/*
 * 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.transport;

import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.Writeable;
import org.elasticsearch.core.Releasable;
import org.elasticsearch.core.Releasables;
import org.elasticsearch.tasks.CancellableTask;
import org.elasticsearch.tasks.Task;
import org.elasticsearch.tasks.TaskManager;
import org.elasticsearch.telemetry.tracing.Tracer;

import java.io.IOException;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.util.concurrent.Executor;

import static org.elasticsearch.core.Releasables.assertOnce;

public class RequestHandlerRegistry<Request extends TransportRequest> implements ResponseStatsConsumer {

    private final String action;
    private final TransportRequestHandler<Request> handler;
    private final boolean forceExecution;
    private final boolean canTripCircuitBreaker;
    private final Executor executor;
    private final TaskManager taskManager;
    private final Tracer tracer;
    private final Writeable.Reader<Request> requestReader;
    @SuppressWarnings("unused") // only accessed via #STATS_TRACKER_HANDLE, lazy initialized because instances consume non-trivial heap
    private TransportActionStatsTracker statsTracker;

    private static final VarHandle STATS_TRACKER_HANDLE;

    static {
        try {
            STATS_TRACKER_HANDLE = MethodHandles.lookup()
                .findVarHandle(RequestHandlerRegistry.class, "statsTracker", TransportActionStatsTracker.class);
        } catch (Exception e) {
            throw new ExceptionInInitializerError(e);
        }
    }

    public RequestHandlerRegistry(
        String action,
        Writeable.Reader<Request> requestReader,
        TaskManager taskManager,
        TransportRequestHandler<Request> handler,
        Executor executor,
        boolean forceExecution,
        boolean canTripCircuitBreaker,
        Tracer tracer
    ) {
        this.action = action;
        this.requestReader = requestReader;
        this.handler = handler;
        this.forceExecution = forceExecution;
        this.canTripCircuitBreaker = canTripCircuitBreaker;
        this.executor = executor;
        this.taskManager = taskManager;
        this.tracer = tracer;
    }

    public String getAction() {
        return action;
    }

    public Request newRequest(StreamInput in) throws IOException {
        return requestReader.read(in);
    }

    public void processMessageReceived(Request request, TransportChannel channel) throws Exception {
        final Task task = taskManager.register("transport", action, request);
        Releasable unregisterTask = () -> taskManager.unregister(task);
        try {
            if (channel instanceof TcpTransportChannel tcpTransportChannel && task instanceof CancellableTask cancellableTask) {
                final TcpChannel tcpChannel = tcpTransportChannel.getChannel();
                final Releasable stopTracking = taskManager.startTrackingCancellableChannelTask(tcpChannel, cancellableTask);
                unregisterTask = Releasables.wrap(unregisterTask, stopTracking);
            }
            final TaskTransportChannel taskTransportChannel = new TaskTransportChannel(task.getId(), channel, assertOnce(unregisterTask));
            handler.messageReceived(request, taskTransportChannel, task);
            unregisterTask = null;
        } finally {
            Releasables.close(unregisterTask);
        }
    }

    public boolean isForceExecution() {
        return forceExecution;
    }

    public boolean canTripCircuitBreaker() {
        return canTripCircuitBreaker;
    }

    public Executor getExecutor() {
        return executor;
    }

    public TransportRequestHandler<Request> getHandler() {
        return handler;
    }

    @Override
    public String toString() {
        return handler.toString();
    }

    public static <R extends TransportRequest> RequestHandlerRegistry<R> replaceHandler(
        RequestHandlerRegistry<R> registry,
        TransportRequestHandler<R> handler
    ) {
        return new RequestHandlerRegistry<>(
            registry.action,
            registry.requestReader,
            registry.taskManager,
            handler,
            registry.executor,
            registry.forceExecution,
            registry.canTripCircuitBreaker,
            registry.tracer
        );
    }

    public void addRequestStats(int messageSize) {
        statsTracker().addRequestStats(messageSize);
    }

    @Override
    public void addResponseStats(int messageSize) {
        statsTracker().addResponseStats(messageSize);
    }

    public TransportActionStats getStats() {
        var statsTracker = existingStatsTracker();
        if (statsTracker == null) {
            return TransportActionStats.EMPTY;
        }
        return statsTracker.getStats();
    }

    private TransportActionStatsTracker statsTracker() {
        var tracker = existingStatsTracker();
        if (tracker == null) {
            var newTracker = new TransportActionStatsTracker();
            if ((tracker = (TransportActionStatsTracker) STATS_TRACKER_HANDLE.compareAndExchange(this, null, newTracker)) == null) {
                tracker = newTracker;
            }
        }
        return tracker;
    }

    private TransportActionStatsTracker existingStatsTracker() {
        return (TransportActionStatsTracker) STATS_TRACKER_HANDLE.getAcquire(this);
    }
}