Get recurring dates within date interval - php

Question

I guess I’m stuck with this problem, so I’m hoping that you can give me some ideas how I can solve this task.
I’m working on an app that allows you to get an overview about your recurring payments (I know, this stuff exists already, this is just a side project) and your expenses.
The API is nearly finished but I struggle with this section: I need to know, if a recurring payment is due within a given time span.
The recurring events (contracts) contain amongst other fields startDate, endDate, intervalType (enum [weekly, monthly, quarterly, biannually, annually])
Currently I have this as my doctrine query:
return $this->createQueryBuilder('e')
->andWhere('e.startDate >= :start')
->andWhere('e.endDate <= :end')
->andWhere('e.user = :user')
->setParameter('start', $start)
->setParameter('end', $end)
->setParameter('user', $user)
->getQuery()
->getResult();
where the parameters start and end are the frame of interval.
But how can I check if and how often the contracts are due within the selected frame?
Afaik this would only be possible by iterating over the result of the query and check if the contract intersects with the timeframe and also note how often and when it occurs during this time.
But I have no idea how I can do this.
Example Data:
[name, intervalType, startDate, endDate, amount]
rent, monthly, 2019-01-01, 2020-10-11, -500
utility, monthly, 2019-01-01, 2020-10-11, -150
salary, monthly, 2019-01-01, 2020-10-11, 1700
investment, biannually, 2019-02-10, null , 2500
food, weekly, 2019-01-01, null , -50
If I have the timeframe (2019-05-01 - 2019-05-31) of this month I would get those contracts:
rent 2019-05-01
utility 2019-05-01
salary 2019-05-01
food 2019-05-01
food 2019-05-08
food 2019-05-15
food 2019-05-22
food 2019-05-29
If I'd choose the following 2 months (2019-07-01 - 2019-08-31) I would get this:
rent 2019-07-01
rent 2019-08-01
utility 2019-07-01
utility 2019-08-01
salary 2019-07-01
salary 2019-08-01
food 2019-07-01
food 2019-07-08
food 2019-07-15
food 2019-07-22
food 2019-07-29
food 2019-08-01
food 2019-08-08
food 2019-08-15
food 2019-08-22
food 2019-08-29
investment 2019-08-01
Would this be possible with DateTime and DateInterval?

Answer 1

The logic with the weekly interval looks wrong to me. At least with my bank app a weekly schedule would always fall on the same weekday, with 7 days between two consecutive occurrences.
So with that logic you could use this function:
function getScheduleBetween($data, $intervalStart, $intervalEnd) {
$ref = [
"yearly" => [12, "months"],
"annually" => [12, "months"],
"biannually" => [6, "months"],
"quarterly" => [3, "months"],
"monthly" => [1, "months"],
"weekly" => [7, "days"],
"daily" => [1, "days"]
];
$intervalStart = new DateTime($intervalStart);
$intervalEnd = new DateTime($intervalEnd);
$result = [];
foreach($data as $schedule) {
// Convert start/end to DateTime
$startDate = new DateTime($schedule["startDate"]);
$endDate = $schedule["endDate"] ? min(new DateTime($schedule["endDate"]), $intervalEnd) : $intervalEnd;
$name = $schedule["name"];
$interval = $schedule["intervalType"];
if (!isset($ref[$interval])) throw "Invalid interval type";
list($coeff, $interval) = $ref[$interval];
$match = clone $startDate;
if ($match < $intervalStart) {
$diff = $intervalStart->diff($match);
$count = $interval == "days" ? $diff->format("%a") : $diff->m + $diff->y * 12 + ($diff->d ? 1 : 0);
$count = ceil($count / $coeff) * $coeff;
$match->modify("+$count $interval");
}
while ($match <= $endDate) {
$temp = clone $match;
$result[] = ["name" => $name, "date" => $temp->format("Y-m-d")];
$match->modify("+$coeff $interval");
}
}
array_multisort(array_column($result, "date"), $result);
return $result;
}
Example use:
$data = [
["name" => "rent", "intervalType" => "monthly", "startDate" => "2019-01-01", "endDate" => "2020-10-11", "amount" => -500],
["name" => "utility", "intervalType" => "monthly", "startDate" => "2019-01-01", "endDate" => "2020-10-11", "amount" => -150],
["name" => "salary", "intervalType" => "monthly", "startDate" => "2019-01-01", "endDate" => "2020-10-11", "amount" => 1700],
["name" => "investment", "intervalType" => "biannually", "startDate" => "2019-02-10", "endDate" => null, "amount" => 2500],
["name" => "food", "intervalType" => "weekly", "startDate" => "2019-01-01", "endDate" => null, "amount" => -50],
];
$result = getScheduleBetween($data, "2019-05-01", "2019-05-31");
print_r($result);
With the larger period:
$result = getScheduleBetween($data, "2019-05-01", "2019-08-31");
print_r($result);
If you have other types of intervals I believe you can easily extend this function to support them, even with the other logic of "weekly".