<?php

if ( ! defined('LEXER_ENTER')) {
    define('LEXER_ENTER',     1);
    define('LEXER_MATCHED',   2);
    define('LEXER_UNMATCHED', 3);
    define('LEXER_EXIT',      4);
    define('LEXER_SPECIAL',   5);
}

/**
 * Compounded regular expression.
 * Any of the contained patterns could match and when one does, it's label is returned.
 */
class ParallelRegex
{
    private $patterns;
    private $labels;
    private $regex;
    private $case;

    /**
     * Constructor. Starts with no patterns.
     *
     * @param bool $case    True for case sensitive, false for insensitive.
     */
    public function __construct($case)
    {
        $this->case     = $case;
        $this->patterns = array();
        $this->labels   = array();
        $this->regex    = null;
    }

    /**
     * Adds a pattern with an optional label.
     *
     * @param string $pattern      Perl style regex, but ( and ) lose the usual meaning.
     * @param string $label        Label of regex to be returned on a match.
     */
    public function addPattern($pattern, $label = true)
    {
        $count                  = count($this->patterns);
        $this->patterns[$count] = $pattern;
        $this->labels[$count]   = $label;
        $this->regex            = null;
    }

    /**
     * Attempts to match all patterns at once against a string.
     *
     * @param string $subject      String to match against.
     * @param string $match        First matched portion of subject.
     *
     * @return bool             True on success.
     */
    public function match($subject, &$match)
    {
        if (count($this->patterns) === 0) {
            return false;
        }
        if (! preg_match($this->getCompoundedRegex(), $subject, $matches)) {
            $match = '';

            return false;
        }
        $match = $matches[0];
        for ($i = 1; $i < count($matches); $i++) {
            if ($matches[$i]) {
                return $this->labels[$i - 1];
            }
        }

        return true;
    }

    /**
     * Compounds the patterns into a single regular expression separated with the "or" operator.
     * Caches the regex. Will automatically escape (, ) and / tokens.
     *
     * @param array $patterns    List of patterns in order.
     */
    protected function getCompoundedRegex()
    {
        if ($this->regex === null) {
            for ($i = 0, $count = count($this->patterns); $i < $count; $i++) {
                $this->patterns[$i] = '(' . str_replace(
                        array('/', '(', ')'),
                        array('\/', '\(', '\)'),
                        $this->patterns[$i] ?? '') . ')';
            }
            $this->regex = '/' . implode('|', $this->patterns) . '/' . $this->getPerlMatchingFlags();
        }

        return $this->regex;
    }

    /**
     * Accessor for perl regex mode flags to use.
     *
     * @return string       Perl regex flags.
     */
    protected function getPerlMatchingFlags()
    {
        return ($this->case ? 'msS' : 'msSi');
    }
}

/**
 * States for a stack machine.
 */
class SimpleStateStack
{
    private $stack;

    /**
     * Constructor. Starts in named state.
     *
     * @param string $start        Starting state name.
     */
    public function __construct($start)
    {
        $this->stack = array($start);
    }

    /**
     * Accessor for current state.
     *
     * @return string       State.
     */
    public function getCurrent()
    {
        return $this->stack[count($this->stack) - 1];
    }

    /**
     * Adds a state to the stack and sets it to be the current state.
     *
     * @param string $state        New state.
     */
    public function enter($state)
    {
        array_push($this->stack, $state);
    }

    /**
     * Leaves the current state and reverts to the previous one.
     *
     * @return bool    False if we drop off the bottom of the list.
     */
    public function leave()
    {
        if (count($this->stack) === 1) {
            return false;
        }
        array_pop($this->stack);

        return true;
    }
}

/**
 * Accepts text and breaks it into tokens.
 * Some optimisation to make the sure the content is only scanned by the PHP regex parser once.
 * Lexer modes must not start with leading underscores.
 */
class SimpleLexer
{
    private $regexes;
    private $parser;
    private $mode;
    private $mode_handlers;
    private $case;

