node-data-modeling/src/guarded-collections/array.js

"use strict";

const errors = require("../errors");
const getValueType = require("../util/get-value-type");

let indexRegex = /^[0-9]+$/;

module.exports = function createGuardedArray(array, guard, _, parent) {
	function generateArraySignatureError() {
		let wantedSignature = {
			_guardedCollectionType: "array",
			_itemType: guard._rule
		};

		return new errors.ValidationError(`Expected an array or ${getValueType(wantedSignature)}, got ${getValueType(array)} instead`);
	}

	if (array._guardedCollectionType === "array") {
		if (guard === array._itemType) {
			return array;
		} else {
			throw generateArraySignatureError();
		}
	} else if (Array.isArray(array)) {
		for (let value of array) {
			check(value);
		}

		/* We shallow-clone the array here, to keep users from accidentally mutating the source array outside the purview of the guards specified here. */
		let targetArray = array.slice();

		function check(value) {
			let guardResult = guard.call(parent, value);

			if (guardResult === true) {
				return true;
			} else {
				throw guardResult;
			}
		}

		let guardedForEach = guardedIterationMethod.bind(undefined, "forEach");
		let guardedFilter = guardedIterationMethod.bind(undefined, "filter");
		let guardedMap = guardedIterationMethod.bind(undefined, "map");
		let guardedSome = guardedIterationMethod.bind(undefined, "some");
		let guardedEvery = guardedIterationMethod.bind(undefined, "every");
		let guardedFind = guardedIterationMethod.bind(undefined, "find");

		let proxyAPI = {
			_guardedCollectionType: "array",
			_itemType: guard,
			push: guardedPush,
			reduce: guardedReduce,
			reduceRight: guardedReduceRight,
			filter: guardedFilter,
			map: guardedMap,
			forEach: guardedForEach,
			some: guardedSome,
			every: guardedEvery,
			find: guardedFind,
			unshift: guardedUnshift,
			fill: guardedFill,
			splice: guardedSplice
		};

		let proxy = new Proxy(targetArray, {
			get: function (target, property) {
				if (proxyAPI[property] != null) {
					return proxyAPI[property];
				} else {
					return target[property];
				}
			},
			set: function (target, property, value) {
				if (indexRegex.test(property)) {
					check(value);
				}

				target[property] = value;
				return true;
			}
		});

		function guardedUnshift(...items) {
			for (let item of items) {
				check(item);
			}

			return targetArray.unshift(...items);
		}

		function guardedPush(value) {
			if (check(value) === true) {
				return targetArray.push(value);
			}
		}

		function guardedFill(value) {
			if (check(value) === true) {
				return targetArray.fill(value);
			}
		}

		function guardedSplice(start, deleteCount, ...items) {
			for (let item of items) {
				check(item);
			}

			return targetArray.splice(start, deleteCount, ...items);
		}

		/* We provide the proxy instead of the original array as the 'array' argument for iteration functions, to prevent direct access to the underlying array; otherwise the user could accidentally mutate the underlying array from within a forEach callback, bypassing the validation requirements. */

		function guardedIterationMethod(method, callback, thisArg) {
			return targetArray[method]((value, index, _array) => {
				return callback(value, index, proxy);
			}, thisArg);
		}

		function guardedReduce(callback, initialValue) {
			return targetArray.reduce((accumulator, value, index, _array) => {
				return callback(accumulator, value, index, proxy);
			}, initialValue);
		}

		function guardedReduceRight(callback, initialValue) {
			return targetArray.reduceRight((accumulator, value, index, _array) => {
				return callback(accumulator, value, index, proxy);
			}, initialValue);
		}

		return proxy;
	} else {
		throw generateArraySignatureError();
	}
};