<?php

/**
 * Iterates individual characters (Unicode codepoints) of DOM text and CDATA nodes
 * while keeping track of their position in the document.
 *
 * Example:
 *
 *  $doc = new DOMDocument();
 *  $doc->load('example.xml');
 *  foreach(new DOMLettersIterator($doc) as $letter) echo $letter;
 *
 * NB: If you only need characters without their position
 *     in the document, use DOMNode->textContent instead.
 *
 * @author porneL http://pornel.net
 * @license Public Domain
 *
 */
final class DOMLettersIterator implements Iterator
{
    private $start, $current;
    private $offset, $key, $letters;

    /**
     * expects DOMElement or DOMDocument (see DOMDocument::load and DOMDocument::loadHTML)
     */
    function __construct(DOMNode $el)
    {
        if ($el instanceof DOMDocument) $this->start = $el->documentElement;
        else if ($el instanceof DOMElement) $this->start = $el;
        else throw new InvalidArgumentException("Invalid arguments, expected DOMElement or DOMDocument");
    }

    /**
     * Returns position in text as DOMText node and character offset.
     * (it's NOT a byte offset, you must use mb_substr() or similar to use this offset properly).
     * node may be NULL if iterator has finished.
     *
     * @return array
     */
    function currentTextPosition()
    {
        return array($this->current, $this->offset);
    }

    /**
     * Returns DOMElement that is currently being iterated or NULL if iterator has finished.
     *
     * @return DOMElement
     */
    function currentElement()
    {
        return $this->current ? $this->current->parentNode : NULL;
    }

    // Implementation of Iterator interface
    function key()
    {
        return $this->key;
    }

    function next()
    {
        if (!$this->current) return;

        if ($this->current->nodeType == XML_TEXT_NODE || $this->current->nodeType == XML_CDATA_SECTION_NODE)
        {
            if ($this->offset == -1)
            {
                // fastest way to get individual Unicode chars and does not require mb_* functions
                preg_match_all('/./us',$this->current->textContent,$m); $this->letters = $m[0];
            }
            $this->offset++; $this->key++;
            if ($this->offset < count($this->letters)) return;
            $this->offset = -1;
        }

        while($this->current->nodeType == XML_ELEMENT_NODE && $this->current->firstChild)
        {
            $this->current = $this->current->firstChild;
            if ($this->current->nodeType == XML_TEXT_NODE || $this->current->nodeType == XML_CDATA_SECTION_NODE) return $this->next();
        }

        while(!$this->current->nextSibling && $this->current->parentNode)
        {
            $this->current = $this->current->parentNode;
            if ($this->current === $this->start) {$this->current = NULL; return;}
        }

        $this->current = $this->current->nextSibling;

        return $this->next();
    }

    function current()
    {
        if ($this->current) return $this->letters[$this->offset];
        return NULL;
    }

    function valid()
    {
        return !!$this->current;
    }

    function rewind()
    {
        $this->offset = -1; $this->letters = array();
        $this->current = $this->start;
        $this->next();
    }
}