    /**
     * Sets up the lexer in case insensitive matching by default.
     *
     * @param SimpleSaxParser $parser  Handling strategy by reference.
     * @param string $start            Starting handler.
     * @param bool $case            True for case sensitive.
     */
    public function __construct($parser, $start = 'accept', $case = false)
    {
        $this->case          = $case;
        $this->regexes       = array();
        $this->parser        = $parser;
        $this->mode          = new SimpleStateStack($start);
        $this->mode_handlers = array($start => $start);
    }

    /**
     * Adds a token search pattern for a particular parsing mode.
     * The pattern does not change the current mode.
     *
     * @param string $pattern      Perl style regex, but ( and ) lose the usual meaning.
     * @param string $mode         Should only apply this pattern when dealing with this type of
     * input.
     */
    public function addPattern($pattern, $mode = 'accept')
    {
        if (! isset($this->regexes[$mode])) {
            $this->regexes[$mode] = new ParallelRegex($this->case);
        }
        $this->regexes[$mode]->addPattern($pattern);
        if (! isset($this->mode_handlers[$mode])) {
            $this->mode_handlers[$mode] = $mode;
        }
    }

    /**
     * Adds a pattern that will enter a new parsing mode.
     * Useful for entering parenthesis, strings, tags, etc.
     *
     * @param string $pattern      Perl style regex, but ( and ) lose the usual meaning.
     * @param string $mode         Should only apply this pattern when dealing with this type of
     * input.
     * @param string $new_mode     Change parsing to this new nested mode.
     */
    public function addEntryPattern($pattern, $mode, $new_mode)
    {
        if (! isset($this->regexes[$mode])) {
            $this->regexes[$mode] = new ParallelRegex($this->case);
        }
        $this->regexes[$mode]->addPattern($pattern, $new_mode);
        if (! isset($this->mode_handlers[$new_mode])) {
            $this->mode_handlers[$new_mode] = $new_mode;
        }
    }

    /**
     * Adds a pattern that will exit the current mode and re-enter the previous one.
     *
     * @param string $pattern      Perl style regex, but ( and ) lose the usual meaning.
     * @param string $mode         Mode to leave.
     */
    public function addExitPattern($pattern, $mode)
    {
        if (! isset($this->regexes[$mode])) {
            $this->regexes[$mode] = new ParallelRegex($this->case);
        }
        $this->regexes[$mode]->addPattern($pattern, '__exit');
        if (! isset($this->mode_handlers[$mode])) {
            $this->mode_handlers[$mode] = $mode;
        }
    }

    /**
     * Adds a pattern that has a special mode.
     * Acts as an entry and exit pattern in one go,
     * effectively calling a special parser handler for this token only.
     *
     * @param string $pattern      Perl style regex, but ( and ) lose the usual meaning.
     * @param string $mode         Should only apply this pattern when dealing with this type of
     * input.
     * @param string $special      Use this mode for this one token.
     */
    public function addSpecialPattern($pattern, $mode, $special)
    {
        if (! isset($this->regexes[$mode])) {
            $this->regexes[$mode] = new ParallelRegex($this->case);
        }
        $this->regexes[$mode]->addPattern($pattern, "_$special");
        if (! isset($this->mode_handlers[$special])) {
            $this->mode_handlers[$special] = $special;
        }
    }

    /**
     * Adds a mapping from a mode to another handler.
     *
     * @param string $mode        Mode to be remapped.
     * @param string $handler     New target handler.
     */
    public function mapHandler($mode, $handler)
    {
        $this->mode_handlers[$mode] = $handler;
    }

    /**
     * Splits the page text into tokens.
     * Will fail if the handlers report an error or if no content is consumed.
     * If successful then each unparsed and parsed token invokes a call to the held listener.
     *
     * @param string $raw        Raw HTML text.
     *
     * @return bool           True on success, else false.
     */
    public function parse($raw)
    {
        if (! isset($this->parser)) {
            return false;
        }
        $length = strlen($raw);
        while (is_array($parsed = $this->reduce($raw))) {
            list($raw, $unmatched, $matched, $mode) = $parsed;
            if (! $this->dispatchTokens($unmatched, $matched, $mode)) {
                return false;
            }
            if ($raw === '') {
                return true;
            }
            if (strlen($raw) == $length) {
                return false;
            }
            $length = strlen($raw);
        }
        if (! $parsed) {
            return false;
        }

