How to display date at new posts in log

I am building an application, and apart of it is a log of conversation, similar to the way how u see messages in whatsapp. The problem I am facing is that the system cannot adapt to different dates nor showcases those in order like:

2018-03-16
item1
item2

2018-03-11
item3
item4

I am making usage of smarty to pull in my data object to my screen:

The back-end

// Fetch info about the support ticket's conversations
$query = "
      SELECT
        conversation_content,
        posted_at,
        is_internal,
        IF(emp_id IS NULL, 0, 1) AS belongsToEmployee,
        EmployeeTBL.EmpFirstname,
        EmployeeTBL.EmpInsertion,
        EmployeeTBL.EmpLastname

      FROM
        ticket_conversation

      INNER JOIN tickets ON ticket_conversation.ticket_id=tickets.id
      LEFT JOIN EmployeeTBL ON ticket_conversation.emp_id=EmployeeTBL.EmpID

      WHERE
        ticket_conversation.ticket_id = :id

      ORDER BY
        ticket_conversation.posted_at
      DESC
      ";
$binds = array(':id' => $_GET['id']);
$ticketConversationList = $db->select($query, $binds);
// Set date container
$ticketDates = [];

// Loop through all the tickets and add their date as a ticket entry
foreach($ticketConversationList as $ticket){
    $ticketDate = date('d-m-Y',strtotime($ticket['posted_at']));
    $ticketDates[$ticketDate][] = $ticket;
}
//var_dump($ticketDates);
// Count all conversations
$conversationCount = count($ticketConversationList);

// Assign the variables
$smarty->assign("ticketDates", $ticketDates);
$smarty->assign("ticketConversationList", $ticketConversationList);
$smarty->assign("conversationCount", $conversationCount);

In my front-end, I am working with the variables provided, as to loop through my array of objects.

The front-end

                <div class="form-group">
                    <label>{$ticketChatHistoryLabel}</label>
                    <hr style="border-color: transparent;">

                    {foreach from=$ticketConversationList key=index item=ticketConversation}

                        {if $index != 0}
                            {$index = $index - 1}
                        {/if}

                        {$dateOfConversation = date('d-m-Y',strtotime($ticketConversation.posted_at))}
                        {$dateOfPreviousConversation = date('d-m-Y',strtotime($ticketConversationList[$index].posted_at))}
                        {$dateOfConversation = date('d-m-Y',strtotime($ticketConversation.posted_at))}
                        {$timeOfConversation = date('H:i',strtotime($ticketConversation.posted_at))}

                        {if $dateOfPreviousConversation < $dateOfConversation || $index == 0}
                            <div>
                                <div class="btn btn-default" style="margin-left: 44%; margin-bottom: 20px;">{$dateOfConversation}</div>
                            </div>
                        {/if}

                        <div class="holder
                            {if $ticketConversation.belongsToEmployee == 1}
                                pull-right
                            {else}pull-left
                            {/if}" style="border-radius: 0; border: 1px solid; padding: 5px; width: 90%;
                        {if $ticketConversation.belongsToEmployee != 0 && $ticketConversation.is_internal == 0}
                                background-color: #c0eed5;
                        {elseif $ticketConversation.belongsToEmployee != 0 && $ticketConversation.is_internal == 1}
                                background-color: #eeeeee;
                        {/if}">
                            {$ticketConversation.conversation_content}
                            <i class="{if $ticketConversation.belongsToEmployee}
                                pull-right
                            {else}pull-left
                            {/if}" style="color: #999999">
                                {$ticketHistoryPostedAt}{$dateOfConversation} {$atLabel} {$timeOfConversation} {$hoursLabel}
                            </i>
                            {if $ticketConversation.belongsToEmployee}
                            <i class="pull-left" style="color: #999999">
                                {$ticketHistoryPostAuthor}{$ticketConversation.EmpFirstname} {$ticketConversation.EmpInsertion} {$ticketConversation.EmpLastname}
                            </i>
                            {/if}
                        </div>
                        <div class="clearfix"></div>
                    {/foreach}

                    <div>
                        <h4 style="text-align: center; color: #afafaf;">- {$endOfTicketConversation} -</h4>
                    </div>
                </div>

At the moment this is the output:

Ticket history as is with current code

Then, I switch

{if $index != 0}
{$index = $index - 1}
{/if}

And I set the green response data as 2018-03-15 (yesterday from time of posting this). The result is as follows:

Ticket history with edited code

Solution

RESOLVED
Required fake 0 check since we're -1'ing

{foreach from=$ticketConversationList key=index item=ticketConversation}

                        {$fake = $index != 0}
                        {if $index != 0}
                            {$index = $index - 1}
                        {/if}

                        {$dateOfConversation = date('d-m-Y',strtotime($ticketConversation.posted_at))}
                        {$dateOfPreviousConversation = date('d-m-Y',strtotime($ticketConversationList[$index].posted_at))}
                        {$dateOfConversation = date('d-m-Y',strtotime($ticketConversation.posted_at))}
                        {$timeOfConversation = date('H:i',strtotime($ticketConversation.posted_at))}

                        {if (( $index == 0 && !$fake )|| $dateOfPreviousConversation != $dateOfConversation) }
                            <div>
                                <div class="btn btn-default" style="margin-left: 44%; margin-bottom: 20px;">{$dateOfConversation}</div>
                            </div>
                        {/if}