calculate interest by day in real time - php

Question

i am a creating a system where users can do investments and gain interest. Now i want to calculate interest per day in real time, so the interest accumulate by day until the end date . I want this to be in real time, meaning i want to calculate the interest and up until the end date but my code only displays the results all at once. For instance if the start day is monday and end date is is friday the code should accumulate the interest everyday until friday in real time.
$interest = 89;
$startdate = '2022-06-06';
$enddate = '2023-06-04'
$days = (($enddate - $startdate) / 60 / 60 / 24);
$previousday = date('Y/m/d',strtotime("-1 days"));
$currentdate = date('Y/m/d');
$totalEarning = 0;
$Earningsbyday = [];
if ($startdate <= $enddate && $previousday < $currentdate ) {
for ($i = 0; $i < $days; $i++) {
$totalEarning += $interest;
$Earningsbyday[$i] = $totalEarning;
}
echo var_dump($Earningsbyday)."\n"."\n";
}

Answer 1

You can do this quite simply. First, use create_date to create a DateTime in PHP. With these two converted dates, we can pass it to date_diff and format the amount of days between the two dates.
From here, we can use array_fill to fill an array of nth days with the interest. The total is simply just the array_sum.
We can now array_walk and calculate the previous day + the current interest to build the array you're expecting.
class InterestCalculator
{
private array $dailyInterest = [];
private static int $interest = 89;
public function calculateDailyInterest(string $start, string $end): array
{
$this->dailyInterest = array_fill(0, date_diff(date_create($start), date_create($end))->format('%a'), self::$interest);
$total = array_sum($this->dailyInterest);
array_walk($this->dailyInterest, function (int &$value, int $key): void {
$value = ($this->dailyInterest[$key -1] ?? 0) + $value;
});
return compact('total') + ['dailyInterest' => $this->dailyInterest];
}
}
// total => 32307, dailyInterest => [0 => 89, 1 => 178, 2 => 267, ....]
print_r((new InterestCalculator)->calculateDailyInterest('2022-06-06', '2023-06-04'));
References:
https://www.php.net/manual/en/function.date-create.php
https://www.php.net/manual/en/datetime.diff.php
https://www.php.net/manual/en/function.array-fill.php
https://www.php.net/manual/en/function.array-walk.php
https://www.php.net/manual/en/language.references.pass.php
https://www.php.net/manual/es/function.compact.php
Hopefully, this completes what you need. Feel free to comment if I miss understood your question.
See it working over at 3v4l.org