        return $this->invokeParser($raw, LEXER_UNMATCHED);
    }

    /**
     * Sends the matched token and any leading unmatched text
     * to the parser changing the lexer to a new mode if one is listed.
     *
     * @param string $unmatched    Unmatched leading portion.
     * @param string $matched      Actual token match.
     * @param string $mode         Mode after match. A boolean false mode causes no change.
     *
     * @return bool             False if there was any error from the parser.
     */
    protected function dispatchTokens($unmatched, $matched, $mode = false)
    {
        if (! $this->invokeParser($unmatched, LEXER_UNMATCHED)) {
            return false;
        }
        if (is_bool($mode)) {
            return $this->invokeParser($matched, LEXER_MATCHED);
        }
        if ($this->isModeEnd($mode)) {
            if (! $this->invokeParser($matched, LEXER_EXIT)) {
                return false;
            }

            return $this->mode->leave();
        }
        if ($this->isSpecialMode($mode)) {
            $this->mode->enter($this->decodeSpecial($mode));
            if (! $this->invokeParser($matched, LEXER_SPECIAL)) {
                return false;
            }

            return $this->mode->leave();
        }
        $this->mode->enter($mode);

        return $this->invokeParser($matched, LEXER_ENTER);
    }

    /**
     * Tests to see if the new mode is actually to leave the
     * current mode and pop an item from the matching mode stack.
     *
     * @param string $mode    Mode to test.
     *
     * @return bool        True if this is the exit mode.
     */
    protected function isModeEnd($mode)
    {
        return ($mode === '__exit');
    }

    /**
     * Test to see if the mode is one where this mode is entered
     * for this token only and automatically leaves immediately afterwoods.
     *
     * @param string $mode    Mode to test.
     *
     * @return bool        True if this is the exit mode.
     */
    protected function isSpecialMode($mode)
    {
        return (strncmp($mode, '_', 1) == 0);
    }

    /**
     * Strips the magic underscore marking single token modes.
     *
     * @param string $mode    Mode to decode.
     *
     * @return string         Underlying mode name.
     */
    protected function decodeSpecial($mode)
    {
        return substr($mode, 1);
    }

    /**
     * Calls the parser method named after the current mode.
     * Empty content will be ignored.
     * The lexer has a parser handler for each mode in the lexer.
     *
     * @param string $content        Text parsed.
     * @param bool $is_match      Token is recognised rather than unparsed data.
     */
    protected function invokeParser($content, $is_match)
    {
        if (($content === '') || ($content === false)) {
            return true;
        }
        $handler = $this->mode_handlers[$this->mode->getCurrent()];

        return $this->parser->$handler($content, $is_match);
    }

    /**
     * Tries to match a chunk of text and
     * if successful removes the recognised chunk and any leading unparsed data.
     * Empty strings will not be matched.
     *
     * @param string $raw         The subject to parse. This is the content that will be eaten.
     *
     * @return array/boolean      Three item list of unparsed content followed by the recognised
     * token and finally the action the parser is to take. True if no match, false if there is a
     * parsing error.
     */
    protected function reduce($raw)
    {
        if ($action = $this->regexes[$this->mode->getCurrent()]->match($raw, $match)) {
            $unparsed_character_count = strpos($raw, strval($match));
            $unparsed                 = substr($raw, 0, $unparsed_character_count);
            $raw                      = substr($raw, $unparsed_character_count + strlen($match));

            return array($raw, $unparsed, $match, $action);
        }

        return true;
    }
}

/**
 * Breaks HTML into SAX events.
 */
class SimpleHtmlLexer extends SimpleLexer
{
    /**
     * Sets up the lexer with case insensitive matching and adds the HTML handlers.
     *
     * @param SimpleSaxParser $parser  Handling strategy by reference.
     */
    public function __construct($parser)
    {
        parent::__construct($parser, 'text');
        $this->mapHandler('text', 'acceptTextToken');
        $this->addSkipping();
        foreach ($this->getParsedTags() as $tag) {
            $this->addTag($tag);
        }
        $this->addInTagTokens();
    }

