feat: alert evaluation logic (target/atl/drop) with dedup

src/lib/alerts/evaluate.ts

@@ -0,0 +1,62 @@
+export type AlertType = 'target_price' | 'all_time_low' | 'percent_drop'
+
+export interface AlertInput {
+  type: AlertType
+  config: Record<string, unknown>
+  lastTriggeredAt: Date | null
+}
+
+export interface SnapshotInput {
+  price: number
+  scrapedAt: Date
+}
+
+export interface EvalInput {
+  alert: AlertInput
+  currentPrice: number
+  history: SnapshotInput[]
+}
+
+export interface EvalResult {
+  triggered: boolean
+  context: Record<string, number | string>
+}
+
+const DEDUP_HOURS = 24
+
+export function evaluateAlert(input: EvalInput): EvalResult {
+  const { alert, currentPrice, history } = input
+
+  if (alert.lastTriggeredAt) {
+    const ageMs = Date.now() - alert.lastTriggeredAt.getTime()
+    if (ageMs < DEDUP_HOURS * 60 * 60 * 1000) {
+      return { triggered: false, context: { reason: 'dedup-cooldown' } }
+    }
+  }
+
+  switch (alert.type) {
+    case 'target_price': {
+      const threshold = Number(alert.config.threshold)
+      if (!Number.isFinite(threshold)) return { triggered: false, context: { reason: 'bad-config' } }
+      return { triggered: currentPrice <= threshold, context: { threshold, currentPrice } }
+    }
+    case 'all_time_low': {
+      if (history.length === 0) return { triggered: false, context: { reason: 'no-history' } }
+      const prevMin = Math.min(...history.map((s) => s.price))
+      return { triggered: currentPrice < prevMin, context: { prevMin, currentPrice } }
+    }
+    case 'percent_drop': {
+      const lookbackDays = Number(alert.config.lookback_days)
+      const percent = Number(alert.config.percent)
+      if (!Number.isFinite(lookbackDays) || !Number.isFinite(percent)) {
+        return { triggered: false, context: { reason: 'bad-config' } }
+      }
+      const cutoff = Date.now() - lookbackDays * 86400_000
+      const window = history.filter((s) => s.scrapedAt.getTime() >= cutoff)
+      if (window.length === 0) return { triggered: false, context: { reason: 'no-history-in-window' } }
+      const avg = window.reduce((s, x) => s + x.price, 0) / window.length
+      const dropPct = ((avg - currentPrice) / avg) * 100
+      return { triggered: dropPct >= percent, context: { avg, percent: Number(dropPct.toFixed(2)), currentPrice } }
+    }
+  }
+}

tests/alerts/evaluate.test.ts

@@ -0,0 +1,112 @@
+import { describe, it, expect } from 'vitest'
+import { evaluateAlert, type SnapshotInput } from '@/lib/alerts/evaluate'
+
+function snap(price: number, daysAgo: number): SnapshotInput {
+  const d = new Date()
+  d.setDate(d.getDate() - daysAgo)
+  return { price, scrapedAt: d }
+}
+
+describe('evaluateAlert', () => {
+  describe('target_price', () => {
+    it('triggers when current price <= threshold', () => {
+      const r = evaluateAlert({
+        alert: { type: 'target_price', config: { threshold: 100 }, lastTriggeredAt: null },
+        currentPrice: 99,
+        history: [],
+      })
+      expect(r.triggered).toBe(true)
+    })
+
+    it('does not trigger when price > threshold', () => {
+      const r = evaluateAlert({
+        alert: { type: 'target_price', config: { threshold: 100 }, lastTriggeredAt: null },
+        currentPrice: 101,
+        history: [],
+      })
+      expect(r.triggered).toBe(false)
+    })
+  })
+
+  describe('all_time_low', () => {
+    it('triggers when current is below all previous successful prices', () => {
+      const r = evaluateAlert({
+        alert: { type: 'all_time_low', config: {}, lastTriggeredAt: null },
+        currentPrice: 50,
+        history: [snap(60, 1), snap(70, 5), snap(80, 10)],
+      })
+      expect(r.triggered).toBe(true)
+      expect(r.context.prevMin).toBe(60)
+    })
+
+    it('does not trigger when current equals previous min', () => {
+      const r = evaluateAlert({
+        alert: { type: 'all_time_low', config: {}, lastTriggeredAt: null },
+        currentPrice: 60,
+        history: [snap(60, 1)],
+      })
+      expect(r.triggered).toBe(false)
+    })
+
+    it('does not trigger with no history (first scrape)', () => {
+      const r = evaluateAlert({
+        alert: { type: 'all_time_low', config: {}, lastTriggeredAt: null },
+        currentPrice: 50,
+        history: [],
+      })
+      expect(r.triggered).toBe(false)
+    })
+  })
+
+  describe('percent_drop', () => {
+    it('triggers when price drops >= percent vs lookback avg', () => {
+      const r = evaluateAlert({
+        alert: { type: 'percent_drop', config: { lookback_days: 7, percent: 10 }, lastTriggeredAt: null },
+        currentPrice: 80,
+        history: [snap(100, 1), snap(100, 3), snap(100, 6), snap(50, 30)],
+      })
+      expect(r.triggered).toBe(true)
+      expect(r.context.percent).toBeGreaterThanOrEqual(10)
+    })
+
+    it('does not trigger when drop is smaller than threshold', () => {
+      const r = evaluateAlert({
+        alert: { type: 'percent_drop', config: { lookback_days: 7, percent: 10 }, lastTriggeredAt: null },
+        currentPrice: 95,
+        history: [snap(100, 1), snap(100, 3)],
+      })
+      expect(r.triggered).toBe(false)
+    })
+
+    it('does not trigger with no history in lookback window', () => {
+      const r = evaluateAlert({
+        alert: { type: 'percent_drop', config: { lookback_days: 7, percent: 10 }, lastTriggeredAt: null },
+        currentPrice: 50,
+        history: [snap(100, 30)],
+      })
+      expect(r.triggered).toBe(false)
+    })
+  })
+
+  describe('dedup', () => {
+    it('does not trigger if last triggered within 24h', () => {
+      const recent = new Date(Date.now() - 1000 * 60 * 60 * 12)
+      const r = evaluateAlert({
+        alert: { type: 'target_price', config: { threshold: 100 }, lastTriggeredAt: recent },
+        currentPrice: 50,
+        history: [],
+      })
+      expect(r.triggered).toBe(false)
+    })
+
+    it('triggers if last triggered > 24h ago', () => {
+      const old = new Date(Date.now() - 1000 * 60 * 60 * 25)
+      const r = evaluateAlert({
+        alert: { type: 'target_price', config: { threshold: 100 }, lastTriggeredAt: old },
+        currentPrice: 50,
+        history: [],
+      })
+      expect(r.triggered).toBe(true)
+    })
+  })
+})