DynamoDB Simple Change-Feed Lambda Trigger

LambdaDDBChangeFeedTrigger.js

/**
 * @license
 * Lodash (Custom Build) lodash.com/license | Underscore.js 1.8.3 underscorejs.org/LICENSE
 * Build: `lodash include="isObject,isEqual"`
 */
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function unique(value, index, self) {
	return self.indexOf(value) === index;
}

function isEmpty(obj) {
	return !obj || !Object.keys(obj).length;
}

function isArray(obj) {
	return !!(obj && obj.concat);
}

function isObject(value) {
	var type = typeof value;
	return value != null && (type == 'object' || type == 'function');
}

function diff(template, override) {
	if (!isObject(override)) {
		return undefined;
	}

	// handle arrays
	if (!isObject(template) || (isArray(override) || isArray(template)) && !_.isEqual(template, override)) {
		return override;
	}

	var ret = {},
		hasDiff = false,
		oVal, tVal,
		keys = Object.keys(template).concat(Object.keys(override)).filter(unique);
	
	keys.forEach(function(name) {
		oVal = override[name];
		tVal = template[name];

		if (tVal && isObject(oVal) && !isArray(oVal)) {
			var _diff = diff(tVal, oVal);
			if (!isEmpty(_diff)) {
				hasDiff = true;
				ret[name] = _diff;
			}
		} else if (!_.isEqual(tVal, oVal)) {
			hasDiff = true;
			ret[name] = oVal;
		}
	});

	return hasDiff ? ret : null;
}



function mapper(data, setType) {

	var keys = Object.keys(data),
		ret = data.concat ? [] : {};

	console.log("keys", keys);

	while (keys.length) {
		var key = keys.shift(),
			obj = data[key];

		console.log("key", key, obj);

		if (setType) {
			switch(setType) {
				case "BB":
				case "SS":		ret[key] = obj;						break;
				case "NN":		ret[key] = parseFloat(obj);			break;
			}

		} else if (typeof obj === "object" && obj !== null) {
			var type = Object.keys(obj)[0];
			switch(type) {
				case "S":
				case "B":
				case "BOOL":	ret[key] = obj[type];				break;

				case "N":		ret[key] = parseFloat(obj[type]);	break;

				case "NULL":	ret[key] = null;					break;
				
				case "L":
				case "M":		ret[key] = mapper(obj[type]);		break;

				case "SS":
				case "NN":
				case "BB":		ret[key] = mapper(obj[type], type);	break;
			}
		}
	}

	return ret;
}

exports.handler = function(event, context, callback) {
    var items = [];
    if (event.Records) {
        event.Records.forEach(function(r) {
            var ddb = r.dynamodb,
                o = ddb.OldImage,
                n = ddb.NewImage,
                rec = {
                    "eventName": r.eventName,
                    "ts": ddb && ddb.ApproximateCreationDateTime
                };
            
            if (o && n) {
                rec.diff = diff(mapper(o), mapper(n));
            } else {
                o && (rec.old = mapper(o));
                n && (rec.new = mapper(n));
            }
            
            items.push(rec);
        });
    }
    callback(null, items);
};