    /**
     * List of parsed tags. Others are ignored.
     *
     * @return array        List of searched for tags.
     */
    protected function getParsedTags()
    {
        return array('a', 'base', 'title', 'form', 'input', 'button', 'textarea', 'select',
                'option', 'frameset', 'frame', 'label');
    }

    /**
     * The lexer has to skip certain sections such as server code, client code and styles.
     */
    protected function addSkipping()
    {
        $this->mapHandler('css', 'ignore');
        $this->addEntryPattern('<style', 'text', 'css');
        $this->addExitPattern('</style>', 'css');
        $this->mapHandler('js', 'ignore');
        $this->addEntryPattern('<script', 'text', 'js');
        $this->addExitPattern('</script>', 'js');
        $this->mapHandler('comment', 'ignore');
        $this->addEntryPattern('<!--', 'text', 'comment');
        $this->addExitPattern('-->', 'comment');
    }

    /**
     * Pattern matches to start and end a tag.
     *
     * @param string $tag          Name of tag to scan for.
     */
    protected function addTag($tag)
    {
        $this->addSpecialPattern("</$tag>", 'text', 'acceptEndToken');
        $this->addEntryPattern("<$tag", 'text', 'tag');
    }

    /**
     * Pattern matches to parse the inside of a tag including the attributes and their quoting.
     */
    protected function addInTagTokens()
    {
        $this->mapHandler('tag', 'acceptStartToken');
        $this->addSpecialPattern('\s+', 'tag', 'ignore');
        $this->addAttributeTokens();
        $this->addExitPattern('/>', 'tag');
        $this->addExitPattern('>', 'tag');
    }

    /**
     * Matches attributes that are either single quoted, double quoted or unquoted.
     */
    protected function addAttributeTokens()
    {
        $this->mapHandler('dq_attribute', 'acceptAttributeToken');
        $this->addEntryPattern('=\s*"', 'tag', 'dq_attribute');
        $this->addPattern('\\\\"', 'dq_attribute');
        $this->addExitPattern('"', 'dq_attribute');
        $this->mapHandler('sq_attribute', 'acceptAttributeToken');
        $this->addEntryPattern("=\s*'", 'tag', 'sq_attribute');
        $this->addPattern("\\\\'", 'sq_attribute');
        $this->addExitPattern("'", 'sq_attribute');
        $this->mapHandler('uq_attribute', 'acceptAttributeToken');
        $this->addSpecialPattern('=\s*[^>\s]*', 'tag', 'uq_attribute');
    }
}

/**
 * Converts HTML tokens into selected SAX events.
 */
class SimpleHtmlSaxParser
{
    private $lexer;
    private $listener;
    private $tag;
    private $attributes;
    private $current_attribute;

    /**
     * Sets the listener.
     *
     * @param SimplePhpPageBuilder $listener    SAX event handler.
     */
    public function __construct($listener)
    {
        $this->listener          = $listener;
        $this->lexer             = $this->createLexer($this);
        $this->tag               = '';
        $this->attributes        = array();
        $this->current_attribute = '';
    }

    /**
     * Runs the content through the lexer which should call back to the acceptors.
     *
     * @param string $raw      Page text to parse.
     *
     * @return bool         False if parse error.
     */
    public function parse($raw)
    {
        return $this->lexer->parse($raw);
    }

    /**
     * Sets up the matching lexer. Starts in 'text' mode.
     *
     * @param SimpleSaxParser $parser    Event generator, usually $self.
     *
     * @return SimpleLexer               Lexer suitable for this parser.
     */
    public static function createLexer(&$parser)
    {
        return new SimpleHtmlLexer($parser);
    }

