/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.nifi.processors.gcp.storage;

import com.google.api.gax.paging.Page;
import com.google.cloud.storage.Acl;
import com.google.cloud.storage.Blob;
import com.google.cloud.storage.BlobInfo;
import com.google.cloud.storage.Storage;
import org.apache.nifi.annotation.behavior.InputRequirement;
import org.apache.nifi.annotation.behavior.InputRequirement.Requirement;
import org.apache.nifi.annotation.behavior.PrimaryNodeOnly;
import org.apache.nifi.annotation.behavior.Stateful;
import org.apache.nifi.annotation.behavior.TriggerSerially;
import org.apache.nifi.annotation.behavior.TriggerWhenEmpty;
import org.apache.nifi.annotation.behavior.WritesAttribute;
import org.apache.nifi.annotation.behavior.WritesAttributes;
import org.apache.nifi.annotation.configuration.DefaultSchedule;
import org.apache.nifi.annotation.documentation.CapabilityDescription;
import org.apache.nifi.annotation.documentation.SeeAlso;
import org.apache.nifi.annotation.documentation.Tags;
import org.apache.nifi.components.ConfigVerificationResult;
import org.apache.nifi.components.ConfigVerificationResult.Outcome;
import org.apache.nifi.annotation.lifecycle.OnScheduled;
import org.apache.nifi.annotation.notification.OnPrimaryNodeStateChange;
import org.apache.nifi.annotation.notification.PrimaryNodeState;
import org.apache.nifi.components.AllowableValue;
import org.apache.nifi.components.PropertyDescriptor;
import org.apache.nifi.components.state.Scope;
import org.apache.nifi.components.state.StateMap;
import org.apache.nifi.expression.ExpressionLanguageScope;
import org.apache.nifi.flowfile.FlowFile;
import org.apache.nifi.logging.ComponentLog;
import org.apache.nifi.processor.ProcessContext;
import org.apache.nifi.processor.ProcessSession;
import org.apache.nifi.processor.Relationship;
import org.apache.nifi.processor.exception.ProcessException;
import org.apache.nifi.processor.util.StandardValidators;
import org.apache.nifi.processor.util.list.ListableEntityWrapper;
import org.apache.nifi.processor.util.list.ListedEntity;
import org.apache.nifi.processor.util.list.ListedEntityTracker;
import org.apache.nifi.scheduling.SchedulingStrategy;
import org.apache.nifi.schema.access.SchemaNotFoundException;
import org.apache.nifi.serialization.RecordSetWriter;
import org.apache.nifi.serialization.RecordSetWriterFactory;
import org.apache.nifi.serialization.SimpleRecordSchema;
import org.apache.nifi.serialization.WriteResult;
import org.apache.nifi.serialization.record.MapRecord;
import org.apache.nifi.serialization.record.Record;
import org.apache.nifi.serialization.record.RecordField;
import org.apache.nifi.serialization.record.RecordFieldType;
import org.apache.nifi.serialization.record.RecordSchema;

import java.io.IOException;
import java.io.OutputStream;
import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.TimeUnit;
import java.util.function.Function;
import java.util.stream.Collectors;

import static org.apache.nifi.processors.gcp.storage.StorageAttributes.BUCKET_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.BUCKET_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CACHE_CONTROL_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CACHE_CONTROL_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.COMPONENT_COUNT_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.COMPONENT_COUNT_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CONTENT_DISPOSITION_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CONTENT_DISPOSITION_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CONTENT_ENCODING_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CONTENT_ENCODING_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CONTENT_LANGUAGE_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CONTENT_LANGUAGE_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CRC32C_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CRC32C_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CREATE_TIME_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.CREATE_TIME_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.ENCRYPTION_ALGORITHM_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.ENCRYPTION_ALGORITHM_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.ENCRYPTION_SHA256_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.ENCRYPTION_SHA256_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.ETAG_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.ETAG_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.GENERATED_ID_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.GENERATED_ID_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.GENERATION_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.GENERATION_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.KEY_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.KEY_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.MD5_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.MD5_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.MEDIA_LINK_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.MEDIA_LINK_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.METAGENERATION_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.METAGENERATION_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.OWNER_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.OWNER_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.OWNER_TYPE_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.OWNER_TYPE_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.SIZE_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.SIZE_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.UPDATE_TIME_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.UPDATE_TIME_DESC;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.URI_ATTR;
import static org.apache.nifi.processors.gcp.storage.StorageAttributes.URI_DESC;

