#PHP html meta-tag (OGP, FB app, Twitter Cards, etc) helper.

meta_tag.php

<?php

function meta_tag()
{
    static $buffer = array();
    $charset = 'utf-8';
    $num = func_num_args();
    $args = func_get_args();

    if (2 === $num && is_string($args[0]) && is_string($args[1])) {
        $name = trim(htmlspecialchars($args[0], ENT_COMPAT, $charset));
        $content = htmlspecialchars($args[1], ENT_COMPAT, $charset);
        if('charset' == $name) {
            $buffer[$name][] = '<meta charset="'.$content.'">';
        } else {
            $prop = 'name';
            if (0 === strpos($name, 'og:') || 0 === strpos($name, 'fb:')) {
                $prop = 'property';
            } elseif(false !== strpos($name, '-')) {
                $prop = 'http-equiv';
            }

            if (false !== strpos($name, ':image')) {
                if (empty($buffer[$name])) {
                    $buffer[$name] = array();
                }
                $buffer[$name][$content] = '<meta '.$prop.'="'.$name.'" content="'.$content.'">';
            } else {
                $buffer[$name] = '<meta '.$prop.'="'.$name.'" content="'.$content.'">';
            }
        }
    } elseif(1 === $num && is_array($args[0])) {
        foreach($args[0] as $key => $value) {
            if (is_array($value)) {
                foreach($value as $val) {
                    meta($key, $val);
                }
            } else {
                meta($key, $value);
            }
        }
    } elseif (0 === $num && !empty($buffer)) {
        ksort($buffer);
        $tags = array();
        foreach($buffer as $value) {
            if (is_array($value)) {
                foreach($value as $val) {
                    $tags[] = $val;
                }
            } else {
                $tags[] = $value;
            }
        }

        return implode(PHP_EOL, $tags).PHP_EOL;
    }
}

/*
// Usage

meta_tag('description', 'Page Description');
meta_tag('twitter:card', 'summary');
meta_tag('og:image', 'http://example.com/image1.jpg');
meta_tag('og:image', 'http://example.com/image2.jpg');

// OR

meta_tag(array(
    'description' => 'Page Description',
    'twitter:card' => 'summary',
    'og:image' => array(
        'http://example.com/image1.jpg',
        'http://example.com/image2.jpg',
    ),
));

// Render
echo meta();
*/