// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.prelude.statistics;

import com.yahoo.component.chain.dependencies.Before;
import com.yahoo.concurrent.CopyOnWriteHashMap;
import com.yahoo.container.Server;
import com.yahoo.container.protect.Error;
import com.yahoo.jdisc.Metric;
import com.yahoo.log.LogLevel;
import com.yahoo.metrics.simple.MetricSettings;
import com.yahoo.metrics.simple.MetricReceiver;
import com.yahoo.search.Result;
import com.yahoo.search.Searcher;
import com.yahoo.search.result.ErrorHit;
import com.yahoo.search.result.ErrorMessage;
import com.yahoo.search.searchchain.Execution;
import com.yahoo.search.searchchain.PhaseNames;
import com.yahoo.statistics.Callback;
import com.yahoo.statistics.Counter;
import com.yahoo.statistics.Handle;
import com.yahoo.statistics.Value;

import java.util.HashMap;
import java.util.Map;
import java.util.Optional;
import java.util.logging.Level;

import static com.yahoo.container.protect.Error.*;


/**
 * <p>A searcher to gather statistics such as queries completed and query latency.  There
 * may be more than 1 StatisticsSearcher in the Searcher chain, each identified by a
 * Searcher ID.  The statistics accumulated by all StatisticsSearchers are stored
 * in the singleton StatisticsManager object. </p>
 * <p>
 * TODO: Fix events to handle more than one of these searchers properly.
 *
 * @author Gene Meyers
 * @author Steinar Knutsen
 * @author bergum
 */
@Before(PhaseNames.RAW_QUERY)
public class StatisticsSearcher extends Searcher {

    private static final String MAX_QUERY_LATENCY_METRIC = "max_query_latency";
    private static final String EMPTY_RESULTS_METRIC = "empty_results";
    private static final String HITS_PER_QUERY_METRIC = "hits_per_query";
    private static final String TOTALHITS_PER_QUERY_METRIC = "totalhits_per_query";
    private static final String FAILED_QUERIES_METRIC = "failed_queries";
    private static final String MEAN_QUERY_LATENCY_METRIC = "mean_query_latency";
    private static final String QUERY_LATENCY_METRIC = "query_latency";
    private static final String QUERIES_METRIC = "queries";
    private static final String ACTIVE_QUERIES_METRIC = "active_queries";
    private static final String PEAK_QPS_METRIC = "peak_qps";

    private Counter queries; // basic counter
    private Counter failedQueries; // basic counter
    private Counter nullQueries; // basic counter
    private Counter illegalQueries; // basic counter
    private Value queryLatency; // mean pr 5 min
    private Value queryLatencyBuckets;
    private Value maxQueryLatency; // separate to avoid name mangling
    @SuppressWarnings("unused") // all the work is done by the callback
    private Value activeQueries; // raw measure every 5 minutes
    private Value peakQPS; // peak 1s QPS
    private Counter emptyResults; // number of results containing no concrete hits
    private Value hitsPerQuery; // mean number of hits per query
    private long prevMaxQPSTime; // previous measurement time of QPS
    private double queriesForQPS = 0.0;
    private final Object peakQpsLock = new Object();

    private Metric metric;
    private Map<String, Metric.Context> chainContexts = new CopyOnWriteHashMap<>();
    private Map<String, Metric.Context> statePageOnlyContexts = new CopyOnWriteHashMap<>();


    private void initEvents(com.yahoo.statistics.Statistics manager, MetricReceiver metricReceiver) {
        queries = new Counter(QUERIES_METRIC, manager, false);
        failedQueries = new Counter(FAILED_QUERIES_METRIC, manager, false);
        nullQueries = new Counter("null_queries", manager, false);
        illegalQueries = new Counter("illegal_queries", manager, false);
        queryLatency = new Value(MEAN_QUERY_LATENCY_METRIC, manager,
                new Value.Parameters().setLogRaw(false).setLogMean(true).setNameExtension(false));
        maxQueryLatency = new Value(MAX_QUERY_LATENCY_METRIC, manager,
                new Value.Parameters().setLogRaw(false).setLogMax(true).setNameExtension(false));
        queryLatencyBuckets = Value.buildValue("query_latency", manager, null);
        activeQueries = new Value(ACTIVE_QUERIES_METRIC, manager,
                new Value.Parameters().setLogRaw(true).setCallback(new ActivitySampler()));
        peakQPS = new Value(PEAK_QPS_METRIC, manager, new Value.Parameters().setLogRaw(false).setLogMax(true)
                .setNameExtension(false));
        hitsPerQuery = new Value(HITS_PER_QUERY_METRIC, manager,
                new Value.Parameters().setLogRaw(false).setLogMean(true).setNameExtension(false));
        emptyResults = new Counter(EMPTY_RESULTS_METRIC, manager, false);
        metricReceiver.declareGauge(QUERY_LATENCY_METRIC, Optional.empty(), new MetricSettings.Builder().histogram(true).build());
    }

