In this article, I have developed an event calendar class that will populate all the days in a month based on the specified date, along with the events that we can add to the calendar.

While PHP doesn't include a built-in calendar API per se (without including additional extensions), it does, however, give you a broad range of date and time methods that we can use to manipulate to build our own solution. In addition, we can use these methods to populate the pages showing the days, weeks, and months of a particular year.

Why should I use the calendar class?

It's entirely up to you and your requirements. I have decided to take it upon myself to write my own class as I work on many projects that require an event-based calendar system. I've searched countless times for a minimal, dependency-free, and modern library but couldn't find a solution that seamlessly integrates with my projects. Therefore, I created a PHP class that can easily be integrated with any project, whether the project's size is small or large.

The class is lightweight and easy to use, as it doesn't require any additional libraries or extensions to be installed on your server. You can simply include the class in your project and start using it immediately.

It utilizes the PHP date function to get the number of days in a month, the first day of the week, and the last day of the previous month. We can then use this information to populate the calendar with the days of the month.

Source Code

Create a new file Calendar.php and add the following code:

PHP 
<?php
class Calendar {

    private $active_year, $active_month, $active_day;
    private $events = [];

    public function __construct($date = null) {
        $this->active_year = $date != null ? date('Y', strtotime($date)) : date('Y');
        $this->active_month = $date != null ? date('m', strtotime($date)) : date('m');
        $this->active_day = $date != null ? date('d', strtotime($date)) : date('d');
    }

    public function add_event($txt, $date, $days = 1, $color = '') {
        $color = $color ? ' ' . $color : $color;
        $this->events[] = [$txt, $date, $days, $color];
    }

    public function __toString() {
        $num_days = date('t', strtotime($this->active_day . '-' . $this->active_month . '-' . $this->active_year));
        $num_days_last_month = date('j', strtotime('last day of previous month', strtotime($this->active_day . '-' . $this->active_month . '-' . $this->active_year)));
        $days = [0 => 'Sun', 1 => 'Mon', 2 => 'Tue', 3 => 'Wed', 4 => 'Thu', 5 => 'Fri', 6 => 'Sat'];
        $first_day_of_week = array_search(date('D', strtotime($this->active_year . '-' . $this->active_month . '-1')), $days);
        $html = '<div class="calendar">';
        $html .= '<div class="header">';
        $html .= '<div class="month-year">';
        $html .= date('F Y', strtotime($this->active_year . '-' . $this->active_month . '-' . $this->active_day));
        $html .= '</div>';
        $html .= '</div>';
        $html .= '<div class="days">';
        foreach ($days as $day) {
            $html .= '
                <div class="day_name">
                    ' . $day . '
                </div>
            ';
        }
        for ($i = $first_day_of_week; $i > 0; $i--) {
            $html .= '
                <div class="day_num ignore">
                    ' . ($num_days_last_month-$i+1) . '
                </div>
            ';
        }
        for ($i = 1; $i <= $num_days; $i++) {
            $selected = '';
            if ($i == $this->active_day) {
                $selected = ' selected';
            }
            $html .= '<div class="day_num' . $selected . '">';
            $html .= '<span>' . $i . '</span>';
            foreach ($this->events as $event) {
                for ($d = 0; $d <= ($event[2]-1); $d++) {
                    if (date('y-m-d', strtotime($this->active_year . '-' . $this->active_month . '-' . $i . ' -' . $d . ' day')) == date('y-m-d', strtotime($event[1]))) {
                        $html .= '<div class="event' . $event[3] . '">';
                        $html .= $event[0];
                        $html .= '</div>';
                    }
                }
            }
            $html .= '</div>';
        }
        for ($i = 1; $i <= (42-$num_days-max($first_day_of_week, 0)); $i++) {
            $html .= '
                <div class="day_num ignore">
                    ' . $i . '
                </div>
            ';
        }
        $html .= '</div>';
        $html .= '</div>';
        return $html;
    }

}
?>

Add the following code to your stylesheet (CSS) or create a new file calendar.css:

CSS 
.calendar {
    display: flex;
    flex-flow: column;
}
.calendar .header .month-year {
    font-size: 20px;
    font-weight: bold;
    color: #636e73;
    padding: 20px 0;
}
.calendar .days {
    display: flex;
    flex-flow: wrap;
}
.calendar .days .day_name {
    width: calc(100% / 7);
    border-right: 1px solid #2c7aca;
    padding: 20px;
    text-transform: uppercase;
    font-size: 12px;
    font-weight: bold;
    color: #818589;
    color: #fff;
    background-color: #448cd6;
}
.calendar .days .day_name:nth-child(7) {
    border: none;
}
.calendar .days .day_num {
    display: flex;
    flex-flow: column;
    width: calc(100% / 7);
    border-right: 1px solid #e6e9ea;
    border-bottom: 1px solid #e6e9ea;
    padding: 15px;
    font-weight: bold;
    color: #7c878d;
    cursor: pointer;
    min-height: 100px;
}
.calendar .days .day_num span {
    display: inline-flex;
    width: 30px;
    font-size: 14px;
}
.calendar .days .day_num .event {
    margin-top: 10px;
    font-weight: 500;
    font-size: 14px;
    padding: 3px 6px;
    border-radius: 4px;
    background-color: #f7c30d;
    color: #fff;
    word-wrap: break-word;
}
.calendar .days .day_num .event.green {
    background-color: #51ce57;
}
.calendar .days .day_num .event.blue {
    background-color: #518fce;
}
.calendar .days .day_num .event.red {
    background-color: #ce5151;
}
.calendar .days .day_num:nth-child(7n+1) {
    border-left: 1px solid #e6e9ea;
}
.calendar .days .day_num:hover {
    background-color: #fdfdfd;
}
.calendar .days .day_num.ignore {
    background-color: #fdfdfd;
    color: #ced2d4;
    cursor: inherit;
}
.calendar .days .day_num.selected {
    background-color: #f1f2f3;
    cursor: inherit;
}

How To Use

Let's create a simple example to demonstrate how to use the calendar class.

Include the class in your project and create a new instance.

PHP 
include 'Calendar.php';
$calendar = new Calendar();

We can specify a date while creating a new instance:

PHP 
include 'Calendar.php';
$calendar = new Calendar('2024-05-12');

Add new events to the calendar:

PHP 
$calendar->add_event('Holiday', '2024-05-14');

We can specify the number of days the event should last by binding an additional value to the add_event method:

PHP 
$calendar->add_event('Holiday', '2024-05-14', 7); // Event will last for 7 days

We can also change the color:

PHP 
$calendar->add_event('Holiday', '2024-05-14', 7, 'red');

Only red, blue, and green will work (the default is orange). You can add more colors to the CSS file.

We can populate the calendar in HTML format with the following code:

PHP 
echo $calendar;

Example Code

Create a new file example.php and add the following code:

PHP 
<?php
include 'Calendar.php';
$calendar = new Calendar('2024-05-12');
$calendar->add_event('Birthday', '2024-05-03', 1, 'green');
$calendar->add_event('Doctors', '2024-05-04', 1, 'red');
$calendar->add_event('Holiday', '2024-05-16', 7);
?>
<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>Event Calendar</title>
		<link href="style.css" rel="stylesheet" type="text/css">
		<link href="calendar.css" rel="stylesheet" type="text/css">
	</head>
	<body>
	    <nav class="navtop">
	    	<div>
	    		<h1>Event Calendar</h1>
	    	</div>
	    </nav>
		<div class="content home">
			<?=$calendar?>
		</div>
	</body>
</html>

The stylesheet (style.css) for our example page:

CSS 
* {
    box-sizing: border-box;
    font-family: -apple-system, BlinkMacSystemFont, "segoe ui", roboto, oxygen, ubuntu, cantarell, "fira sans", "droid sans", "helvetica neue", Arial, sans-serif;
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}
body {
    background-color: #FFFFFF;
    margin: 0;
}
.navtop {
    background-color: #3b4656;
    height: 60px;
    width: 100%;
    border: 0;
}
.navtop div {
    display: flex;
    margin: 0 auto;
    width: 800px;
    height: 100%;
}
.navtop div h1, .navtop div a {
    display: inline-flex;
    align-items: center;
}
.navtop div h1 {
    flex: 1;
    font-size: 24px;
    padding: 0;
    margin: 0;
    color: #ebedee;
    font-weight: normal;
}
.navtop div a {
    padding: 0 20px;
    text-decoration: none;
    color: #c4c8cc;
    font-weight: bold;
}
.navtop div a i {
    padding: 2px 8px 0 0;
}
.navtop div a:hover {
    color: #ebedee;
}
.content {
    width: 800px;
    margin: 0 auto;
}
.content h2 {
    margin: 0;
    padding: 25px 0;
    font-size: 22px;
    border-bottom: 1px solid #ebebeb;
    color: #666666;
}

And now, if we navigate to our example page, it will resemble the following:

http://localhost/phpcalendar/example.php
Event Calendar Interface with PHP, HTML and CSS

If there aren't any events populated on the calendar, make sure the dates are correct and your server timezone is set correctly. You can change the timezone using the code below.

PHP 
date_default_timezone_set('America/Los_Angeles');

The full list of supported timezones are available here.

Conclusion

While the calendar class I've created isn't a complete solution, it will most definitely help you integrate the class into any project seamlessly and extend the base code with additional features.

Drop a comment below and let me know if you encounter any issues with the class. Don't forget to follow us on social media and share our articles, as this will help our website grow, and therefore provide more quality content and updates.

Released under the MIT License. If you're going to redistribute the code, please include my name and link to this article or purchase the advanced package, which doesn't require attribution.

Thank you for reading!