How Jump to with collections of data in laravel - laravel-5

Question

I'm implementing the Jump to... functionality in my project. What I want is:
If the user is in the first item the left button is NOT included.
If the user is in the last item the right button is NOT included.
The left button should have a link same with the link before the current/selected item.
The right button should have a link same with the link after the current/selected item.
Please see my code below:
Controller
$course = Course::with([
'assignments' => $undeleted,
'quizzes' => $undeleted,
'add_links' => $undeleted
])->findOrFail($id);
$course_items = collect($course->assignments);
$course_items = $course_items->merge(collect($course->quizzes));
$course_items = $course_items->merge(collect($course->add_links));
$course_items = $course_items->sortBy('item_number');
View
<div class="jump-to">
<div class="pull-right">
<div class="btn-group" role="group">
#foreach($course->topics as $topic)
#foreach(collect($topic->assignments)->merge(collect($topic->quizzes))->merge(collect($topic->add_links))->sortBy('item_number') as $first_item)
#if($first_item->id != $assignment->id)
<a href="#" class="btn btn-primary">
<i class="fa fa-angle-left"></i>
</a>
#endif
<?php break 2; ?>
#endforeach
#endforeach
<div class="btn-group" role="group">
<button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
Jump to <div class="caret"></div>
</button>
<ul class="dropdown-menu" role="menu">
#foreach($course->topics as $topic)
<li class="jdivider">
Topic {{ $topic->topic_number }}
</li>
#foreach(collect($topic->assignments)->merge(collect($topic->quizzes))->merge(collect($topic->add_links))->sortBy('item_number') as $topic_item)
<li>
#if($topic_item->item_type() == 'assignment')
<a title="Assignment: {{ $topic_item->name }}" class="regular-link" href="{{ route('assignment.view', ['course_id' => $course->id, 'id' => $topic_item->id]) }}">
<i class="fa fa-tasks"></i> {{ str_limit($topic_item->name, 15) }}
</a>
#elseif($topic_item->item_type() == 'quiz')
<a title="Quiz: {{ $topic_item->name }}" class="regular-link" href="{{ route('quiz.view', ['course_id' => $course->id, 'id' => $topic_item->id]) }}">
<i class="fa fa-file-text"></i> {{ str_limit($topic_item->name, 15) }}
</a>
#elseif($topic_item->item_type() == 'add_link')
<a href="#">
#if(!empty($topic_item->file_location) && in_array(strtolower(last(explode('.', $topic_item->file_location))), ['pdf', 'docx', 'doc']))
<i class="fa fa-file-pdf-o"></i>
#elseif(empty($topic_item->file_location))
<i class="fa fa-globe"></i>
#else
<i class="fa fa-file-text-o"></i>
#endif
{{ str_limit($topic_item->name, 15) }}
</a>
#endif
</li>
#endforeach
#endforeach
</ul>
</div>
<a href="#" class="btn btn-primary">
<i class="fa fa-angle-right"></i>
</a>
</div>
</div>
</div>
Example
dropdown links:
Assignment1
Assignment2
Quiz1
QUiz2
Reviewer1
If I clicked Assignment2, the left button, has the id or link to Assignment1. If I clicked Reviewer1, the right button disappears and the left button has the id or link to Quiz2 and same with the other links.