package net.onrc.onos.core.util;

import java.util.Map.Entry;
import java.util.Queue;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedQueue;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Class for collecting performance measurements.
 */
public class PerformanceMonitor {
    private static final Logger log = LoggerFactory.getLogger(PerformanceMonitor.class);

    // experiment name -> PerformanceMonitor
    private static final ConcurrentHashMap<String, PerformanceMonitor> PERF_MONS = new ConcurrentHashMap<>();

    public static PerformanceMonitor experiment(String name) {
        PerformanceMonitor pm = PERF_MONS.get(name);
        if (pm == null) {
            pm = new PerformanceMonitor();
            PerformanceMonitor existing = PERF_MONS.putIfAbsent(name, pm);
            if (existing != null) {
                pm = existing;
            }
        }
        return pm;
    }

    // tag -> Measurements
    private final ConcurrentHashMap<String, Queue<Measurement>> map = new ConcurrentHashMap<>();
    private long overhead;
    private long experimentStart = Long.MAX_VALUE;
    private static final double NORMALIZATION = Math.pow(10, 6);

    /**
     * Start a performance measurement, identified by a tag.
     * <p/>
     * Note: Only a single measurement can use the same tag at a time.
     * ..... not true anymore.
     *
     * @param tag for performance measurement
     */
    public Measurement startStep(String tag) {
        long start = System.nanoTime();
        if (start < experimentStart) {
            experimentStart = start;
        }
        Queue<Measurement> list = map.get(tag);
        if (list == null) {
            list = new ConcurrentLinkedQueue<Measurement>();
            Queue<Measurement> existingList = map.putIfAbsent(tag, list);
            if (existingList != null) {
                // someone concurrently added, using theirs
                list = existingList;
            }
        }
        Measurement m = new Measurement();
        list.add(m);
        m.start();
        overhead += System.nanoTime() - start;
        return m;
    }

    /**
     * Stop a performance measurement.
     * <p/>
     * You must have already started a measurement with tag.
     *
     * @param tag for performance measurement
     */
    public void stopStep(String tag) {
        long time = System.nanoTime();
        Queue<Measurement> list = map.get(tag);
        if (list == null || list.size() == 0) {
            log.error("Tag {} does not exist", tag);
            overhead += System.nanoTime() - time;
            return;
        }
        list.peek().stop(time);
        if (list.size() > 1) {
            log.error("Tag {} has multiple measurements", tag);
        }
        overhead += System.nanoTime() - time;
    }

    /**
     * Clear all performance measurements.
     */
    public void reset() {
        map.clear();
        overhead = 0;
        experimentStart = Long.MAX_VALUE;
    }

    /**
     * Write all performance measurements to the log.
     */
    public void reportAll() {
        StringBuilder result = new StringBuilder();

        result.append("Performance Results: (avg/start/stop/count)\n");
        if (map.size() == 0) {
            result.append("No Measurements");
            log.error(result.toString());
            return;
        }
        long experimentEnd = -1;
        for (Entry<String, Queue<Measurement>> e : map.entrySet()) {
            String key = e.getKey();
            Queue<Measurement> list = e.getValue();
            long total = 0, count = 0;
            long start = Long.MAX_VALUE, stop = -1;
            for (Measurement m : list) {
                if (m.stop < 0) {
                    continue; // measurement has not been stopped
                }
                // Collect overall start and end times
                if (m.start < start) {
                    start = m.start;
                }
                if (m.stop > stop) {
                    stop = m.stop;
                    if (stop > experimentEnd) {
                        experimentEnd = stop;
                    }
                }
                // Collect statistics for average
                total += m.elapsed();
                count++;
            }
            double avg = (double) total / count;
            // Normalize start/stop
            start -= experimentStart;
            stop -= experimentStart;
            result.append(key + '=' +
                    (avg / NORMALIZATION) + '/' +
                    (start / NORMALIZATION) + '/' +
                    (stop / NORMALIZATION) + '/' +
                    count + '\n');
        }
        double overheadMs = overhead / NORMALIZATION;
        double experimentElapsed = (experimentEnd - experimentStart) / NORMALIZATION;
        result.append("TotalTime:" + experimentElapsed + "/Overhead:" + overheadMs);
        log.error(result.toString());
//      log.error("Performance Results: {} with measurement overhead: {} ms", map, overheadMilli);
    }

