Add delta OR set implementation

DeltaBased/2-or-set.js

@@ -0,0 +1,124 @@
+'use strict';
+
+const crypto = require('node:crypto');
+
+const init = () => ({ added: {}, removed: {} });
+
+class DeltaORSet {
+  #added;
+  #removed;
+
+  constructor({ added = {}, removed = {} } = {}) {
+    this.#added = { ...added };
+    this.#removed = { ...removed };
+  }
+
+  add(item, tag = crypto.randomUUID()) {
+    const result = init();
+    const added = this.#added[item];
+    result.added[item] = added ? new Set([...added, tag]) : new Set([tag]);
+    return result;
+  }
+
+  remove(item) {
+    const result = init();
+    const added = this.#added[item];
+
+    if (!added) return result;
+
+    const removed = this.#removed[item];
+    result.removed[item] = removed
+      ? new Set([...removed, ...added])
+      : new Set([...added]);
+
+    return result;
+  }
+
+  join(delta) {
+    const added = Object.entries(delta.added);
+    for (const [item, tags] of added) {
+      const deltaTags = tags || new Set();
+
+      const added = this.#added[item];
+      this.#added[item] = added
+        ? new Set([...added, ...deltaTags])
+        : new Set([...deltaTags]);
+    }
+    const removed = Object.entries(delta.removed);
+    for (const [item, tags] of removed) {
+      const deltaTags = tags || new Set();
+      const removed = this.#removed[item];
+      this.#removed[item] = removed
+        ? new Set([...removed, ...deltaTags])
+        : new Set([...deltaTags]);
+    }
+  }
+
+  get value() {
+    const result = [];
+    for (const item of Object.keys(this.#added)) {
+      const addTags = this.#added[item] || new Set();
+      const remTags = this.#removed[item] || new Set();
+      for (const tag of addTags) {
+        if (!remTags.has(tag)) {
+          result.push(item);
+          break;
+        }
+      }
+    }
+    return result;
+  }
+
+  get added() {
+    return this.#added;
+  }
+
+  get removed() {
+    return this.#removed;
+  }
+}
+
+// Usage
+
+console.log('--------------------------------');
+console.log('Delta CRDT OR-Set');
+console.log('--------------------------------');
+
+console.log('Replica 0');
+const set0 = new DeltaORSet();
+const delta01 = set0.add('a');
+set0.join(delta01);
+const delta02 = set0.add('b');
+set0.join(delta02);
+const delta03 = set0.remove('a');
+console.log({ delta03 });
+set0.join(delta03);
+console.log({ id0: set0.value });
+console.log({ id0: set0.added });
+console.log({ id0: set0.removed });
+
+console.log('Replica 1');
+const set1 = new DeltaORSet();
+const delta11 = set1.add('b');
+set1.join(delta11);
+const delta12 = set1.add('c');
+set1.join(delta12);
+const delta13 = set1.remove('b');
+set1.join(delta13);
+const delta14 = set1.add('c');
+set1.join(delta14);
+const delta15 = set1.remove('b');
+set1.join(delta15);
+console.log({ id1: set1.value });
+
+console.log('Sync');
+set0.join(set1);
+set1.join(set0);
+console.log({ id0Added: set0.added });
+console.log({ id0Removed: set0.removed });
+console.log({ id1Added: set1.added });
+console.log({ id1Removed: set1.removed });
+
+console.log('Get value');
+console.log({ id0: set0.value });
+console.log({ id1: set1.value });