Generalise functionality to shuffle things in //base

Author: RussellLVP

javascript/base/shuffle.js

@@ -0,0 +1,46 @@
+// Copyright 2020 Las Venturas Playground. All rights reserved.
+// Use of this source code is governed by the MIT license, a copy of which can
+// be found in the LICENSE file.
+
+import { random } from 'base/random.js';
+
+// Shuffles the given |value| with the Fisher-Yates algorithm. Any iterable value is supported,
+// although recomposition is limited to arrays (default), strings, Set and Map. The given |value|
+// will not be modified, although each of its values will not be cloned.
+//
+// https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
+export function shuffle(value) {
+    if (!isIterable(value))
+        throw new Error('Only iterable values can be shuffled.');
+
+    const values = [ ...value ];
+    let counter = values.length;
+
+    while (counter > 0) {
+        const index = random(counter--);
+        const temp = values[counter];
+
+        values[counter] = values[index];
+        values[index] = temp;
+    }
+
+    // Specializations for returning shuffled data in particular data types.
+    switch (Object.prototype.toString.call(value)) {
+        case '[object Map]':
+            return new Map(values);
+
+        case '[object Set]':
+            return new Set(values);
+
+        case '[object String]':
+            return values.join('');
+    }
+
+    // Default to returning the |values| as an array.
+    return values;
+}
+
+// Returns whether the given |value| is iterable.
+function isIterable(value) {
+    return value !== null && typeof value[Symbol.iterator] === 'function';
+}

javascript/base/shuffle.test.js

@@ -0,0 +1,56 @@
+// Copyright 2020 Las Venturas Playground. All rights reserved.
+// Use of this source code is governed by the MIT license, a copy of which can
+// be found in the LICENSE file.
+
+import { shuffle } from 'base/shuffle.js';
+
+describe('shuffle', it => {
+    it('should be able to shuffle iterables', assert => {
+        assert.throws(() => shuffle());
+        assert.throws(() => shuffle(3.14));
+        assert.throws(() => shuffle({ yo: 1 }));
+        assert.throws(() => shuffle(null));
+
+        // Arrays
+        const array = shuffle([ 1, 2, 3, 4, 5 ]);
+
+        assert.isTrue(Array.isArray(array));
+        assert.equal(array.length, 5);
+        assert.deepEqual(array.sort(), [ 1, 2, 3, 4, 5 ]);
+
+        // Maps
+        const map = shuffle(new Map([ [ 'a', 1 ], [ 'c', 3 ], [ 'b', 2 ] ]));
+        const sortedMap = [ ...map ].sort((lhs, rhs) => lhs[1] > rhs[1] ? 1 : -1);
+
+        assert.instanceOf(map, Map);
+        assert.equal(map.size, 3);
+
+        assert.deepEqual(sortedMap, [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', 3 ] ]);
+
+        // Sets
+        const set = shuffle(new Set([ 'aap', 'noot', 'mies' ]));
+
+        assert.instanceOf(set, Set);
+        assert.equal(set.size, 3);
+        assert.deepEqual([ ...set ].sort(), [ 'aap', 'mies', 'noot' ]);
+
+        // Strings
+        const string = shuffle('banana');
+
+        assert.typeOf(string, 'string');
+        assert.equal(string.length, 6);
+        assert.deepEqual([ ...'banana' ].sort(), [ ...string ].sort());
+
+        // Distribution
+        //
+        // The letters in the string 'banana' can be arranged in 60 different ways, because both the
+        // 'A' and 'B' occur multiple times. Given 1000 attempts, we should see at least 50 of those
+        // ways, or there's something seriously wrong with the PRNG.
+        const distribution = new Set();
+
+        for (let iteration = 0; iteration < 1000; ++iteration)
+            distribution.add(shuffle('banana'));
+
+        assert.isAboveOrEqual(distribution.size, 50);
+    });
+});