    // Callback to measure queries in flight every five minutes
    private class ActivitySampler implements Callback {
        public void run(Handle h, boolean firstRun) {
            if (firstRun) {
                metric.set(ACTIVE_QUERIES_METRIC, 0, null);
                return;
            }
            // TODO Server.get() is to be removed
            int searchQueriesInFlight = Server.get().searchQueriesInFlight();
            ((Value) h).put(searchQueriesInFlight);
            metric.set(ACTIVE_QUERIES_METRIC, searchQueriesInFlight, null);
        }
    }

    StatisticsSearcher(Metric metric) {
        this(com.yahoo.statistics.Statistics.nullImplementation, metric, MetricReceiver.nullImplementation);
    }

    public StatisticsSearcher(com.yahoo.statistics.Statistics manager, Metric metric, MetricReceiver metricReceiver) {
        this.metric = metric;
        initEvents(manager, metricReceiver);
    }

    public String getMyID() {
        return (getId().stringValue());
    }

    private void qps(long now, Metric.Context metricContext) {
        // We can either have peakQpsLock _or_ have prevMaxQpsTime as a volatile
        // and queriesForQPS as an AtomicInteger. That would lead no locking,
        // but two memory barriers in the common case. Don't change till we know
        // that is actually better.
        synchronized (peakQpsLock) {
            if ((now - prevMaxQPSTime) >= (1000)) {
                double ms = (double) (now - prevMaxQPSTime);
                final double peakQPS = queriesForQPS / (ms / 1000);
                this.peakQPS.put(peakQPS);
                metric.set(PEAK_QPS_METRIC, peakQPS, metricContext);
                queriesForQPS = 1.0d;
                prevMaxQPSTime = now;
            } else {
                queriesForQPS += 1.0d;
            }
        }
    }

    private Metric.Context getChainMetricContext(String chainName) {
        Metric.Context context = chainContexts.get(chainName);
        if (context == null) {
            Map<String, String> dimensions = new HashMap<>();
            dimensions.put("chain", chainName);
            context = this.metric.createContext(dimensions);
            chainContexts.put(chainName, context);
        }
        return context;
    }

    /**
     * Generate statistics for the query passing through this Searcher
     * 1) Add 1 to total query count
     * 2) Add response time to total response time (time from entry to return)
     * 3) .....
     */
    public Result search(com.yahoo.search.Query query, Execution execution) {
        Metric.Context metricContext = getChainMetricContext(execution.chain().getId().stringValue());

        incrQueryCount(metricContext);
        logQuery(query);
        long start = System.currentTimeMillis(); // Start time, in millisecs.
        qps(start, metricContext);
        Result result;
        //handle exceptions thrown below in searchers
        try {
            result = execution.search(query); // Pass on down the chain
        } catch (Exception  e) {
            incrErrorCount(null, metricContext);
            throw e;
        }


        long end = System.currentTimeMillis(); // Start time, in millisecs.
        long latency = end - start;
        if (latency >= 0) {
            addLatency(latency, metricContext);
        } else {
            getLogger().log(LogLevel.WARNING,
                            "Apparently negative latency measure, start: " + start
                            + ", end: " + end + ", for query: " + query.toString());
        }
        if (result.hits().getError() != null) {
            incrErrorCount(result, metricContext);
            incrementStatePageOnlyErrors(result, execution);
        }
        int hitCount = result.getConcreteHitCount();
        hitsPerQuery.put((double) hitCount);
        metric.set(HITS_PER_QUERY_METRIC, (double) hitCount, metricContext);
        metric.set(TOTALHITS_PER_QUERY_METRIC, (double) result.getTotalHitCount(), metricContext);
        if (hitCount == 0) {
            emptyResults.increment();
            metric.add(EMPTY_RESULTS_METRIC, 1, metricContext);
        }

