<?php
/**
 * Plugin Name: HTML links
 * Description: Example : <code>&lt;a href="http://example.com/"&gt;link text&lt;/a&gt;</code>
 * Version: 1.0
 * Author: Janis Elsts
 * ModuleID: link
 * ModuleCategory: parser
 * ModuleClassName: blcHTMLLink
 * ModuleContext: on-demand
 * ModuleLazyInit: true
 * ModulePriority: 1000
*/

class blcHTMLLink extends blcParser {
	var $supported_formats = array( 'html' );

	/**
	 * Parse a string for HTML links - <a href="URL">anchor text</a>
	 *
	 * @param string $content The text to parse.
	 * @param string $base_url The base URL to use for normalizing relative URLs. If ommitted, the blog's root URL will be used.
	 * @param string $default_link_text
	 * @return array An array of new blcLinkInstance objects. The objects will include info about the links found, but not about the corresponding container entity.
	 */
	function parse( $content, $base_url = '', $default_link_text = '' ) {
		$content = apply_filters( 'blc-parser-html-link-content', $content );

		//remove all <code></code> blocks first
		$content = preg_replace( '/<code[^>]*>.+?<\/code>/si', ' ', $content );

		//Find links
		$params = array(
			'base_url'          => $base_url,
			'default_link_text' => $default_link_text,
		);

		$instances = $this->map( $content, array( $this, 'parser_callback' ), $params );

		//The parser callback returns NULL when it finds an invalid link. Filter out those nulls
		//from the list of instances.
		$instances = array_filter( $instances );

		return $instances;
	}

	/**
	 * blcHTMLLink::parser_callback()
	 *
	 * @access private
	 *
	 * @param array $link
	 * @param array $params
	 * @return blcLinkInstance|null
	 */
	function parser_callback( $link, $params ) {
		global $blclog;

		$base_url = $params['base_url'];

		$url = $link['href'];
		$raw_url = $link['href'];
		$url = trim( $url );
		//$blclog->debug(__CLASS__ .':' . __FUNCTION__ . ' Found a link, raw URL = "' . $raw_url . '"');

		//Sometimes links may contain shortcodes. Execute them.
		$url = do_shortcode( $url );

		//Skip empty URLs
		if ( empty( $url ) ) {
			$blclog->warn( __CLASS__ . ':' . __FUNCTION__ . ' Skipping the link (empty URL)' );
			return null;
		}

		//Attempt to parse the URL
		$parts = @parse_url( $url );
		if ( ! $parts ) {
			$blclog->warn( __CLASS__ . ':' . __FUNCTION__ . ' Skipping the link (parse_url failed)', $url );
			return null; //Skip invalid URLs
		}

		if ( ! isset( $parts['scheme'] ) ) {
			//No scheme - likely a relative URL. Turn it into an absolute one.
			//TODO: Also log the original URL and base URL.
			$url = $this->relative2absolute( $url, $base_url ); //$base_url comes from $params
			$blclog->info( __CLASS__ . ':' . __FUNCTION__ . ' Convert relative URL to absolute. Absolute URL = "' . $url . '"' );
		}

		//Skip invalid links (again)
		if ( ! $url || ( strlen( $url ) < 6 ) ) {
			$blclog->info( __CLASS__ . ':' . __FUNCTION__ . ' Skipping the link (invalid/short URL)', $url );
			return null;
		}

		//Remove left-to-right marks. See: https://en.wikipedia.org/wiki/Left-to-right_mark
		$ltrm = json_decode( '"\u200E"' );
		$url  = str_replace( $ltrm, '', $url );

		$text = $link['#link_text'];

		//The URL is okay, create and populate a new link instance.
		$instance = new blcLinkInstance();

		$instance->set_parser( $this );
		$instance->raw_url   = $raw_url;
		$instance->link_text = $text;

