fontoxpath/src/selectors/operators/compares/nodeCompare.js

A minimalistic XPath 3.1 engine in JavaScript

import isSubtypeOf from '../../dataTypes/isSubtypeOf';
import Sequence from '../../dataTypes/Sequence';
import zipSingleton from '../../util/zipSingleton';

/**
 * @param   {string}     operator
 * @param   {!../../dataTypes/Sequence}  firstSequence
 * @param   {!../../dataTypes/Sequence}  secondSequence
 * @return  {!Sequence}
 */
export default function nodeCompare (operator, firstSequence, secondSequence) {
	// https://www.w3.org/TR/xpath-31/#doc-xpath31-NodeComp
	return firstSequence.switchCases({
		default: () => {
			throw new Error('XPTY0004: Sequences to compare are not singleton');
		},
		singleton: () => secondSequence.switchCases({
			default: () => {
				throw new Error('XPTY0004: Sequences to compare are not singleton');
			},
			singleton: () => {
				if (operator !== 'is') {
					throw new Error('Node ordering comparisons are not implemented.');
				}
			return zipSingleton(
				[firstSequence, secondSequence],
				([first, second]) => {
					if (!isSubtypeOf(first.type, 'node()') || !isSubtypeOf(second.type, 'node()')) {
						throw new Error('XPTY0004: Sequences to compare are not nodes');
					}

					return first === second ?
						Sequence.singletonTrueSequence() :
						Sequence.singletonFalseSequence();
				});
			}
		})
	});
}