/**
 * Internal dependencies
 */
import { getSibling } from './utils';

function isFormattingSpace( character: string ): boolean {
	return (
		character === ' ' ||
		character === '\r' ||
		character === '\n' ||
		character === '\t'
	);
}

/**
 * Removes spacing that formats HTML.
 *
 * @see https://www.w3.org/TR/css-text-3/#white-space-processing
 *
 * @param node The node to be processed.
 */
export default function htmlFormattingRemover( node: Node ): void {
	if ( node.nodeType !== node.TEXT_NODE ) {
		return;
	}

	// Ignore pre content. Note that this does not use Element#closest due to
	// a combination of (a) node may not be Element and (b) node.parentElement
	// does not have full support in all browsers (Internet Exporer).
	//
	// See: https://developer.mozilla.org/en-US/docs/Web/API/Node/parentElement#Browser_compatibility

	let parent: Node | null = node;
	while ( ( parent = parent.parentNode ) ) {
		if (
			parent.nodeType === parent.ELEMENT_NODE &&
			parent.nodeName === 'PRE'
		) {
			return;
		}
	}

	const textNode = node as Text;

	// First, replace any sequence of HTML formatting space with a single space.
	let newData = textNode.data.replace( /[ \r\n\t]+/g, ' ' );

	// Remove the leading space if the text element is at the start of a block,
	// is preceded by a line break element, or has a space in the previous
	// node.
	if ( newData[ 0 ] === ' ' ) {
		const previousSibling = getSibling( node, 'previous' );

		if (
			! previousSibling ||
			previousSibling.nodeName === 'BR' ||
			previousSibling.textContent!.slice( -1 ) === ' '
		) {
			newData = newData.slice( 1 );
		}
	}

	// Remove the trailing space if the text element is at the end of a block,
	// is succeeded by a line break element, or has a space in the next text
	// node.
	if ( newData[ newData.length - 1 ] === ' ' ) {
		const nextSibling = getSibling( node, 'next' );

		if (
			! nextSibling ||
			nextSibling.nodeName === 'BR' ||
			( nextSibling.nodeType === nextSibling.TEXT_NODE &&
				isFormattingSpace( nextSibling.textContent![ 0 ] ) )
		) {
			newData = newData.slice( 0, -1 );
		}
	}

	// If there's no data left, remove the node, so `previousSibling` stays
	// accurate. Otherwise, update the node data.
	if ( ! newData ) {
		node.parentNode!.removeChild( node );
	} else {
		textNode.data = newData;
	}
}