/**
 * List objects in a google cloud storage bucket by object name pattern.
 */
@PrimaryNodeOnly
@TriggerSerially
@TriggerWhenEmpty
@InputRequirement(Requirement.INPUT_FORBIDDEN)
@Tags({"google cloud", "google", "storage", "gcs", "list"})
@CapabilityDescription("Retrieves a listing of objects from a GCS bucket. For each object that is listed, creates a FlowFile that represents "
        + "the object so that it can be fetched in conjunction with FetchGCSObject. This Processor is designed to run on Primary Node only "
        + "in a cluster. If the primary node changes, the new Primary Node will pick up where the previous node left off without duplicating "
        + "all of the data.")
@Stateful(scopes = Scope.CLUSTER, description = "After performing a listing of keys, the timestamp of the newest key is stored, "
        + "along with the keys that share that same timestamp. This allows the Processor to list only keys that have been added or modified after "
        + "this date the next time that the Processor is run. State is stored across the cluster so that this Processor can be run on Primary Node only and if a new Primary "
        + "Node is selected, the new node can pick up where the previous node left off, without duplicating the data.")
@SeeAlso({PutGCSObject.class, DeleteGCSObject.class, FetchGCSObject.class})
@WritesAttributes({
        @WritesAttribute(attribute = "filename", description = "The name of the file"),
        @WritesAttribute(attribute = BUCKET_ATTR, description = BUCKET_DESC),
        @WritesAttribute(attribute = KEY_ATTR, description = KEY_DESC),
        @WritesAttribute(attribute = SIZE_ATTR, description = SIZE_DESC),
        @WritesAttribute(attribute = CACHE_CONTROL_ATTR, description = CACHE_CONTROL_DESC),
        @WritesAttribute(attribute = COMPONENT_COUNT_ATTR, description = COMPONENT_COUNT_DESC),
        @WritesAttribute(attribute = CONTENT_DISPOSITION_ATTR, description = CONTENT_DISPOSITION_DESC),
        @WritesAttribute(attribute = CONTENT_ENCODING_ATTR, description = CONTENT_ENCODING_DESC),
        @WritesAttribute(attribute = CONTENT_LANGUAGE_ATTR, description = CONTENT_LANGUAGE_DESC),
        @WritesAttribute(attribute = "mime.type", description = "The MIME/Content-Type of the object"),
        @WritesAttribute(attribute = CRC32C_ATTR, description = CRC32C_DESC),
        @WritesAttribute(attribute = CREATE_TIME_ATTR, description = CREATE_TIME_DESC),
        @WritesAttribute(attribute = UPDATE_TIME_ATTR, description = UPDATE_TIME_DESC),
        @WritesAttribute(attribute = ENCRYPTION_ALGORITHM_ATTR, description = ENCRYPTION_ALGORITHM_DESC),
        @WritesAttribute(attribute = ENCRYPTION_SHA256_ATTR, description = ENCRYPTION_SHA256_DESC),
        @WritesAttribute(attribute = ETAG_ATTR, description = ETAG_DESC),
        @WritesAttribute(attribute = GENERATED_ID_ATTR, description = GENERATED_ID_DESC),
        @WritesAttribute(attribute = GENERATION_ATTR, description = GENERATION_DESC),
        @WritesAttribute(attribute = MD5_ATTR, description = MD5_DESC),
        @WritesAttribute(attribute = MEDIA_LINK_ATTR, description = MEDIA_LINK_DESC),
        @WritesAttribute(attribute = METAGENERATION_ATTR, description = METAGENERATION_DESC),
        @WritesAttribute(attribute = OWNER_ATTR, description = OWNER_DESC),
        @WritesAttribute(attribute = OWNER_TYPE_ATTR, description = OWNER_TYPE_DESC),
        @WritesAttribute(attribute = URI_ATTR, description = URI_DESC)
})
@DefaultSchedule(strategy = SchedulingStrategy.TIMER_DRIVEN, period = "1 min")
public class ListGCSBucket extends AbstractGCSProcessor {
    public static final AllowableValue BY_TIMESTAMPS = new AllowableValue("timestamps", "Tracking Timestamps",
        "This strategy tracks the latest timestamp of listed entity to determine new/updated entities." +
            " Since it only tracks few timestamps, it can manage listing state efficiently." +
            " This strategy will not pick up any newly added or modified entity if their timestamps are older than the tracked latest timestamp." +
            " Also may miss files when multiple subdirectories are being written at the same time while listing is running.");

    public static final AllowableValue BY_ENTITIES = new AllowableValue("entities", "Tracking Entities",
        "This strategy tracks information of all the listed entities within the latest 'Entity Tracking Time Window' to determine new/updated entities." +
            " This strategy can pick entities having old timestamp that can be missed with 'Tracing Timestamps'." +
            " Works even when multiple subdirectories are being written at the same time while listing is running." +
            " However an additional DistributedMapCache controller service is required and more JVM heap memory is used." +
            " For more information on how the 'Entity Tracking Time Window' property works, see the description.");

    public static final AllowableValue NO_TRACKING = new AllowableValue("none", "No Tracking",
            "This strategy lists all entities without any tracking. The same entities will be listed each time" +
                    " this processor is scheduled. It is recommended to change the default run schedule value." +
                    " Any property that relates to the persisting state will be ignored.");

