEntry(this.timeToLive, this.timeUnit);
            this.leased.add(entry);
            request.completed(entry);
            if (this.connPoolListener != null) {
                this.connPoolListener.onLease(entry.getRoute(), this);
            }
            return true;
        }
        return false;
    }

    private void fireCallbacks() {
        LeaseRequest<T, C> request;
        while ((request = this.completedRequests.poll()) != null) {
            final BasicFuture<PoolEntry<T, C>> future = request.getFuture();
            final Exception ex = request.getException();
            final PoolEntry<T, C> result = request.getResult();
            boolean successfullyCompleted = false;
            if (ex != null) {
                future.failed(ex);
            } else if (result != null) {
                if (future.completed(result)) {
                    successfullyCompleted = true;
                }
            } else {
                future.cancel();
            }
            if (!successfullyCompleted) {
                release(result, true);
            }
        }
    }

    public void validatePendingRequests() {
        this.lock.lock();
        try {
            final long now = System.currentTimeMillis();
            final ListIterator<LeaseRequest<T, C>> it = this.leasingRequests.listIterator();
            while (it.hasNext()) {
                final LeaseRequest<T, C> request = it.next();
                final long deadline = request.getDeadline();
                if (now > deadline) {
                    it.remove();
                    request.failed(new TimeoutException());
                    this.completedRequests.add(request);
                }
            }
        } finally {
            this.lock.unlock();
        }
        fireCallbacks();
    }

    private int getMax(final T route) {
        final Integer v = this.maxPerRoute.get(route);
        if (v != null) {
            return v.intValue();
        }
        return this.defaultMaxPerRoute;
    }

    @Override
    public void setMaxTotal(final int max) {
        Args.positive(max, "Max value");
        this.lock.lock();
        try {
            this.maxTotal = max;
        } finally {
            this.lock.unlock();
        }
    }

    @Override
    public int getMaxTotal() {
        this.lock.lock();
        try {
            return this.maxTotal;
        } finally {
            this.lock.unlock();
        }
    }

    @Override
    public void setDefaultMaxPerRoute(final int max) {
        Args.positive(max, "Max value");
        this.lock.lock();
        try {
            this.defaultMaxPerRoute = max;
        } finally {
            this.lock.unlock();
        }
    }

    @Override
    public int getDefaultMaxPerRoute() {
        this.lock.lock();
        try {
            return this.defaultMaxPerRoute;
        } finally {
            this.lock.unlock();
        }
    }

    @Override
    public void setMaxPerRoute(final T route, final int max) {
        Args.notNull(route, "Route");
        Args.positive(max, "Max value");
        this.lock.lock();
        try {
            this.maxPerRoute.put(route, Integer.valueOf(max));
        } finally {
            this.lock.unlock();
        }
    }

    @Override
    public int getMaxPerRoute(final T route) {
        Args.notNull(route, "Route");
        this.lock.lock();
        try {
            return getMax(route);
        } finally {
            this.lock.unlock();
        }
    }

    @Override
    public PoolStats getTotalStats() {
        this.lock.lock();
        try {
            return new PoolStats(
                    this.leased.size(),
                    this.leasingRequests.size(),
                    this.available.size(),
                    this.maxTotal);
        } finally {
            this.lock.unlock();
        }
    }

    @Override
    public PoolStats getStats(final T route) {
        Args.notNull(route, "Route");
        this.lock.lock();
        try {
            final RoutePool<T, C> pool = getPool(route);
            int pendingCount = 0;
            for (LeaseRequest<T, C> request: leasingRequests) {
                if (LangUtils.equals(route, request.getRoute())) {
                    pendingCount++;
                }
            }
            return new PoolStats(
                    pool.getLeasedCount(),
                    pendingCount,
                    pool.getAvailableCount(),
                    getMax(route));
        } finally {
            this.lock.unlock();
        }
    }

    /**
     * Returns snapshot of all knows routes
     *
     * @since 4.4
     */
    public Set<T> getRoutes() {
        this.lock.lock();
        try {
            return new HashSet<>(routeToPool.keySet());
        } finally {
            this.lock.unlock();
        }
    }

    /**
     * Enumerates all available connections.
     *
     * @since 4.3
     */
    public void enumAvailable(final Callback<PoolEntry<T, C>> callback) {
        this.lock.lock();
        try {
            final Iterator<PoolEntry<T, C>> it = this.available.iterator();
            while (it.hasNext()) {
                final PoolEntry<T, C> entry = it.next();
                callback.execute(entry);
                if (!entry.hasConnection()) {
                    final RoutePool<T, C> pool = getPool(entry.getRoute());
                    pool.remove(entry);
                    it.remove();
                }
            }
            processPendingRequests();
            purgePoolMap();
        } finally {
            this.lock.unlock();
        }
    }

    /**
     * Enumerates all leased connections.
     *
     * @since 4.3
     */
    public void enumLeased(final Callback<PoolEntry<T, C>> callback) {
        this.lock.lock();
        try {
            final Iterator<PoolEntry<T, C>> it = this.leased.iterator();
            while (it.hasNext()) {
                final PoolEntry<T, C> entry = it.next();
                callback.execute(entry);
            }
            processPendingRequests();
        } finally {
            this.lock.unlock();
        }
    }

    private void purgePoolMap() {
        final Iterator<Map.Entry<T, RoutePool<T, C>>> it = this.routeToPool.entrySet().iterator();
        while (it.hasNext()) {
            final Map.Entry<T, RoutePool<T, C>> entry = it.next();
            final RoutePool<T, C> pool = entry.getValue();
            if (pool.getAllocatedCount() == 0) {
                it.remove();
            }
        }
    }

    @Override
    public void closeIdle(final long idletime, final TimeUnit tunit) {
        Args.notNull(tunit, "Time unit");
        long time = tunit.toMillis(idletime);
        if (time < 0) {
            time = 0;
        }
        final long deadline = System.currentTimeMillis() - time;
        enumAvailable(new Callback<PoolEntry<T, C>>() {

            @Override
            public void execute(final PoolEntry<T, C> entry) {
                if (entry.getUpdated() <= deadline) {
                    entry.discardConnection();
                }
            }

        });
    }

    @Override
    public void closeExpired() {
        final long now = System.currentTimeMillis();
        enumAvailable(new Callback<PoolEntry<T, C>>() {

            @Override
            public void execute(final PoolEntry<T, C> entry) {
                if (entry.getExpiry() < now) {
                    entry.discardConnection();
                }
            }

        });
    }

    @Override
    public String toString() {
        final StringBuilder buffer = new StringBuilder();
        buffer.append("[leased: ");
        buffer.append(this.leased.size());
        buffer.append("][available: ");
        buffer.append(this.available.size());
        buffer.append("][pending: ");
        buffer.append(this.leasingRequests.size());
        buffer.append("]");
        return buffer.toString();
    }

}