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/*
 * Copyright (C) 2020 Graylog, Inc.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the Server Side Public License, version 1,
 * as published by MongoDB, Inc.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * Server Side Public License for more details.
 *
 * You should have received a copy of the Server Side Public License
 * along with this program. If not, see
 * .
 */
package org.graylog2.inputs.extractors;

import com.codahale.metrics.MetricRegistry;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.auto.value.AutoValue;
import com.google.common.base.Joiner;
import com.google.common.base.Predicate;
import com.google.common.collect.Maps;
import org.graylog.autovalue.WithBeanGetter;
import org.graylog2.ConfigurationException;
import org.graylog2.jackson.TypeReferences;
import org.graylog2.plugin.inputs.Converter;
import org.graylog2.plugin.inputs.Extractor;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.annotation.Nullable;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.regex.Pattern;

import static com.google.common.base.MoreObjects.firstNonNull;
import static com.google.common.base.Strings.isNullOrEmpty;

public class JsonExtractor extends Extractor {
    private static final Logger LOG = LoggerFactory.getLogger(JsonExtractor.class);
    private static final String CK_FLATTEN = "flatten";
    private static final String CK_LIST_SEPARATOR = "list_separator";
    private static final String CK_KEY_SEPARATOR = "key_separator";
    private static final String CK_KV_SEPARATOR = "kv_separator";
    private static final String CK_REPLACE_KEY_WHITESPACE = "replace_key_whitespace";
    private static final String CK_KEY_WHITESPACE_REPLACEMENT = "key_whitespace_replacement";
    private static final String CK_KEY_PREFIX = "key_prefix";
    private static final Pattern WHITE_SPACE_PATTERN = Pattern.compile("\\s");
    private static final RemoveNullPredicate REMOVE_NULL_PREDICATE = new RemoveNullPredicate();

    private final ObjectMapper mapper = new ObjectMapper();
    private final boolean flatten;
    private final String listSeparator;
    private final String keySeparator;
    private final String kvSeparator;
    private final boolean replaceKeyWhitespace;
    private final String keyWhitespaceReplacement;
    private final String keyPrefix;

    public JsonExtractor(final MetricRegistry metricRegistry,
                         final String id,
                         final String title,
                         final long order,
                         final CursorStrategy cursorStrategy,
                         final String sourceField,
                         final String targetField,
                         final Map extractorConfig,
                         final String creatorUserId,
                         final List converters,
                         final ConditionType conditionType,
                         final String conditionValue) throws ReservedFieldException, ConfigurationException {
        super(metricRegistry, id, title, order, Type.JSON, cursorStrategy, sourceField, targetField, extractorConfig, creatorUserId, converters, conditionType, conditionValue);

        if (extractorConfig == null) {
            throw new ConfigurationException("Missing extractor configuration");
        }

        this.flatten = firstNonNull((Boolean) extractorConfig.get(CK_FLATTEN), false);
        this.listSeparator = firstNonNull((String) extractorConfig.get(CK_LIST_SEPARATOR), ", ");
        this.keySeparator = firstNonNull((String) extractorConfig.get(CK_KEY_SEPARATOR), "_");
        this.kvSeparator = firstNonNull((String) extractorConfig.get(CK_KV_SEPARATOR), "=");
        this.replaceKeyWhitespace = firstNonNull((Boolean) extractorConfig.get(CK_REPLACE_KEY_WHITESPACE), false);
        this.keyWhitespaceReplacement = firstNonNull((String) extractorConfig.get(CK_KEY_WHITESPACE_REPLACEMENT), "_");
        this.keyPrefix = firstNonNull((String) extractorConfig.get(CK_KEY_PREFIX), "");
    }

    @Override
    protected Result[] run(String value) {
        final Map extractedJson;
        try {
            extractedJson = extractJson(value);
        } catch (IOException e) {
            throw new ExtractorException(e);
        }
        final List results = new ArrayList<>(extractedJson.size());
        for (Map.Entry entry : extractedJson.entrySet()) {
            results.add(new Result(entry.getValue(), entry.getKey(), -1, -1));
        }

        return results.toArray(new Result[results.size()]);
    }

    public Map extractJson(String value) throws IOException {
        if (isNullOrEmpty(value)) {
            return Collections.emptyMap();
        }

        final Map json;
        json = mapper.readValue(value, TypeReferences.MAP_STRING_OBJECT);

        final Map results = new HashMap<>(json.size());
        for (Map.Entry mapEntry : json.entrySet()) {
            for (Entry entry : parseValue(keyPrefix + mapEntry.getKey(), mapEntry.getValue())) {
                results.put(entry.key(), entry.value());
            }
        }

        return results;
    }

    private String parseKey(String key) {
        if (replaceKeyWhitespace && key.contains(" ")) {
            return WHITE_SPACE_PATTERN.matcher(key).replaceAll(keyWhitespaceReplacement);
        } else {
            if (LOG.isDebugEnabled() && key.contains(" ")) {
                LOG.debug("Invalid key \"{}\" in JSON object!", key);
            }

            return key;
        }
    }

    private Collection parseValue(String key, Object value) {
        final String processedKey = parseKey(key);
        if (value instanceof Boolean) {
            return Collections.singleton(Entry.create(processedKey, value));
        } else if (value instanceof Number) {
            return Collections.singleton(Entry.create(processedKey, value));
        } else if (value instanceof String) {
            return Collections.singleton(Entry.create(processedKey, value));
        } else if (value instanceof Map) {
            @SuppressWarnings("unchecked")
            final Map map = (Map) value;
            final Map withoutNull = Maps.filterEntries(map, REMOVE_NULL_PREDICATE);
            if (flatten) {
                final Joiner.MapJoiner joiner = Joiner.on(listSeparator).withKeyValueSeparator(kvSeparator);
                return Collections.singleton(Entry.create(processedKey, joiner.join(withoutNull)));
            } else {
                final List result = new ArrayList<>(map.size());
                for (Map.Entry entry : map.entrySet()) {
                    result.addAll(parseValue(processedKey + keySeparator + entry.getKey(), entry.getValue()));
                }

                return result;
            }
        } else if (value instanceof List) {
            final List values = (List) value;
            final Joiner joiner = Joiner.on(listSeparator).skipNulls();
            return Collections.singleton(Entry.create(processedKey, joiner.join(values)));
        } else if (value == null) {
            // Ignore null values so we don't try to create fields for that in the message.
            return Collections.emptySet();
        } else {
            LOG.debug("Unknown type \"{}\" in key \"{}\"", value.getClass(), key);
            return Collections.emptySet();
        }
    }

    @AutoValue
    @WithBeanGetter
    protected abstract static class Entry {
        public abstract String key();

        @Nullable
        public abstract Object value();

        public static Entry create(String key, @Nullable Object value) {
            return new AutoValue_JsonExtractor_Entry(key, value);
        }
    }

    protected final static class RemoveNullPredicate implements Predicate {
        @Override
        public boolean apply(@Nullable Map.Entry input) {
            return input != null && input.getKey() != null && input.getValue() != null;
        }
    }
}