Issue with PHP foreach loop on overlapping datetimes

Question

DATA SUMMARY

---

I have the following data, an $existing_events array of existing events and a request for a new event ($requested_start and $requested_end). Normally pulled from SQL, but I've replicated the issue here w/ static arrays:

$existing_events = array(
    0   => array(
        'time_start' => '2015-09-05 11:30:00',
        'time_end'   => '2015-09-05 18:45:00'
    ),
    1   => array(
        'time_start' => '2015-09-05 07:15:00',
        'time_end'   => '2015-09-05 10:30:00'
    )
);

$requested_start    =   strtotime('2015-09-05 3:30:00 AM');
$requested_end  =   strtotime('2015-09-05 9:30:00 AM');

RESULTS ARRAY

---

A $results array for tracking how many times the comparison is made ('comparison_counter') and how many conflicts are discovered ('conflicts'):

$results = array(
    'conflicts' => 0,
    'comparison_counter' => 0
);

FOREACH LOOP

---

And finally, before dumping out json_encode'd results, the foreach loop that compares start & end time for the requested new event, against start & end time for each preexisting event, using this logic. Note the comparison_counter and conflict increments—the former runs every time the loop runs, and the latter is only "reached" in its if-statement, when there is a conflict between the requested event time and the current event time being tested.

if (!empty($existing_events)){
    foreach ($existing_events as $existing_event){
        $existing_start = strtotime($existing_event['time_start']);
        $existing_end = strtotime($existing_event['time_end']);
        $results['comparison_counter']++;
        if ($requested_start > $existing_end) {
            break;
        } elseif ($requested_end < $existing_start) {
            break;
        } else {
            $results["conflicts"]++;
        }
    }
}

echo json_encode($results);
exit;

ACTUAL RESPONSE

---

What I receive, though, makes it appear that the foreach loop is only executing once, despite the fact that there are two items in my $existing_events array. Here's what I receive with the data above:

comparison_counter: 1
conflicts: 0

vs. what I expect:

comparison_counter: 2
conflicts: 1

Oddly, as soon as I make the following change to 11:30 start-time(to attempt to overlap with both events):

$requested_end  =   strtotime('2015-09-05 11:30:00 AM');

...the comparison_counter now works. I now receive the following:

comparison_counter: 2
conflicts: 2

MY QUESTION

---

Why does the foreach loop not function properly, based on what's in the array I pass? I would expect it to at least hit its $results['comparison_counter']++; every time it fires.

Answer 1

I think this might be what you're looking for:

if (!empty($results['same_day'])){
    foreach ($results['same_day'] as $same_day){
        $exist_start = strtotime($same_day->time_start);
        $exist_end = strtotime($same_day->time_end);
        // Check if new meeting plans to start during existing meeting
        if ( ($requested_start > $exist_start) && ($requested_start < $exist_end) ) {
            $results["conflicts"]++;
            break;
        }
        // Check if new meeting plans to end during existing meeting
        if ( ($requested_end > $exist_start) && ($requested_end < $exist_end) ) {
            $results["conflicts"]++;
            break;
        }
        // Check if existing meeting starts during new meeting
        if ( ($exist_start > $requested_start) && ($exist_start < $requested_end) ) {
            $results["conflicts"]++;
            break;
        }
        // Check if existing meeting ends during new meeting
        if ( ($exist_end > $requested_start) && ($exist_end < $requested_end) ) {
            $results["conflicts"]++;
            break;
        }
    }
}

Full code I used to test:

<?php

$a = new stdClass();
$b = new stdClass();

$a->time_start = "2015-09-05 11:30:00";
$a->time_end = "2015-09-05 18:45:00";

$b->time_start = "2015-09-05 07:15:00";
$b->time_end = "2015-09-05 10:30:00";

$results['same_day'] = array( $a, $b );
$results['conflicts'] = 0;

$requested_start = strtotime( "2015-09-05 03:00" );
$requested_end = strtotime( "2015-09-05 11:00" );


if (!empty($results['same_day'])){
    foreach ($results['same_day'] as $same_day){
        $exist_start = strtotime($same_day->time_start);
        $exist_end = strtotime($same_day->time_end);
        // Check if new meeting plans to start during existing meeting
        if ( ($requested_start > $exist_start) && ($requested_start < $exist_end) ) {
            $results["conflicts"]++;
            break;
        }
        // Check if new meeting plans to end during existing meeting
        if ( ($requested_end > $exist_start) && ($requested_end < $exist_end) ) {
            $results["conflicts"]++;
            break;
        }
        // Check if existing meeting starts during new meeting
        if ( ($exist_start > $requested_start) && ($exist_start < $requested_end) ) {
            $results["conflicts"]++;
            break;
        }
        // Check if existing meeting ends during new meeting
        if ( ($exist_end > $requested_start) && ($exist_end < $requested_end) ) {
            $results["conflicts"]++;
            break;
        }
    }
}

var_dump( $results );

?>

Answer 2

This should have been a much more immediate realization than it was. If you use break, you're basically saying "I found what I want, quit the foreach entirely." If you use a continue, it just drops out of the current iteration (as I understand it) and continues (see what they did, there?) on to the next iteration. Found this "diagram" that explains it nicely and seems to apply to foreach loops, not just while:

while ($foo) {   <--------------------┐
    continue;    --- goes back here --┘
    break;       ----- jumps here ----┐
}                                     |
                 <--------------------┘

Hope this helps somebody else down the line!