index.js

/**
 * The regular expression for an HTML element.
 *
 * @type {String}
 */
const htmlSplitRegex = ( () => {
	/* eslint-disable no-multi-spaces */
	const comments =
		'!' +           // Start of comment, after the <.
		'(?:' +         // Unroll the loop: Consume everything until --> is found.
			'-(?!->)' + // Dash not followed by end of comment.
			'[^\\-]*' + // Consume non-dashes.
		')*' +          // Loop possessively.
		'(?:-->)?';     // End of comment. If not found, match all input.

	const cdata =
		'!\\[CDATA\\[' + // Start of comment, after the <.
		'[^\\]]*' +      // Consume non-].
		'(?:' +          // Unroll the loop: Consume everything until ]]> is found.
			'](?!]>)' +  // One ] not followed by end of comment.
			'[^\\]]*' +  // Consume non-].
		')*?' +          // Loop possessively.
		'(?:]]>)?';      // End of comment. If not found, match all input.

	const escaped =
		'(?=' +              // Is the element escaped?
			'!--' +
		'|' +
			'!\\[CDATA\\[' +
		')' +
		'((?=!-)' +          // If yes, which type?
			comments +
		'|' +
			cdata +
		')';

	const regex =
		'(' +               // Capture the entire match.
			'<' +           // Find start of element.
			'(' +           // Conditional expression follows.
				escaped +   // Find end of escaped element.
			'|' +           // ... else ...
				'[^>]*>?' + // Find end of normal element.
			')' +
		')';

	return new RegExp( regex );
	/* eslint-enable no-multi-spaces */
} )();

/**
 * Separate HTML elements and comments from the text.
 *
 * @param  {String} input The text which has to be formatted.
 * @return {Array}        The formatted text.
 */
function htmlSplit( input ) {
	const parts = [];
	let workingInput = input;

	let match;
	while ( ( match = workingInput.match( htmlSplitRegex ) ) ) {
		parts.push( workingInput.slice( 0, match.index ) );
		parts.push( match[ 0 ] );
		workingInput = workingInput.slice( match.index + match[ 0 ].length );
	}

	if ( workingInput.length ) {
		parts.push( workingInput );
	}

	return parts;
}

/**
 * Replace characters or phrases within HTML elements only.
 *
 * @param  {String} haystack     The text which has to be formatted.
 * @param  {Object} replacePairs In the form {from: 'to', ...}.
 * @return {String}              The formatted text.
 */
function replaceInHtmlTags( haystack, replacePairs ) {
	// Find all elements.
	const textArr = htmlSplit( haystack );
	let changed = false;

	// Extract all needles.
	const needles = Object.keys( replacePairs );

	// Loop through delimiters (elements) only.
	for ( let i = 1; i < textArr.length; i += 2 ) {
		for ( let j = 0; j < needles.length; j++ ) {
			const needle = needles[ j ];
			if ( -1 !== textArr[ i ].indexOf( needle ) ) {
				textArr[ i ] = textArr[ i ].replace( new RegExp( needle, 'g' ), replacePairs[ needle ] );
				changed = true;
				// After one strtr() break out of the foreach loop and look at next element.
				break;
			}
		}
	}

	if ( changed ) {
		haystack = textArr.join( '' );
	}

	return haystack;
}

/**
 * Replaces double line-breaks with paragraph elements.
 *
 * A group of regex replaces used to identify text formatted with newlines and
 * replace double line-breaks with HTML paragraph tags. The remaining line-
 * breaks after conversion become <<br />> tags, unless br is set to 'false'.
 *
 * @param  {String}    text The text which has to be formatted.
 * @param  {Boolean}   br   Optional. If set, will convert all remaining line-
 *                          breaks after paragraphing. Default true.
 * @return {String}         Text which has been converted into paragraph tags.
 */
export function autop( text, br = true ) {
	const preTags = [];

	if ( text.trim() === '' ) {
		return '';
	}

	// Just to make things a little easier, pad the end.
	text = text + '\n';

	/*
	 * Pre tags shouldn't be touched by autop.
	 * Replace pre tags with placeholders and bring them back after autop.
	 */
	if ( text.indexOf( '<pre' ) !== -1 ) {
		const textParts = text.split( '</pre>' );
		const lastText = textParts.pop();
		text = '';

		for ( let i = 0; i < textParts.length; i++ ) {
			const textPart = textParts[ i ];
			const start = textPart.indexOf( '<pre' );

