Estimate the reading time of your markdown-based articles, as detailed by Medium: https://blog.medium.com/read-time-and-you-bc2048ab620c

readingTimeEstimate.php

<?php

const WPM = 250

const READING_TIME_PER_IMAGE = 12; // seconds
const IMAGE_THRESHOLD = 10; // After this threshold each image counts for 3 seconds

function readingTimeEstimate($markdown) {
    $markdown = strip_tags($markdown);
    $markdown = str_replace("\n", ' ', $markdown);

    $wordCount = str_word_count($markdown);
    $estimatedTimeForWords = $wordCount / WPM;

    $imageCount = preg_match_all('/!\[[\w\s]+]\(.*?\)/', $markdown);

    // We only calculate the sum of the series for the first ten images.
    // Everything else is overage.
    $imageSeries = min($imageCount, IMAGE_THRESHOLD);

    // We subtract the threshold from the image count.
    // If it's more than 10 we'll get an overage costing 3 seconds each.
    // If it's less than 10 we'll be calculating with 3 * 0 = 0 extra seconds
    $imageOverage = max(0, $imageCount - IMAGE_THRESHOLD);

    // See: https://math.stackexchange.com/a/556810
    $estimatedTimeForImages = $imageSeries + (READING_TIME_PER_IMAGE * $imageSeries) - (($imageSeries / 2) * ($imageSeries + 1)) + ($imageOverage * 3);
    
    $readingTimeEstimate = round(($estimatedTimeForImages / 60) + $estimatedTimeForWords);

    return match((int) $readingTimeEstimate) {
        0 => 'Less than a minute',
        1 => '1 minute',
        default => sprintf('%d minutes', $readingTimeEstimate),
    };
}