HTML_To_Markdown.php

<?php
/**
 * Class HTML_To_Markdown
 *
 * A helper class to convert HTML to Markdown.
 *
 * @version 2.1.1
 * @author Nick Cernis <nick@cern.is>
 * @link https://github.com/nickcernis/html2markdown/ Latest version on GitHub.
 * @link http://twitter.com/nickcernis Nick on twitter.
 * @license http://www.opensource.org/licenses/mit-license.php MIT
 
 * Certain elements of the below have been modified by Sally Jenkinson for use in her WordPress XML export to Kirby text file project. For the original, unmodified version, please see the original project on GitHub.
 
 */
class HTML_To_Markdown
{
    /**
     * @var DOMDocument The root of the document tree that holds our HTML.
     */
    private $document;

    /**
     * @var string|boolean The Markdown version of the original HTML, or false if conversion failed
     */
    private $output;

    /**
     * @var array Class-wide options users can override.
     */
    private $options = array(
        'header_style'    => 'setext', // Set to "atx" to output H1 and H2 headers as # Header1 and ## Header2
        'suppress_errors' => true, // Set to false to show warnings when loading malformed HTML
        'strip_tags'      => false, // Set to true to strip tags that don't have markdown equivalents. N.B. Strips tags, not their content. Useful to clean MS Word HTML output.
        'bold_style'      => '**', // Set to '__' if you prefer the underlined style
        'italic_style'    => '*', // Set to '_' if you prefer the underlined style
    );


    /**
     * Constructor
     *
     * Set up a new DOMDocument from the supplied HTML, convert it to Markdown, and store it in $this->$output.
     *
     * @param string $html The HTML to convert to Markdown.
     * @param array $overrides [optional] List of style and error display overrides.
     */
    public function __construct($html = null, $overrides = null)
    {
        if ($overrides)
            $this->options = array_merge($this->options, $overrides);

        if ($html)
            $this->convert($html);
    }


    /**
     * Setter for conversion options
     *
     * @param $name
     * @param $value
     */
    public function set_option($name, $value)
    {
        $this->options[$name] = $value;
    }


    /**
     * Convert
     *
     * Loads HTML and passes to get_markdown()
     *
     * @param $html
     * @return string The Markdown version of the html
     */
    public function convert($html)
    {
        $html = preg_replace('~>\s+<~', '><', $html); // Strip white space between tags to prevent creation of empty #text nodes

        $this->document = new DOMDocument();

        if ($this->options['suppress_errors'])
            libxml_use_internal_errors(true); // Suppress conversion errors (from http://bit.ly/pCCRSX )

        $this->document->loadHTML('<?xml encoding="UTF-8">' . $html); // Hack to load utf-8 HTML (from http://bit.ly/pVDyCt )
        $this->document->encoding = 'UTF-8';

        if ($this->options['suppress_errors'])
            libxml_clear_errors();

        return $this->get_markdown($html);
    }


    /**
     * Is Child Of?
     *
     * Is the node a child of the given parent tag?
     *
     * @param $parent_name string The name of the parent node to search for (e.g. 'code')
     * @param $node
     * @return bool
     */
    private static function is_child_of($parent_name, $node)
    {
        for ($p = $node->parentNode; $p != false; $p = $p->parentNode) {
            if (is_null($p))
                return false;

            if ($p->nodeName == $parent_name)
                return true;
        }
        return false;
    }


    /**
     * Convert Children
     *
     * Recursive function to drill into the DOM and convert each node into Markdown from the inside out.
     *
     * Finds children of each node and convert those to #text nodes containing their Markdown equivalent,
     * starting with the innermost element and working up to the outermost element.
     *
     * @param $node
     */
    private function convert_children($node)
    {
        // Don't convert HTML code inside <code> blocks to Markdown - that should stay as HTML
        if (self::is_child_of('code', $node))
            return;

        // If the node has children, convert those to Markdown first
        if ($node->hasChildNodes()) {
            $length = $node->childNodes->length;

            for ($i = 0; $i < $length; $i++) {
                $child = $node->childNodes->item($i);
                $this->convert_children($child);
            }
        }

        // Now that child nodes have been converted, convert the original node
        $this->convert_to_markdown($node);
    }


