HTML builder for PHP

html_builder.php

<?php

/**
 * HTML builder
 * @author Chris Lyon <flushot@gmail.com>
 * 
 * This functional HTML builder was inspired by JSX and eliminates the need to use the unsightly
 * and error-prone string concatenation method of building HTML markup. You can now cleanly use
 * nested functions as children and associative arrays as tag attributes.
 *
 * Example usage:
 *
 *     echo tag('h1', function() {
 *              return [
 *                  tag('a', [
 *                         'href' => 'http://www.google.com',
 *                         'class' => ['foo', 'bar'],
 *                         'style' => [
 *                             'text-decoration' => 'underline',
 *                             'font-style' => 'italic'
 *                         ]
 *                     ], 'hello'),
 *                  tag('br'),
 *                  'world'
 *              ];
 *          });
 * 
 * Outputs:
 * 
 *     <h1><a href="http://www.google.com" class="foo bar" style="text-decoration: underline; font-style: italic">hello</a><br/>world</h1>
 *
 * @param $tagName name of the tag.
 * @param $attrsOrChild associative array of attributes or a child (see $child).
 * @param $child child element(s) to render under this tag. can be a string, array of strings, or callable.
 * @return HTML markup as a string.
 */
function tag($tagName, $attrsOrChild=null, $child=null) {
    if (!is_string($tagName))
        throw new InvalidArgumentException('$tagName must be a string');

    $realChild = null;

    // Handle polymorphic args
    if (is_null($attrsOrChild)) {
        $attrs = array();
        $realChild = $child;
    }
    else {
        if (is_array($attrsOrChild)) {
            // Assume array is associative if keys aren't numeric
            $isAssociative = (bool)count(array_filter(array_keys($attrsOrChild), 'is_string'));
            // Handle as attributes
            if ($isAssociative) {            
                $attrs = $attrsOrChild;
                $realChild = $child;
            }
            // Handle as array of children
            else {
                $attrs = array();
                $realChild = $attrsOrChild;
            }
        }
        // Handle as child
        elseif (is_string($attrsOrChild) || is_callable($attrsOrChild)) {
            if (!is_null($child))
                throw new InvalidArgumentException('Ambiguous children: $attrsOrChild and $child');
            $attrs = array();
            $realChild = $attrsOrChild;
        }
    }

    // Evaluate child
    if (!is_null($realChild)) {
        if (is_callable($realChild))
            $realChild = $realChild();
		
        if (is_array($realChild))
            $realChild = implode("\n", $realChild);
		
        if (!is_string($realChild))
            throw new InvalidArgumentException('Child must be a string or a callable');
    }

    // Doing this because unclear on how array_reduce() callback can handle associative arrays
    $reducedAttrs = '';
    foreach ($attrs as $k => $v) {
        if (is_array($v)) {
            switch ($k) {
                case 'class':
                    // val1 valN ...
                    $value = implode(' ', $v);
                    break;
                case 'style':
                    // key1: val1; keyN: valN; ...
                    $value = implode('; ', array_map(
                                function($styleKey) use ($v) {
                                    return "$styleKey: " . 
                                        htmlspecialchars($v[$styleKey], ENT_QUOTES, 'UTF-8');
                                }, array_keys($v)));  // array_map() doesn't iterate keys+vals
                    break;
                default:
                    throw new InvalidArgumentException('array attributes are only valid for class or style');
            }
        }
        else {
            $value = htmlspecialchars($v, ENT_QUOTES, 'UTF-8');
        }
        
        $reducedAttrs .= " $k=\"$value\"";
    }

    // These tags allow the short closing "/>" syntax.
    // See EMPTY elements defined in: http://www.w3.org/TR/xhtml1/dtds.html#a_dtd_XHTML-1.0-Strict
    $emptyTags = array('base', 'meta', 'link', 'hr', 'br', 'param', 'img', 'area', 'input', 'col');

    $markup = '<' . $tagName . $reducedAttrs;
    if (is_null($realChild) && in_array(strtolower($tagName), $emptyTags)) {
        // Short close tag
        $markup .= '/>';
    }
    else {
        // Render children
        $markup .= '>' . $realChild . '</' . $tagName . '>';
    }

    return $markup;
}

?>