    /**
     * Accepts a token from the tag mode.
     * If the starting element completes then the element is
     * dispatched and the current attributes set back to empty.
     * The element or attribute name is converted to lower case.
     *
     * @param string $token     Incoming characters.
     * @param int $event    Lexer event type.
     *
     * @return bool          False if parse error.
     */
    public function acceptStartToken($token, $event)
    {
        if ($event == LEXER_ENTER) {
            $this->tag = strtolower(substr($token, 1));

            return true;
        }
        if ($event == LEXER_EXIT) {
            $success = $this->listener->startElement(
                    $this->tag,
                    $this->attributes);
            $this->tag        = '';
            $this->attributes = array();

            return $success;
        }
        if ($token !== '=') {
            $this->current_attribute                    = strtolower(html_entity_decode($token, ENT_QUOTES));
            $this->attributes[$this->current_attribute] = '';
        }

        return true;
    }

    /**
     * Accepts a token from the end tag mode. The element name is converted to lower case.
     *
     * @param string $token     Incoming characters.
     * @param int $event    Lexer event type.
     *
     * @return bool          False if parse error.
     */
    public function acceptEndToken($token, $event)
    {
        if (! preg_match('/<\/(.*)>/', $token, $matches)) {
            return false;
        }

        return $this->listener->endElement(strtolower($matches[1]));
    }

    /**
     * Part of the tag data.
     *
     * @param string $token     Incoming characters.
     * @param int $event    Lexer event type.
     *
     * @return bool          False if parse error.
     */
    public function acceptAttributeToken($token, $event)
    {
        if ($this->current_attribute) {
            if ($event == LEXER_UNMATCHED) {
                $this->attributes[$this->current_attribute] .=
                        html_entity_decode($token, ENT_QUOTES);
            }
            if ($event == LEXER_SPECIAL) {
                $this->attributes[$this->current_attribute] .=
                        preg_replace('/^=\s*/', '', html_entity_decode($token, ENT_QUOTES));
            }
        }

        return true;
    }

    /**
     * A character entity.
     *
     * @param string $token    Incoming characters.
     * @param int $event   Lexer event type.
     *
     * @return bool         False if parse error.
     */
    public function acceptEntityToken($token, $event)
    {
    }

    /**
     * Character data between tags regarded as important.
     *
     * @param string $token     Incoming characters.
     * @param int $event    Lexer event type.
     *
     * @return bool          False if parse error.
     */
    public function acceptTextToken($token, $event)
    {
        return $this->listener->addContent($token);
    }

    /**
     * Incoming data to be ignored.
     *
     * @param string $token     Incoming characters.
     * @param int $event    Lexer event type.
     *
     * @return bool          False if parse error.
     */
    public function ignore($token, $event)
    {
        return true;
    }
}

/**
 * SAX event handler. Maintains a list of open tags and dispatches them as they close.
 */
class SimplePhpPageBuilder
{
    private $tags;
    private $page;
    private $private_content_tag;
    private $open_forms             = array();
    private $complete_forms         = array();
    private $frameset               = false;
    private $loading_frames         = array();
    private $frameset_nesting_level = 0;
    private $left_over_labels       = array();

    /**
     * Frees up any references so as to allow the PHP garbage collection from unset() to work.
     */
    public function free()
    {
        unset($this->tags);
        unset($this->page);
        unset($this->private_content_tags);
        $this->open_forms             = array();
        $this->complete_forms         = array();
        $this->frameset               = false;
        $this->loading_frames         = array();
        $this->frameset_nesting_level = 0;
        $this->left_over_labels       = array();
    }

    /**
     * This builder is always available.
     *
     * @return bool       Always true.
     */
    public function can()
    {
        return true;
    }

    /**
     * Reads the raw content and send events into the page to be built.
     *
     * @param $response SimpleHttpResponse  Fetched response.
     *
     * @return SimplePage                   Newly parsed page.
     */
    public function parse($response)
    {
        $this->tags = array();
        $this->page = $this->createPage($response);
        $parser     = $this->createParser($this);
        $parser->parse($response->getContent());
        $this->acceptPageEnd();
        $page = $this->page;
        $this->free();

        return $page;
    }

    /**
     * Creates an empty page.
     *
     * @return SimplePage        New unparsed page.
     */
    protected function createPage($response)
    {
        return new SimplePage($response);
    }