    /**
     * Get Markdown
     *
     * Sends the body node to convert_children() to change inner nodes to Markdown #text nodes, then saves and
     * returns the resulting converted document as a string in Markdown format.
     *
     * @return string|boolean The converted HTML as Markdown, or false if conversion failed
     */
    private function get_markdown()
    {
        // Use the body tag as our root element
        $body = $this->document->getElementsByTagName("body")->item(0);

        // Try the head tag if there's no body tag (e.g. the user's passed a single <script> tag for conversion)
        if (!$body)
            $body = $this->document->getElementsByTagName("head")->item(0);

        if (!$body)
            return false;

        // Convert all children of the body element. The DOMDocument stored in $this->doc will
        // then consist of #text nodes, each containing a Markdown version of the original node
        // that it replaced.
        $this->convert_children($body);

        // Sanitize and return the body contents as a string.
        $markdown = $this->document->saveHTML(); // stores the DOMDocument as a string
        $markdown = html_entity_decode($markdown, ENT_QUOTES, 'UTF-8');
        $markdown = html_entity_decode($markdown, ENT_QUOTES, 'UTF-8'); // Double decode to cover cases like &amp;nbsp; http://www.php.net/manual/en/function.htmlentities.php#99984
        $markdown = preg_replace("/<!DOCTYPE [^>]+>/", "", $markdown); // Strip doctype declaration
        $unwanted = array('<html>', '</html>', '<body>', '</body>', '<head>', '</head>', '<?xml encoding="UTF-8">', '&#xD;');
        $markdown = str_replace($unwanted, '', $markdown); // Strip unwanted tags
        $markdown = trim($markdown, "\n\r\0\x0B");
        $this->output = $markdown;

        return $markdown;
    }


    /**
     * Convert to Markdown
     *
     * Converts an individual node into a #text node containing a string of its Markdown equivalent.
     *
     * Example: An <h3> node with text content of "Title" becomes a text node with content of "### Title"
     *
     * @param $node
     */
    private function convert_to_markdown($node)
    {
        $tag = $node->nodeName; // the type of element, e.g. h1
        $value = $node->nodeValue; // the value of that element, e.g. The Title

        switch ($tag) {
            case "p":
            case "pre":
                $markdown = (trim($value)) ? rtrim($value) . PHP_EOL . PHP_EOL : '';
                break;
            case "h1":
            case "h2":
                $markdown = $this->convert_header($tag, $node);
                break;
            case "h3":
                $markdown = "### " . $value . PHP_EOL . PHP_EOL;
                break;
            case "h4":
                $markdown = "#### " . $value . PHP_EOL . PHP_EOL;
                break;
            case "h5":
                $markdown = "##### " . $value . PHP_EOL . PHP_EOL;
                break;
            case "h6":
                $markdown = "###### " . $value . PHP_EOL . PHP_EOL;
                break;
            case "em":
            case "i":
            case "strong":
            case "b":
                $markdown = $this->convert_emphasis($tag, $value);
                break;
            case "hr":
                $markdown = "- - - - - -" . PHP_EOL . PHP_EOL;
                break;
            case "br":
                $markdown = "  " . PHP_EOL;
                break;
            case "blockquote":
                $markdown = $this->convert_blockquote($node);
                break;
            case "code":
                $markdown = $this->convert_code($node);
                break;
            case "ol":
            case "ul":
                $markdown = $value . PHP_EOL;
                break;
            case "li":
                $markdown = $this->convert_list($node);
                break;
            case "img":
                $markdown = $this->convert_image($node);
                break;
            case "a":
                $markdown = $this->convert_anchor($node);
                break;
            case "#text":
                $markdown = preg_replace('~\s+~', ' ', $value);
                break;
            case "#comment":
                $markdown = '';
                break;
            default:
                // If strip_tags is false (the default), preserve tags that don't have Markdown equivalents,
                // such as <span> and #text nodes on their own. C14N() canonicalizes the node to a string.
                // See: http://www.php.net/manual/en/domnode.c14n.php
                $markdown = ($this->options['strip_tags']) ? $value : html_entity_decode($node->C14N());
        }

        // Create a DOM text node containing the Markdown equivalent of the original node
        $markdown_node = $this->document->createTextNode($markdown);

        // Replace the old $node e.g. "<h3>Title</h3>" with the new $markdown_node e.g. "### Title"
        $node->parentNode->replaceChild($markdown_node, $node);
    }


