Add id based database load and save functions

Add functions to save and load a Map of objects indexed by the id
property in the objects.

lib/database.js

@@ -31,9 +31,10 @@ function mapToObject(map) {
 }
 
 /**
- * Load JSON file as a Map
+ * Load JSON object file as a Map
  *
- * Loads the JSON file specified by path an converts it into a JavaScript Map.
+ * Loads the JSON file specified by path containing an object with
+ * properties as key value pairs and converts it into a JavaScript Map.
  * Returns an empty Map if the file does not exist.
  *
  * @param {string} filePath - The path to the JSON file to load.
@@ -71,7 +72,7 @@ async function loadJsonAsMap(filePath) {
 }
 
 /**
- * Save a Map as a JSON file
+ * Save a Map as a JSON object file
  *
  * Save the content of a key-value Map with only string keys as a JSON file.
  * If the directory the file is to be saved into doesn't exist it will be
@@ -87,6 +88,76 @@ async function saveMapAsJson(filePath, map) {
 	await fs.outputFile(filePath, JSON.stringify(obj, null, 4));
 }
 
+/**
+ * Load JSON array file as a Map
+ *
+ * Loads the JSON file specified by path containing an array of objects that
+ * each have an id property into a Map from the id to the object.
+ *
+ * @param {string} filePath - The path to the JSON file to load.
+ * @throws {Error} If JSON file did not contain an array.
+ * @throws {Error} If there are objects in the array without an id property.
+ * @throws {Error} If an error occured reading the file.
+ */
+async function loadJsonArrayAsMap(filePath) {
+	try {
+		let content = await fs.readFile(filePath);
+		let parsed = JSON.parse(content);
+
+		if (parsed === null) {
+			throw new Error(`Expected array but got null`);
+		}
+
+		if (typeof parsed !== "object") {
+			throw new Error(`Expected array but got ${typeof parsed}`);
+		}
+
+		if (!(parsed instanceof Array)) {
+			throw new Error(`Expected array but got object`);
+		}
+
+		let map = new Map();
+		for (let element of parsed) {
+			if (element === null || element instanceof Array || typeof element !== "object") {
+				throw new Error(`Expected all elements to be objects`);
+			}
+
+			if (element.id === undefined) {
+				throw new Error(`Expected all elements to have an id property`);
+			}
+
+			map.set(element.id, element);
+		}
+		return map;
+
+	} catch (err) {
+		if (err.code == "ENOENT") {
+			// File does not exist, return empty map
+			return new Map();
+
+		} else {
+			throw err;
+		}
+	}
+}
+
+/**
+ * Save a Map as a JSON array file
+ *
+ * Save the values of a Map with objects containing an id property that is
+ * equal to the key the objects are stored at into a JSON file.
+ *
+ * @param {string} filePath - The path to the JSON file that will be saved.
+ * @param {Map} map -
+ *     Map with objects containing an id property equal to the key they are
+ *     stored under.
+ * @throws {Error} if an error occured writing to the file.
+ */
+async function saveMapAsJsonArray(filePath, map) {
+	await fs.outputFile(filePath, JSON.stringify([...map.values()], null, 4));
+}
+
+
 
 function checkName(name) {
 	if (typeof name !== "string") {
@@ -227,5 +298,7 @@ module.exports = {
 	mapToObject,
 	loadJsonAsMap,
 	saveMapAsJson,
+	loadJsonArrayAsMap,
+	saveMapAsJsonArray,
 	ItemDatabase,
 }

test/json/array_null.json

@@ -0,0 +1 @@
+[null]

test/json/array_object.json

@@ -0,0 +1 @@
+[{}]

test/json/load_array_map.json

@@ -0,0 +1 @@
+[{"id":"a"},{"id":"b"}]

test/json/save_map.json

@@ -0,0 +1,10 @@
+[
+    [
+        "c",
+        {}
+    ],
+    [
+        "d",
+        "foo"
+    ]
+]

test/lib/database.js

@@ -60,7 +60,7 @@ describe("lib/database", function() {
 
 	describe("saveMapAsJson()", function() {
 		it("should save a mapping as JSON", async function() {
-			let testFile = 'test/json/save_map.json';
+			let testFile = 'test/temp/save_map.json';
 			async function deleteTestFile() {
 				try {
 					await fs.unlink(testFile);
@@ -81,7 +81,80 @@ describe("lib/database", function() {
 				await fs.readFile(testFile, {encoding: 'utf-8'}),
 				'{\n    "c": {},\n    "d": "foo"\n}'
 			);
+		});
+	});
+
+	describe("loadJsonArrayAsMap()", function() {
+		let badTypes = ['null', 'object', 'number', 'string', 'boolean'];
+
+		for (let type of badTypes) {
+			it(`should reject on ${type} JSON`, async function() {
+				await assert.rejects(
+					database.loadJsonArrayAsMap(`test/json/${type}.json`),
+					new Error(`Expected array but got ${type}`)
+				);
+			});
+		}
+
+		it("should reject on null element", async function() {
+			await assert.rejects(
+				database.loadJsonArrayAsMap('test/json/array_null.json'),
+				new Error("Expected all elements to be objects")
+			);
+		});
+
+		it("should reject on element missing id", async function() {
+			await assert.rejects(
+				database.loadJsonArrayAsMap('test/json/array_object.json'),
+				new Error("Expected all elements to have an id property")
+			);
+		});
+
+		it("should work on empty array JSON", async function() {
+			assert.deepEqual(
+				await database.loadJsonArrayAsMap('test/json/array.json'),
+				new Map()
+			);
+		});
+
+		it("should work on array JSON", async function() {
+			assert.deepEqual(
+				await database.loadJsonArrayAsMap('test/json/load_array_map.json'),
+				new Map([['a', {id: 'a'}], ['b', {id: 'b'}]])
+			);
+		});
+
+		it("should give an empty Map for non-existant file", async function() {
+			assert.deepEqual(
+				await database.loadJsonArrayAsMap('test/json/does-not-exist'),
+				new Map()
+			);
+		});
+	});
+
+	describe("saveMapAsJsonArray()", function() {
+		it("should save a mapping as JSON", async function() {
+			let testFile = 'test/temp/save_array_map.json';
+			async function deleteTestFile() {
+				try {
+					await fs.unlink(testFile);
+				} catch (err) {
+					/* istanbul ignore if */
+					if (err.code !== 'ENOENT') {
+						throw err;
+					}
+				}
+			}
+
 			await deleteTestFile();
+			await database.saveMapAsJsonArray(
+				testFile, new Map([['c', {id: 'c'}], ['d', {id: 'd'}]])
+			);
+
+			assert.equal(
+				await fs.readFile(testFile, {encoding: 'utf-8'}),
+				'[\n    {\n        "id": "c"\n    },\n    {\n        "id": "d"\n    }\n]'
+			);
 		});
 	});