[exams] Add check and warning for colliding exams

If two (or more) exams share at least one location and their start/end
times overlap, display a warning to the user.

4 files changed, 69 insertions, 4 deletions

diff --git a/modules-available/exams/lang/de/template-tags.json b/modules-available/exams/lang/de/template-tags.json
index f88ce5af..0ac88155 100644
--- a/modules-available/exams/lang/de/template-tags.json
+++ b/modules-available/exams/lang/de/template-tags.json
@@ -11,6 +11,7 @@
     "lang_begin_date": "Beginn Datum",
     "lang_begin_time": "Uhrzeit",
     "lang_checkLocationSelectionHint": "Stellen Sie sicher, dass die gew\u00fcnschte(n) Pr\u00fcfungsveranstaltung(en) in ihrer Raumbeschr\u00e4nkung mit den hier ausgew\u00e4hlten R\u00e4umen \u00fcbereinstimmen.",
+    "lang_collision": "Kollision",
     "lang_comfirmGlobalExam": "Wollen Sie wirklich eine globale Pr\u00fcfung definieren? Im gew\u00e4hlten Zeitraum werden s\u00e4mtliche R\u00e4ume in den Pr\u00fcfungsmodus geschaltet.",
     "lang_currentlyActiveExams": "Aktuell laufende Pr\u00fcfungen",
     "lang_dateTime": "Datum\/Uhrzeit",
@@ -26,6 +27,7 @@
     "lang_examStartAfterLectureEnd": "Der gew\u00e4hlte Klausurzeitraum beginnt, nachdem die gew\u00e4hlte Veranstaltung endet, oder kurz vor derem Ende.",
     "lang_examStartAfterLectureStart": "Der gew\u00e4hlte Klausurzeitraum beginnt sp\u00e4ter, als die gew\u00e4hlte Veranstaltung startet.",
     "lang_examStartBeforeLectureStart": "Der gew\u00e4hlte Klausurzeitraum beginnt, bevor die gew\u00e4hlte Veranstaltung startet. Ein Autostart der Veranstaltung wird fehlschlagen.",
+    "lang_examsWithCollisions": "Sich r\u00e4umlich und zeitlich \u00fcberschneidende Pr\u00fcfungen",
     "lang_global": "Global",
     "lang_headingAddExam": "Zeitraum hinzuf\u00fcgen",
     "lang_headingAllExamLectures": "Ausstehende Pr\u00fcfungsveranstaltungen (30 Tage)",
diff --git a/modules-available/exams/lang/en/template-tags.json b/modules-available/exams/lang/en/template-tags.json
index 59c159e9..97b6ce21 100644
--- a/modules-available/exams/lang/en/template-tags.json
+++ b/modules-available/exams/lang/en/template-tags.json
@@ -11,6 +11,7 @@
     "lang_begin_date": "Begin Date",
     "lang_begin_time": "Time",
     "lang_checkLocationSelectionHint": "Make sure that the according lecture(s) will have their location restrictions set accordingly.",
+    "lang_collision": "Collision",
     "lang_comfirmGlobalExam": "Do you really want to create a global exam? Every single room will be set to lecture mode during the selected time period.",
     "lang_currentlyActiveExams": "Currently running exams",
     "lang_dateTime": "Date\/Time",
@@ -26,6 +27,7 @@
     "lang_examStartAfterLectureEnd": "Specified exam interval starts after selected lecture ends (or shortly before it ends).",
     "lang_examStartAfterLectureStart": "Specified exam interval starts after selected lecture starts.",
     "lang_examStartBeforeLectureStart": "Specified exam interval starts before selected lecture starts. (Auto-)starting the lecture before it's valid will fail.",
+    "lang_examsWithCollisions": "Exams with conflicting schedule and location",
     "lang_global": "Global",
     "lang_headingAddExam": "Add Exam Period",
     "lang_headingAllExamLectures": "Upcoming Lectures Marked As Exams (30 Days)",
diff --git a/modules-available/exams/page.inc.php b/modules-available/exams/page.inc.php
index f42711a2..2bd7a215 100644
--- a/modules-available/exams/page.inc.php
+++ b/modules-available/exams/page.inc.php
@@ -224,8 +224,51 @@ class Page_Exams extends Page
 	{
 		$out = [];
 		$now = time();
+
+		// Pre-compute collisions: exams overlap in time and share at least one location
+		$collisionFlags = [];
+		$parsedExams = [];
 		if (is_array($this->exams)) {
-			foreach ($this->exams as $exam) {
+			foreach ($this->exams as $idx => $exam) {
+				IF ($exam['endtime'] < $now)
+					continue; // Don't care about past exams
+				// Parse location IDs: treat NULL as global (0) to be consistent with permission checks
+				if (empty($exam['locationids'])) {
+					$lids = Location::getAllLocationIds(0);
+				} else {
+					$lids = array_map(function($val) {
+						return Location::getAllLocationIds($val, true);
+					}, explode(',', (string)$exam['locationids']));
+					$lids = array_unique(array_merge(...$lids));
+				}
+				$parsedExams[$idx] = [
+					'start' => (int)$exam['starttime'],
+					'end'   => (int)$exam['endtime'],
+					'lids'  => $lids,
+				];
+				$collisionFlags[$idx] = false;
+			}
+
+			$indices = array_keys($parsedExams);
+			$cnt = count($indices);
+			for ($i = 0; $i < $cnt; $i++) {
+				for ($j = $i + 1; $j < $cnt; $j++) {
+					$a = $parsedExams[$indices[$i]];
+					$b = $parsedExams[$indices[$j]];
+					// Time overlap if startA < endB and startB < endA
+					if ($a['start'] < $b['end'] && $b['start'] < $a['end']) {
+						// Location overlap
+						if (!empty(array_intersect($a['lids'], $b['lids']))) {
+							$collisionFlags[$indices[$i]] = true;
+							$collisionFlags[$indices[$j]] = true;
+						}
+					}
+				}
+			}
+
+			// Build output, attaching visual classes and collision flag
+			$numCollisions = 0;
+			foreach ($this->exams as $idx => $exam) {
 				if ($exam['endtime'] < $now) {
 					$exam['rowClass'] = 'text-muted';
 					$exam['btnClass'] = 'btn-default';
@@ -238,10 +281,15 @@ class Page_Exams extends Page
 				}
 				$exam['starttime_s'] = date('Y-m-d H:i', $exam['starttime']);
 				$exam['endtime_s'] = date('Y-m-d H:i', $exam['endtime']);
+				if ($collisionFlags[$idx] ?? false) {
+					$exam['rowClass'] = 'danger slx-bold';
+					$exam['collision'] = true;
+					$numCollisions++;
+				}
 				$out[] = $exam;
 			}
 		}
-		return ['exams' => $out];
+		return ['exams' => $out, 'collisions' => $numCollisions];
 	}
 
