/*!
 * The reveal.js markdown plugin. Handles parsing of
 * markdown inside of presentations as well as loading
 * of external markdown documents.
 */

import marked from './marked.js'

export default {

	id: 'markdown',

	/**
	 * Starts processing and converting Markdown within the
	 * current reveal.js deck.
	 */
	init: function( deck ) {
		// This should no longer be needed, as long as the highlight.js
		// plugin is included after the markdown plugin
		// if( typeof window.hljs !== 'undefined' ) {
		// 	marked.setOptions({
		// 		highlight: function( code, lang ) {
		// 			return window.hljs.highlightAuto( code, lang ? [lang] : null ).value;
		// 		}
		// 	});
		// }

		// marked can be configured via reveal.js config options
		var options = deck.getConfig().markdown;
		if( options ) {
			marked.setOptions( options );
		}

		return processSlides( deck.getRevealElement() ).then( convertSlides );

	},

	// TODO: Do these belong in the API?
	processSlides: processSlides,
	convertSlides: convertSlides,
	slidify: slidify,
	marked: marked

};

var DEFAULT_SLIDE_SEPARATOR = '^\r?\n---\r?\n$',
	DEFAULT_NOTES_SEPARATOR = 'notes?:',
	DEFAULT_ELEMENT_ATTRIBUTES_SEPARATOR = '\\\.element\\\s*?(.+?)$',
	DEFAULT_SLIDE_ATTRIBUTES_SEPARATOR = '\\\.slide:\\\s*?(\\\S.+?)$';

var SCRIPT_END_PLACEHOLDER = '__SCRIPT_END__';


/**
 * Retrieves the markdown contents of a slide section
 * element. Normalizes leading tabs/whitespace.
 */
function getMarkdownFromSlide( section ) {

	// look for a <script> or <textarea data-template> wrapper
	var template = section.querySelector( '[data-template]' ) || section.querySelector( 'script' );

	// strip leading whitespace so it isn't evaluated as code
	var text = ( template || section ).textContent;

	// restore script end tags
	text = text.replace( new RegExp( SCRIPT_END_PLACEHOLDER, 'g' ), '</script>' );

	var leadingWs = text.match( /^\n?(\s*)/ )[1].length,
		leadingTabs = text.match( /^\n?(\t*)/ )[1].length;

	if( leadingTabs > 0 ) {
		text = text.replace( new RegExp('\\n?\\t{' + leadingTabs + '}','g'), '\n' );
	}
	else if( leadingWs > 1 ) {
		text = text.replace( new RegExp('\\n? {' + leadingWs + '}', 'g'), '\n' );
	}

	return text;

}

/**
 * Given a markdown slide section element, this will
 * return all arguments that aren't related to markdown
 * parsing. Used to forward any other user-defined arguments
 * to the output markdown slide.
 */
function getForwardedAttributes( section ) {

	var attributes = section.attributes;
	var result = [];

	for( var i = 0, len = attributes.length; i < len; i++ ) {
		var name = attributes[i].name,
			value = attributes[i].value;

		// disregard attributes that are used for markdown loading/parsing
		if( /data\-(markdown|separator|vertical|notes)/gi.test( name ) ) continue;

		if( value ) {
			result.push( name + '="' + value + '"' );
		}
		else {
			result.push( name );
		}
	}

	return result.join( ' ' );

}

/**
 * Inspects the given options and fills out default
 * values for what's not defined.
 */
function getSlidifyOptions( options ) {

	options = options || {};
	options.separator = options.separator || DEFAULT_SLIDE_SEPARATOR;
	options.notesSeparator = options.notesSeparator || DEFAULT_NOTES_SEPARATOR;
	options.attributes = options.attributes || '';

	return options;

}

/**
 * Helper function for constructing a markdown slide.
 */
function createMarkdownSlide( content, options ) {

	options = getSlidifyOptions( options );

	var notesMatch = content.split( new RegExp( options.notesSeparator, 'mgi' ) );

	if( notesMatch.length === 2 ) {
		content = notesMatch[0] + '<aside class="notes">' + marked(notesMatch[1].trim()) + '</aside>';
	}

	// prevent script end tags in the content from interfering
	// with parsing
	content = content.replace( /<\/script>/g, SCRIPT_END_PLACEHOLDER );

	return '<script type="text/template">' + content + '</script>';

