/**
 * WordPress dependencies
 */
import { isTextContent } from '@wordpress/dom';

/**
 * Checks if the given node should be considered inline content, optionally
 * depending on a context tag.
 *
 * @param node       Node name.
 * @param contextTag Tag name.
 *
 * @return True if the node is inline content, false if not.
 */
function isInline( node: Node, contextTag?: string ): boolean {
	if ( isTextContent( node ) ) {
		return true;
	}

	if ( ! contextTag ) {
		return false;
	}

	const tag = node.nodeName.toLowerCase();
	const inlineAllowedTagGroups = [
		[ 'ul', 'li', 'ol' ],
		[ 'h1', 'h2', 'h3', 'h4', 'h5', 'h6' ],
	];

	return inlineAllowedTagGroups.some(
		( tagGroup ) =>
			[ tag, contextTag ].filter( ( t ) => ! tagGroup.includes( t ) )
				.length === 0
	);
}

function deepCheck( nodes: Element[], contextTag?: string ): boolean {
	return nodes.every(
		( node ) =>
			isInline( node, contextTag ) &&
			deepCheck( Array.from( node.children ), contextTag )
	);
}

function isDoubleBR( node: Element ): boolean {
	return (
		node.nodeName === 'BR' &&
		!! node.previousSibling &&
		node.previousSibling.nodeName === 'BR'
	);
}

export default function isInlineContent(
	HTML: string,
	contextTag?: string
): boolean {
	const doc = document.implementation.createHTMLDocument( '' );

	doc.body.innerHTML = HTML;

	const nodes = Array.from( doc.body.children );

	return ! nodes.some( isDoubleBR ) && deepCheck( nodes, contextTag );
}