 	protected function makeLectureExamList(): array
diff --git a/modules-available/exams/templates/page-exams.html b/modules-available/exams/templates/page-exams.html
index 178a4f8b..e4b6328c 100644
--- a/modules-available/exams/templates/page-exams.html
+++ b/modules-available/exams/templates/page-exams.html
@@ -4,6 +4,12 @@
 		{{lang_allExamPeriods}}
 	</div>
 	<div class="panel-body">
+		{{#collisions}}
+			<div class="alert alert-danger">
+				<span class="glyphicon glyphicon-warning-sign"></span>
+				{{lang_examsWithCollisions}}: {{.}}
+			</div>
+		{{/collisions}}
 		{{#active_exams}}
 			<div class="alert alert-info">
 				<span class="glyphicon glyphicon-info-sign"></span>
@@ -28,6 +34,9 @@
 					<tr class="{{rowClass}}">
 						<td>{{examid}}</td>
 						<td width="100%">
+							{{#collision}}
+								<span class="glyphicon glyphicon-flash" title="{{lang_collision}}"></span>
+							{{/collision}}
 							{{locationnames}}
 							{{^locationnames}}
 							<i>{{lang_global}}</i>
@@ -44,8 +53,12 @@
 								{{/description}}
 							</div>
 						</td>
-						<td class="text-nowrap" data-sort-value={{starttime}}>{{starttime_s}}</td>
-						<td class="text-nowrap" data-sort-value={{endtime}}>{{endtime_s}}</td>
+						<td class="text-nowrap" data-sort-value={{starttime}}>
+							{{starttime_s}}
+						</td>
+						<td class="text-nowrap" data-sort-value={{endtime}}>
+							{{endtime_s}}
+						</td>
 						<td class="text-nowrap text-right">
 							{{^liesInPast}}
 							<a onclick="slxShow({{starttime}}, {{endtime}})" class="btn btn-default btn-sm"><span class="glyphicon glyphicon-eye-open"></span></a>