package org.jgroups.protocols;

import org.jgroups.*;
import org.jgroups.annotations.MBean;
import org.jgroups.annotations.ManagedAttribute;
import org.jgroups.annotations.Property;
import org.jgroups.stack.Protocol;
import org.jgroups.util.Average;
import org.jgroups.util.MessageBatch;

import java.io.DataInput;
import java.io.DataOutput;
import java.util.function.Supplier;

/**
 * Protocol measuring latency between stacks. On {@link Protocol#down(org.jgroups.Event)}, a header is added to the
 * message with the ID of the PERF protocol and the start time is set in the header.
 * On {@link Protocol#up(org.jgroups.Event)}, the time difference is computed and a rolling average is updated in PERF.<p/>
 * Note that we can have several measurements by inserting PERF protocols with different IDs (Protocol.id) into the stack.</p>
 * If PERF is used to measure latency between nodes running on different physical boxes, it is important that the clocks
 * are synchronized, or else latency cannot be computed correctly (may even be negative).
 * @author Bela Ban
 * @since  3.5
 */
@MBean(description="Measures latency between PERF instances")
public class PERF extends Protocol {
    protected Average avg;
    protected Address local_addr;

    @Property(description="Number of samples to maintain for rolling average")
    protected int     avg_size=20;

    @ManagedAttribute(description="Average latency in ns")
    public double latencyInNs() {return avg.getAverage();}

    @ManagedAttribute(description="Average latency in ms")
    public double latencyInMs() {return avg.getAverage() / 1000000.0;}

    public void init() throws Exception {
        super.init();
        avg=new Average();
    }

    public void resetStats() {
        super.resetStats();
        avg.clear();
    }

    public Object down(Event evt) {
        switch(evt.getType()) {
            case Event.SET_LOCAL_ADDRESS:
                local_addr=evt.getArg();
                break;
        }
        return down_prot.down(evt);
    }

    public Object down(Message msg) {
        msg.putHeader(id, new PerfHeader(System.nanoTime()));
        return down_prot.down(msg);
    }

    public Object up(Message msg) {
        PerfHeader hdr=msg.getHeader(id);
        if(hdr == null)
            log.error("%s: no perf header found", local_addr);
        else {
            long time=System.nanoTime() - hdr.start_time;
            if(time <= 0)
                log.error("%d: time is <= 0", time);
            else
                avg.add(time);
        }
        return up_prot.up(msg);
    }

    public void up(MessageBatch batch) {
        for(Message msg: batch) {
            PerfHeader hdr=msg.getHeader(id);
            if(hdr == null)
                log.error("%s: no perf header found", local_addr);
            else {
                long time=System.nanoTime() - hdr.start_time;
                if(time <= 0)
                    log.error("%d: time is <= 0", time);
                else
                    avg.add(time);
            }
        }

        super.up(batch);
    }

    protected static class PerfHeader extends Header {
        protected long start_time; // in ns

        public PerfHeader() {
        }

        public PerfHeader(long start_time) {
            this.start_time=start_time;
        }
        public short getMagicId() {return 84;}
        public Supplier<? extends Header> create() {
            return PerfHeader::new;
        }

        public int serializedSize() {
            return Global.LONG_SIZE;
        }

        public void writeTo(DataOutput out) throws Exception {
            out.writeLong(start_time);
        }

        public void readFrom(DataInput in) throws Exception {
            start_time=in.readLong();
        }
    }
}
