php 51 lines · 8 steps

Merging overlapping busy time blocks in PHP

A service that normalizes calendar events and collapses overlapping intervals into clean busy blocks.

Explained by highlit

Intermediate interval-merging sorting datetime array-transformation

1<?php
2 
3namespace App\Services;
4 
5use DateTimeImmutable;
6 
7final class BusyBlockMerger
8{
9    public function merge(array $events): array
10    {
11        $ranges = [];
12 
13        foreach ($events as $event) {
14            $start = $event['start'] instanceof DateTimeImmutable
15                ? $event['start']
16                : new DateTimeImmutable($event['start']);
17            $end = $event['end'] instanceof DateTimeImmutable
18                ? $event['end']
19                : new DateTimeImmutable($event['end']);
20 
21            if ($end <= $start) {
22                continue;
23            }
24 
25            $ranges[] = [$start, $end];
26        }
27 
28        usort($ranges, fn (array $a, array $b) => $a[0] <=> $b[0]);
29 
30        $merged = [];
31 
32        foreach ($ranges as [$start, $end]) {
33            $last = array_key_last($merged);
34 
35            if ($last !== null && $start <= $merged[$last]['end']) {
36                if ($end > $merged[$last]['end']) {
37                    $merged[$last]['end'] = $end;
38                }
39                continue;
40            }
41 
42            $merged[] = ['start' => $start, 'end' => $end];
43        }
44 
45        return array_map(static fn (array $block) => [
46            'start' => $block['start']->format(DATE_ATOM),
47            'end' => $block['end']->format(DATE_ATOM),
48            'duration_minutes' => (int) (($block['end']->getTimestamp() - $block['start']->getTimestamp()) / 60),
49        ], $merged);
50    }
51}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Sorting intervals by start time turns overlap detection into a single linear pass.
2Normalizing inputs to a common type early lets the rest of the logic stay simple.
3Extending the last kept range in place is the whole trick to merging overlaps.

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