		$link_obj = new blcLink( $url ); //Creates or loads the link
		$instance->set_link( $link_obj );

		return $instance;
	}

	/**
	 * Change all links that have a certain URL to a new URL.
	 *
	 * @param string $content Look for links in this string.
	 * @param string $new_url Change the links to this URL.
	 * @param string $old_url The URL to look for.
	 * @param string $old_raw_url The raw, not-normalized URL of the links to look for. Optional.
	 * @param string $new_text New link text. Optional.
	 *
	 * @return array|WP_Error If successful, the return value will be an associative array with two
	 * keys : 'content' - the modified content, and 'raw_url' - the new raw, non-normalized URL used
	 * for the modified links. In most cases, the returned raw_url will be equal to the new_url.
	 */
	function edit( $content, $new_url, $old_url, $old_raw_url, $new_text = null ) {
		if ( empty( $old_raw_url ) ) {
			$old_raw_url = $old_url;
		}

		//Save the old & new URLs for use in the edit callback.
		$args = array(
			'old_url'  => $old_raw_url,
			'new_url'  => $new_url,
			'new_text' => $new_text,
		);

		//Find all links and replace those that match $old_url.
		$content = $this->multi_edit( $content, array( &$this, 'edit_callback' ), $args );

		$result = array(
			'content' => $content,
			'raw_url' => $new_url,
		);

		if ( isset( $new_text ) ) {
			$result['link_text'] = $new_text;
		}

		return $result;
	}

	function edit_callback( $link, $params ) {
		if ( $link['href'] === $params['old_url'] ) {
			$modified = array(
				'href' => $params['new_url'],
			);

			if ( isset( $params['new_text'] ) ) {
				$modified['#link_text'] = $params['new_text'];
			}

			return $modified;
		} else {
			return $link['#raw'];
		}
	}

	public function is_link_text_editable() {
		return true;
	}

	public function is_url_editable() {
		return true;
	}

	/**
	 * Remove all links that have a certain URL, leaving anchor text intact.
	 *
	 * @param string $content Look for links in this string.
	 * @param string $url The URL to look for.
	 * @param string $raw_url The raw, non-normalized version of the URL to look for. Optional.
	 * @return string Input string with all matching links removed.
	 */
	function unlink( $content, $url, $raw_url ) {
		if ( empty( $raw_url ) ) {
			$raw_url = $url;
		}

		$args = array(
			'old_url' => $raw_url,
		);

		//Find all links and remove those that match $raw_url.
		$content = $this->multi_edit( $content, array( &$this, 'unlink_callback' ), $args );

		return $content;
	}

	/**
	 * blcHTMLLink::unlink_callback()
	 *
	 * @access private
	 *
	 * @param array $link
	 * @param array $params
	 * @return string
	 */
	function unlink_callback( $link, $params ) {
		//Skip links that don't match the specified URL
		if ( $link['href'] !== $params['old_url'] ) {
			return $link['#raw'];
		}

		$config = blc_get_configuration();
		if ( $config->options['mark_removed_links'] ) {
			//Leave only the anchor text + the removed_link CSS class
			return sprintf(
				'<span class="removed_link" title="%s">%s</span>',
				esc_attr( $link['href'] ),
				$link['#link_text']
			);
		} else {
			//Just the anchor text
			return $link['#link_text'];
		}
	}

	/**
	 * Get the link text for printing in the "Broken Links" table.
	 * Sub-classes should override this method and display the link text in a way appropriate for the link type.
	 *
	 * @param blcLinkInstance $instance
	 * @param string $context
	 * @return string HTML
	 */
	function ui_get_link_text( $instance, $context = 'display' ) {
		return strip_tags( $instance->link_text );
	}

	/**
	 * Apply a callback function to all HTML links found in a string and return the results.
	 *
	 * The link data array will contain at least these keys :
	 *  'href' - the URL of the link (with htmlentitydecode() already applied).
	 *  '#raw' - the raw link code, e.g. the entire '<a href="...">...</a>' tag of a HTML link.
	 *  '#offset' - the offset within $content at which the first character of the link tag was found.
	 *  '#link_text' - the link's anchor text, if any. May contain HTML tags.
	 *
	 * Any attributes of the link tag will also be included in the returned array as attr_name => attr_value
	 * pairs. This function will also automatically decode any HTML entities found in attribute values.
	 *
	 * @see blcParser::map()
	 *
	 * @param string $content A text string to parse for links.
	 * @param callback $callback Callback function to apply to all found links.
	 * @param mixed $extra If the optional $extra param. is supplied, it will be passed as the second parameter to the function $callback.
	 * @return array An array of all detected links after applying $callback to each of them.
	 */
	function map( $content, $callback, $extra = null ) {
		$results = array();