    /**
     * Creates the parser used with the builder.
     *
     * @param SimplePhpPageBuilder $listener   Target of parser.
     *
     * @return SimpleSaxParser              Parser to generate events for the builder.
     */
    protected function createParser(&$listener)
    {
        return new SimpleHtmlSaxParser($listener);
    }

    /**
     * Start of element event. Opens a new tag.
     *
     * @param string $name         Element name.
     * @param hash $attributes     Attributes without content are marked as true.
     *
     * @return bool             False on parse error.
     */
    public function startElement($name, $attributes)
    {
        $factory = new SimpleTagBuilder();
        $tag     = $factory->createTag($name, $attributes);
        if (! $tag) {
            return true;
        }
        if ($tag->getTagName() === 'label') {
            $this->acceptLabelStart($tag);
            $this->openTag($tag);

            return true;
        }
        if ($tag->getTagName() === 'form') {
            $this->acceptFormStart($tag);

            return true;
        }
        if ($tag->getTagName() === 'frameset') {
            $this->acceptFramesetStart($tag);

            return true;
        }
        if ($tag->getTagName() === 'frame') {
            $this->acceptFrame($tag);

            return true;
        }
        if ($tag->isPrivateContent() && ! isset($this->private_content_tag)) {
            $this->private_content_tag = $tag;
        }
        if ($tag->expectEndTag()) {
            $this->openTag($tag);

            return true;
        }
        $this->acceptTag($tag);

        return true;
    }

    /**
     * End of element event.
     *
     * @param string $name        Element name.
     *
     * @return bool            False on parse error.
     */
    public function endElement($name)
    {
        if ($name === 'label') {
            $this->acceptLabelEnd();

            return true;
        }
        if ($name === 'form') {
            $this->acceptFormEnd();

            return true;
        }
        if ($name === 'frameset') {
            $this->acceptFramesetEnd();

            return true;
        }
        if ($this->hasNamedTagOnOpenTagStack($name)) {
            $tag = array_pop($this->tags[$name]);
            if ($tag->isPrivateContent() && $this->private_content_tag->getTagName() == $name) {
                unset($this->private_content_tag);
            }
            $this->addContentTagToOpenTags($tag);
            $this->acceptTag($tag);

            return true;
        }

        return true;
    }

    /**
     * Test to see if there are any open tags awaiting closure that match the tag name.
     *
     * @param string $name        Element name.
     *
     * @return bool            True if any are still open.
     */
    protected function hasNamedTagOnOpenTagStack($name)
    {
        return isset($this->tags[$name]) && (count($this->tags[$name]) > 0);
    }

    /**
     * Unparsed, but relevant data. The data is added to every open tag.
     *
     * @param string $text        May include unparsed tags.
     *
     * @return bool            False on parse error.
     */
    public function addContent($text)
    {
        if (isset($this->private_content_tag)) {
            $this->private_content_tag->addContent($text);
        } else {
            $this->addContentToAllOpenTags($text);
        }

        return true;
    }

    /**
     * Any content fills all currently open tags unless it is part of an option tag.
     *
     * @param string $text        May include unparsed tags.
     */
    protected function addContentToAllOpenTags($text)
    {
        foreach (array_keys($this->tags) as $name) {
            for ($i = 0, $count = count($this->tags[$name]); $i < $count; $i++) {
                $this->tags[$name][$i]->addContent($text);
            }
        }
    }

    /**
     * Parsed data in tag form.
     * The parsed tag is added to every open tag.
     * Used for adding options to select fields only.
     *
     * @param SimpleTag $tag        Option tags only.
     */
    protected function addContentTagToOpenTags(&$tag)
    {
        if ($tag->getTagName() != 'option') {
            return;
        }
        foreach (array_keys($this->tags) as $name) {
            for ($i = 0, $count = count($this->tags[$name]); $i < $count; $i++) {
                $this->tags[$name][$i]->addTag($tag);
            }
        }
    }

