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friendica/library/html-to-markdown/HTML_To_Markdown.php

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18 KiB
PHP
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<?php
/**
* Class HTML_To_Markdown
*
* A helper class to convert HTML to Markdown.
*
* @version 2.2.1
* @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
*/
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
'remove_nodes' => '', // space-separated list of dom nodes that should be removed. example: "meta style script"
);
/**
* 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|array The name of the parent node(s) to search for e.g. 'code' or array('pre', '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 ( is_array($parent_name) && in_array($p->nodeName, $parent_name) )
return true;
if ($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> and <pre> blocks to Markdown - that should stay as HTML
if (self::is_child_of(array('pre', '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
$markdown = $this->convert_to_markdown($node);
// 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);
}
/**
* 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()
{
// Work on the entire DOM tree (including head and body)
$input = $this->document->getElementsByTagName("html")->item(0);
if (!$input)
return false;
// Convert all children of this root 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.
$this->convert_children($input);
// 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 $node
* @return string The converted HTML as Markdown
*/
private function convert_to_markdown($node)
{
$tag = $node->nodeName; // the type of element, e.g. h1
$value = $node->nodeValue; // the value of that element, e.g. The Title
// Strip nodes named in remove_nodes
$tags_to_remove = explode(' ', $this->options['remove_nodes']);
if ( in_array($tag, $tags_to_remove) )
return false;
switch ($tag) {
case "p":
$markdown = (trim($value)) ? rtrim($value) . PHP_EOL . PHP_EOL : '';
break;
case "pre":
$markdown = PHP_EOL . $this->convert_code($node) . 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);
$markdown = preg_replace('~^#~', '\\\\#', $markdown);
break;
case "#comment":
$markdown = '';
break;
case "div":
$markdown = ($this->options['strip_tags']) ? $value . PHP_EOL . PHP_EOL : html_entity_decode($node->C14N());
break;
default:
// If strip_tags is false (the default), preserve tags that don't have Markdown equivalents,
// such as <span> 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());
}
return $markdown;
}
/**
* 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")
*
* @param $node
* @return string
*/
private function convert_image($node)
{
$src = $node->getAttribute('src');
$alt = $node->getAttribute('alt');
$title = $node->getAttribute('title');
if ($title != "") {
$markdown = '![' . $alt . '](' . $src . ' "' . $title . '")'; // No newlines added. <img> should be in a block-level element.
} else {
$markdown = '![' . $alt . '](' . $src . ')';
}
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")
*
* @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 . '")';
} else {
$markdown = '[' . $text . '](' . $href . ')';
}
if (! $href)
$markdown = html_entity_decode($node->C14N());
// 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 DOMNode $node
* @return string
*/
private function convert_code($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);
$code_content = str_replace(array("<pre>", "</pre>"), "", $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 || $node->nodeName === 'pre') {
// 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;
}
}
}
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