/*
 * 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.action.get;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.lucene.store.AlreadyClosedException;
import org.elasticsearch.ElasticsearchException;
import org.elasticsearch.ExceptionsHelper;
import org.elasticsearch.action.ActionListener;
import org.elasticsearch.action.ActionListenerResponseHandler;
import org.elasticsearch.action.ActionRunnable;
import org.elasticsearch.action.ActionType;
import org.elasticsearch.action.NoShardAvailableActionException;
import org.elasticsearch.action.admin.indices.refresh.TransportShardRefreshAction;
import org.elasticsearch.action.support.ActionFilters;
import org.elasticsearch.action.support.ContextPreservingActionListener;
import org.elasticsearch.action.support.replication.BasicReplicationRequest;
import org.elasticsearch.action.support.single.shard.TransportSingleShardAction;
import org.elasticsearch.client.internal.node.NodeClient;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.ClusterStateObserver;
import org.elasticsearch.cluster.ProjectState;
import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
import org.elasticsearch.cluster.metadata.ProjectId;
import org.elasticsearch.cluster.node.DiscoveryNode;
import org.elasticsearch.cluster.project.ProjectResolver;
import org.elasticsearch.cluster.routing.ShardIterator;
import org.elasticsearch.cluster.service.ClusterService;
import org.elasticsearch.common.io.stream.Writeable;
import org.elasticsearch.core.TimeValue;
import org.elasticsearch.index.IndexNotFoundException;
import org.elasticsearch.index.IndexService;
import org.elasticsearch.index.engine.Engine;
import org.elasticsearch.index.get.GetResult;
import org.elasticsearch.index.shard.IllegalIndexShardStateException;
import org.elasticsearch.index.shard.IndexShard;
import org.elasticsearch.index.shard.ShardId;
import org.elasticsearch.index.shard.ShardNotFoundException;
import org.elasticsearch.indices.ExecutorSelector;
import org.elasticsearch.indices.IndicesService;
import org.elasticsearch.injection.guice.Inject;
import org.elasticsearch.node.NodeClosedException;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.transport.TransportService;

import java.io.IOException;
import java.util.concurrent.Executor;

/**
 * Performs the get operation.
 */
public class TransportGetAction extends TransportSingleShardAction<GetRequest, GetResponse> {

    public static final ActionType<GetResponse> TYPE = new ActionType<>("indices:data/read/get");
    private static final Logger logger = LogManager.getLogger(TransportGetAction.class);

    private final IndicesService indicesService;
    private final ExecutorSelector executorSelector;
    private final NodeClient client;

    @Inject
    public TransportGetAction(
        ClusterService clusterService,
        TransportService transportService,
        IndicesService indicesService,
        ThreadPool threadPool,
        ActionFilters actionFilters,
        ProjectResolver projectResolver,
        IndexNameExpressionResolver indexNameExpressionResolver,
        ExecutorSelector executorSelector,
        NodeClient client
    ) {
        super(
            TYPE.name(),
            threadPool,
            clusterService,
            transportService,
            actionFilters,
            projectResolver,
            indexNameExpressionResolver,
            GetRequest::new,
            threadPool.executor(ThreadPool.Names.GET)
        );
        this.indicesService = indicesService;
        this.executorSelector = executorSelector;
        this.client = client;
        // register the internal TransportGetFromTranslogAction
        new TransportGetFromTranslogAction(transportService, indicesService, actionFilters);
    }

    @Override
    protected boolean resolveIndex(GetRequest request) {
        return true;
    }

    @Override
    protected ShardIterator shards(ProjectState project, InternalRequest request) {
        ShardIterator iterator = clusterService.operationRouting()
            .getShards(
                project,
                request.concreteIndex(),
                request.request().id(),
                request.request().routing(),
                request.request().preference()
            );
        if (iterator == null) {
            return null;
        }
        return ShardIterator.allSearchableShards(iterator);
    }