    public static final PropertyDescriptor LISTING_STRATEGY = new PropertyDescriptor.Builder()
        .name("listing-strategy")
        .displayName("Listing Strategy")
        .description("Specify how to determine new/updated entities. See each strategy descriptions for detail.")
        .required(true)
        .allowableValues(BY_TIMESTAMPS, BY_ENTITIES, NO_TRACKING)
        .defaultValue(BY_TIMESTAMPS.getValue())
        .build();

    public static final PropertyDescriptor TRACKING_STATE_CACHE = new PropertyDescriptor.Builder()
        .fromPropertyDescriptor(ListedEntityTracker.TRACKING_STATE_CACHE)
        .dependsOn(LISTING_STRATEGY, BY_ENTITIES)
        .required(true)
        .build();

    public static final PropertyDescriptor INITIAL_LISTING_TARGET = new PropertyDescriptor.Builder()
        .fromPropertyDescriptor(ListedEntityTracker.INITIAL_LISTING_TARGET)
        .dependsOn(LISTING_STRATEGY, BY_ENTITIES)
        .build();

    public static final PropertyDescriptor TRACKING_TIME_WINDOW = new PropertyDescriptor.Builder()
        .fromPropertyDescriptor(ListedEntityTracker.TRACKING_TIME_WINDOW)
        .dependsOn(INITIAL_LISTING_TARGET, ListedEntityTracker.INITIAL_LISTING_TARGET_WINDOW)
        .required(true)
        .build();

    public static final PropertyDescriptor BUCKET = new PropertyDescriptor
            .Builder().name("gcs-bucket")
            .displayName("Bucket")
            .description(BUCKET_DESC)
            .required(true)
            .expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
            .addValidator(StandardValidators.NON_EMPTY_EL_VALIDATOR)
            .build();

    public static final PropertyDescriptor PREFIX = new PropertyDescriptor.Builder()
            .name("gcs-prefix")
            .displayName("Prefix")
            .description("The prefix used to filter the object list. In most cases, it should end with a forward slash ('/').")
            .required(false)
            .expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
            .addValidator(StandardValidators.NON_EMPTY_EL_VALIDATOR)
            .build();

    public static final PropertyDescriptor USE_GENERATIONS = new PropertyDescriptor.Builder()
            .name("gcs-use-generations")
            .displayName("Use Generations")
            .expressionLanguageSupported(ExpressionLanguageScope.NONE)
            .required(true)
            .addValidator(StandardValidators.BOOLEAN_VALIDATOR)
            .allowableValues("true", "false")
            .defaultValue("false")
            .description("Specifies whether to use GCS Generations, if applicable.  If false, only the latest version of each object will be returned.")
            .build();

    public static final PropertyDescriptor RECORD_WRITER = new PropertyDescriptor.Builder()
        .name("record-writer")
        .displayName("Record Writer")
        .description("Specifies the Record Writer to use for creating the listing. If not specified, one FlowFile will be created for each entity that is listed. If the Record Writer is specified, " +
            "all entities will be written to a single FlowFile instead of adding attributes to individual FlowFiles.")
        .required(false)
        .identifiesControllerService(RecordSetWriterFactory.class)
        .build();


    @Override
    public List<PropertyDescriptor> getSupportedPropertyDescriptors() {
        final List<PropertyDescriptor> descriptors = new ArrayList<>();
        descriptors.add(LISTING_STRATEGY);
        descriptors.add(TRACKING_STATE_CACHE);
        descriptors.add(INITIAL_LISTING_TARGET);
        descriptors.add(TRACKING_TIME_WINDOW);
        descriptors.add(BUCKET);
        descriptors.add(RECORD_WRITER);
        descriptors.addAll(super.getSupportedPropertyDescriptors());
        descriptors.add(PREFIX);
        descriptors.add(USE_GENERATIONS);
        return Collections.unmodifiableList(descriptors);
    }

    private static final Set<Relationship> relationships = Collections.singleton(REL_SUCCESS);

    @Override
    public Set<Relationship> getRelationships() {
        return relationships;
    }

    // State tracking
    public static final String CURRENT_TIMESTAMP = "currentTimestamp";
    public static final String CURRENT_KEY_PREFIX = "key-";
    private volatile long currentTimestamp = 0L;
    private final Set<String> currentKeys = Collections.synchronizedSet(new HashSet<>());

    private volatile boolean justElectedPrimaryNode = false;
    private volatile boolean resetEntityTrackingState = false;
    private volatile ListedEntityTracker<ListableBlob> listedEntityTracker;

    @OnPrimaryNodeStateChange
    public void onPrimaryNodeChange(final PrimaryNodeState newState) {
        justElectedPrimaryNode = (newState == PrimaryNodeState.ELECTED_PRIMARY_NODE);
    }

