/*
 * Copyright (c) 2015 Pantheon Technologies s.r.o. and others. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.openflowjava.protocol.impl.core.connection;

import com.google.common.base.Preconditions;
import com.google.common.base.Verify;
import com.google.common.util.concurrent.FutureCallback;
import io.netty.channel.Channel;
import java.util.Iterator;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import javax.annotation.Nonnull;
import javax.annotation.concurrent.GuardedBy;
import org.opendaylight.yang.gen.v1.urn.opendaylight.openflow.protocol.rev130731.OfHeader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

final class StackedOutboundQueue extends AbstractStackedOutboundQueue {
    private static final Logger LOG = LoggerFactory.getLogger(StackedOutboundQueue.class);
    private static final AtomicLongFieldUpdater<StackedOutboundQueue> BARRIER_XID_UPDATER = AtomicLongFieldUpdater.newUpdater(StackedOutboundQueue.class, "barrierXid");

    private volatile long allocatedXid = -1;
    private volatile long barrierXid = -1;

    StackedOutboundQueue(final AbstractOutboundQueueManager<?, ?> manager) {
        super(manager);
    }

    @GuardedBy("unflushedSegments")
    private void ensureSegment(final StackedSegment first, final int offset) {
        final int segmentOffset = offset / StackedSegment.SEGMENT_SIZE;
        LOG.debug("Queue {} slow offset {} maps to {} segments {}", this, offset, segmentOffset, unflushedSegments.size());

        for (int i = unflushedSegments.size(); i <= segmentOffset; ++i) {
            final StackedSegment newSegment = StackedSegment.create(first.getBaseXid() + (StackedSegment.SEGMENT_SIZE * i));
            LOG.debug("Adding segment {}", newSegment);
            unflushedSegments.add(newSegment);
        }

        allocatedXid = uncompletedSegments.get(uncompletedSegments.size() - 1).getEndXid();
    }

    /*
     * This method is expected to be called from multiple threads concurrently.
     */
    @Override
    public Long reserveEntry() {
        final long xid = LAST_XID_UPDATER.incrementAndGet(this);
        final StackedSegment fastSegment = firstSegment;

        if (xid >= fastSegment.getBaseXid() + StackedSegment.SEGMENT_SIZE) {
           if (xid >= allocatedXid) {
                // Multiple segments, this a slow path
                LOG.debug("Queue {} falling back to slow reservation for XID {}", this, xid);

                synchronized (unflushedSegments) {
                    LOG.debug("Queue {} executing slow reservation for XID {}", this, xid);

                    // Shutdown was scheduled, need to fail the reservation
                    if (shutdownOffset != null) {
                        LOG.debug("Queue {} is being shutdown, failing reservation", this);
                        return null;
                    }

                    // Ensure we have the appropriate segment for the specified XID
                    final StackedSegment slowSegment = firstSegment;
                    final int slowOffset = (int) (xid - slowSegment.getBaseXid());
                    Verify.verify(slowOffset >= 0);

                    // Now, we let's see if we need to allocate a new segment
                    ensureSegment(slowSegment, slowOffset);

                    LOG.debug("Queue {} slow reservation finished", this);
                }
            } else {
                LOG.debug("Queue {} XID {} is already backed", this, xid);
            }
        }

        LOG.trace("Queue {} allocated XID {}", this, xid);
        return xid;
    }

    /*
     * This method is expected to be called from multiple threads concurrently
     */
    @Override
    public void commitEntry(final Long xid, final OfHeader message, final FutureCallback<OfHeader> callback) {
        final StackedSegment fastSegment = firstSegment;
        final long calcOffset = xid - fastSegment.getBaseXid();
        Preconditions.checkArgument(calcOffset >= 0, "Commit of XID %s does not match up with base XID %s", xid, fastSegment.getBaseXid());

        Verify.verify(calcOffset <= Integer.MAX_VALUE);
        final int fastOffset = (int) calcOffset;

        final OutboundQueueEntry entry;
        if (fastOffset >= StackedSegment.SEGMENT_SIZE) {
            LOG.debug("Queue {} falling back to slow commit of XID {} at offset {}", this, xid, fastOffset);

            final StackedSegment segment;
            final int slowOffset;
            synchronized (unflushedSegments) {
                final StackedSegment slowSegment = firstSegment;
                final long slowCalcOffset = xid - slowSegment.getBaseXid();
                Verify.verify(slowCalcOffset >= 0 && slowCalcOffset <= Integer.MAX_VALUE);
                slowOffset = (int) slowCalcOffset;