    @Override
    protected void resolveRequest(ProjectState state, InternalRequest request) {
        // update the routing (request#index here is possibly an alias)
        request.request().routing(state.metadata().resolveIndexRouting(request.request().routing(), request.request().index()));
    }

    @Override
    protected void asyncShardOperation(GetRequest request, ShardId shardId, ActionListener<GetResponse> listener) throws IOException {
        IndexService indexService = indicesService.indexServiceSafe(shardId.getIndex());
        IndexShard indexShard = indexService.getShard(shardId.id());
        if (indexShard.routingEntry().isPromotableToPrimary() == false) {
            handleGetOnUnpromotableShard(request, indexShard, listener);
            return;
        }
        assert DiscoveryNode.isStateless(clusterService.getSettings()) == false
            : "in Stateless a promotable to primary shard should not receive a TransportGetAction";
        if (request.realtime()) { // we are not tied to a refresh cycle here anyway
            asyncGet(request, shardId, listener);
        } else {
            indexShard.ensureShardSearchActive(b -> {
                try {
                    asyncGet(request, shardId, listener);
                } catch (Exception ex) {
                    listener.onFailure(ex);
                }
            });
        }
    }

    @Override
    protected GetResponse shardOperation(GetRequest request, ShardId shardId) throws IOException {
        var indexShard = getIndexShard(shardId);
        GetResult result = indexShard.getService()
            .get(
                request.id(),
                request.storedFields(),
                request.realtime(),
                request.version(),
                request.versionType(),
                request.fetchSourceContext(),
                request.isForceSyntheticSource()
            );
        return new GetResponse(result);
    }

    @Override
    protected Writeable.Reader<GetResponse> getResponseReader() {
        return GetResponse::new;
    }

    @Override
    protected Executor getExecutor(ShardId shardId) {
        final ClusterState clusterState = clusterService.state();
        if (projectResolver.getProjectMetadata(clusterState).getIndexSafe(shardId.getIndex()).isSystem()) {
            return threadPool.executor(executorSelector.executorForGet(shardId.getIndexName()));
        } else {
            return super.getExecutor(shardId);
        }
    }

    private void asyncGet(GetRequest request, ShardId shardId, ActionListener<GetResponse> listener) throws IOException {
        if (request.refresh() && request.realtime() == false) {
            getExecutor(shardId).execute(ActionRunnable.wrap(listener, l -> {
                var indexShard = getIndexShard(shardId);
                indexShard.externalRefresh("refresh_flag_get", l.map(r -> shardOperation(request, shardId)));
            }));
        } else {
            super.asyncShardOperation(request, shardId, listener);
        }
    }

    private void handleGetOnUnpromotableShard(GetRequest request, IndexShard indexShard, ActionListener<GetResponse> listener)
        throws IOException {
        ShardId shardId = indexShard.shardId();
        if (request.refresh()) {
            logger.trace("send refresh action for shard {}", shardId);
            var refreshRequest = new BasicReplicationRequest(shardId);
            refreshRequest.setParentTask(request.getParentTask());
            client.executeLocally(
                TransportShardRefreshAction.TYPE,
                refreshRequest,
                listener.delegateFailureAndWrap((l, replicationResponse) -> super.asyncShardOperation(request, shardId, l))
            );
            return;
        }
        if (request.realtime()) {
            final var state = clusterService.state();
            final var observer = new ClusterStateObserver(
                state,
                clusterService,
                TimeValue.timeValueSeconds(60),
                logger,
                threadPool.getThreadContext()
            );
            getFromTranslog(request, indexShard, projectResolver.getProjectState(state), observer, listener);
        } else {
            // A non-real-time get with no explicit refresh requested.
            super.asyncShardOperation(request, shardId, listener);
        }
    }

