feat: add outlier score formula and save decision

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/lib/score.js

@@ -0,0 +1,9 @@
+export function computeScore(views, subscribers) {
+  if (subscribers === null || subscribers === undefined) return null;
+  return Math.round((views / Math.max(subscribers, 1)) * 100) / 100;
+}
+
+export function shouldSave({ views, score, vidiqScore }, { threshold, minViews }) {
+  if (vidiqScore !== null && vidiqScore !== undefined) return true;
+  return score !== null && score !== undefined && views >= minViews && score >= threshold;
+}

test/score.test.js

@@ -0,0 +1,44 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { computeScore, shouldSave } from '../src/lib/score.js';
+
+test('computeScore divides views by subscribers', () => {
+  assert.equal(computeScore(100000, 20000), 5);
+  assert.equal(computeScore(2500, 1000), 2.5);
+});
+
+test('computeScore rounds to two decimals', () => {
+  assert.equal(computeScore(10000, 3000), 3.33);
+});
+
+test('computeScore never divides by zero', () => {
+  assert.equal(computeScore(5000, 0), 5000);
+});
+
+test('computeScore returns null when subscribers are unknown', () => {
+  assert.equal(computeScore(5000, null), null);
+  assert.equal(computeScore(5000, undefined), null);
+});
+
+const settings = { threshold: 5, minViews: 10000 };
+
+test('shouldSave accepts a video exactly at both limits', () => {
+  assert.equal(shouldSave({ views: 10000, score: 5, vidiqScore: null }, settings), true);
+});
+
+test('shouldSave rejects a score below the threshold', () => {
+  assert.equal(shouldSave({ views: 50000, score: 4.99, vidiqScore: null }, settings), false);
+});
+
+test('shouldSave rejects views below the minimum even with a huge score', () => {
+  assert.equal(shouldSave({ views: 9999, score: 50, vidiqScore: null }, settings), false);
+});
+
+test('shouldSave rejects a null score without a VidIQ score', () => {
+  assert.equal(shouldSave({ views: 500000, score: null, vidiqScore: null }, settings), false);
+});
+
+test('shouldSave accepts any video that has a VidIQ score', () => {
+  assert.equal(shouldSave({ views: 100, score: null, vidiqScore: 7.5 }, settings), true);
+  assert.equal(shouldSave({ views: 100, score: 0.01, vidiqScore: 3 }, settings), true);
+});