			// Malformed html?
			if ( start === -1 ) {
				text += textPart;
				continue;
			}

			const name = '<pre wp-pre-tag-' + i + '></pre>';
			preTags.push( [ name, textPart.substr( start ) + '</pre>' ] );

			text += textPart.substr( 0, start ) + name;
		}

		text += lastText;
	}
	// Change multiple <br>s into two line breaks, which will turn into paragraphs.
	text = text.replace( /<br\s*\/?>\s*<br\s*\/?>/g, '\n\n' );

	const allBlocks = '(?:table|thead|tfoot|caption|col|colgroup|tbody|tr|td|th|div|dl|dd|dt|ul|ol|li|pre|form|map|area|blockquote|address|math|style|p|h[1-6]|hr|fieldset|legend|section|article|aside|hgroup|header|footer|nav|figure|figcaption|details|menu|summary)';

	// Add a double line break above block-level opening tags.
	text = text.replace( new RegExp( '(<' + allBlocks + '[\s\/>])', 'g' ), '\n\n$1' );

	// Add a double line break below block-level closing tags.
	text = text.replace( new RegExp( '(<\/' + allBlocks + '>)', 'g' ), '$1\n\n' );

	// Standardize newline characters to "\n".
	text = text.replace( /\r\n|\r/g, '\n' );

	// Find newlines in all elements and add placeholders.
	text = replaceInHtmlTags( text, { '\n': ' <!-- wpnl --> ' } );

	// Collapse line breaks before and after <option> elements so they don't get autop'd.
	if ( text.indexOf( '<option' ) !== -1 ) {
		text = text.replace( /\s*<option/g, '<option' );
		text = text.replace( /<\/option>\s*/g, '</option>' );
	}

	/*
	 * Collapse line breaks inside <object> elements, before <param> and <embed> elements
	 * so they don't get autop'd.
	 */
	if ( text.indexOf( '</object>' ) !== -1 ) {
		text = text.replace( /(<object[^>]*>)\s*/g, '$1' );
		text = text.replace( /\s*<\/object>/g, '</object>' );
		text = text.replace( /\s*(<\/?(?:param|embed)[^>]*>)\s*/g, '$1' );
	}

	/*
	 * Collapse line breaks inside <audio> and <video> elements,
	 * before and after <source> and <track> elements.
	 */
	if ( text.indexOf( '<source' ) !== -1 || text.indexOf( '<track' ) !== -1 ) {
		text = text.replace( /([<\[](?:audio|video)[^>\]]*[>\]])\s*/g, '$1' );
		text = text.replace( /\s*([<\[]\/(?:audio|video)[>\]])/g, '$1' );
		text = text.replace( /\s*(<(?:source|track)[^>]*>)\s*/g, '$1' );
	}

	// Collapse line breaks before and after <figcaption> elements.
	if ( text.indexOf( '<figcaption' ) !== -1 ) {
		text = text.replace( /\s*(<figcaption[^>]*>)/, '$1' );
		text = text.replace( /<\/figcaption>\s*/, '</figcaption>' );
	}

	// Remove more than two contiguous line breaks.
	text = text.replace( /\n\n+/g, '\n\n' );

	// Split up the contents into an array of strings, separated by double line breaks.
	const texts = text.split( /\n\s*\n/ ).filter( Boolean );

	// Reset text prior to rebuilding.
	text = '';

	// Rebuild the content as a string, wrapping every bit with a <p>.
	texts.forEach( ( textPiece ) => {
		text += '<p>' + textPiece.replace( /^\n*|\n*$/g, '' ) + '</p>\n';
	} );

	// Under certain strange conditions it could create a P of entirely whitespace.
	text = text.replace( /<p>\s*<\/p>/g, '' );

	// Add a closing <p> inside <div>, <address>, or <form> tag if missing.
	text = text.replace( /<p>([^<]+)<\/(div|address|form)>/g, '<p>$1</p></$2>' );

	// If an opening or closing block element tag is wrapped in a <p>, unwrap it.
	text = text.replace( new RegExp( '<p>\s*(<\/?' + allBlocks + '[^>]*>)\s*<\/p>', 'g' ), '$1' );