    /**
     * Convert Header
     *
     * Converts h1 and h2 headers to Markdown-style headers in setext style,
     * matching the number of underscores with the length of the title.
     *
     * e.g.     Header 1    Header Two
     *          ========    ----------
     *
     * Returns atx headers instead if $this->options['header_style'] is "atx"
     *
     * e.g.    # Header 1   ## Header Two
     *
     * @param string $level The header level, including the "h". e.g. h1
     * @param string $node The node to convert.
     * @return string The Markdown version of the header.
     */
    private function convert_header($level, $node)
    {
        $content = $node->nodeValue;

        if (!$this->is_child_of('blockquote', $node) && $this->options['header_style'] == "setext") {
            $length = (function_exists('mb_strlen')) ? mb_strlen($content, 'utf-8') : strlen($content);
            $underline = ($level == "h1") ? "=" : "-";
            $markdown = $content . PHP_EOL . str_repeat($underline, $length) . PHP_EOL . PHP_EOL; // setext style
        } else {
            $prefix = ($level == "h1") ? "# " : "## ";
            $markdown = $prefix . $content . PHP_EOL . PHP_EOL; // atx style
        }

        return $markdown;
    }


    /**
     * Converts inline styles
     * This function is used to render strong and em tags
     * 
     * eg <strong>bold text</strong> becomes **bold text** or __bold text__
     * 
     * @param string $tag
     * @param string $value
     * @return string
     */
     private function convert_emphasis($tag, $value)
     {
        if ($tag == 'i' || $tag == 'em') {
            $markdown = $this->options['italic_style'] . $value . $this->options['italic_style'];
        } else {
            $markdown = $this->options['bold_style'] . $value . $this->options['bold_style'];
        }
        
        return $markdown;
     }


    /**
     * Convert Image
     *
     * Converts <img /> tags to Markdown.
     *
     * e.g.     <img src="/path/img.jpg" alt="alt text" title="Title" />
     * becomes  ![alt text](/path/img.jpg "Title")
     * 
     * Amended for Paul
     * <figure>
     * (image: Emile-in-trenches.jpg alt: Emile in a night time German trench with his K9 companion.)
     * <figcaption>A poignant sequence of the game takes place in a German trench network.</figcaption>
     * </figure>
     *
     * @param $node
     * @return string
     */
    private function convert_image($node)
    {
        $src = $node->getAttribute('src');
        $alt = $node->getAttribute('alt');
        //$title = $node->getAttribute('title');

        //if ($title != "") {
            // No newlines added. <img> should be in a block-level element.
            //$markdown = '![' . $alt . '](' . $src . ' "' . $title . '")';
            $markdown = '<figure>' . PHP_EOL . '(image: ' . $src . ' alt: ' . $alt . ')' . PHP_EOL . '<figcaption>' . $alt . '</figcaption>' . PHP_EOL . '</figure>' . PHP_EOL . PHP_EOL; 
        /*} else {
            //$markdown = '![' . $alt . '](' . $src . ')';
            $markdown = PHP_EOL . '<figure>' . PHP_EOL . '(image: ' . $src . ' alt: ' . $alt . ')' . PHP_EOL . '<figcaption>' . $alt . '</figcaption>' . PHP_EOL . '</figure>' . PHP_EOL; 
        }*/

        return $markdown;
    }


    /**
     * Convert Anchor
     *
     * Converts <a> tags to Markdown.
     *
     * e.g.     <a href="http://modernnerd.net" title="Title">Modern Nerd</a>
     * becomes  [Modern Nerd](http://modernnerd.net "Title")
     * amended to (link: https://www.youtube.com/watch?v=GbjsW1WbZgM text: Medal of Honour: Allied Assault popup: true title: Opening scene of the game)
     *
     * @param $node
     * @return string
     */
    private function convert_anchor($node)
    {
        $href = $node->getAttribute('href');
        $title = $node->getAttribute('title');
        $text = $node->nodeValue;

        if ($title != "") {
            //$markdown = '[' . $text . '](' . $href . ' "' . $title . '")';
            $markdown = '(link: ' . $href . ' text: ' . $text . ' popup: true title: ' . $title . ')';
        } else {
            //$markdown = '[' . $text . '](' . $href . ')';
            $markdown = '(link: ' . $href . ' text: ' . $text . ')';
        }

