Refactor Value Metrics Class To Enable Easier Customization

[MannikJ]

I find the Laravel\Nova\Metrics\Value::aggregate function a bit too verbose. If you try to customize the behavior, you end up with a lot of copy paste. In fact the default implementation also contains code duplication to build the result value. This makes it quite hard to read for my taste.

I would suggest changing into something like the following, which divides the same aggregation code into three functions:

    protected function aggregate($request, $model, $function, $column = null, $dateColumn = null)
    {
        $query = $model instanceof Builder ? $model : (new $model)->newQuery();

        $column = $column ?? $query->getModel()->getQualifiedKeyName();

        if ($request->range === 'ALL') {
            return $this->result(
                round(with(clone $query)->{$function}($column), $this->precision)
            );
        }

        $timezone = Nova::resolveUserTimezone($request) ?? $request->timezone;

        return $this->result(
            $this->getRawResult(
                with(clone $query),
                $this->currentRange($request->range, $timezone),
                $function,
                $column
            )
        )->previous($this->getRawResult(
            with(clone $query),
            $this->previousRange($request->range, $timezone),
            $function,
            $column
        ));
    }

    protected function applyRange($query, $range)
    {
        return $query->whereBetween(
            $dateColumn ?? $query->getModel()->getQualifiedCreatedAtColumn(),
            array_map(function ($datetime) {
                return $this->asQueryDatetime($datetime);
            }, $range)
        );
    }

    protected function getRawResult($query, $range, $function, $column)
    {
        return round(
            $this->applyRange($query, $range)->{$function}($column),
            $this->precision
        );
    }

This doesn't really save lines of cod, but it encapsules business logic so it is easier to adapt for more complex cases.