why-cant-we-deploy-today/plugin/highlight/highlight.js

import hljs from './highlight-core.js'
import './highlight-line-numbers.js'

/*!
 * reveal.js plugin that adds syntax highlight support.
 */

let Plugin = {

	id: 'highlight',

	HIGHLIGHT_STEP_DELIMITER: '|',
	HIGHLIGHT_LINE_DELIMITER: ',',
	HIGHLIGHT_LINE_RANGE_DELIMITER: '-',

	/**
	 * Highlights code blocks withing the given deck.
	 *
	 * Note that this can be called multiple times if
	 * there are multiple presentations on one page.
	 *
	 * @param {Reveal} reveal the reveal.js instance
	 */
	init: function( reveal ) {

		// Read the plugin config options and provide fallbacks
		var config = reveal.getConfig().highlight || {};
		config.highlightOnLoad = typeof config.highlightOnLoad === 'boolean' ? config.highlightOnLoad : true;
		config.escapeHTML = typeof config.escapeHTML === 'boolean' ? config.escapeHTML : true;

		[].slice.call( reveal.getRevealElement().querySelectorAll( 'pre code' ) ).forEach( function( block ) {

			// Trim whitespace if the "data-trim" attribute is present
			if( block.hasAttribute( 'data-trim' ) && typeof block.innerHTML.trim === 'function' ) {
				block.innerHTML = betterTrim( block );
			}

			// Escape HTML tags unless the "data-noescape" attrbute is present
			if( config.escapeHTML && !block.hasAttribute( 'data-noescape' )) {
				block.innerHTML = block.innerHTML.replace( /</g,"&lt;").replace(/>/g, '&gt;' );
			}

			// Re-highlight when focus is lost (for contenteditable code)
			block.addEventListener( 'focusout', function( event ) {
				hljs.highlightBlock( event.currentTarget );
			}, false );

			if( config.highlightOnLoad ) {
				Plugin.highlightBlock( block );
			}

		} );

		// If we're printing to PDF, scroll the code highlights of
		// all blocks in the deck into view at once
		reveal.on( 'pdf-ready', function() {
			[].slice.call( reveal.getRevealElement().querySelectorAll( 'pre code[data-line-numbers].current-fragment' ) ).forEach( function( block ) {
				Plugin.scrollHighlightedLineIntoView( block, {}, true );
			} );
		} );

	},

	/**
	 * Highlights a code block. If the <code> node has the
	 * 'data-line-numbers' attribute we also generate slide
	 * numbers.
	 *
	 * If the block contains multiple line highlight steps,
	 * we clone the block and create a fragment for each step.
	 */
	highlightBlock: function( block ) {

		hljs.highlightBlock( block );

		// Don't generate line numbers for empty code blocks
		if( block.innerHTML.trim().length === 0 ) return;

		if( block.hasAttribute( 'data-line-numbers' ) ) {
			hljs.lineNumbersBlock( block, { singleLine: true } );

			var scrollState = { currentBlock: block };

			// If there is at least one highlight step, generate
			// fragments
			var highlightSteps = Plugin.deserializeHighlightSteps( block.getAttribute( 'data-line-numbers' ) );
			if( highlightSteps.length > 1 ) {

				// If the original code block has a fragment-index,
				// each clone should follow in an incremental sequence
				var fragmentIndex = parseInt( block.getAttribute( 'data-fragment-index' ), 10 );

				if( typeof fragmentIndex !== 'number' || isNaN( fragmentIndex ) ) {
					fragmentIndex = null;
				}

				// Generate fragments for all steps except the original block
				highlightSteps.slice(1).forEach( function( highlight ) {

					var fragmentBlock = block.cloneNode( true );
					fragmentBlock.setAttribute( 'data-line-numbers', Plugin.serializeHighlightSteps( [ highlight ] ) );
					fragmentBlock.classList.add( 'fragment' );
					block.parentNode.appendChild( fragmentBlock );
					Plugin.highlightLines( fragmentBlock );

					if( typeof fragmentIndex === 'number' ) {
						fragmentBlock.setAttribute( 'data-fragment-index', fragmentIndex );
						fragmentIndex += 1;
					}
					else {
						fragmentBlock.removeAttribute( 'data-fragment-index' );
					}

					// Scroll highlights into view as we step through them
					fragmentBlock.addEventListener( 'visible', Plugin.scrollHighlightedLineIntoView.bind( Plugin, fragmentBlock, scrollState ) );
					fragmentBlock.addEventListener( 'hidden', Plugin.scrollHighlightedLineIntoView.bind( Plugin, fragmentBlock.previousSibling, scrollState ) );

