Calculates the date when adding days excluding weekends and bank holidays in England and Wales

calculate_date_excluding_weekend_and_bank_holidays.php

<?php 

/**
 * Checks to see if a given date is a bank holiday in the UK
 * 
 * 1. Set the current year
 * 2. Get the bank holidays in the UK
 * 3. Parse out the bank holidays in the UK that are within the current year
 * 4. Check to see if the if $check_date is within the current years bank holidays
 *  4.1 Return true if it is
 *  4.2 Return false if it is not
 *
 * @param string $check_date
 * @return void
 */
function check_if_date_is_bank_holiday($check_date)
{
    // Set current year
    $year = (new DateTime('today'))->format('Y');
    
    // Get the bank holidays in the UK
    $json = file_get_contents('https://www.gov.uk/bank-holidays.json');

    // Convert JSON data into associative array and get the date column from sub arrays to create array of dates
    $event_years = array_column(json_decode($json, true)['england-and-wales']['events'], 'date');

    // Filter through the $event_years array and get only the years that start with the current year e.g. 2022
    $current_year_events = array_filter($event_years, fn($event_year) => str_starts_with($event_year, $year));

    // Return boolean whether $check_date is in $current_year_events
    return in_array($check_date, $current_year_events);
}


/**
 * Calculates the date, excluding weekends and UK bank holidays.
 * 
 * 1. Set the current day
 * 2. Perform a loop for the number of days passed to the function
 * 3. Check to see which day of the week the current date is
 *  3.1 If 5 (Friday) then add 3 days to exclude the weekend and get the following Monday
 *  3.2 If 6 (Saturday) then add 2 to exclude Sunday and get the upcoming Monday
 *  3.3 Otherwise add 1 day to the current date and continue the loop
 *
 * @param integer $days
 * @param boolean $include_current_day
 * @return DateTime
 */
function calculate_date($days, $include_current_day = true)
{
    // Set the current date
    $date = new DateTime('today');
 
    do {
        // Check to see whether to include the current day to skip the first iteration modifying $date
        if ($include_current_day) {
            // Set $include_current_day so the loop can modify $date
            $include_current_day = false;
        } else {
            // Check to see which day of the week the current date is and days to current day
            $add_days = match ($date->format('N')) {
                '5' => 3,
                '6' => 2,
                default => 1
            };

            // Check to see if the current day is a bank holiday and add any days to current day
            if (check_if_date_is_bank_holiday($date->format('Y-m-d'))) {
                $add_days++;
            }
            
            // Add days to date
            $date->modify('+' . $add_days . ' day');
        }

        // Decrement days so we can eventually break from the loop
        $days--;
    } while ($days > 0);

    // Return the calculate date
    return $date;
}

print_r(calculate_date(13));

/**
 * Example data output
 * 
 * Next bank holiday: 02/05/22
 * Current date: 29/04/2022
 * 
 * Running calculate_date(5) should give us 06/05/22 
 * skipping the weekend (30/05/22 & 01/05/2022) and skipping the
 * bank holiday (02/05/22)
 * 
 * Running calculate_date(5, false) should give us 09/05/22
 * skipping the both weekends (30/05/22 & 01/05/2022) & (07/05/22 & 08/05/2022)
 * and skipping the bank holiday (02/05/22)
 */