bibdle/tests/stats-signals.test.ts

import { describe, test, expect } from 'bun:test';
import { evaluateSignals, detectAnomaly, sortSignals } from '$lib/server/stats/signals';
import { SETTINGS_DEFAULTS, type SnapshotPayload } from '$lib/types/stats';

function makePayload(overrides: {
	kpis?: Partial<SnapshotPayload['kpis']>;
	activity?: Partial<SnapshotPayload['activity']>;
	dailySeries?: SnapshotPayload['dailySeries'];
} = {}): SnapshotPayload {
	return {
		asOfDate: '2026-09-14',
		activity: {
			dau: 100,
			wau: 300,
			mau: 800,
			core: 50,
			returningShare: 40,
			newPlayers: 20,
			resurrected: 5,
			churned: 18,
			netGrowth: 7,
			corePrevious: 45,
			previous: { dau: 95, wau: 290, mau: 790, core: 45 },
			...overrides.activity
		},
		dailySeries: overrides.dailySeries ?? [],
		kpis: {
			d1Return: 25,
			return7: 30,
			overallReturnRate: 22,
			completionRate: 80,
			shareRate: 30,
			firstTryRate: 25,
			avgGuesses: 4.1,
			...overrides.kpis
		},
		retention: {
			cohorts: [],
			curves: { d1: [], d7: [], d30: [] },
			timeToSecondPlay: [],
			segmentMix: []
		},
		growth: { lifecycleFunnel: [], signups: [] },
		totals: { completions: 0, players: 0, yesterdayCompletions: 0, yesterdayAvgGuesses: null, bestDay: null },
		verseMix: {
			coverage: [],
			testamentMix: [],
			entropy: [],
			repeatIntervals: [],
			firstTryByBook: [],
			retentionByBook: [],
			retentionByGuessBucket: [],
			achievability: []
		},
		habit: { streakSurvival: [], streakLengths: [], calendar: [], weekdayHour: [] },
		signals: [],
		meta: { hasStartedData: true, hasShareData: true, firstEventDate: null }
	};
}

const settings = { ...SETTINGS_DEFAULTS };

describe('evaluateSignals', () => {
	test('all-good payload yields no warn/bad signals', () => {
		const signals = evaluateSignals(makePayload(), settings);
		expect(signals.some((s) => s.severity === 'bad' || s.severity === 'warn')).toBe(false);
	});

	test('low D1 return is bad and recommends an action', () => {
		const signals = evaluateSignals(makePayload({ kpis: { d1Return: 9 } }), settings);
		const d1 = signals.find((s) => s.id === 'd1_return')!;
		expect(d1.severity).toBe('bad');
		expect(d1.action).toBeTruthy();
	});

	test('missed-but-not-red targets are warnings', () => {
		const signals = evaluateSignals(makePayload({ kpis: { d1Return: 16 } }), settings);
		expect(signals.find((s) => s.id === 'd1_return')!.severity).toBe('warn');
	});

	test('first-try rate outside the band is flagged', () => {
		const tooEasy = evaluateSignals(makePayload({ kpis: { firstTryRate: 60 } }), settings);
		expect(tooEasy.find((s) => s.id === 'first_try')!.severity).toBe('bad');
		const tooHard = evaluateSignals(makePayload({ kpis: { firstTryRate: 5 } }), settings);
		expect(tooHard.find((s) => s.id === 'first_try')!.severity).toBe('bad');
	});

	test('missing metrics surface as info, not failure', () => {
		const signals = evaluateSignals(
			makePayload({ kpis: { completionRate: null, shareRate: null } }),
			settings
		);
		expect(signals.find((s) => s.id === 'completion')!.severity).toBe('info');
		expect(signals.find((s) => s.id === 'share_rate')!.severity).toBe('info');
	});

	test('declining core players is a warning', () => {
		const signals = evaluateSignals(
			makePayload({ activity: { core: 30, corePrevious: 50 } }),
			settings
		);
		expect(signals.find((s) => s.id === 'core_players')!.severity).toBe('warn');
	});

	test('sortSignals puts bad first', () => {
		const signals = sortSignals(evaluateSignals(makePayload({ kpis: { d1Return: 5 } }), settings));
		expect(signals[0].severity).toBe('bad');
	});
});

describe('detectAnomaly', () => {
	function series(values: number[], startWeekdayOffset = 0) {
		// Build consecutive days starting 2026-08-01 so weekdays repeat every 7.
		const out = values.map((value, i) => {
			const d = new Date('2026-08-01T00:00:00Z');
			d.setUTCDate(d.getUTCDate() + i);
			return { date: d.toISOString().slice(0, 10), value };
		});
		void startWeekdayOffset;
		return out;
	}

	test('flags a large weekday-aware spike', () => {
		// 5 weeks of varying same-weekday values, then a spike.
		const base: number[] = [];
		for (let i = 0; i < 35; i++) base.push(100 + ((i * 13) % 17));
		const spike = [...base, 500];
		const anomaly = detectAnomaly(series(spike), 2);
		expect(anomaly).not.toBeNull();
		expect(anomaly!.value).toBe(500);
	});

	test('returns null for a flat series', () => {
		expect(detectAnomaly(series(Array(35).fill(100)), 2)).toBeNull();
	});

	test('returns null without enough history', () => {
		expect(detectAnomaly(series([1, 2, 3]), 2)).toBeNull();
	});
});