<?php

namespace PhpOffice\PhpSpreadsheet\Calculation\Database;

use PhpOffice\PhpSpreadsheet\Calculation\Statistical\Averages;

class DAverage extends DatabaseAbstract
{
    /**
     * DAVERAGE.
     *
     * Averages the values in a column of a list or database that match conditions you specify.
     *
     * Excel Function:
     *        DAVERAGE(database,field,criteria)
     *
     * @param mixed[] $database The range of cells that makes up the list or database.
     *                          A database is a list of related data in which rows of related
     *                              information are records, and columns of data are fields. The
     *                              first row of the list contains labels for each column.
     * @param int|string $field Indicates which column is used in the function. Enter the
     *                              column label enclosed between double quotation marks, such as
     *                              "Age" or "Yield," or a number (without quotation marks) that
     *                              represents the position of the column within the list: 1 for
     *                              the first column, 2 for the second column, and so on.
     * @param mixed[] $criteria The range of cells that contains the conditions you specify.
     *                          You can use any range for the criteria argument, as long as it
     *                              includes at least one column label and at least one cell below
     *                              the column label in which you specify a condition for the
     *                              column.
     *
     * @return null|float|string
     */
    public static function evaluate($database, $field, $criteria)
    {
        $field = self::fieldExtract($database, $field);
        if ($field === null) {
            return null;
        }

        return Averages::average(
            self::getFilteredColumn($database, $field, $criteria)
        );
    }
}