/*
 * 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.
 */
package org.apache.tomcat.dbcp.pool2.impl;

import java.io.PrintWriter;
import java.time.Clock;
import java.time.Duration;
import java.time.Instant;
import java.util.Deque;

import org.apache.tomcat.dbcp.pool2.PooledObject;
import org.apache.tomcat.dbcp.pool2.PooledObjectState;
import org.apache.tomcat.dbcp.pool2.TrackedUse;

/**
 * This wrapper is used to track the additional information, such as state, for
 * the pooled objects.
 * <p>
 * This class is intended to be thread-safe.
 * </p>
 *
 * @param <T> the type of object in the pool
 * @since 2.0
 */
public class DefaultPooledObject<T> implements PooledObject<T> {

    private final T object;
    private PooledObjectState state = PooledObjectState.IDLE; // @GuardedBy("this") to ensure transitions are valid
    private final Clock systemClock = Clock.systemUTC();
    private final Instant createInstant = now();

    private volatile Instant lastBorrowInstant = createInstant;
    private volatile Instant lastUseInstant = createInstant;
    private volatile Instant lastReturnInstant = createInstant;
    private volatile boolean logAbandoned;
    private volatile CallStack borrowedBy = NoOpCallStack.INSTANCE;
    private volatile CallStack usedBy = NoOpCallStack.INSTANCE;
    private volatile long borrowedCount;

    /**
     * Creates a new instance that wraps the provided object so that the pool can
     * track the state of the pooled object.
     *
     * @param object The object to wrap
     */
    public DefaultPooledObject(final T object) {
        this.object = object;
    }

    /**
     * Allocates the object.
     *
     * @return {@code true} if the original state was {@link PooledObjectState#IDLE IDLE}
     */
    @Override
    public synchronized boolean allocate() {
        if (state == PooledObjectState.IDLE) {
            state = PooledObjectState.ALLOCATED;
            lastBorrowInstant = now();
            lastUseInstant = lastBorrowInstant;
            borrowedCount++;
            if (logAbandoned) {
                borrowedBy.fillInStackTrace();
            }
            return true;
        }
        if (state == PooledObjectState.EVICTION) {
            // TODO Allocate anyway and ignore eviction test
            state = PooledObjectState.EVICTION_RETURN_TO_HEAD;
        }
        // TODO if validating and testOnBorrow == true then pre-allocate for
        // performance
        return false;
    }

    @Override
    public int compareTo(final PooledObject<T> other) {
        final int compareTo = getLastReturnInstant().compareTo(other.getLastReturnInstant());
        if (compareTo == 0) {
            // Make sure the natural ordering is broadly consistent with equals
            // although this will break down if distinct objects have the same
            // identity hash code.
            // see java.lang.Comparable Javadocs
            return System.identityHashCode(this) - System.identityHashCode(other);
        }
        return compareTo;
    }

    /**
     * Deallocates the object and sets it {@link PooledObjectState#IDLE IDLE}
     * if it is currently {@link PooledObjectState#ALLOCATED ALLOCATED}
     * or {@link PooledObjectState#RETURNING RETURNING}.
     *
     * @return {@code true} if the state was {@link PooledObjectState#ALLOCATED ALLOCATED}
     *         or {@link PooledObjectState#RETURNING RETURNING}.
     */
    @Override
    public synchronized boolean deallocate() {
        if (state == PooledObjectState.ALLOCATED || state == PooledObjectState.RETURNING) {
            state = PooledObjectState.IDLE;
            lastReturnInstant = now();
            borrowedBy.clear();
            return true;
        }

        return false;
    }

    @Override
    public synchronized boolean endEvictionTest(
            final Deque<PooledObject<T>> idleQueue) {
        if (state == PooledObjectState.EVICTION) {
            state = PooledObjectState.IDLE;
            return true;
        }
        if (state == PooledObjectState.EVICTION_RETURN_TO_HEAD) {
            state = PooledObjectState.IDLE;
            idleQueue.offerFirst(this);
        }

        return false;
    }

    @Override
    public long getActiveTimeMillis() {
        return getActiveDuration().toMillis();
    }

    /**
     * Gets the number of times this object has been borrowed.
     * @return The number of times this object has been borrowed.
     * @since 2.1
     */
    @Override
    public long getBorrowedCount() {
        return borrowedCount;
    }

    @Override
    public Instant getCreateInstant() {
        return createInstant;
    }

    @Override
    public long getCreateTime() {
        return createInstant.toEpochMilli();
    }

