node-data-modeling/src/serialization/placeholder-manager.js

"use strict";

const isPlaceholder = require("../util/is-placeholder");

module.exports = function createPlaceholderManager() {
	let placeholders = [];

	return {
		markProperty: function (object, property) {
			placeholders.push({
				type: "property",
				object: object,
				property: property
			});
		},
		markSet: function (set) {
			placeholders.push({
				type: "set",
				set: set
			});
		},
		markArray: function (array) {
			placeholders.push({
				type: "array",
				array: array
			});
		},
		markMap: function (map) {
			placeholders.push({
				type: "map",
				map: map
			});
		},
		fillInPlaceholders: function (seen) {
			function getSeenItem(placeholder) {
				if (seen.has(placeholder._deserializationId)) {
					return seen.get(placeholder._deserializationId);
				} else {
					throw new Error(`Did not encounter an object with the ID ${placeholder._deserializationId}`);
				}
			}

			function fillInSetPlaceholders(set) {
				let originalItems = Array.from(set.values());
				set.clear();

				for (let item of originalItems) {
					if (isPlaceholder(item)) {
						set.add(getSeenItem(item));
					} else {
						set.add(item);
					}
				}
			}

			function fillInArrayPlaceholders(array) {
				array.forEach((item, i) => {
					if (isPlaceholder(item)) {
						array[i] = getSeenItem(item);
					}
				});
			}

			function fillInMapPlaceholders(map) {
				let originalItems = Array.from(map.entries());
				map.clear();

				for (let [key, value] of originalItems) {
					let newKey, newValue;

					if (isPlaceholder(key)) {
						newKey = getSeenItem(key);
					} else {
						newKey = key;
					}

					if (isPlaceholder(value)) {
						newValue = getSeenItem(value);
					} else {
						newValue = value;
					}

					map.set(newKey, newValue);
				}
			}

			function fillInPlaceholderProperty(object, property) {
				object[property] = getSeenItem(object[property]);
			}

			placeholders.forEach((marker) => {
				/* NOTE: The Set/Map implementations below are probably slow. Maybe there's a faster implementation? */
				if (marker.type === "set") {
					fillInSetPlaceholders(marker.set);
				} else if (marker.type === "array") {
					fillInArrayPlaceholders(marker.array);
				} else if (marker.type === "map") {
					fillInMapPlaceholders(marker.map);
				} else if (marker.type === "property") {
					fillInPlaceholderProperty(marker.object, marker.property);
				} else {
					throw new Error(`Unrecognized placeholder marker type: ${marker.type}`);
				}
			});

			/* To ensure that any accidental future invocations of this function will fail loudly. */
			placeholders = null;
		}
	};
};