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<?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
*/
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' => 'atx', // 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 = PHP_EOL . $content . PHP_EOL . str_repeat( $underline, $length ) . PHP_EOL . PHP_EOL; // setext style
} else {
$prefix = ( $level == 'h1' ) ? '# ' : '## ';
$markdown = PHP_EOL . $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 . ')';
}
// 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;
// Add this with the backticks
$markdown .= '```' . PHP_EOL;
foreach ( $lines as $line ) {
$line = str_replace( '&#xD;', '', $line );
// Remove the leading tab from the lines (we're using backticks)
// $markdown .= ' ' . $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;
}
}
}