    @OnScheduled
    public void initListedEntityTracker(ProcessContext context) {
        final boolean isTrackingEntityStrategy = BY_ENTITIES.getValue().equals(context.getProperty(LISTING_STRATEGY).getValue());
        if (listedEntityTracker != null && (resetEntityTrackingState || !isTrackingEntityStrategy)) {
            try {
                listedEntityTracker.clearListedEntities();
            } catch (IOException e) {
                throw new RuntimeException("Failed to reset previously listed entities", e);
            }
        }
        resetEntityTrackingState = false;

        if (isTrackingEntityStrategy) {
            if (listedEntityTracker == null) {
                listedEntityTracker = createListedEntityTracker();
            }
        } else {
            listedEntityTracker = null;
        }
    }

    protected ListedEntityTracker<ListableBlob> createListedEntityTracker() {
        return new ListedBlobTracker();
    }

    private Set<String> extractKeys(final StateMap stateMap) {
        return stateMap.toMap().entrySet().parallelStream()
                .filter(x -> x.getKey().startsWith(CURRENT_KEY_PREFIX))
                .map(Map.Entry::getValue)
                .collect(Collectors.toSet());
    }

    void restoreState(final ProcessSession session) throws IOException {
        final StateMap stateMap = session.getState(Scope.CLUSTER);
        if (stateMap.getVersion() == -1L || stateMap.get(CURRENT_TIMESTAMP) == null || stateMap.get(CURRENT_KEY_PREFIX+"0") == null) {
            currentTimestamp = 0L;
            currentKeys.clear();
        } else {
            currentTimestamp = Long.parseLong(stateMap.get(CURRENT_TIMESTAMP));
            currentKeys.clear();
            currentKeys.addAll(extractKeys(stateMap));
        }
    }

    void persistState(final ProcessSession session, final long timestamp, final Set<String> keys) {
        final Map<String, String> state = new HashMap<>();
        state.put(CURRENT_TIMESTAMP, String.valueOf(timestamp));

        int i = 0;
        for (final String key : keys) {
            state.put(CURRENT_KEY_PREFIX+i, key);
            i++;
        }

        try {
            session.setState(state, Scope.CLUSTER);
        } catch (IOException ioe) {
            getLogger().error("Failed to save cluster-wide state. If NiFi is restarted, data duplication may occur", ioe);
        }
    }

    Set<String> getStateKeys() {
        return Collections.unmodifiableSet(currentKeys);
    }

    long getStateTimestamp() {
        return currentTimestamp;
    }

    @Override
    protected List<String> getRequiredPermissions() {
        return Collections.singletonList("storage.objects.list");
    }

    @Override
    protected String getBucketName(final ProcessContext context, final Map<String, String> attributes) {
        return context.getProperty(BUCKET).evaluateAttributeExpressions().getValue();
    }

    @Override
    public List<ConfigVerificationResult> verify(final ProcessContext context, final ComponentLog verificationLogger, final Map<String, String> attributes) {
        final List<ConfigVerificationResult> results = new ArrayList<>(super.verify(context, verificationLogger, attributes));
        final String bucketName = getBucketName(context, attributes);

        try {
            final VerifyListingAction listingAction = new VerifyListingAction(context);
            listBucket(context, listingAction);
            final int blobCount = listingAction.getBlobWriter().getCount();
            results.add(new ConfigVerificationResult.Builder()
                    .verificationStepName("List GCS Bucket")
                    .outcome(Outcome.SUCCESSFUL)
                    .explanation(String.format("Successfully listed Bucket [%s], finding %s blobs matching the filter", bucketName, blobCount))
                    .build());
        } catch (final Exception e) {
            verificationLogger.error("Failed to list GCS Bucket", e);
            results.add(new ConfigVerificationResult.Builder()
                    .verificationStepName("List GCS Bucket")
                    .outcome(Outcome.FAILED)
                    .explanation(String.format("Failed to list Bucket [%s]: %s", bucketName, e.getMessage()))
                    .build());
        }
        return results;
    }

    @Override
    public void onTrigger(final ProcessContext context, final ProcessSession session) {
        final String listingStrategy = context.getProperty(LISTING_STRATEGY).getValue();

        if (BY_TIMESTAMPS.equals(listingStrategy)) {
            listByTrackingTimestamps(context, session);
        } else if (BY_ENTITIES.equals(listingStrategy)) {
            listByTrackingEntities(context, session);
        } else if (NO_TRACKING.equals(listingStrategy)) {
            listNoTracking(context, session);
        } else {
            throw new ProcessException("Unknown listing strategy: " + listingStrategy);
        }
    }

    private void listNoTracking(ProcessContext context, ProcessSession session) {
        final long startNanos = System.nanoTime();
        final ListingAction listingAction = new NoTrackingListingAction(context, session);

        try {
            listBucket(context, listingAction);
        } catch (final Exception e) {
            getLogger().error("Failed to list contents of GCS Bucket", e);
            listingAction.getBlobWriter().finishListingExceptionally(e);
            session.rollback();
            context.yield();
            return;
        }