}

/**
 * Parses a data string into multiple slides based
 * on the passed in separator arguments.
 */
function slidify( markdown, options ) {

	options = getSlidifyOptions( options );

	var separatorRegex = new RegExp( options.separator + ( options.verticalSeparator ? '|' + options.verticalSeparator : '' ), 'mg' ),
		horizontalSeparatorRegex = new RegExp( options.separator );

	var matches,
		lastIndex = 0,
		isHorizontal,
		wasHorizontal = true,
		content,
		sectionStack = [];

	// iterate until all blocks between separators are stacked up
	while( matches = separatorRegex.exec( markdown ) ) {
		var notes = null;

		// determine direction (horizontal by default)
		isHorizontal = horizontalSeparatorRegex.test( matches[0] );

		if( !isHorizontal && wasHorizontal ) {
			// create vertical stack
			sectionStack.push( [] );
		}

		// pluck slide content from markdown input
		content = markdown.substring( lastIndex, matches.index );

		if( isHorizontal && wasHorizontal ) {
			// add to horizontal stack
			sectionStack.push( content );
		}
		else {
			// add to vertical stack
			sectionStack[sectionStack.length-1].push( content );
		}

		lastIndex = separatorRegex.lastIndex;
		wasHorizontal = isHorizontal;
	}

	// add the remaining slide
	( wasHorizontal ? sectionStack : sectionStack[sectionStack.length-1] ).push( markdown.substring( lastIndex ) );

	var markdownSections = '';

	// flatten the hierarchical stack, and insert <section data-markdown> tags
	for( var i = 0, len = sectionStack.length; i < len; i++ ) {
		// vertical
		if( sectionStack[i] instanceof Array ) {
			markdownSections += '<section '+ options.attributes +'>';

			sectionStack[i].forEach( function( child ) {
				markdownSections += '<section data-markdown>' + createMarkdownSlide( child, options ) + '</section>';
			} );

			markdownSections += '</section>';
		}
		else {
			markdownSections += '<section '+ options.attributes +' data-markdown>' + createMarkdownSlide( sectionStack[i], options ) + '</section>';
		}
	}

	return markdownSections;

}

/**
 * Parses any current data-markdown slides, splits
 * multi-slide markdown into separate sections and
 * handles loading of external markdown.
 */
function processSlides( scope ) {

	return new Promise( function( resolve ) {

		var externalPromises = [];

		[].slice.call( scope.querySelectorAll( '[data-markdown]:not([data-markdown-parsed])') ).forEach( function( section, i ) {

			if( section.getAttribute( 'data-markdown' ).length ) {

				externalPromises.push( loadExternalMarkdown( section ).then(

					// Finished loading external file
					function( xhr, url ) {
						section.outerHTML = slidify( xhr.responseText, {
							separator: section.getAttribute( 'data-separator' ),
							verticalSeparator: section.getAttribute( 'data-separator-vertical' ),
							notesSeparator: section.getAttribute( 'data-separator-notes' ),
							attributes: getForwardedAttributes( section )
						});
					},

					// Failed to load markdown
					function( xhr, url ) {
						section.outerHTML = '<section data-state="alert">' +
							'ERROR: The attempt to fetch ' + url + ' failed with HTTP status ' + xhr.status + '.' +
							'Check your browser\'s JavaScript console for more details.' +
							'<p>Remember that you need to serve the presentation HTML from a HTTP server.</p>' +
							'</section>';
					}

				) );

			}
			else if( section.getAttribute( 'data-separator' ) || section.getAttribute( 'data-separator-vertical' ) || section.getAttribute( 'data-separator-notes' ) ) {

				section.outerHTML = slidify( getMarkdownFromSlide( section ), {
					separator: section.getAttribute( 'data-separator' ),
					verticalSeparator: section.getAttribute( 'data-separator-vertical' ),
					notesSeparator: section.getAttribute( 'data-separator-notes' ),
					attributes: getForwardedAttributes( section )
				});

			}
			else {
				section.innerHTML = createMarkdownSlide( getMarkdownFromSlide( section ) );
			}

		});

		Promise.all( externalPromises ).then( resolve );

	} );

}

function loadExternalMarkdown( section ) {

	return new Promise( function( resolve, reject ) {

		var xhr = new XMLHttpRequest(),
			url = section.getAttribute( 'data-markdown' );

		var datacharset = section.getAttribute( 'data-charset' );

		// see https://developer.mozilla.org/en-US/docs/Web/API/element.getAttribute#Notes
		if( datacharset != null && datacharset != '' ) {
			xhr.overrideMimeType( 'text/html; charset=' + datacharset );
		}

		xhr.onreadystatechange = function( section, xhr ) {
			if( xhr.readyState === 4 ) {
				// file protocol yields status code 0 (useful for local debug, mobile applications etc.)
				if ( ( xhr.status >= 200 && xhr.status < 300 ) || xhr.status === 0 ) {

					resolve( xhr, url );

