jiff/lib/commute.js

JSON diff and patch based on rfc6902

var patches = require('./patches');

module.exports = commute;

commute.rtl = commuteRtL;

/**
 * Given adjacent patch pair p1,p2, commute them to create a new
 * adjacent pair p2',p1'
 * @param {array} p1 JSON Patch
 * @param {array} p2 JSON Patch
 * @returns {array<array>} pair [commutedRight, commutedLeft]
 */
function commute(p1, p2) {
	return p1.reduceRight(function(a, p1) {
		var commuted = commuteOneFully(p1, a[1]);
		a[0].unshift(commuted[0]);
		var b = [a[0], commuted[1]];
		return  b;
	}, [[], p2]);
}

function commuteOneFully(op, p) {
	return p.reduce(function(a, p) {
		var commuted = commuteOne(a[0], p);
		a[0] = commuted[1];
		a[1].push(commuted[0]);
		return a;
	}, [op, []])
}
/**
 * Commute left and right and return only the newly commuted left, throwing
 * away the newly commuted right.
 * @param p1
 * @param p2
 * @returns {*}
 */
function commuteRtL(p1, p2) {
	return p2.reduce(function(accum, p2) {
		accum.push(p1.reduceRight(function(p2c, p1) {
			return commuteOne(p1, p2c)[0];
		}, p2));
		return accum;
	}, []);
}

function commuteOne (p1, p2) {
	var patch = patches[p2.op];
	if (patch === void 0 || typeof patch.commute !== 'function') {
		throw new TypeError('patches cannot be commuted');
	}

	return patch.commute(p1, p2);
}