        // Update running averages
        //setAverages();

        return result;
    }

    private void logQuery(com.yahoo.search.Query query) {
        // Don't parse the query if it's not necessary for the logging Query.toString triggers parsing
        if (getLogger().isLoggable(Level.FINER)) {
            getLogger().finer("Query: " + query.toString());
        }
    }

    private void addLatency(long latency, Metric.Context metricContext) {
        //myStats.addLatency(latency);
        queryLatency.put(latency);
        metric.set(QUERY_LATENCY_METRIC, latency, metricContext);
        metric.set(MEAN_QUERY_LATENCY_METRIC, latency, metricContext);
        maxQueryLatency.put(latency);
        metric.set(MAX_QUERY_LATENCY_METRIC, latency, metricContext);
        queryLatencyBuckets.put(latency);
    }

    private void incrQueryCount(Metric.Context metricContext) {
        //myStats.incrQueryCnt();
        queries.increment();
        metric.add(QUERIES_METRIC, 1, metricContext);
    }

    private void incrErrorCount(Result result, Metric.Context metricContext) {
        failedQueries.increment();
        metric.add(FAILED_QUERIES_METRIC, 1, metricContext);

        if (result == null) // the chain threw an exception
            metric.add("error.unhandled_exception", 1, metricContext);
        else if (result.hits().getErrorHit().hasOnlyErrorCode(Error.NULL_QUERY.code))
            nullQueries.increment();
        else if (result.hits().getErrorHit().hasOnlyErrorCode(Error.ILLEGAL_QUERY.code))
            illegalQueries.increment();
    }

    /**
     * Creates error metric for StateHandler only. These metrics are only exposed on /state/v1/metrics page
     * and not forwarded to the log file.
     *
     * @param result The result to check for errors
     */
    private void incrementStatePageOnlyErrors(Result result, Execution execution) {
        if (result == null) return;

        ErrorHit error = result.hits().getErrorHit();
        if (error == null) return;

        for (ErrorMessage m : error.errors()) {
            int code = m.getCode();
            Metric.Context c = getDimensions(m.getSource(), result, execution);
            if (code == TIMEOUT.code) {
                metric.add("error.timeout", 1, c);
            } else if (code == NO_BACKENDS_IN_SERVICE.code) {
                metric.add("error.backends_oos", 1, c);
            } else if (code == ERROR_IN_PLUGIN.code) {
                metric.add("error.plugin_failure", 1, c);
            } else if (code == BACKEND_COMMUNICATION_ERROR.code) {
                metric.add("error.backend_communication_error", 1, c);
            } else if (code == EMPTY_DOCUMENTS.code) {
                metric.add("error.empty_document_summaries", 1, c);
            } else if (code == ILLEGAL_QUERY.code) {
                metric.add("error.illegal_query", 1, c);
            } else if (code == INVALID_QUERY_PARAMETER.code) {
                metric.add("error.invalid_query_parameter", 1, c);
            } else if (code == INTERNAL_SERVER_ERROR.code) {
                metric.add("error.internal_server_error", 1, c);
            } else if (code == SERVER_IS_MISCONFIGURED.code) {
                metric.add("error.misconfigured_server", 1, c);
            } else if (code == INVALID_QUERY_TRANSFORMATION.code) {
                metric.add("error.invalid_query_transformation", 1, c);
            } else if (code == RESULT_HAS_ERRORS.code) {
                metric.add("error.result_with_errors", 1, c);
            } else if (code == UNSPECIFIED.code) {
                metric.add("error.unspecified", 1, c);
            }
        }
    }

    private Metric.Context getDimensions(String source, Result r, Execution execution) {
        Metric.Context context = statePageOnlyContexts.get(source == null ? "" : source);
        if (context == null) {
            Map<String, String> dims = new HashMap<>();
            if (source != null) {
                dims.put("source", source);
            }
            context = this.metric.createContext(dims);
            statePageOnlyContexts.put(source == null ? "" : source, context);
        }
        // TODO add other relevant metric dimensions
        // Would be nice to have chain as a dimension as
        // we can separate errors from different chains
        return context;
    }

}