From db383f251eb530cb7eaecf82c25bad9b82b682cf Mon Sep 17 00:00:00 2001
From: Marek Rusinowski <marekrusinowski@gmail.com>
Date: Sun, 5 Jan 2025 01:01:49 +0100
Subject: [PATCH] Add MultiIndex data structure

---
 src/multiIndex.test.ts |  47 +++++++++++++++++++
 src/multiIndex.ts      | 100 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 147 insertions(+)
 create mode 100644 src/multiIndex.test.ts
 create mode 100644 src/multiIndex.ts

diff --git a/src/multiIndex.test.ts b/src/multiIndex.test.ts
new file mode 100644
index 0000000..336abcd
--- /dev/null
+++ b/src/multiIndex.test.ts
@@ -0,0 +1,47 @@
+import { test, suite } from 'node:test';
+import assert from 'node:assert/strict';
+import { MultiIndex } from './multiIndex.js';
+
+suite('MultiIndex', () => {
+	test('set', () => {
+		const mi = new MultiIndex({ a1: '', a2: 0, a3: '' });
+		assert.equal(mi.set({ a1: 'a1.1', a2: 1, a3: 'a3.1' }), true);
+		assert.equal(mi.set({ a1: 'a1.2', a2: 2, a3: 'a3.2' }), true);
+		assert.equal(mi.set({ a1: 'a1.2', a2: 2, a3: 'a3.2' }), false);
+		assert.throws(() => {
+			mi.set({ a1: 'a1.2', a2: 2, a3: 'a3.2_prime' });
+		});
+		assert.equal(mi.size, 2);
+	});
+
+	test('get', () => {
+		const mi = new MultiIndex({ a1: '', a2: 0, a3: '' });
+		mi.set({ a1: 'a1.1', a2: 1, a3: 'a3.1' });
+
+		assert.equal(mi.get('a1', 'a1.1')?.a3, 'a3.1');
+		assert.equal(mi.get('a2', 1)?.a1, 'a1.1');
+		assert.equal(mi.get('a3', 'a3.1')?.a1, 'a1.1');
+
+		assert.equal(mi.get('a1', 'non-existent'), undefined);
+	});
+
+	test('has', () => {
+		const mi = new MultiIndex({ a1: '', a2: 0 });
+		mi.set({ a1: 'a1.1', a2: 1 });
+
+		assert.equal(mi.has('a1', 'a1.1'), true);
+		assert.equal(mi.has('a1', 'non-existent'), false);
+	});
+
+	test('delete', () => {
+		const mi = new MultiIndex({ a1: '', a2: 0 });
+		mi.set({ a1: 'a1.1', a2: 1 });
+		mi.set({ a1: 'a1.2', a2: 2 });
+		assert.equal(mi.size, 2);
+
+		assert.equal(mi.delete('a1', 'a1.1'), true);
+		assert.ok(!mi.hasAny({ a1: 'a1.1', a2: 1 }));
+		assert.ok(mi.hasAll({ a1: 'a1.2', a2: 2 }));
+		assert.equal(mi.size, 1);
+	});
+});
diff --git a/src/multiIndex.ts b/src/multiIndex.ts
new file mode 100644
index 0000000..dea934c
--- /dev/null
+++ b/src/multiIndex.ts
@@ -0,0 +1,100 @@
+/**
+ * MultiIndex is a n-way mapping between values. In mathematical sense,
+ * it's a bijection between n-sets of values.
+ *
+ * Each of the sets has a name and type: modeled by the template type argument:
+ *
+ *   {
+ *     'set_name1': type
+ *     'set_name2': some_type2
+ *   }
+ *
+ * The multi-index supports adding new elements and looking up values from all
+ * the sets given the value from only one of them.
+ */
+export class MultiIndex<K extends object> {
+	private m: { [key in keyof K]: Map<K[key], K> };
+
+	/**
+	 * Constructs a new MultiIndex.
+	 *
+	 * @param idx Any index key. It's not added to the multi-index, just needed
+	 * because of the type erasure.
+	 */
+	constructor(private idx: K) {
+		this.m = {} as typeof this.m;
+		for (const k in idx) {
+			this.m[k] = new Map();
+		}
+	}
+
+	/**
+	 * Tests if any of the values from the index key are already in the set.
+	 */
+	hasAny(idx: K): boolean {
+		for (const k in idx) {
+			if (this.m[k].has(idx[k])) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * Tests if the whole index key is already in the set.
+	 */
+	hasAll(idx: K): boolean {
+		for (const k in this.m) {
+			const v = this.m[k].get(idx[k]);
+			if (v) {
+				for (const k in idx) {
+					if (v[k] != idx[k]) {
+						return false;
+					}
+				}
+				return true;
+			}
+			break;
+		}
+		return false;
+	}
+
+	set(idx: K): boolean {
+		if (this.hasAll(idx)) {
+			return false;
+		}
+		if (this.hasAny(idx)) {
+			throw new Error('Trying to set incompatible index key');
+		}
+		for (const k in idx) {
+			this.m[k].set(idx[k], idx);
+		}
+		return true;
+	}
+
+	get<U extends keyof K>(set: U, key: K[U]): K | undefined {
+		return this.m[set].get(key);
+	}
+
+	has<U extends keyof K>(set: U, key: K[U]): boolean {
+		return this.m[set].has(key);
+	}
+
+	delete<U extends keyof K>(set: U, key: K[U]): boolean {
+		const k = this.m[set].get(key);
+		if (!k) {
+			return false;
+		}
+		for (const i in k) {
+			this.m[i].delete(k[i]);
+		}
+		return true;
+	}
+
+	get size(): number {
+		for (const k in this.m) {
+			return this.m[k].size;
+		}
+		return 0;
+	}
+}