/*
 * 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.index.fielddata;

import org.apache.lucene.index.NumericDocValues;
import org.apache.lucene.search.DoubleValues;

import java.io.IOException;
import java.util.function.DoubleToLongFunction;

/**
 * DoubleValues implementation that is guaranteed to have a value
 * for every document in a reader
 */
public abstract class DenseDoubleValues extends DoubleValues {

    @Override
    public final boolean advanceExact(int doc) throws IOException {
        doAdvanceExact(doc);
        return true;
    }

    protected abstract void doAdvanceExact(int doc) throws IOException;

    /**
     * Represent a DenseDoubleValues as a NumericDocValues instance
     * @param in        the DenseDoubleValues to wrap
     * @param maxDoc    the maxDoc of the current reader
     * @param converter a function to convert the double-valued output of DenseDoubleValues to a long
     */
    public static NumericDocValues asNumericDocValues(DenseDoubleValues in, int maxDoc, DoubleToLongFunction converter) {
        return new NumericDocValues() {

            int doc = -1;

            @Override
            public long longValue() throws IOException {
                return converter.applyAsLong(in.doubleValue());
            }

            @Override
            public boolean advanceExact(int target) throws IOException {
                doc = target;
                return in.advanceExact(target);
            }

            @Override
            public int docID() {
                return doc;
            }

            @Override
            public int nextDoc() throws IOException {
                return advance(doc + 1);
            }

            @Override
            public int advance(int target) throws IOException {
                if (target >= maxDoc) {
                    return doc = NO_MORE_DOCS;
                }
                in.advanceExact(target);
                return doc = target;
            }

            @Override
            public long cost() {
                return maxDoc;
            }
        };
    }
}