				} );

				block.removeAttribute( 'data-fragment-index' )
				block.setAttribute( 'data-line-numbers', Plugin.serializeHighlightSteps( [ highlightSteps[0] ] ) );

			}

			// Scroll the first highlight into view when the slide
			// becomes visible. Note supported in IE11 since it lacks
			// support for Element.closest.
			var slide = typeof block.closest === 'function' ? block.closest( 'section:not(.stack)' ) : null;
			if( slide ) {
				var scrollFirstHighlightIntoView = function() {
					Plugin.scrollHighlightedLineIntoView( block, scrollState, true );
					slide.removeEventListener( 'visible', scrollFirstHighlightIntoView );
				}
				slide.addEventListener( 'visible', scrollFirstHighlightIntoView );
			}

			Plugin.highlightLines( block );

		}

	},

	/**
	 * Animates scrolling to the first highlighted line
	 * in the given code block.
	 */
	scrollHighlightedLineIntoView: function( block, scrollState, skipAnimation ) {

		cancelAnimationFrame( scrollState.animationFrameID );

		// Match the scroll position of the currently visible
		// code block
		if( scrollState.currentBlock ) {
			block.scrollTop = scrollState.currentBlock.scrollTop;
		}

		// Remember the current code block so that we can match
		// its scroll position when showing/hiding fragments
		scrollState.currentBlock = block;

		var highlightBounds = this.getHighlightedLineBounds( block )
		var viewportHeight = block.offsetHeight;

		// Subtract padding from the viewport height
		var blockStyles = getComputedStyle( block );
		viewportHeight -= parseInt( blockStyles.paddingTop ) + parseInt( blockStyles.paddingBottom );

		// Scroll position which centers all highlights
		var startTop = block.scrollTop;
		var targetTop = highlightBounds.top + ( Math.min( highlightBounds.bottom - highlightBounds.top, viewportHeight ) - viewportHeight ) / 2;

		// Account for offsets in position applied to the
		// <table> that holds our lines of code
		var lineTable = block.querySelector( '.hljs-ln' );
		if( lineTable ) targetTop += lineTable.offsetTop - parseInt( blockStyles.paddingTop );

		// Make sure the scroll target is within bounds
		targetTop = Math.max( Math.min( targetTop, block.scrollHeight - viewportHeight ), 0 );

		if( skipAnimation === true || startTop === targetTop ) {
			block.scrollTop = targetTop;
		}
		else {

			// Don't attempt to scroll if there is no overflow
			if( block.scrollHeight <= viewportHeight ) return;

			var time = 0;
			var animate = function() {
				time = Math.min( time + 0.02, 1 );

				// Update our eased scroll position
				block.scrollTop = startTop + ( targetTop - startTop ) * Plugin.easeInOutQuart( time );

				// Keep animating unless we've reached the end
				if( time < 1 ) {
					scrollState.animationFrameID = requestAnimationFrame( animate );
				}
			};

			animate();

		}

	},

	/**
	 * The easing function used when scrolling.
	 */
	easeInOutQuart: function( t ) {

		// easeInOutQuart
		return t<.5 ? 8*t*t*t*t : 1-8*(--t)*t*t*t;

	},

	getHighlightedLineBounds: function( block ) {

		var highlightedLines = block.querySelectorAll( '.highlight-line' );
		if( highlightedLines.length === 0 ) {
			return { top: 0, bottom: 0 };
		}
		else {
			var firstHighlight = highlightedLines[0];
			var lastHighlight = highlightedLines[ highlightedLines.length -1 ];

			return {
				top: firstHighlight.offsetTop,
				bottom: lastHighlight.offsetTop + lastHighlight.offsetHeight
			}
		}

	},

	/**
	 * Visually emphasize specific lines within a code block.
	 * This only works on blocks with line numbering turned on.
	 *
	 * @param {HTMLElement} block a <code> block
	 * @param {String} [linesToHighlight] The lines that should be
	 * highlighted in this format:
	 * "1" 		= highlights line 1
	 * "2,5"	= highlights lines 2 & 5
	 * "2,5-7"	= highlights lines 2, 5, 6 & 7
	 */
	highlightLines: function( block, linesToHighlight ) {

		var highlightSteps = Plugin.deserializeHighlightSteps( linesToHighlight || block.getAttribute( 'data-line-numbers' ) );

		if( highlightSteps.length ) {

			highlightSteps[0].forEach( function( highlight ) {

				var elementsToHighlight = [];

