class Input

<?php

function _($x) {
    return htmlspecialchars($x);
}

class Input {

    // The type of the input-field is stored in the attribute-slot.
    private $typeName;

    // This is an array of elements that will be rendered when the input-field
    // type requires sub-elements, such as the `select` input-field. The values
    // inserted here depend on the input-field type. They will be ignored when
    // the input-field type does not require sub-elements.
    private $subElements;

    // Attributes of the input-field are saved in this array.
    private $attributes;

    // This array contains all css-classes for the input-field and will be
    // treated special from the $attributes slot. The class-value generated
    // here will overwrite attributes set in the $attributes array.
    private $classes;

    public function __construct($typeName, $id=null, $class=null) {
        $this->typeName = $typeName;
        $this->subElements = array();
        $this->attributes = array();
        $this->classes = array();

        if ($id !== null)
            $this->setAttribute('id', $id);
        if ($class !== null)
            $this->setClasses(explode(' ', $class));
    }

    public function setClasses($classes) {
        if (!is_array($classes))
            throw new InvalidArgumentException('expected array.');

        $this->classes = $classes;
    }

    public function addClass(/* ... */) {
        $args = func_get_args();
        foreach ($args as $className) {
            $contained = array_search($className, $this->classes);
            if ($contained === false) {
                array_push($this->classes, $className);
            }
        }
    }

    public function removeClass($className) {
        $index = array_search($className, $this->classes);
        if ($index !== false) {
            unset($this->classes[$index]);
        }
    }

    public function setAttribute($name, $value) {
        if ($name == 'class' or $name == 'type') {
            throw new LogicException('class and type attributes are treated differently.');
        }
        $this->attributes[$name] = $value;
    }

    // removeAttribute()
    // hasAttribute()

    public function render() {
        $string = '<input type="' . _($this->typeName) . '" ';

        // Render the class-names.
        if ($this->classes) {
            $classNames = implode(' ', $this->classes);
            $string .= 'class="' . $classNames . '" ';
        }

        // Render the rest of the attributes.
        foreach ($this->attributes as $key => $value) {
            $string .= $key . '="' . _($value) . '" ';
        }
        $string .= '>';

        // Special treatment for `select`, etc..

        $string .= '</input>';

        return $string;
    }

}

$i = new Input('text', 'myInput', 'foo bar');
$i->addClass('foo', 'baar', 'spam', 'eggs');
print $i->render();