    /**
     * Write the performance measurement for a tag to the log.
     *
     * @param tag the tag name.
     */
    public void reportStep(String tag) {
        Queue<Measurement> list = map.get(tag);
        if (list == null) {
            return; //TODO
        }
        //TODO: fix this;
        Measurement m = list.peek();
        if (m != null) {
            log.error("Performance Result: tag = {} start = {} stop = {} elapsed = {}",
                    tag, m.start, m.stop, m.toString());
        } else {
            log.error("Performance Result: unknown tag {}", tag);
        }
    }

    /**
     * A single performance measurement.
     */
    public static class Measurement {
        long start;
        long stop = -1;

        /**
         * Start the measurement.
         */
        public void start() {
            if (start <= 0) {
                start = System.nanoTime();
            }
        }

        /**
         * Stop the measurement.
         */
        public void stop() {
            long now = System.nanoTime();
            stop(now);
        }

        /**
         * Stop the measurement at a specific time.
         *
         * @param time to stop
         */
        public void stop(long time) {
            if (stop <= 0) {
                stop = time;
            }
        }

        /**
         * Compute the elapsed time of the measurement in nanoseconds.
         *
         * @return the measurement time in nanoseconds, or -1 if the measurement is stil running.
         */
        public long elapsed() {
            if (stop <= 0) {
                return -1;
            } else {
                return stop - start;
            }
        }

        /**
         * Returns the number of milliseconds for the measurement as a String.
         */
        @Override
        public String toString() {
            double milli = elapsed() / NORMALIZATION;
            double startMs = start / NORMALIZATION;
            double stopMs = stop / NORMALIZATION;

            return milli + "ms/" + startMs + '/' + stopMs;
        }
    }

    @Deprecated
    private static final PerformanceMonitor PERFORMANCE_MONITOR_INSTANCE = new PerformanceMonitor();

    @Deprecated
    public static Measurement start(String tag) {
        return PERFORMANCE_MONITOR_INSTANCE.startStep(tag);
    }

    @Deprecated
    public static void stop(String tag) {
        PERFORMANCE_MONITOR_INSTANCE.stopStep(tag);
    }

    @Deprecated
    public static void clear() {
        PERFORMANCE_MONITOR_INSTANCE.reset();
    }

    @Deprecated
    public static void report() {
        PERFORMANCE_MONITOR_INSTANCE.reportAll();
    }

    @Deprecated
    public static void report(String tag) {
        PERFORMANCE_MONITOR_INSTANCE.reportStep(tag);
    }

    public static void main(String[] args) {
        // test the measurement overhead
        String tag;
        for (int i = 0; i < 2; i++) {
            tag = "foo foo foo";
            Measurement m;
            m = start(tag);
            System.out.println(tag);
            m.stop();
            m = start(tag);
            System.out.println(tag);
            m.stop();
            m = start(tag);
            System.out.println(tag);
            m.stop();
            m = start(tag);
            System.out.println(tag);
            m.stop();
            tag = "bar";
            start(tag);
            stop(tag);
            tag = "baz";
            start(tag);
            stop(tag);
            report();
            clear();
        }
        for (int i = 0; i < 100; i++) {
            tag = "a";
            start(tag);
            stop(tag);
            start(tag);
            stop(tag);

            start(tag);
            stop(tag);
            start(tag);
            stop(tag);
            start(tag);
            stop(tag);
            start(tag);
            stop(tag);
            start(tag);
            stop(tag);
            start(tag);
            stop(tag);

            tag = "b";
            start(tag);
            stop(tag);
            tag = "c";
            start(tag);
            stop(tag);
            report();
            clear();
        }
    }
}