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/*
 * 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 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 or the Server
 * Side Public License, v 1.
 */

package org.elasticsearch.index.query;

import org.apache.lucene.index.Term;
import org.apache.lucene.search.BooleanClause;
import org.apache.lucene.search.BooleanQuery;
import org.apache.lucene.search.ConstantScoreQuery;
import org.apache.lucene.search.MatchNoDocsQuery;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.TermQuery;
import org.elasticsearch.Version;
import org.elasticsearch.common.ParsingException;
import org.elasticsearch.common.Strings;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;
import org.elasticsearch.index.mapper.FieldNamesFieldMapper;
import org.elasticsearch.index.mapper.MappedFieldType;
import org.elasticsearch.xcontent.ParseField;
import org.elasticsearch.xcontent.XContentBuilder;
import org.elasticsearch.xcontent.XContentParser;

import java.io.IOException;
import java.util.Collection;
import java.util.Objects;
import java.util.Set;
import java.util.stream.Collectors;

/**
 * Constructs a query that only match on documents that the field has a value in them.
 */
public class ExistsQueryBuilder extends AbstractQueryBuilder {
    public static final String NAME = "exists";

    public static final ParseField FIELD_FIELD = new ParseField("field");

    private final String fieldName;

    public ExistsQueryBuilder(String fieldName) {
        if (Strings.isEmpty(fieldName)) {
            throw new IllegalArgumentException("field name is null or empty");
        }
        this.fieldName = fieldName;
    }

    /**
     * Read from a stream.
     */
    public ExistsQueryBuilder(StreamInput in) throws IOException {
        super(in);
        fieldName = in.readString();
    }

    @Override
    protected void doWriteTo(StreamOutput out) throws IOException {
        out.writeString(fieldName);
    }

    /**
     * @return the field name that has to exist for this query to match
     */
    public String fieldName() {
        return this.fieldName;
    }

    @Override
    protected QueryBuilder doRewrite(QueryRewriteContext queryRewriteContext) throws IOException {
        SearchExecutionContext context = queryRewriteContext.convertToSearchExecutionContext();
        if (context != null) {
            if (getMappedFields(context, fieldName).isEmpty()) {
                return new MatchNoneQueryBuilder();
            }
        }
        return super.doRewrite(queryRewriteContext);
    }

    @Override
    protected void doXContent(XContentBuilder builder, Params params) throws IOException {
        builder.startObject(NAME);
        builder.field(FIELD_FIELD.getPreferredName(), fieldName);
        printBoostAndQueryName(builder);
        builder.endObject();
    }

    public static ExistsQueryBuilder fromXContent(XContentParser parser) throws IOException {
        String fieldPattern = null;
        String queryName = null;
        float boost = AbstractQueryBuilder.DEFAULT_BOOST;

        XContentParser.Token token;
        String currentFieldName = null;
        while ((token = parser.nextToken()) != XContentParser.Token.END_OBJECT) {
            if (token == XContentParser.Token.FIELD_NAME) {
                currentFieldName = parser.currentName();
            } else if (token.isValue()) {
                if (FIELD_FIELD.match(currentFieldName, parser.getDeprecationHandler())) {
                    fieldPattern = parser.text();
                } else if (AbstractQueryBuilder.NAME_FIELD.match(currentFieldName, parser.getDeprecationHandler())) {
                    queryName = parser.text();
                } else if (AbstractQueryBuilder.BOOST_FIELD.match(currentFieldName, parser.getDeprecationHandler())) {
                    boost = parser.floatValue();
                } else {
                    throw new ParsingException(
                        parser.getTokenLocation(),
                        "[" + ExistsQueryBuilder.NAME + "] query does not support [" + currentFieldName + "]"
                    );
                }
            } else {
                throw new ParsingException(
                    parser.getTokenLocation(),
                    "[" + ExistsQueryBuilder.NAME + "] unknown token [" + token + "] after [" + currentFieldName + "]"
                );
            }
        }

        if (fieldPattern == null) {
            throw new ParsingException(parser.getTokenLocation(), "[" + ExistsQueryBuilder.NAME + "] must be provided with a [field]");
        }

        ExistsQueryBuilder builder = new ExistsQueryBuilder(fieldPattern);
        builder.queryName(queryName);
        builder.boost(boost);
        return builder;
    }

    @Override
    protected Query doToQuery(SearchExecutionContext context) throws IOException {
        return newFilter(context, fieldName, true);
    }

    public static Query newFilter(SearchExecutionContext context, String fieldPattern, boolean checkRewrite) {
        Collection fields = getMappedFields(context, fieldPattern).stream()
            .map(context::getFieldType)
            .collect(Collectors.toList());

        if (fields.isEmpty()) {
            if (checkRewrite) {
                throw new IllegalStateException("Rewrite first");
            } else {
                return new MatchNoDocsQuery("unmapped field:" + fieldPattern);
            }
        }

        if (context.indexVersionCreated().before(Version.V_6_1_0)) {
            return newLegacyExistsQuery(fields);
        }

        if (fields.size() == 1) {
            MappedFieldType field = fields.iterator().next();
            return new ConstantScoreQuery(field.existsQuery(context));
        }

        BooleanQuery.Builder boolFilterBuilder = new BooleanQuery.Builder();
        for (MappedFieldType field : fields) {
            boolFilterBuilder.add(field.existsQuery(context), BooleanClause.Occur.SHOULD);
        }
        return new ConstantScoreQuery(boolFilterBuilder.build());
    }

    private static Query newLegacyExistsQuery(Collection fields) {
        // We create TermsQuery directly here rather than using FieldNamesFieldType.termsQuery()
        // so we don't end up with deprecation warnings
        if (fields.size() == 1) {
            return new ConstantScoreQuery(new TermQuery(new Term(FieldNamesFieldMapper.NAME, fields.iterator().next().name())));
        }

        BooleanQuery.Builder boolFilterBuilder = new BooleanQuery.Builder();
        for (MappedFieldType field : fields) {
            Query filter = new TermQuery(new Term(FieldNamesFieldMapper.NAME, field.name()));
            boolFilterBuilder.add(filter, BooleanClause.Occur.SHOULD);
        }
        return new ConstantScoreQuery(boolFilterBuilder.build());
    }

    private static Collection getMappedFields(SearchExecutionContext context, String fieldPattern) {
        Set matchingFieldNames = context.getMatchingFieldNames(fieldPattern);
        if (matchingFieldNames.isEmpty()) {
            // might be an object field, so try matching it as an object prefix pattern
            matchingFieldNames = context.getMatchingFieldNames(fieldPattern + ".*");
        }
        return matchingFieldNames;
    }

    @Override
    protected int doHashCode() {
        return Objects.hash(fieldName);
    }

    @Override
    protected boolean doEquals(ExistsQueryBuilder other) {
        return Objects.equals(fieldName, other.fieldName);
    }

    @Override
    public String getWriteableName() {
        return NAME;
    }
}