npmbar/src/db/json-db.js

'use strict';

/* Rolling your own database is a bad idea. In this particular
 * case, I am doing it anyway, because there are very clear
 * constraints, no extreme performance requirements, and most
 * importantly, all the other in-memory databases seem to
 * -suck- from an API/usability point of view.
 *
 * Limitations:
 *   - Only one process can use the DB at the same time. Yes,
 *     it's a reading lock.
 *   - Persistence is not guaranteed. If the process crashes,
 *     writes may be lost.
 *   - No performance guarantees, whatsoever.
 *   - No schemas.
 */

const Promise = require("bluebird");
const fs = Promise.promisifyAll(require("fs"));
const matchObject = require("match-object");
const uuid = require("uuid");
const pick = require("object-pick");
const rfr = require("rfr");

const promiseDebounce = rfr("lib/util/promise-debounce");
const escapeCollectionName = rfr("lib/db/escape-collection-name"); // FIXME: Actually split this up into collections...

function getLockPath(path) {
	return `${path}.lock`;
}

function obtainLock(path) {
	return Promise.try(() => {
		return fs.writeFileAsync(getLockPath(path), "", {
			flag: "wx"
		});
	});
}

function releaseLock(path) {
	return Promise.try(() => {
		return fs.unlinkAsync(getLockPath(path));
	});
}

function loadDatabase(path) {
	return Promise.try(() => {
		return obtainLock(path);
	}).then(() => {
		return fs.readFileAsync(path);
	}).then((data) => {
		return JSON.parse(data);
	}).catch({code: "ENOENT"}, (err) => {
		/* Initialize a blank database */
		return {};
	});
}

function saveDatabase(path, collections) {
	return Promise.try(() => {
		return fs.writeFileAsync(path, JSON.stringify(collections));
	});
}

module.exports = function(path) {
	return Promise.try(() => {
		return loadDatabase(path);
	}).then((collections) => {
		let queueWrite = promiseDebounce(function() {
			if (db.opened === true) {
				saveDatabase(path, collections);
			}
		});

		function getCollection(name) {
			let indexes; // TODO

			function findIdIndex(id) {
				if (id == null) {
					return null;
				}

				return collections[name].findIndex((item) => item.$id === id);
			}

			return {
				find: function(query) {
					return collections[name].filter((item) => matchObject(query, item));
				},
				findOne: function(query) {
					let result = collections[name].find((item) => matchObject(query, item));

					if (result == null) {
						throw new Error("No results found");
					} else {
						return result;
					}
				},
				insert: function(object, options = {}) {
					/* Intentional mutation. */
					Object.assign(object, {$id: uuid.v4()});
					collections[name].push(object);
					queueWrite();
				},
				update: function(object, options = {}) {
					let index;
					if (index = findIdIndex(object.$id)) {
						if (options.patch === true) {
							Object.assign(collections[name][index], object);
						} else {
							collections[name][index] = object;
						}

						queueWrite();
					} else {
						throw new Error("No such object exists");
					}
				},
				upsert: function(object, options = {}) {
					try {
						this.update(object, options);
					} catch (err) {
						this.insert(object, options);
					}
				},
				upsertBy: function(keys, object, options = {}) {
					let query = pick(object, keys);

					try {
						let result = this.findOne(query);
						// FIXME: The following shouldn't be in the try block...
						object.$id = result.$id;
						return this.update(object, options);
					} catch (err) {
						return this.insert(object, options);
					}

				},
				delete: function(object) {
					let index;
					if (index = findIdIndex(object.$id)) {
						collections[name].splice(index, 1);
						queueWrite();
					} else {
						throw new Error("No such object exists");
					}
				},
				deleteBy: function(query) {
					collections[name] = collections[name].filter((item) => !matchObject(query, item));
					queueWrite();
				},
				ensureIndex: function(property) {
					// TODO
				}
			}
		}

		// TODO: Cache/TTL collections
		// TODO: .bak file

		let db = {
			opened: true,
			close: function() {
				return Promise.try(() => {
					return queueWrite();
				}).then(() => {
					return releaseLock(path);
				}).then(() => {
					this.opened = false;
				});
			},
			collection: function(name) {
				if (collections[name] == null) {
					collections[name] = [];
				}

				return getCollection(name);
			}
		}

		function cleanup() {
			console.log("Doing cleanup...");
			if (db.opened === true) {
				db.close();
			}
		}

		if (process.versions.electron != null) {
			/* Running in Electron */
			require("electron").app.on("will-quit", () => {
				cleanup();
			})
		} else {
			/* Running in a different Node-y environment */
			process.on("beforeExit", () => {
				cleanup();
			});
		}

		return db;
	});
}