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
 */
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;
		}
	}
}