        final long listMillis = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startNanos);
        getLogger().info("Successfully listed GCS bucket {} in {} millis", context.getProperty(BUCKET).evaluateAttributeExpressions().getValue(), listMillis);
    }

    private void listByTrackingTimestamps(ProcessContext context, ProcessSession session) {
        try {
            restoreState(session);
        } catch (IOException e) {
            getLogger().error("Failed to restore processor state; yielding", e);
            context.yield();
            return;
        }

        final long startNanos = System.nanoTime();

        final ListingAction listingAction = new TriggerListingAction(context, session);
        try {
            listBucket(context, listingAction);
        } catch (final Exception e) {
            getLogger().error("Failed to list contents of GCS Bucket", e);
            listingAction.getBlobWriter().finishListingExceptionally(e);
            session.rollback();
            context.yield();
            return;
        }

        final long listMillis = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startNanos);
        getLogger().info("Successfully listed GCS bucket {} in {} millis", context.getProperty(BUCKET).evaluateAttributeExpressions().getValue(), listMillis);
    }

    private void listBucket(final ProcessContext context, final ListingAction listingAction) throws IOException, SchemaNotFoundException {
        final String bucket = context.getProperty(BUCKET).evaluateAttributeExpressions().getValue();
        final List<Storage.BlobListOption> listOptions = getBlobListOptions(context);

        final Storage storage = listingAction.getCloudService();

        long maxTimestamp = 0L;
        final Set<String> keysMatchingTimestamp = new HashSet<>();

        final BlobWriter writer = listingAction.getBlobWriter();

        writer.beginListing();

        Page<Blob> blobPage = storage.list(bucket, listOptions.toArray(new Storage.BlobListOption[0]));
        int listCount = 0;

        do {
            for (final Blob blob : blobPage.getValues()) {
                long lastModified = blob.getUpdateTime();
                if (listingAction.skipBlob(blob)) {
                    continue;
                }

                writer.addToListing(blob);

                // Update state
                if (lastModified > maxTimestamp) {
                    maxTimestamp = lastModified;
                    keysMatchingTimestamp.clear();
                }
                if (lastModified == maxTimestamp) {
                    keysMatchingTimestamp.add(blob.getName());
                }

                listCount++;
            }

            if (writer.isCheckpoint()) {
                listingAction.commit(listCount);
                listCount = 0;
            }

            blobPage = blobPage.getNextPage();
        } while (blobPage != null);

        writer.finishListing();

        listingAction.finishListing(listCount, maxTimestamp, keysMatchingTimestamp);
    }

    private List<Storage.BlobListOption> getBlobListOptions(ProcessContext context) {
        final String prefix = context.getProperty(PREFIX).evaluateAttributeExpressions().getValue();
        final boolean useGenerations = context.getProperty(USE_GENERATIONS).asBoolean();

        final List<Storage.BlobListOption> listOptions = new ArrayList<>();

        if (prefix != null) {
            listOptions.add(Storage.BlobListOption.prefix(prefix));
        }
        if (useGenerations) {
            listOptions.add(Storage.BlobListOption.versions(true));
        }

        return listOptions;
    }

    private void listByTrackingEntities(ProcessContext context, ProcessSession session) {
        listedEntityTracker.trackEntities(context, session, justElectedPrimaryNode, Scope.CLUSTER, minTimestampToList -> {
            List<ListableBlob> listedEntities = new ArrayList<>();

            Storage storage = getCloudService();
            String bucket = context.getProperty(BUCKET).evaluateAttributeExpressions().getValue();
            final List<Storage.BlobListOption> listOptions = getBlobListOptions(context);

            Page<Blob> blobPage = storage.list(bucket, listOptions.toArray(new Storage.BlobListOption[0]));
            int pageNr=0;
            do {
                for (final Blob blob : blobPage.getValues()) {
                    if (blob.getUpdateTime() >= minTimestampToList) {
                        listedEntities.add(new ListableBlob(
                            blob,
                            pageNr
                        ));
                    }
                }
                blobPage = blobPage.getNextPage();
                pageNr++;
            } while (blobPage != null);

            return listedEntities;
        }, null);

        justElectedPrimaryNode = false;
    }

    private void commit(final ProcessSession session, final int listCount) {
        if (listCount > 0) {
            getLogger().info("Successfully listed {} new files from GCS; routing to success", listCount);
            session.commitAsync();
        }
    }

    private interface ListingAction<T extends BlobWriter> {
        boolean skipBlob(final Blob blob);

        T getBlobWriter();

