PHP, repeating events check next one with unix timestamps

I have a problem with php that i don't really know how to solve. I have an array full of unix timestamps coming from a mysql query.

These timestamps are events that repeat every week ( For example, every Tuesday and Thursday ). They can repeat various days or just one.

Knowing the days that repeat, which day will be the next one.

For example:

In the Array I have :

1595289600 --> 2020/07/21 (Tuesday)

1595116800 --> 2020/07/19 (Sunday)

Today we are at 1595376000 (Wednesday) , so it should return 1595116800 + 604800 (Sunday).

In 5 days ( next monday) it should return 1595289600 + 604800 = 1595721600 (First tuesday + one week )

in one week (next Wednesday) , it should return the next Sunday (2020/08/02 ): 1596326400

And so on...

Thank you!

Solution

For every timestamp you have - calculate next timestamp (add a week) until it is after current timestamp. Then return lowest from those as that one will be the closest to now (but also in the future).

So lets say it is 2020-07-22 Wednesday. Your 2020-07-21 Tuesday is in the past, so add a week: 2020-07-28 Tuesday - its in the future, so its our candidate. Your 2020-07-19 Sunday is also in the past, so add a week: 2020-07-26 Sunday - its in the future so its out second candidate.

Now pick lower from 2 candidates: 2020-07-26 Sunday.

If the dates are more in the past then you will need more a week to them more times.

Something like this:

<?php

// those are your timestamps: $timestamps = [1595289600, 1595116800];
// $time is optional int for when you want to perform the calculation. defaults to current timestamp
function nextOccurence(array $timestamps, $time = null) { 
  $now = $time ?? time();

  $nextTimestamps = [];
  foreach ($timestamps as $timestamp) {
    while ($timestamp < $now) {
      $timestamp += 604800;
    }

    $nextTimestamps[] = $timestamp;
  }

  return min($nextTimestamps);
}