                LOG.debug("Queue {} recalculated offset of XID {} to {}", this, xid, slowOffset);
                segment = unflushedSegments.get(slowOffset / StackedSegment.SEGMENT_SIZE);
            }

            final int segOffset = slowOffset % StackedSegment.SEGMENT_SIZE;
            entry = segment.getEntry(segOffset);
            LOG.debug("Queue {} slow commit of XID {} completed at offset {} (segment {} offset {})", this, xid, slowOffset, segment, segOffset);
        } else {
            entry = fastSegment.getEntry(fastOffset);
        }

        entry.commit(message, callback);
        if (entry.isBarrier()) {
            long my = xid;
            for (;;) {
                final long prev = BARRIER_XID_UPDATER.getAndSet(this, my);
                if (prev < my) {
                    LOG.debug("Queue {} recorded pending barrier XID {}", this, my);
                    break;
                }

                // We have traveled back, recover
                LOG.debug("Queue {} retry pending barrier {} >= {}", this, prev, my);
                my = prev;
            }
        }

        LOG.trace("Queue {} committed XID {}", this, xid);
        manager.ensureFlushing();
    }

    @Override
    int writeEntries(@Nonnull final Channel channel, final long now) {
        // Local cache
        StackedSegment segment = firstSegment;
        int entries = 0;

        while (channel.isWritable()) {
            final OutboundQueueEntry entry = segment.getEntry(flushOffset);
            if (!entry.isCommitted()) {
                LOG.debug("Queue {} XID {} segment {} offset {} not committed yet", this, segment.getBaseXid() + flushOffset, segment, flushOffset);
                break;
            }

            LOG.trace("Queue {} flushing entry at offset {}", this, flushOffset);
            final OfHeader message = entry.takeMessage();
            flushOffset++;
            entries++;

            if (message != null) {
                manager.writeMessage(message, now);
            } else {
                entry.complete(null);
            }

            if (flushOffset >= StackedSegment.SEGMENT_SIZE) {
                /*
                 * Slow path: purge the current segment unless it's the last one.
                 * If it is, we leave it for replacement when a new reservation
                 * is run on it.
                 *
                 * This costs us two slow paths, but hey, this should be very rare,
                 * so let's keep things simple.
                 */
                synchronized (unflushedSegments) {
                    LOG.debug("Flush offset {} unflushed segments {}", flushOffset, unflushedSegments.size());

                    // We may have raced ahead of reservation code and need to allocate a segment
                    ensureSegment(segment, flushOffset);

                    // Remove the segment, update the firstSegment and reset flushOffset
                    final StackedSegment oldSegment = unflushedSegments.remove(0);
                    if (oldSegment.isComplete()) {
                        uncompletedSegments.remove(oldSegment);
                        oldSegment.recycle();
                    }

                    // Reset the first segment and add it to the uncompleted list
                    segment = unflushedSegments.get(0);
                    uncompletedSegments.add(segment);

                    // Update the shutdown offset
                    if (shutdownOffset != null) {
                        shutdownOffset -= StackedSegment.SEGMENT_SIZE;
                    }

                    // Allow reservations back on the fast path by publishing the new first segment
                    firstSegment = segment;

                    flushOffset = 0;
                    LOG.debug("Queue {} flush moved to segment {}", this, segment);
                }
            }
        }

        return entries;
    }

    Long reserveBarrierIfNeeded() {
        final long bXid = barrierXid;
        final long fXid = firstSegment.getBaseXid() + flushOffset;
        if (bXid >= fXid) {
            LOG.debug("Barrier found at XID {} (currently at {})", bXid, fXid);
            return null;
        }
        return reserveEntry();
    }

    @Override
    boolean pairRequest(final OfHeader message) {
        Iterator<StackedSegment> it = uncompletedSegments.iterator();
        while (it.hasNext()) {
            final StackedSegment queue = it.next();
            final OutboundQueueEntry entry = queue.pairRequest(message);
            if (entry == null) {
                continue;
            }

            LOG.trace("Queue {} accepted response {}", queue, message);

            // This has been a barrier request, we need to flush all
            // previous queues
            if (entry.isBarrier() && uncompletedSegments.size() > 1) {
                LOG.trace("Queue {} indicated request was a barrier", queue);

                it = uncompletedSegments.iterator();
                while (it.hasNext()) {
                    final StackedSegment q = it.next();

                    // We want to complete all queues before the current one, we will
                    // complete the current queue below
                    if (!queue.equals(q)) {
                        LOG.trace("Queue {} is implied finished", q);
                        q.completeAll();
                        it.remove();
                        q.recycle();
                    } else {
                        break;
                    }
                }
            }

            if (queue.isComplete()) {
                LOG.trace("Queue {} is finished", queue);
                it.remove();
                queue.recycle();
            }

            return true;
        }

        LOG.debug("Failed to find completion for message {}", message);
        return false;
    }
}