How to check for conflict with multiple datetime RANGES

I am stumped about how to go about checking to see if multiple *date/time value -ranges- (meaning: start and end times) are in conflict with one another.

Summary & samples of data I need to work with.

I have an (app) events table, that is used to create a form for the user to go through and check off (checkboxes) all the sessions/events they attended.

The names of the checkboxes are generated using info about the session. (month/day start/end times along with a session id)

ie: hours_9_5_p02_800_845

9 = month
5 = date
p02 = session id/event code
800 = start time
845 = end time

all delimited by an underscore ("_")

If the user checks (and submits) multiple sessions, there will be many of these values to check for a time conflict..

hours_9_5_p08_755_800
hours_9_5_p02_800_845
hours_9_5_p02_800_855
hours_9_5_p03_800_845
hours_9_5_p04_820_835
hours_9_5_p04_845_900
hours_9_5_REG_900_915
hours_9_5_REG_1300_1305
hours_9_5_REG_1310_1335
hours_9_5_REG_1320_1335

The above is an example of the fieldlist/array that I 'could' get as a user selection/submission that I need to check for any possible conflicts (obviously the user couldnt be two places at once) :) And the above have many/several overlapping of just the same exact time slots selected.

** I am open to either PHP, (checking after the user submits) or javascript/jQuery (if it can do the date/time RANGE conflict checking, it might be easier to then highlight those rows/elements on the page if done on the front end)

I'd image, first you need to parse those checkbox names/strings from the fieldlist array...

which I have done like so: (php)

function conflictParse($delimiter, $targetString){
    //echo 'fired';
    $breakDown = explode($delimiter, $targetString);
    $startTime = substr_replace($breakDown[4] , ':', -2, 0);
    $endTime = substr_replace($breakDown[5] , ':', -2, 0);
    $startString = "$breakDown[1]/$breakDown[2]/2015 $startTime";
    $endString = "$breakDown[1]/$breakDown[2]/2015 $endTime";
    $startFormat = strtotime($startString);
    $endFormat = strtotime($endString);
    $start = date('m/d/Y G:i',$startFormat);
    $end = date('m/d/Y G:i',$endFormat);

    return "Session Times: $start -- $end <br>";
}
echo conflictParse('_','hours_9_5_p02_800_845');

but I am not clear on HOW to go about using this RANGE of a date start & end time to check against MULTIPLE other date start/end time RANGES?

maybe just sticking with having PHP parse/check conflict upon submit and then return some array of the (original) names page to the page (for some jQuery to use and highlight the elements..etc (but I can handle that aspect later.. for right now I am need help on how I can get the above parse 'date/time' start/end range values checked for conflicts against other 'date/time' start/end range values

update:

Here is the current nested associative array I have to work with for comparing:

I need to convert your js functions over to PHP and of course use the fullStart/fullEnd variables in my time compares I guess..??

(but your function is still confusing me as I see references to event1, event 2.. (to match your example)..

update 2:

The above is my object/array (associative array) that I got from selecting some check boxes, and submitting my form...

Here is my attempt to convert your JS code to PHP based [with some update variablenames]: (and the commented out lines just to try and get some sort of output somewhere)

print_r($conflict_list);

    function checkFirst($cf_presX, $cf_presY) {
        //$cf_presX['fullStart'] < $cf_presY['fallStart'] ? checkConflict($cf_presX, $cf_presY) : checkConflict($cf_presY, $cf_presX);

        echo 'Pres Check: '.$cf_presX[0] . '<br>';
        echo 'Pres Check: '.$cf_presY[0] . '<br>';
        /*
        function checkConflict ($cc_presX, $cc_presY) {      
            if ($cc_presX.['fullEnd'] > $cc_presY.['fullStart']) {
                $cc_presX.['hasConflict'] = true;
                $cc_presY.['hasConflict'] = true;
            }
        }
        */
    }

    function setConflicts($events) {
        for ($i = 0; $i < count($events); $i++) {
            for ($j = 0; $i < count($events); $j++) {
              // if it is not the same event
              // if (i !== j) is the same $age['Peter']
              if ($events[$i]['id'] !== $events[$j]['id']) {
                checkFirst($events[$i], $events[$j]);
              }
            }
        }
    }
    setConflicts($conflict_list);

I just keep getting a loop with undefined offset: (counting up to the 100k+ mark)

Notice: Undefined offset: 0 in C:\wamp\www\projects\misc\conflict_check_new.php on line 49 Pres Check:

Notice: Undefined offset: 0 in C:\wamp\www\projects\misc\conflict_check_new.php on line 50 Pres Check:

Notice: Undefined offset: 0 in C:\wamp\www\projects\misc\conflict_check_new.php on line 49 Pres Check:

Solution

The same logic could apply in PHP, but assuming you can get your events out into JavaScript and create an array of objects with start and end dates like so:

var events = [
  {
    id: 'event1',
    start: new Date('1/1/1 5:00'),
    end: new Date('1/1/1 6:00'),
    hasConflict: false
  },
  {
    id: 'event2',
    start: new Date('1/1/1 5:30'),
    end: new Date('1/1/1 6:30'),
    hasConflict: false
  },
  {
    id: 'event3',
    start: new Date('1/1/1 7:30'),
    end: new Date('1/1/1 8:30'),
    hasConflict: false
  }
]

You can compare events to see if the one that starts first, has an end time that's later the second one's start time.

function checkFirst (event1, event2) {
  event1.start < event2.start 
    ? checkConflict(event1, event2) 
    : checkConflict(event2, event1)

  function checkConflict (first, second) {      
    if (first.end > second.start) {
      first.hasConflict = second.hasConflict = true
    }
  }
}

Then you can check events against each other. Here's a not particularly efficient, but at least suitable loop:

function flagAllEventsWithConflicts (events) {
  events.forEach(event1 => {
    events.forEach(event2 => {
      event1.id !== event2.id && checkFirst(event1, event2)
    })
  })
}

Update: The above function can also be written as a nested for loop:

function flagAllEventsWithConflicts (events) {
  for (var i = 0; i < events.length; i++) {
    for (var j = 0; j < events.length; j++ {
      // if it is not the same event
      // if (i !== j) is the same
      if (events[i].id !== events[j].id) {
        checkFirst(events[i], events[j])
      }
    }
  }
}

Then check to see if hasConflict is true or false:

flagAllEventsWithConflicts(events)
console.table(events)

Run this fiddle and checkout the console