		//Find all links
		$links = blcUtility::extract_tags( $content, 'a', false, true );

		//Iterate over the links and apply $callback to each
		foreach ( $links as $link ) {

			//Massage the found link into a form required for the callback function
			$param = $link['attributes'];
			$param = array_merge(
				$param,
				array(
					'#raw'       => $link['full_tag'],
					'#offset'    => $link['offset'],
					'#link_text' => $link['contents'],
					'href'       => isset( $link['attributes']['href'] ) ? $link['attributes']['href'] : '',
				)
			);

			//Prepare arguments for the callback
			$params = array( $param );
			if ( isset( $extra ) ) {
				$params[] = $extra;
			}

			//Execute & store :)
			$results[] = call_user_func_array( $callback, $params );
		}

		return $results;
	}

	/**
	 * Modify all HTML links found in a string using a callback function.
	 *
	 * The callback function should return either an associative array or a string. If
	 * a string is returned, the parser will replace the current link with the contents
	 * of that string. If an array is returned, the current link will be modified/rebuilt
	 * by substituting the new values for the old ones.
	 *
	 * htmlentities() will be automatically applied to attribute values (but not to #link_text).
	 *
	 * @see blcParser::multi_edit()
	 *
	 * @param string $content A text string containing the links to edit.
	 * @param callback $callback Callback function used to modify the links.
	 * @param mixed $extra If supplied, $extra will be passed as the second parameter to the function $callback.
	 * @return string The modified input string.
	 */
	function multi_edit( $content, $callback, $extra = null ) {
		//Just reuse map() + a little helper func. to apply the callback to all links and get modified links
		$modified_links = $this->map( $content, array( &$this, 'execute_edit_callback' ), array( $callback, $extra ) );

		//Replace each old link with the modified one
		$offset = 0;
		foreach ( $modified_links as $link ) {
			if ( isset( $link['#new_raw'] ) ) {
				$new_html = $link['#new_raw'];
			} else {
				//Assemble the new link tag
				$new_html = '<a';
				foreach ( $link as $name => $value ) {

					//Skip special keys like '#raw' and '#offset'
					if ( substr( $name, 0, 1 ) === '#' ) {
						continue;
					}

					$new_html .= sprintf( ' %s="%s"', $name, esc_attr( $value ) );
				}
				$new_html .= '>' . $link['#link_text'] . '</a>';
			}

			$content = substr_replace( $content, $new_html, $link['#offset'] + $offset, strlen( $link['#raw'] ) );
			//Update the replacement offset
			$offset += ( strlen( $new_html ) - strlen( $link['#raw'] ) );
		}

		return $content;
	}

	/**
	 * Helper function for blcHtmlLink::multi_edit()
	 * Applies the specified callback function to each link and merges
	 * the result with the current link attributes. If the callback returns
	 * a replacement HTML tag instead, it will be stored in the '#new_raw'
	 * key of the return array.
	 *
	 * @access protected
	 *
	 * @param array $link
	 * @param array $info The callback function and the extra argument to pass to that function (if any).
	 * @return array
	 */
	function execute_edit_callback( $link, $info ) {
		list($callback, $extra) = $info;

		//Prepare arguments for the callback
		$params = array( $link );
		if ( isset( $extra ) ) {
			$params[] = $extra;
		}

		$new_link = call_user_func_array( $callback, $params );

		if ( is_array( $new_link ) ) {
			$link = array_merge( $link, $new_link );
		} elseif ( is_string( $new_link ) ) {
			$link['#new_raw'] = $new_link;
		}

		return $link;
	}
}