    /**
     * Opens a tag for receiving content.
     * Multiple tags will be receiving input at the same time.
     *
     * @param SimpleTag $tag        New content tag.
     */
    protected function openTag($tag)
    {
        $name = $tag->getTagName();
        if (! in_array($name, array_keys($this->tags))) {
            $this->tags[$name] = array();
        }
        $this->tags[$name][] = $tag;
    }

    /**
     * Adds a tag to the page.
     *
     * @param SimpleTag $tag        Tag to accept.
     */
    protected function acceptTag($tag)
    {
        if ($tag->getTagName() === 'a') {
            $this->page->addLink($tag);
        } elseif ($tag->getTagName() === 'base') {
            $this->page->setBase($tag->getAttribute('href'));
        } elseif ($tag->getTagName() === 'title') {
            $this->page->setTitle($tag);
        } elseif ($this->isFormElement($tag->getTagName())) {
            for ($i = 0; $i < count($this->open_forms); $i++) {
                $this->open_forms[$i]->addWidget($tag);
            }
            $this->last_widget = $tag;
        }
    }

    /**
     * Opens a label for a described widget.
     *
     * @param SimpleFormTag $tag      Tag to accept.
     */
    protected function acceptLabelStart($tag)
    {
        $this->label = $tag;
        unset($this->last_widget);
    }

    /**
     * Closes the most recently opened label.
     */
    protected function acceptLabelEnd()
    {
        if (isset($this->label)) {
            if (isset($this->last_widget)) {
                $this->last_widget->setLabel($this->label->getText());
                unset($this->last_widget);
            } else {
                $this->left_over_labels[] = (clone $this->label);
            }
            unset($this->label);
        }
    }

    /**
     * Tests to see if a tag is a possible form element.
     *
     * @param string $name     HTML element name.
     *
     * @return bool         True if form element.
     */
    protected function isFormElement($name)
    {
        return in_array($name, array('input', 'button', 'textarea', 'select'));
    }

    /**
     * Opens a form. New widgets go here.
     *
     * @param SimpleFormTag $tag      Tag to accept.
     */
    protected function acceptFormStart($tag)
    {
        $this->open_forms[] = new SimpleForm($tag, $this->page);
    }

    /**
     * Closes the most recently opened form.
     */
    protected function acceptFormEnd()
    {
        if (count($this->open_forms)) {
            $this->complete_forms[] = array_pop($this->open_forms);
        }
    }

    /**
     * Opens a frameset. A frameset may contain nested frameset tags.
     *
     * @param SimpleFramesetTag $tag      Tag to accept.
     */
    protected function acceptFramesetStart($tag)
    {
        if (! $this->isLoadingFrames()) {
            $this->frameset = $tag;
        }
        $this->frameset_nesting_level++;
    }

    /**
     * Closes the most recently opened frameset.
     */
    protected function acceptFramesetEnd()
    {
        if ($this->isLoadingFrames()) {
            $this->frameset_nesting_level--;
        }
    }

    /**
     * Takes a single frame tag and stashes it in the current frame set.
     *
     * @param SimpleFrameTag $tag      Tag to accept.
     */
    protected function acceptFrame($tag)
    {
        if ($this->isLoadingFrames()) {
            if ($tag->getAttribute('src')) {
                $this->loading_frames[] = $tag;
            }
        }
    }

    /**
     * Test to see if in the middle of reading a frameset.
     *
     * @return bool        True if inframeset.
     */
    protected function isLoadingFrames()
    {
        return $this->frameset and $this->frameset_nesting_level > 0;
    }

    /**
     * Marker for end of complete page. Any work in progress can now be closed.
     */
    protected function acceptPageEnd()
    {
        while (count($this->open_forms)) {
            $this->complete_forms[] = array_pop($this->open_forms);
        }
        foreach ($this->left_over_labels as $label) {
            for ($i = 0, $count = count($this->complete_forms); $i < $count; $i++) {
                $this->complete_forms[$i]->attachLabelBySelector(
                        new SelectById($label->getFor()), $label->getText());
            }
        }
        $this->page->setForms($this->complete_forms);
        $this->page->setFrames($this->loading_frames);
    }
}
