Refactoring Overview

Take a look at the function ordinal_suffix()

function ordinal_suffix($num)
{
    $number = abs($num);
    $lastChar = substr($num, -1, 1);
    switch ($lastChar)
    {
        case '1' : return ($num == '11') ? 'th' : 'st';
        case '2' : return ($num == '12') ? 'th' : 'nd';
        case '3' : return ($num == '13') ? 'th' : 'rd';
    }
    return 'th';
}

Let's see

• function & Param names are vague, because it only works with $num below 100
• $number is useless
• switch combine with ternary operator (?) make logical complexity

Refactor

• Rename for function & param & variables for more descriptive
• Remove var $number
• Use an associative array a.k.a Map a.k.a Dictionary to remove control flow switch
• Apply early-return pattern

function month_day_ordinal_suffix($month_day)
{
    $month_day .= ''; // type casting
    $special_days = ['11', '12', '13'];
    if (in_array($month_day, $special_days)) {
        return 'th';
    }

    $lastchar_suffix_map = [
        '1' => 'st',
        '2' => 'nd',
        '3' => 'rd',
        // others are 'th'
    ];

    $lastchar = substr($month_day, -1, 1);
    $found_in_map = isset($lastchar_suffix_map[$lastchar]);
    return $found_in_map ? $lastchar_suffix_map[$lastchar] : 'th';
}

Unit Test

To make sure after refactoring the function still works correctly, we should have tests. It's better if you can write test cases before refactoring.

Create a new file at /tests/Helpers/DateHelperTest.php

<?php
namespace Tests\Helpers;
use PHPUnit\Framework\TestCase;

// set up the required constant 
if (!defined('BASEPATH')) {
    define('BASEPATH', __DIR__ . "/../../");
}

// include the specific file to test
require BASEPATH . 'application/helpers/application_helper.php';

class DateHelperTest extends TestCase
{

    function testMonthDayOrdinalSuffix()
    {
        // test cases will place here
    }
}

Add test cases to testMonthDayOrdinalSuffix function

function testMonthDayOrdinalSuffix()
{
    // last char with 1 cases
    $this->assertEquals('st', \month_day_ordinal_suffix(1));
    $this->assertEquals('th', \month_day_ordinal_suffix(11));
    $this->assertEquals('st', \month_day_ordinal_suffix(21));
    $this->assertEquals('st', \month_day_ordinal_suffix(31));

    // last char with 2 cases
    $this->assertEquals('nd', \month_day_ordinal_suffix(2));
    $this->assertEquals('th', \month_day_ordinal_suffix(12));
    $this->assertEquals('nd', \month_day_ordinal_suffix(22));

    // last char with 3 cases
    $this->assertEquals('rd', \month_day_ordinal_suffix(3));
    $this->assertEquals('th', \month_day_ordinal_suffix(13));
    $this->assertEquals('rd', \month_day_ordinal_suffix(23));


    // other cases
    $this->assertEquals('th', \month_day_ordinal_suffix(7));
    $this->assertEquals('th', \month_day_ordinal_suffix(13));
    $this->assertEquals('th', \month_day_ordinal_suffix(30));
}

Run the test

Add these code to file /phpunit.xml if not exists

<testsuites>
    <testsuite name="helpers">
        <directory>./tests/Helpers/</directory>
    </testsuite>
</testsuites>

Open terminal and run the test

vendor/bin/phpunit --colors=always --testsuite=helpers

Test result

It will be like this if all test cases pass

And when failing:

Come back to the test case check the issue then make it green.

Good luck!