	// In some cases <li> may get wrapped in <p>, fix them.
	text = text.replace( /<p>(<li.+?)<\/p>/g, '$1' );

	// If a <blockquote> is wrapped with a <p>, move it inside the <blockquote>.
	text = text.replace( /<p><blockquote([^>]*)>/gi, '<blockquote$1><p>' );
	text = text.replace( /<\/blockquote><\/p>/g, '</p></blockquote>' );

	// If an opening or closing block element tag is preceded by an opening <p> tag, remove it.
	text = text.replace( new RegExp( '<p>\s*(<\/?' + allBlocks + '[^>]*>)', 'g' ), '$1' );

	// If an opening or closing block element tag is followed by a closing <p> tag, remove it.
	text = text.replace( new RegExp( '(<\/?' + allBlocks + '[^>]*>)\s*<\/p>', 'g' ), '$1' );

	// Optionally insert line breaks.
	if ( br ) {
		// Replace newlines that shouldn't be touched with a placeholder.
		text = text.replace( /<(script|style).*?<\/\\1>/g, ( match ) => match[ 0 ].replace( /\n/g, '<WPPreserveNewline />' ) );

		// Normalize <br>
		text = text.replace( /<br>|<br\/>/g, '<br />' );

		// Replace any new line characters that aren't preceded by a <br /> with a <br />.
		text = text.replace( /(<br \/>)?\s*\n/g, ( a, b ) => b ? a : '<br />\n' );

		// Replace newline placeholders with newlines.
		text = text.replace( /<WPPreserveNewline \/>/g, '\n' );
	}

	// If a <br /> tag is after an opening or closing block tag, remove it.
	text = text.replace( new RegExp( '(<\/?' + allBlocks + '[^>]*>)\s*<br \/>', 'g' ), '$1' );

	// If a <br /> tag is before a subset of opening or closing block tags, remove it.
	text = text.replace( /<br \/>(\s*<\/?(?:p|li|div|dl|dd|dt|th|pre|td|ul|ol)[^>]*>)/g, '$1' );
	text = text.replace( /\n<\/p>$/g, '</p>' );

	// Replace placeholder <pre> tags with their original content.
	preTags.forEach( ( preTag ) => {
		const [ name, original ] = preTag;
		text = text.replace( name, original );
	} );

	// Restore newlines in all elements.
	if ( -1 !== text.indexOf( '<!-- wpnl -->' ) ) {
		text = text.replace( /\s?<!-- wpnl -->\s?/g, '\n' );
	}

	return text;
}

/**
 * Replaces <p> tags with two line breaks. "Opposite" of autop().
 *
 * Replaces <p> tags with two line breaks except where the <p> has attributes.
 * Unifies whitespace. Indents <li>, <dt> and <dd> for better readability.
 *
 * @param  {String} html The content from the editor.
 * @return {String}      The content with stripped paragraph tags.
 */
export function removep( html ) {
	const blocklist = 'blockquote|ul|ol|li|dl|dt|dd|table|thead|tbody|tfoot|tr|th|td|h[1-6]|fieldset|figure';
	const blocklist1 = blocklist + '|div|p';
	const blocklist2 = blocklist + '|pre';
	const preserve = [];
	let preserveLinebreaks = false;
	let preserveBr = false;

	if ( ! html ) {
		return '';
	}

	// Protect script and style tags.
	if ( html.indexOf( '<script' ) !== -1 || html.indexOf( '<style' ) !== -1 ) {
		html = html.replace( /<(script|style)[^>]*>[\s\S]*?<\/\1>/g, function( match ) {
			preserve.push( match );
			return '<wp-preserve>';
		} );
	}

	// Protect pre tags.
	if ( html.indexOf( '<pre' ) !== -1 ) {
		preserveLinebreaks = true;
		html = html.replace( /<pre[^>]*>[\s\S]+?<\/pre>/g, function( a ) {
			a = a.replace( /<br ?\/?>(\r\n|\n)?/g, '<wp-line-break>' );
			a = a.replace( /<\/?p( [^>]*)?>(\r\n|\n)?/g, '<wp-line-break>' );
			return a.replace( /\r?\n/g, '<wp-line-break>' );
		} );
	}