        // Append a space if the node after this one is also an anchor
        $next_node_name = $this->get_next_node_name($node);

        if ($next_node_name == 'a')
            $markdown = $markdown . ' ';

        return $markdown;
    }


    /**
     * Convert List
     *
     * Converts <ul> and <ol> lists to Markdown.
     *
     * @param $node
     * @return string
     */
    private function convert_list($node)
    {
        // If parent is an ol, use numbers, otherwise, use dashes
        $list_type = $node->parentNode->nodeName;
        $value = $node->nodeValue;

        if ($list_type == "ul") {
            $markdown = "- " . trim($value) . PHP_EOL;
        } else {
            $number = $this->get_position($node);
            $markdown = $number . ". " . trim($value) . PHP_EOL;
        }

        return $markdown;
    }


    /**
     * Convert Code
     *
     * Convert code tags by indenting blocks of code and wrapping single lines in backticks.
     *
     * @param $node
     * @return string
     */
    private function convert_code($node)
    {
        // Store the content of the code block in an array, one entry for each line

        $markdown = '';

        $code_content = html_entity_decode($node->C14N());
        $code_content = str_replace(array("<code>", "</code>"), "", $code_content);

        $lines = preg_split('/\r\n|\r|\n/', $code_content);
        $total = count($lines);

        // If there's more than one line of code, prepend each line with four spaces and no backticks.
        if ($total > 1) {

            // Remove the first and last line if they're empty
            $first_line = trim($lines[0]);
            $last_line = trim($lines[$total - 1]);
            $first_line = trim($first_line, "&#xD;"); //trim XML style carriage returns too
            $last_line = trim($last_line, "&#xD;");

            if (empty($first_line))
                array_shift($lines);

            if (empty($last_line))
                array_pop($lines);

            $count = 1;
            foreach ($lines as $line) {
                $line = str_replace('&#xD;', '', $line);
                $markdown .= "    " . $line;
                // Add newlines, except final line of the code
                if ($count != $total)
                    $markdown .= PHP_EOL;
                $count++;
            }
            $markdown .= PHP_EOL;

        } else { // There's only one line of code. It's a code span, not a block. Just wrap it with backticks.

            $markdown .= "`" . $lines[0] . "`";

        }

        return $markdown;
    }


    /**
     * Convert blockquote
     *
     * Prepend blockquotes with > chars.
     *
     * @param $node
     * @return string
     */
    private function convert_blockquote($node)
    {
        // Contents should have already been converted to Markdown by this point,
        // so we just need to add ">" symbols to each line.

        $markdown = '';

        $quote_content = trim($node->nodeValue);

        $lines = preg_split('/\r\n|\r|\n/', $quote_content);

        $total_lines = count($lines);

        foreach ($lines as $i => $line) {
            $markdown .= "> " . $line . PHP_EOL;
            if ($i + 1 == $total_lines)
                $markdown .= PHP_EOL;
        }

        return $markdown;
    }


    /**
     * Get Position
     *
     * Returns the numbered position of a node inside its parent
     *
     * @param $node
     * @return int The numbered position of the node, starting at 1.
     */
    private function get_position($node)
    {
        // Get all of the nodes inside the parent
        $list_nodes = $node->parentNode->childNodes;
        $total_nodes = $list_nodes->length;

        $position = 1;

        // Loop through all nodes and find the given $node
        for ($a = 0; $a < $total_nodes; $a++) {
            $current_node = $list_nodes->item($a);

            if ($current_node->isSameNode($node))
                $position = $a + 1;
        }

        return $position;
    }


    /**
     * Get Next Node Name
     *
     * Return the name of the node immediately after the passed one.
     *
     * @param $node
     * @return string|null The node name (e.g. 'h1') or null.
     */
    private function get_next_node_name($node)
    {
        $next_node_name = null;

        $current_position = $this->get_position($node);
        $next_node = $node->parentNode->childNodes->item($current_position);

        if ($next_node)
            $next_node_name = $next_node->nodeName;

        return $next_node_name;
    }


    /**
     * To String
     *
     * Magic method to return Markdown output when HTML_To_Markdown instance is treated as a string.
     *
     * @return string
     */
    public function __toString()
    {
        return $this->output();
    }


    /**
     * Output
     *
     * Getter for the converted Markdown contents stored in $this->output
     *
     * @return string
     */
    public function output()
    {
        if (!$this->output) {
            return '';
        } else {
            return $this->output;
        }
    }
}