/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the "Elastic License
 * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
 * Public License v 1"; you may not use this file except in compliance with, at
 * your election, the "Elastic License 2.0", the "GNU Affero General Public
 * License v3.0 only", or the "Server Side Public License, v 1".
 */

package org.elasticsearch.threadpool;

import org.elasticsearch.common.collect.Iterators;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;
import org.elasticsearch.common.io.stream.Writeable;
import org.elasticsearch.common.xcontent.ChunkedToXContent;
import org.elasticsearch.common.xcontent.ChunkedToXContentHelper;
import org.elasticsearch.xcontent.ToXContent;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;

import static java.util.Collections.emptyIterator;
import static org.elasticsearch.common.collect.Iterators.single;

public record ThreadPoolStats(Collection<Stats> stats) implements Writeable, ChunkedToXContent, Iterable<ThreadPoolStats.Stats> {

    public static final ThreadPoolStats IDENTITY = new ThreadPoolStats(List.of());

    public static ThreadPoolStats merge(ThreadPoolStats first, ThreadPoolStats second) {
        var mergedThreadPools = new HashMap<String, Stats>();

        first.forEach(stats -> mergedThreadPools.merge(stats.name, stats, Stats::merge));
        second.forEach(stats -> mergedThreadPools.merge(stats.name, stats, Stats::merge));

        return new ThreadPoolStats(mergedThreadPools.values());
    }

    public record Stats(String name, int threads, int queue, int active, long rejected, int largest, long completed)
        implements
            Writeable,
            ChunkedToXContent,
            Comparable<Stats> {

        public Stats(StreamInput in) throws IOException {
            this(in.readString(), in.readInt(), in.readInt(), in.readInt(), in.readLong(), in.readInt(), in.readLong());
        }

        static Stats merge(Stats firstStats, Stats secondStats) {
            return new Stats(
                firstStats.name,
                sumStat(firstStats.threads, secondStats.threads),
                sumStat(firstStats.queue, secondStats.queue),
                sumStat(firstStats.active, secondStats.active),
                sumStat(firstStats.rejected, secondStats.rejected),
                sumStat(firstStats.largest, secondStats.largest),
                sumStat(firstStats.completed, secondStats.completed)
            );
        }

        static int sumStat(int first, int second) {
            if (first == -1 && second == -1) {
                return -1;
            } else if (first == -1) {
                return second;
            } else if (second == -1) {
                return first;
            } else {
                return first + second;
            }
        }

        static long sumStat(long first, long second) {
            if (first == -1 && second == -1) {
                return -1;
            } else if (first == -1) {
                return second;
            } else if (second == -1) {
                return first;
            } else {
                return first + second;
            }
        }

        @Override
        public void writeTo(StreamOutput out) throws IOException {
            out.writeString(name);
            out.writeInt(threads);
            out.writeInt(queue);
            out.writeInt(active);
            out.writeLong(rejected);
            out.writeInt(largest);
            out.writeLong(completed);
        }

        @Override
        public int compareTo(Stats other) {
            if ((name() == null) && (other.name() == null)) {
                return 0;
            } else if ((name() != null) && (other.name() == null)) {
                return 1;
            } else if (name() == null) {
                return -1;
            } else {
                int compare = name().compareTo(other.name());
                if (compare == 0) {
                    compare = Integer.compare(threads(), other.threads());
                }
                return compare;
            }
        }

        @Override
        public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params outerParams) {
            return Iterators.concat(
                ChunkedToXContentHelper.startObject(name),
                threads != -1 ? single((builder, params) -> builder.field(Fields.THREADS, threads)) : emptyIterator(),
                queue != -1 ? single((builder, params) -> builder.field(Fields.QUEUE, queue)) : emptyIterator(),
                active != -1 ? single((builder, params) -> builder.field(Fields.ACTIVE, active)) : emptyIterator(),
                rejected != -1 ? single((builder, params) -> builder.field(Fields.REJECTED, rejected)) : emptyIterator(),
                largest != -1 ? single((builder, params) -> builder.field(Fields.LARGEST, largest)) : emptyIterator(),
                completed != -1 ? single((builder, params) -> builder.field(Fields.COMPLETED, completed)) : emptyIterator(),
                ChunkedToXContentHelper.endObject()
            );
        }
    }

    public ThreadPoolStats {
        var statsCopy = new ArrayList<>(stats);
        Collections.sort(statsCopy);
        stats = Collections.unmodifiableList(statsCopy);
    }

    public ThreadPoolStats(StreamInput in) throws IOException {
        this(in.readCollectionAsList(Stats::new));
    }

    @Override
    public void writeTo(StreamOutput out) throws IOException {
        out.writeCollection(stats);
    }

    @Override
    public Iterator<Stats> iterator() {
        return stats.iterator();
    }

    static final class Fields {
        static final String THREAD_POOL = "thread_pool";
        static final String THREADS = "threads";
        static final String QUEUE = "queue";
        static final String ACTIVE = "active";
        static final String REJECTED = "rejected";
        static final String LARGEST = "largest";
        static final String COMPLETED = "completed";
    }

    @Override
    public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params params) {
        return ChunkedToXContentHelper.object(Fields.THREAD_POOL, Iterators.flatMap(stats.iterator(), s -> s.toXContentChunked(params)));
    }
}