	// Remove line breaks but keep <br> tags inside image captions.
	if ( html.indexOf( '[caption' ) !== -1 ) {
		preserveBr = true;
		html = html.replace( /\[caption[\s\S]+?\[\/caption\]/g, function( a ) {
			return a.replace( /<br([^>]*)>/g, '<wp-temp-br$1>' ).replace( /[\r\n\t]+/, '' );
		} );
	}

	// Normalize white space characters before and after block tags.
	html = html.replace( new RegExp( '\\s*</(' + blocklist1 + ')>\\s*', 'g' ), '</$1>\n' );
	html = html.replace( new RegExp( '\\s*<((?:' + blocklist1 + ')(?: [^>]*)?)>', 'g' ), '\n<$1>' );

	// Mark </p> if it has any attributes.
	html = html.replace( /(<p [^>]+>.*?)<\/p>/g, '$1</p#>' );

	// Preserve the first <p> inside a <div>.
	html = html.replace( /<div( [^>]*)?>\s*<p>/gi, '<div$1>\n\n' );

	// Remove paragraph tags.
	html = html.replace( /\s*<p>/gi, '' );
	html = html.replace( /\s*<\/p>\s*/gi, '\n\n' );

	// Normalize white space chars and remove multiple line breaks.
	html = html.replace( /\n[\s\u00a0]+\n/g, '\n\n' );

	// Replace <br> tags with line breaks.
	html = html.replace( /(\s*)<br ?\/?>\s*/gi, function( match, space ) {
		if ( space && space.indexOf( '\n' ) !== -1 ) {
			return '\n\n';
		}

		return '\n';
	} );

	// Fix line breaks around <div>.
	html = html.replace( /\s*<div/g, '\n<div' );
	html = html.replace( /<\/div>\s*/g, '</div>\n' );

	// Fix line breaks around caption shortcodes.
	html = html.replace( /\s*\[caption([^\[]+)\[\/caption\]\s*/gi, '\n\n[caption$1[/caption]\n\n' );
	html = html.replace( /caption\]\n\n+\[caption/g, 'caption]\n\n[caption' );

	// Pad block elements tags with a line break.
	html = html.replace( new RegExp( '\\s*<((?:' + blocklist2 + ')(?: [^>]*)?)\\s*>', 'g' ), '\n<$1>' );
	html = html.replace( new RegExp( '\\s*</(' + blocklist2 + ')>\\s*', 'g' ), '</$1>\n' );

	// Indent <li>, <dt> and <dd> tags.
	html = html.replace( /<((li|dt|dd)[^>]*)>/g, ' \t<$1>' );

	// Fix line breaks around <select> and <option>.
	if ( html.indexOf( '<option' ) !== -1 ) {
		html = html.replace( /\s*<option/g, '\n<option' );
		html = html.replace( /\s*<\/select>/g, '\n</select>' );
	}

	// Pad <hr> with two line breaks.
	if ( html.indexOf( '<hr' ) !== -1 ) {
		html = html.replace( /\s*<hr( [^>]*)?>\s*/g, '\n\n<hr$1>\n\n' );
	}

	// Remove line breaks in <object> tags.
	if ( html.indexOf( '<object' ) !== -1 ) {
		html = html.replace( /<object[\s\S]+?<\/object>/g, function( a ) {
			return a.replace( /[\r\n]+/g, '' );
		} );
	}

	// Unmark special paragraph closing tags.
	html = html.replace( /<\/p#>/g, '</p>\n' );

	// Pad remaining <p> tags whit a line break.
	html = html.replace( /\s*(<p [^>]+>[\s\S]*?<\/p>)/g, '\n$1' );

	// Trim.
	html = html.replace( /^\s+/, '' );
	html = html.replace( /[\s\u00a0]+$/, '' );

	if ( preserveLinebreaks ) {
		html = html.replace( /<wp-line-break>/g, '\n' );
	}

	if ( preserveBr ) {
		html = html.replace( /<wp-temp-br([^>]*)>/g, '<br$1>' );
	}

	// Restore preserved tags.
	if ( preserve.length ) {
		html = html.replace( /<wp-preserve>/g, function() {
			return preserve.shift();
		} );
	}

	return html;
}