    @Override
    public Duration getIdleDuration() {
        // elapsed may be negative if:
        // - another thread updates lastReturnInstant during the calculation window
        // - System.currentTimeMillis() is not monotonic (e.g. system time is set back)
        final Duration elapsed = Duration.between(lastReturnInstant, now());
        return elapsed.isNegative() ? Duration.ZERO : elapsed;
    }

    @Override
    public Duration getIdleTime() {
        return getIdleDuration();
    }

    @Override
    public long getIdleTimeMillis() {
        return getIdleDuration().toMillis();
    }

    @Override
    public Instant getLastBorrowInstant() {
        return lastBorrowInstant;
    }

    @Override
    public long getLastBorrowTime() {
        return lastBorrowInstant.toEpochMilli();
    }

    @Override
    public Instant getLastReturnInstant() {
        return lastReturnInstant;
    }

    @Override
    public long getLastReturnTime() {
        return lastReturnInstant.toEpochMilli();
    }

    /**
     * Gets an estimate of the last time this object was used.  If the class
     * of the pooled object implements {@link TrackedUse}, what is returned is
     * the maximum of {@link TrackedUse#getLastUsedInstant()} and
     * {@link #getLastBorrowTime()}; otherwise this method gives the same
     * value as {@link #getLastBorrowTime()}.
     *
     * @return the last Instant this object was used.
     */
    @Override
    public Instant getLastUsedInstant() {
        if (object instanceof TrackedUse) {
            return PoolImplUtils.max(((TrackedUse) object).getLastUsedInstant(), lastUseInstant);
        }
        return lastUseInstant;
    }

    /**
     * Gets an estimate of the last time this object was used.  If the class
     * of the pooled object implements {@link TrackedUse}, what is returned is
     * the maximum of {@link TrackedUse#getLastUsedInstant()} and
     * {@link #getLastBorrowTime()}; otherwise this method gives the same
     * value as {@link #getLastBorrowTime()}.
     *
     * @return the last time this object was used
     */
    @Override
    public long getLastUsedTime() {
        return getLastUsedInstant().toEpochMilli();
    }

    @Override
    public T getObject() {
        return object;
    }

    /**
     * Gets the state of this object.
     * @return state
     */
    @Override
    public synchronized PooledObjectState getState() {
        return state;
    }

    /**
     * Sets the state to {@link PooledObjectState#INVALID INVALID}.
     */
    @Override
    public synchronized void invalidate() {
        state = PooledObjectState.INVALID;
    }

    /**
     * Marks the pooled object as {@link PooledObjectState#ABANDONED ABANDONED}.
     */
    @Override
    public synchronized void markAbandoned() {
        state = PooledObjectState.ABANDONED;
    }

    /**
     * Marks the pooled object as {@link PooledObjectState#RETURNING RETURNING}.
     */
    @Override
    public synchronized void markReturning() {
        state = PooledObjectState.RETURNING;
    }

    /**
     * Gets the current instant of the clock.
     *
     * @return the current instant of the clock.
     */
    private Instant now() {
        return systemClock.instant();
    }

    @Override
    public void printStackTrace(final PrintWriter writer) {
        boolean written = borrowedBy.printStackTrace(writer);
        written |= usedBy.printStackTrace(writer);
        if (written) {
            writer.flush();
        }
    }

    @Override
    public void setLogAbandoned(final boolean logAbandoned) {
        this.logAbandoned = logAbandoned;
    }

    /**
     * Configures the stack trace generation strategy based on whether or not fully
     * detailed stack traces are required. When set to false, abandoned logs may
     * only include caller class information rather than method names, line numbers,
     * and other normal metadata available in a full stack trace.
     *
     * @param requireFullStackTrace the new configuration setting for abandoned object
     *                              logging
     * @since 2.5
     */
    @Override
    public void setRequireFullStackTrace(final boolean requireFullStackTrace) {
        borrowedBy = CallStackUtils.newCallStack("'Pooled object created' " +
            "yyyy-MM-dd HH:mm:ss Z 'by the following code has not been returned to the pool:'",
            true, requireFullStackTrace);
        usedBy = CallStackUtils.newCallStack("The last code to use this object was:",
            false, requireFullStackTrace);
    }

    @Override
    public synchronized boolean startEvictionTest() {
        if (state == PooledObjectState.IDLE) {
            state = PooledObjectState.EVICTION;
            return true;
        }
        return false;
    }

    @Override
    public String toString() {
        final StringBuilder result = new StringBuilder();
        result.append("Object: ");
        result.append(object.toString());
        result.append(", State: ");
        synchronized (this) {
            result.append(state.toString());
        }
        return result.toString();
        // TODO add other attributes
    }

    @Override
    public void use() {
        lastUseInstant = now();
        usedBy.fillInStackTrace();
    }

}