        Storage getCloudService();

        void finishListing(int listCount, long maxTimestamp, Set<String> keysMatchingTimestamp);

        void commit(int listCount);
    }

    private class NoTrackingListingAction implements ListingAction<BlobWriter> {
        final ProcessContext context;
        final ProcessSession session;
        final BlobWriter blobWriter;

        private NoTrackingListingAction(final ProcessContext context, final ProcessSession session) {
            this.context = context;
            this.session = session;

            final RecordSetWriterFactory writerFactory = context.getProperty(RECORD_WRITER).asControllerService(RecordSetWriterFactory.class);
            if (writerFactory == null) {
                blobWriter = new AttributeBlobWriter(session);
            } else {
                blobWriter = new RecordBlobWriter(session, writerFactory, getLogger());
            }
        }

        @Override
        public boolean skipBlob(final Blob blob) {
            return false;
        }

        @Override
        public void commit(final int listCount) {
            ListGCSBucket.this.commit(session, listCount);
        }

        @Override
        public BlobWriter getBlobWriter() {
            return blobWriter;
        }

        @Override
        public Storage getCloudService() {
            return ListGCSBucket.this.getCloudService();
        }

        @Override
        public void finishListing(final int listCount, final long maxTimestamp, final Set<String> keysMatchingTimestamp) {
            // nothing to do
        }
    }

    private class TriggerListingAction implements ListingAction<BlobWriter> {
        final ProcessContext context;
        final ProcessSession session;
        final BlobWriter blobWriter;

        private TriggerListingAction(final ProcessContext context, final ProcessSession session) {
            this.context = context;
            this.session = session;

            final RecordSetWriterFactory writerFactory = context.getProperty(RECORD_WRITER).asControllerService(RecordSetWriterFactory.class);
            if (writerFactory == null) {
                blobWriter = new AttributeBlobWriter(session);
            } else {
                blobWriter = new RecordBlobWriter(session, writerFactory, getLogger());
            }
        }

        @Override
        public boolean skipBlob(final Blob blob) {
            final long lastModified = blob.getUpdateTime();
            return lastModified < currentTimestamp || lastModified == currentTimestamp && currentKeys.contains(blob.getName());
        }

        @Override
        public void commit(final int listCount) {
            ListGCSBucket.this.commit(session, listCount);
        }

        @Override
        public BlobWriter getBlobWriter() {
            return blobWriter;
        }

        @Override
        public Storage getCloudService() {
            return ListGCSBucket.this.getCloudService();
        }

        @Override
        public void finishListing(final int listCount, final long maxTimestamp, final Set<String> keysMatchingTimestamp) {
            if (maxTimestamp == 0) {
                getLogger().debug("No new objects in GCS bucket {} to list. Yielding.", context.getProperty(BUCKET).evaluateAttributeExpressions().getValue());
                context.yield();
            } else {
                commit(listCount);

                currentTimestamp = maxTimestamp;
                currentKeys.clear();
                currentKeys.addAll(keysMatchingTimestamp);
                persistState(session, currentTimestamp, currentKeys);
            }
        }
    }

    protected class ListedBlobTracker extends ListedEntityTracker<ListableBlob> {
        public ListedBlobTracker() {
            super(getIdentifier(), getLogger(), RecordBlobWriter.RECORD_SCHEMA);
        }

        @Override
        protected void createRecordsForEntities(ProcessContext context, ProcessSession session, List<ListableBlob> updatedEntities) throws IOException, SchemaNotFoundException {
            publishListing(context, session, updatedEntities);
        }

        @Override
        protected void createFlowFilesForEntities(ProcessContext context, ProcessSession session, List<ListableBlob> updatedEntities, Function<ListableBlob, Map<String, String>> createAttributes) {
            publishListing(context, session, updatedEntities);
        }

        private void publishListing(ProcessContext context, ProcessSession session, List<ListableBlob> updatedEntities) {
            final BlobWriter writer;
            final RecordSetWriterFactory writerFactory = context.getProperty(RECORD_WRITER).asControllerService(RecordSetWriterFactory.class);
            if (writerFactory == null) {
                writer = new AttributeBlobWriter(session);
            } else {
                writer = new RecordBlobWriter(session, writerFactory, getLogger());
            }

            try {
                writer.beginListing();

                int listCount = 0;
                int pageNr = -1;
                for (ListableBlob listableBlob : updatedEntities) {
                    Blob blob = listableBlob.getRawEntity();
                    int currentPageNr = listableBlob.getPageNr();

                    writer.addToListing(blob);

                    listCount++;

                    if (pageNr != -1 && pageNr != currentPageNr && writer.isCheckpoint()) {
                        commit(session, listCount);
                        listCount = 0;
                    }

                    pageNr = currentPageNr;

                    final ListedEntity listedEntity = new ListedEntity(listableBlob.getTimestamp(), listableBlob.getSize());
                    alreadyListedEntities.put(listableBlob.getIdentifier(), listedEntity);
                }

                writer.finishListing();
            } catch (final Exception e) {
                getLogger().error("Failed to list contents of bucket", e);
                writer.finishListingExceptionally(e);
                session.rollback();
                context.yield();
                return;
            }
        }
    }

    private static class ListableBlob extends ListableEntityWrapper<Blob> {
        private final int pageNr;

        public ListableBlob(
            Blob blob,
            int pageNr
        ) {
            super(
                blob,
                Blob::getName,
                Blob::getGeneratedId,
                Blob::getUpdateTime,
                Blob::getSize
            );
            this.pageNr = pageNr;
        }

        public int getPageNr() {
            return pageNr;
        }
    }

    private class VerifyListingAction implements ListingAction<CountingBlobWriter> {
        final ProcessContext context;
        final CountingBlobWriter blobWriter;

        private VerifyListingAction(final ProcessContext context) {
            this.context = context;
            blobWriter = new CountingBlobWriter();
        }