				// Highlight a range
				if( typeof highlight.end === 'number' ) {
					elementsToHighlight = [].slice.call( block.querySelectorAll( 'table tr:nth-child(n+'+highlight.start+'):nth-child(-n+'+highlight.end+')' ) );
				}
				// Highlight a single line
				else if( typeof highlight.start === 'number' ) {
					elementsToHighlight = [].slice.call( block.querySelectorAll( 'table tr:nth-child('+highlight.start+')' ) );
				}

				if( elementsToHighlight.length ) {
					elementsToHighlight.forEach( function( lineElement ) {
						lineElement.classList.add( 'highlight-line' );
					} );

					block.classList.add( 'has-highlights' );
				}

			} );

		}

	},

	/**
	 * Parses and formats a user-defined string of line
	 * numbers to highlight.
	 *
	 * @example
	 * Plugin.deserializeHighlightSteps( '1,2|3,5-10' )
	 * // [
	 * //   [ { start: 1 }, { start: 2 } ],
	 * //   [ { start: 3 }, { start: 5, end: 10 } ]
	 * // ]
	 */
	deserializeHighlightSteps: function( highlightSteps ) {

		// Remove whitespace
		highlightSteps = highlightSteps.replace( /\s/g, '' );

		// Divide up our line number groups
		highlightSteps = highlightSteps.split( Plugin.HIGHLIGHT_STEP_DELIMITER );

		return highlightSteps.map( function( highlights ) {

			return highlights.split( Plugin.HIGHLIGHT_LINE_DELIMITER ).map( function( highlight ) {

				// Parse valid line numbers
				if( /^[\d-]+$/.test( highlight ) ) {

					highlight = highlight.split( Plugin.HIGHLIGHT_LINE_RANGE_DELIMITER );

					var lineStart = parseInt( highlight[0], 10 ),
						lineEnd = parseInt( highlight[1], 10 );

					if( isNaN( lineEnd ) ) {
						return {
							start: lineStart
						};
					}
					else {
						return {
							start: lineStart,
							end: lineEnd
						};
					}

				}
				// If no line numbers are provided, no code will be highlighted
				else {

					return {};

				}

			} );

		} );

	},

	/**
	 * Serializes parsed line number data into a string so
	 * that we can store it in the DOM.
	 */
	serializeHighlightSteps: function( highlightSteps ) {

		return highlightSteps.map( function( highlights ) {

			return highlights.map( function( highlight ) {

				// Line range
				if( typeof highlight.end === 'number' ) {
					return highlight.start + Plugin.HIGHLIGHT_LINE_RANGE_DELIMITER + highlight.end;
				}
				// Single line
				else if( typeof highlight.start === 'number' ) {
					return highlight.start;
				}
				// All lines
				else {
					return '';
				}

			} ).join( Plugin.HIGHLIGHT_LINE_DELIMITER );

		} ).join( Plugin.HIGHLIGHT_STEP_DELIMITER );

	}

}

// Function to perform a better "data-trim" on code snippets
// Will slice an indentation amount on each line of the snippet (amount based on the line having the lowest indentation length)
function betterTrim(snippetEl) {
	// Helper functions
	function trimLeft(val) {
		// Adapted from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim#Polyfill
		return val.replace(/^[\s\uFEFF\xA0]+/g, '');
	}
	function trimLineBreaks(input) {
		var lines = input.split('\n');

		// Trim line-breaks from the beginning
		for (var i = 0; i < lines.length; i++) {
			if (lines[i].trim() === '') {
				lines.splice(i--, 1);
			} else break;
		}

		// Trim line-breaks from the end
		for (var i = lines.length-1; i >= 0; i--) {
			if (lines[i].trim() === '') {
				lines.splice(i, 1);
			} else break;
		}

		return lines.join('\n');
	}

	// Main function for betterTrim()
	return (function(snippetEl) {
		var content = trimLineBreaks(snippetEl.innerHTML);
		var lines = content.split('\n');
		// Calculate the minimum amount to remove on each line start of the snippet (can be 0)
		var pad = lines.reduce(function(acc, line) {
			if (line.length > 0 && trimLeft(line).length > 0 && acc > line.length - trimLeft(line).length) {
				return line.length - trimLeft(line).length;
			}
			return acc;
		}, Number.POSITIVE_INFINITY);
		// Slice each line with this amount
		return lines.map(function(line, index) {
			return line.slice(pad);
		})
		.join('\n');
	})(snippetEl);
}

export default () => Plugin;