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/*
 * Copyright (c) 2010-2017, KolibriFX AS. Licensed under the Apache License, version 2.0.
 */

package com.kolibrifx.plovercrest.server.internal;

import java.nio.BufferOverflowException;
import java.nio.ByteBuffer;
import com.kolibrifx.plovercrest.server.streams.StreamObserver;

/**
 * Stream observer that appends data (starting with the timestamp) to a ByteBuffer, which must have
 * enough space to contain the timestamp and bytes.
 * 
 * On a buffer overflow, the overflow handler is invoked, and the put operations are retried (once).
 * 
 * The observe() function always returns the ByteBuffer given to the constructor.
 */
public class ByteBufferStreamObserver implements StreamObserver {
    private final ByteBuffer targetBuffer;
    private final OverflowHandler overflowHandler;
    private long lastValidTimestamp = -1;

    public ByteBufferStreamObserver(final ByteBuffer targetBuffer, final OverflowHandler overflowHandler) {
        this.targetBuffer = targetBuffer;
        this.overflowHandler = overflowHandler;
    }

    @Override
    public void onObserve(final long timestamp, final long index, final ByteBuffer element) {
        final int mark = targetBuffer.position();
        try {
            targetBuffer.putLong(timestamp);
            targetBuffer.put(element);
        } catch (final BufferOverflowException e) {
            targetBuffer.position(mark);
            overflowHandler.writeChunk();
            //targetBuffer.clear();
            targetBuffer.putLong(timestamp);
            targetBuffer.put(element);
        }
    }

    @Override
    public void onObserveEnd(final long lastValidTimestamp, final long elementCount) {
        this.lastValidTimestamp = lastValidTimestamp;
    }

    @Override
    public void onObserveFrozen() {
    }

    public long getLastValidTimestamp() {
        return lastValidTimestamp;
    }
}