        @Override
        public boolean skipBlob(final Blob blob) {
            return false;
        }

        @Override
        public void commit(final int listCount) {

        }

        @Override
        public CountingBlobWriter getBlobWriter() {
            return blobWriter;
        }

        @Override
        public Storage getCloudService() {
            // Use the verification context
            return ListGCSBucket.this.getCloudService(context);
        }

        @Override
        public void finishListing(final int listCount, final long maxTimestamp, final Set<String> keysMatchingTimestamp) {

        }
    }

    private interface BlobWriter {
        void beginListing() throws IOException, SchemaNotFoundException;

        void addToListing(Blob blob) throws IOException;

        void finishListing() throws IOException;

        void finishListingExceptionally(Exception cause);

        boolean isCheckpoint();
    }


    static class RecordBlobWriter implements BlobWriter {
        private static final RecordSchema RECORD_SCHEMA;

        public static final String BUCKET = "bucket";
        public static final String NAME = "name";
        public static final String SIZE = "size";
        public static final String CACHE_CONTROL = "cacheControl";
        public static final String COMPONENT_COUNT = "componentCount";
        public static final String CONTENT_DISPOSITION = "contentDisposition";
        public static final String CONTENT_ENCODING = "contentEncoding";
        public static final String CONTENT_LANGUAGE = "contentLanguage";
        public static final String CRC32C = "crc32c";
        public static final String CREATE_TIME = "createTime";
        public static final String UPDATE_TIME = "updateTime";
        public static final String ENCRYPTION_ALGORITHM = "encryptionAlgorithm";
        public static final String ENCRYPTION_KEY_SHA256 = "encryptionKeySha256";
        public static final String ETAG = "etag";
        public static final String GENERATED_ID = "generatedId";
        public static final String GENERATION = "generation";
        public static final String MD5 = "md5";
        public static final String MEDIA_LINK = "mediaLink";
        public static final String METAGENERATION = "metageneration";
        public static final String OWNER = "owner";
        public static final String OWNER_TYPE = "ownerType";
        public static final String URI = "uri";

        static {
            final List<RecordField> fields = new ArrayList<>();
            fields.add(new RecordField(BUCKET, RecordFieldType.STRING.getDataType(), false));
            fields.add(new RecordField(NAME, RecordFieldType.STRING.getDataType(), false));
            fields.add(new RecordField(SIZE, RecordFieldType.LONG.getDataType()));
            fields.add(new RecordField(CACHE_CONTROL, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(COMPONENT_COUNT, RecordFieldType.INT.getDataType()));
            fields.add(new RecordField(CONTENT_DISPOSITION, RecordFieldType.LONG.getDataType()));
            fields.add(new RecordField(CONTENT_ENCODING, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(CONTENT_LANGUAGE, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(CRC32C, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(CREATE_TIME, RecordFieldType.TIMESTAMP.getDataType()));
            fields.add(new RecordField(UPDATE_TIME, RecordFieldType.TIMESTAMP.getDataType()));
            fields.add(new RecordField(ENCRYPTION_ALGORITHM, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(ENCRYPTION_KEY_SHA256, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(ETAG, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(GENERATED_ID, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(GENERATION, RecordFieldType.LONG.getDataType()));
            fields.add(new RecordField(MD5, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(MEDIA_LINK, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(METAGENERATION, RecordFieldType.LONG.getDataType()));
            fields.add(new RecordField(OWNER, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(OWNER_TYPE, RecordFieldType.STRING.getDataType()));
            fields.add(new RecordField(URI, RecordFieldType.STRING.getDataType()));

            RECORD_SCHEMA = new SimpleRecordSchema(fields);
        }


        private final ProcessSession session;
        private final RecordSetWriterFactory writerFactory;
        private final ComponentLog logger;
        private RecordSetWriter recordWriter;
        private FlowFile flowFile;

        public RecordBlobWriter(final ProcessSession session, final RecordSetWriterFactory writerFactory, final ComponentLog logger) {
            this.session = session;
            this.writerFactory = writerFactory;
            this.logger = logger;
        }

        @Override
        public void beginListing() throws IOException, SchemaNotFoundException {
            flowFile = session.create();

            final OutputStream out = session.write(flowFile);
            recordWriter = writerFactory.createWriter(logger, RECORD_SCHEMA, out, flowFile);
            recordWriter.beginRecordSet();
        }

