functions.php

<?php
declare(strict_types=1);

/**
 * @param mixed $var
 * @return bool
 */
function is_int_safe($var): bool
{
    return is_numeric($var) && preg_match('/^-?\d*$/', (string)(float)$var);
}

/**
 * @param array $keys
 * @param array $values
 * @return array
 */
function array_combine_merge(array $keys, array $values): array
{
    $combined = [];
    $keys = array_values($keys);
    $values = array_values($values);
    $count = max(count($keys), count($values));
    for ($i = 0; $i < $count; $i++) {
        $value = $values[$i] ?? null;
        if (array_key_exists($i, $keys)) {
            $combined[$keys[$i]] = $value;
        } else {
            $combined[] = $value;
        }
    }

    return $combined;
}

/**
 * @param string $str
 * @param string $separator
 * @param bool $capitalize
 * @return string
 */
function strtocamel(string $str, string $separator = '_', bool $capitalize = false): string
{
    $str = str_replace($separator, '', ucwords($str, $separator));
    if (!$capitalize) {
        $str = lcfirst($str);
    }

    return $str;
}

/**
 * @param string $str
 * @return string
 */
function strtosnake(string $str): string
{
    /** @var string[][] $matches */
    preg_match_all('!([A-Z][A-Z0-9]*(?=$|[A-Z][a-z0-9])|[A-Za-z][a-z0-9]+)!', $str, $matches);
    foreach ($matches[0] as &$match) {
        $match = $match === strtoupper($match) ? strtolower($match) : lcfirst($match);
    }

    return implode('_', $matches[0]);
}

/**
 * @param string $glue
 * @param array $array
 * @return string
 */
function implode_all(string $glue, array $array): string
{
    $string = '';
    foreach ($array as $item) {
        if (is_array($item)) {
            $string .= implode_all($glue, $item).$glue;
        } else {
            $string .= $item.$glue;
        }
    }
    $string = substr($string, 0, 0 - strlen($glue));

    return $string;
}

/**
 * @param array $array
 * @param string $prefix
 * @param string $glue
 * @return array
 */
function array_flatten(array $array, string $glue = '_', string $prefix = null): array
{
    $result = [];
    foreach ($array as $key => $value) {
        if (is_array($value)) {
            /** @noinspection AdditionOperationOnArraysInspection */
            $result += array_flatten($value, $glue, $prefix.$key.$glue);
        } else {
            $result[$prefix.$key] = $value;
        }
    }

    return $result;
}