				}
				else {

					reject( xhr, url );

				}
			}
		}.bind( this, section, xhr );

		xhr.open( 'GET', url, true );

		try {
			xhr.send();
		}
		catch ( e ) {
			console.warn( 'Failed to get the Markdown file ' + url + '. Make sure that the presentation and the file are served by a HTTP server and the file can be found there. ' + e );
			resolve( xhr, url );
		}

	} );

}

/**
 * Check if a node value has the attributes pattern.
 * If yes, extract it and add that value as one or several attributes
 * to the target element.
 *
 * You need Cache Killer on Chrome to see the effect on any FOM transformation
 * directly on refresh (F5)
 * http://stackoverflow.com/questions/5690269/disabling-chrome-cache-for-website-development/7000899#answer-11786277
 */
function addAttributeInElement( node, elementTarget, separator ) {

	var mardownClassesInElementsRegex = new RegExp( separator, 'mg' );
	var mardownClassRegex = new RegExp( "([^\"= ]+?)=\"([^\"]+?)\"|(data-[^\"= ]+?)(?=[\" ])", 'mg' );
	var nodeValue = node.nodeValue;
	var matches,
		matchesClass;
	if( matches = mardownClassesInElementsRegex.exec( nodeValue ) ) {

		var classes = matches[1];
		nodeValue = nodeValue.substring( 0, matches.index ) + nodeValue.substring( mardownClassesInElementsRegex.lastIndex );
		node.nodeValue = nodeValue;
		while( matchesClass = mardownClassRegex.exec( classes ) ) {
			if( matchesClass[2] ) {
				elementTarget.setAttribute( matchesClass[1], matchesClass[2] );
			} else {
				elementTarget.setAttribute( matchesClass[3], "" );
			}
		}
		return true;
	}
	return false;
}

/**
 * Add attributes to the parent element of a text node,
 * or the element of an attribute node.
 */
function addAttributes( section, element, previousElement, separatorElementAttributes, separatorSectionAttributes ) {

	if ( element != null && element.childNodes != undefined && element.childNodes.length > 0 ) {
		var previousParentElement = element;
		for( var i = 0; i < element.childNodes.length; i++ ) {
			var childElement = element.childNodes[i];
			if ( i > 0 ) {
				var j = i - 1;
				while ( j >= 0 ) {
					var aPreviousChildElement = element.childNodes[j];
					if ( typeof aPreviousChildElement.setAttribute == 'function' && aPreviousChildElement.tagName != "BR" ) {
						previousParentElement = aPreviousChildElement;
						break;
					}
					j = j - 1;
				}
			}
			var parentSection = section;
			if( childElement.nodeName ==  "section" ) {
				parentSection = childElement ;
				previousParentElement = childElement ;
			}
			if ( typeof childElement.setAttribute == 'function' || childElement.nodeType == Node.COMMENT_NODE ) {
				addAttributes( parentSection, childElement, previousParentElement, separatorElementAttributes, separatorSectionAttributes );
			}
		}
	}

	if ( element.nodeType == Node.COMMENT_NODE ) {
		if ( addAttributeInElement( element, previousElement, separatorElementAttributes ) == false ) {
			addAttributeInElement( element, section, separatorSectionAttributes );
		}
	}
}

/**
 * Converts any current data-markdown slides in the
 * DOM to HTML.
 */
function convertSlides() {

	var sections = document.querySelectorAll( '[data-markdown]:not([data-markdown-parsed])');

	[].slice.call( sections ).forEach( function( section ) {

		section.setAttribute( 'data-markdown-parsed', true )

		var notes = section.querySelector( 'aside.notes' );
		var markdown = getMarkdownFromSlide( section );

		section.innerHTML = marked( markdown );
		addAttributes( 	section, section, null, section.getAttribute( 'data-element-attributes' ) ||
						section.parentNode.getAttribute( 'data-element-attributes' ) ||
						DEFAULT_ELEMENT_ATTRIBUTES_SEPARATOR,
						section.getAttribute( 'data-attributes' ) ||
						section.parentNode.getAttribute( 'data-attributes' ) ||
						DEFAULT_SLIDE_ATTRIBUTES_SEPARATOR);

		// If there were notes, we need to re-add them after
		// having overwritten the section's HTML
		if( notes ) {
			section.appendChild( notes );
		}

	} );

	return Promise.resolve();

}