Initial MVP: Cost.dev AI Coding Cost Optimizer Chrome extension

src/background.ts

@@ -0,0 +1,62 @@
+import { loadState, saveState, sumMonthUsages, projectedMonthEnd } from './storage'
+
+const ALARM_NAME = 'costdev_budget_check'
+
+chrome.runtime.onInstalled.addListener(async () => {
+  await chrome.alarms.create(ALARM_NAME, { periodInMinutes: 60 })
+})
+
+chrome.alarms.onAlarm.addListener(async (alarm) => {
+  if (alarm.name !== ALARM_NAME) return
+  const state = await loadState()
+  if (!state.budget.enabled || state.budget.monthlyLimit <= 0) return
+
+  const spent = sumMonthUsages(state.usages)
+  const limit = state.budget.monthlyLimit
+  const threshold = limit * state.budget.alertThreshold
+
+  if (spent >= threshold && spent < limit) {
+    const last = state.lastAlertAt ?? 0
+    if (Date.now() - last > 24 * 60 * 60 * 1000) {
+      chrome.notifications.create('costdev-warning', {
+        type: 'basic',
+        iconUrl: 'icons/icon128.png',
+        title: 'Cost.dev — Budget Alert',
+        message: `You've spent $${spent.toFixed(2)} of your $${limit.toFixed(2)} monthly budget.`,
+        priority: 1,
+      })
+      state.lastAlertAt = Date.now()
+      await saveState(state)
+    }
+  }
+
+  if (spent >= limit) {
+    const last = state.lastAlertAt ?? 0
+    if (Date.now() - last > 24 * 60 * 60 * 1000) {
+      chrome.notifications.create('costdev-over', {
+        type: 'basic',
+        iconUrl: 'icons/icon128.png',
+        title: 'Cost.dev — Budget Overrun',
+        message: `You've exceeded your $${limit.toFixed(2)} monthly budget! Current spend: $${spent.toFixed(2)}.`,
+        priority: 2,
+      })
+      state.lastAlertAt = Date.now()
+      await saveState(state)
+    }
+  }
+})
+
+chrome.runtime.onMessage.addListener((message, _sender, sendResponse) => {
+  ;(async () => {
+    if (message.type === 'budget-check') {
+      const state = await loadState()
+      const spent = sumMonthUsages(state.usages)
+      const limit = state.budget.monthlyLimit
+      const projected = projectedMonthEnd(spent)
+      sendResponse({ spent, limit, projected, enabled: state.budget.enabled })
+    } else {
+      sendResponse({ ok: false })
+    }
+  })()
+  return true
+})