        @Override
        public void addToListing(final Blob blob) throws IOException {
            recordWriter.write(createRecordForListing(blob));
        }

        @Override
        public void finishListing() throws IOException {
            final WriteResult writeResult = recordWriter.finishRecordSet();
            recordWriter.close();

            if (writeResult.getRecordCount() == 0) {
                session.remove(flowFile);
            } else {
                final Map<String, String> attributes = new HashMap<>(writeResult.getAttributes());
                attributes.put("record.count", String.valueOf(writeResult.getRecordCount()));
                flowFile = session.putAllAttributes(flowFile, attributes);

                session.transfer(flowFile, REL_SUCCESS);
            }
        }

        @Override
        public void finishListingExceptionally(final Exception cause) {
            try {
                recordWriter.close();
            } catch (IOException e) {
                logger.error("Failed to write listing as Records", e);
            }

            session.remove(flowFile);
        }

        @Override
        public boolean isCheckpoint() {
            return false;
        }

        private Record createRecordForListing(final Blob blob) {
            final Map<String, Object> values = new HashMap<>();
            values.put(BUCKET, blob.getBucket());
            values.put(NAME, blob.getName());
            values.put(SIZE, blob.getSize());
            values.put(CACHE_CONTROL, blob.getCacheControl());
            values.put(COMPONENT_COUNT, blob.getComponentCount());
            values.put(CONTENT_DISPOSITION, blob.getContentDisposition());
            values.put(CONTENT_ENCODING, blob.getContentEncoding());
            values.put(CONTENT_LANGUAGE, blob.getContentLanguage());
            values.put(CRC32C, blob.getCrc32c());
            values.put(CREATE_TIME, blob.getCreateTime() == null ? null : new Timestamp(blob.getCreateTime()));
            values.put(UPDATE_TIME, blob.getUpdateTime() == null ? null : new Timestamp(blob.getUpdateTime()));

            final BlobInfo.CustomerEncryption encryption = blob.getCustomerEncryption();
            if (encryption != null) {
                values.put(ENCRYPTION_ALGORITHM, encryption.getEncryptionAlgorithm());
                values.put(ENCRYPTION_KEY_SHA256, encryption.getKeySha256());
            }

            values.put(ETAG, blob.getEtag());
            values.put(GENERATED_ID, blob.getGeneratedId());
            values.put(GENERATION, blob.getGeneration());
            values.put(MD5, blob.getMd5());
            values.put(MEDIA_LINK, blob.getMediaLink());
            values.put(METAGENERATION, blob.getMetageneration());

            final Acl.Entity owner = blob.getOwner();
            if (owner != null) {
                if (owner instanceof Acl.User) {
                    values.put(OWNER, ((Acl.User) owner).getEmail());
                    values.put(OWNER_TYPE, "user");
                } else if (owner instanceof Acl.Group) {
                    values.put(OWNER, ((Acl.Group) owner).getEmail());
                    values.put(OWNER_TYPE, "group");
                } else if (owner instanceof Acl.Domain) {
                    values.put(OWNER, ((Acl.Domain) owner).getDomain());
                    values.put(OWNER_TYPE, "domain");
                } else if (owner instanceof Acl.Project) {
                    values.put(OWNER, ((Acl.Project) owner).getProjectId());
                    values.put(OWNER_TYPE, "project");
                }
            }

            values.put(URI, blob.getSelfLink());

            return new MapRecord(RECORD_SCHEMA, values);
        }
    }

    /**
     * Writes Blobs by creating a new FlowFile for each blob and writing information as FlowFile attributes
     */
    private static class AttributeBlobWriter implements BlobWriter {
        private final ProcessSession session;

        public AttributeBlobWriter(final ProcessSession session) {
            this.session = session;
        }

        @Override
        public void beginListing() {
        }

        @Override
        public void addToListing(final Blob blob) {
            final Map<String, String> attributes = StorageAttributes.createAttributes(blob);

            // Create the flowfile
            FlowFile flowFile = session.create();
            flowFile = session.putAllAttributes(flowFile, attributes);
            session.transfer(flowFile, REL_SUCCESS);
        }

        @Override
        public void finishListing() {
        }

        @Override
        public void finishListingExceptionally(final Exception cause) {
        }

        @Override
        public boolean isCheckpoint() {
            return true;
        }
    }

    /**
     * Simply counts the blobs.
     */
    private static class CountingBlobWriter implements BlobWriter {
        private int count = 0;

        @Override
        public void beginListing() {
        }

        @Override
        public void addToListing(final Blob blob) {
            count++;
        }

        @Override
        public void finishListing() {
        }

        @Override
        public void finishListingExceptionally(final Exception cause) {
        }

        @Override
        public boolean isCheckpoint() {
            return false;
        }

        public int getCount() {
            return count;
        }
    }
}