    private void getFromTranslog(
        GetRequest request,
        IndexShard indexShard,
        ProjectState state,
        ClusterStateObserver observer,
        ActionListener<GetResponse> listener
    ) {
        DiscoveryNode node;
        try {
            node = getCurrentNodeOfPrimary(state, indexShard.shardId());
        } catch (Exception e) {
            listener.onFailure(e);
            return;
        }
        ProjectId projectId = state.projectId();
        final var retryingListener = listener.delegateResponse((l, e) -> {
            final var cause = ExceptionsHelper.unwrapCause(e);
            logger.debug("get_from_translog failed", cause);
            // All of the following exceptions can be thrown if the shard is relocated
            if (cause instanceof ShardNotFoundException
                || cause instanceof IndexNotFoundException
                || cause instanceof IllegalIndexShardStateException
                || cause instanceof AlreadyClosedException) {
                logger.debug("retrying get_from_translog");
                observer.waitForNextChange(new ClusterStateObserver.Listener() {
                    @Override
                    public void onNewClusterState(ClusterState state) {
                        getFromTranslog(request, indexShard, state.projectState(projectId), observer, l);
                    }

                    @Override
                    public void onClusterServiceClose() {
                        l.onFailure(new NodeClosedException(clusterService.localNode()));
                    }

                    @Override
                    public void onTimeout(TimeValue timeout) {
                        l.onFailure(new ElasticsearchException("Timed out retrying get_from_translog", cause));
                    }
                });
            } else {
                l.onFailure(e);
            }
        });
        tryGetFromTranslog(request, indexShard, node, retryingListener);
    }

    private void tryGetFromTranslog(GetRequest request, IndexShard indexShard, DiscoveryNode node, ActionListener<GetResponse> listener) {
        ShardId shardId = indexShard.shardId();
        TransportGetFromTranslogAction.Request getFromTranslogRequest = new TransportGetFromTranslogAction.Request(request, shardId);
        getFromTranslogRequest.setParentTask(request.getParentTask());
        transportService.sendRequest(
            node,
            TransportGetFromTranslogAction.NAME,
            getFromTranslogRequest,
            new ActionListenerResponseHandler<>(listener.delegateFailure((l, r) -> {
                if (r.getResult() != null) {
                    logger.debug("received result for real-time get for id '{}' from promotable shard", request.id());
                    l.onResponse(new GetResponse(r.getResult()));
                } else {
                    logger.debug(
                        "no result for real-time get for id '{}' from promotable shard (segment generation to wait for: {})",
                        request.id(),
                        r.segmentGeneration()
                    );
                    if (r.segmentGeneration() == -1) {
                        // Nothing to wait for (no previous unsafe generation), just handle the Get locally.
                        ActionRunnable.supply(l, () -> shardOperation(request, shardId)).run();
                    } else {
                        assert r.segmentGeneration() > -1L;
                        assert r.primaryTerm() > Engine.UNKNOWN_PRIMARY_TERM;
                        final ActionListener<Long> termAndGenerationListener = ContextPreservingActionListener.wrapPreservingContext(
                            listener.delegateFailureAndWrap((ll, aLong) -> super.asyncShardOperation(request, shardId, ll)),
                            threadPool.getThreadContext()
                        );
                        indexShard.waitForPrimaryTermAndGeneration(r.primaryTerm(), r.segmentGeneration(), termAndGenerationListener);
                    }
                }
            }), TransportGetFromTranslogAction.Response::new, getExecutor(shardId))
        );
    }

    static DiscoveryNode getCurrentNodeOfPrimary(ProjectState clusterState, ShardId shardId) {
        final var primaryShard = clusterState.routingTable().shardRoutingTable(shardId).primaryShard();
        if (primaryShard.active() == false) {
            throw new NoShardAvailableActionException(shardId, "primary shard is not active");
        }
        DiscoveryNode node = clusterState.cluster().nodes().get(primaryShard.currentNodeId());
        assert node != null;
        return node;
    }

    private IndexShard getIndexShard(ShardId shardId) {
        IndexService indexService = indicesService.indexServiceSafe(shardId.getIndex());
        return indexService.getShard(shardId.id());
    }
}