openrosa-xpath-evaluator/src/utils/xpath-cast.js

Wrapper for browsers' XPath evaluator with added support for OpenRosa extensions.

const { DATE_STRING, dateToDays, dateStringToDays } = require('./date');
const { toISOLocalString } = require('../date-extensions');

module.exports = {
    asBoolean,
    asNumber,
    asString,
};

// cast to boolean, as per https://www.w3.org/TR/1999/REC-xpath-19991116/#section-Boolean-Functions
function asBoolean(r) {
    if (isDomNode(r)) return !!asString(r).trim();
    switch (r.t) {
        case 'arr':
            return !!r.v.length;
        case 'date':
            return !Number.isNaN(Number(r.v)); // TODO should be handled in an extension rather than core code
        default:
            return !!r.v;
    }
}

// cast to number, as per https://www.w3.org/TR/1999/REC-xpath-19991116/#section-Number-Functions
function asNumber(r) {
    if (r.t === 'num') return r.v;
    if (r.t === 'bool') return r.v ? 1 : 0;
    if (r.t === 'date') return dateToDays(r.v); // TODO should be handled in an extension rather than core code

    const str = asString(r).trim();
    if (str === '') return NaN;
    if (DATE_STRING.test(str)) return dateStringToDays(str); // TODO should be handled in an extension rather than core code
    return +str;
}

// cast to string, as per https://www.w3.org/TR/1999/REC-xpath-19991116/#section-String-Functions
function asString(r) {
    if (isDomNode(r)) return nodeToString(r);
    switch (r.t) {
        case 'str':
            return r.v;
        case 'arr':
            return r.v.length ? r.v[0].textContent || '' : '';
        case 'date':
            return toISOLocalString(r.v).replace(/T00:00:00.000.*/, ''); // TODO should be handled in an extension rather than core code
        case 'num':
        case 'bool':
        default:
            return r.v.toString();
    }
}

// Per https://www.w3.org/TR/1999/REC-xpath-19991116/#dt-string-value:
// 1. > The string-value of the root node is the concatenation of the string-values of all text node descendants of the root node in document order.
// 2. > The string-value of an element node is the concatenation of the string-values of all text node descendants of the element node in document order.
// 3. > An attribute node has a string-value. The string-value is the normalized value as specified by the XML Recommendation [XML]. An attribute whose normalized value is a zero-length string is not treated specially: it results in an attribute node whose string-value is a zero-length string.
// 4. > The string-value of a namespace node is the namespace URI that is being bound to the namespace prefix; if it is relative, it must be resolved just like a namespace URI in an expanded-name.
// 5. > The string-value of a processing instruction node is the part of the processing instruction following the target and any whitespace.
// 6. > The string-value of comment is the content of the comment not including the opening <!-- or the closing -->.
// 7. > The string-value of a text node is the character data.
function nodeToString(node) {
    switch (node.nodeType) {
        case Node.DOCUMENT_NODE:
            return node.documentElement.textContent;
        case Node.TEXT_NODE:
        case Node.CDATA_SECTION_NODE:
        case Node.PROCESSING_INSTRUCTION_NODE:
        case Node.COMMENT_NODE:
        case Node.ELEMENT_NODE:
            return node.textContent; // potentially not to spec for Element, but much simpler than recursing
        case Node.ATTRIBUTE_NODE:
            return node.value;
        default:
            throw new Error(`TODO No handling for node type: ${node.nodeType}`);
    }
}

/**
 * Check if an object is a DOM Node, or one of its subtypes (e.g. Element).
 * @see https://developer.mozilla.org/en-US/docs/Web/API/Node
 */
function isDomNode(thing) {
    return thing instanceof Node;
}