feat(billing): implement G1 AI credits overage flow with billing telemetry (#18590)

packages/core/src/billing/billing.ts

@@ -0,0 +1,186 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type {
+  AvailableCredits,
+  CreditType,
+  GeminiUserTier,
+} from '../code_assist/types.js';
+import {
+  PREVIEW_GEMINI_MODEL,
+  PREVIEW_GEMINI_3_1_MODEL,
+} from '../config/models.js';
+
+/**
+ * Strategy for handling quota exhaustion when AI credits are available.
+ * - 'ask': Prompt the user each time
+ * - 'always': Automatically use credits
+ * - 'never': Never use credits, show standard fallback
+ */
+export type OverageStrategy = 'ask' | 'always' | 'never';
+
+/** Credit type for Google One AI credits */
+export const G1_CREDIT_TYPE: CreditType = 'GOOGLE_ONE_AI';
+
+/**
+ * The set of models that support AI credits overage billing.
+ * Only these models are eligible for the credits-based retry flow.
+ */
+export const OVERAGE_ELIGIBLE_MODELS = new Set([
+  PREVIEW_GEMINI_MODEL,
+  PREVIEW_GEMINI_3_1_MODEL,
+]);
+
+/**
+ * Checks if a model is eligible for AI credits overage billing.
+ * @param model The model name to check.
+ * @returns true if the model supports credits overage, false otherwise.
+ */
+export function isOverageEligibleModel(model: string): boolean {
+  return OVERAGE_ELIGIBLE_MODELS.has(model);
+}
+
+/** Base URL for Google One AI page */
+const G1_AI_BASE_URL = 'https://one.google.com/ai';
+
+/** AccountChooser URL for redirecting with email context */
+const ACCOUNT_CHOOSER_URL = 'https://accounts.google.com/AccountChooser';
+
+/** UTM parameters for CLI tracking */
+const UTM_SOURCE = 'gemini_cli';
+// TODO: change to 'desktop' when G1 service fix is rolled out
+const UTM_MEDIUM = 'web';
+
+/**
+ * Wraps a URL in the AccountChooser redirect to maintain user context.
+ * @param email User's email address for account selection
+ * @param continueUrl The destination URL after account selection
+ * @returns The full AccountChooser redirect URL
+ */
+export function wrapInAccountChooser(
+  email: string,
+  continueUrl: string,
+): string {
+  const params = new URLSearchParams({
+    Email: email,
+    continue: continueUrl,
+  });
+  return `${ACCOUNT_CHOOSER_URL}?${params.toString()}`;
+}
+
+/**
+ * UTM campaign identifiers per the design doc.
+ */
+export const G1_UTM_CAMPAIGNS = {
+  /** From Interception Flow "Manage" link (user has credits) */
+  MANAGE_ACTIVITY: 'hydrogen_cli_settings_ai_credits_activity_page',
+  /** From "Manage" to add more credits */
+  MANAGE_ADD_CREDITS: 'hydrogen_cli_settings_add_credits',
+  /** From Empty Wallet Flow "Get AI Credits" link */
+  EMPTY_WALLET_ADD_CREDITS: 'hydrogen_cli_insufficient_credits_add_credits',
+} as const;
+
+/**
+ * Builds a G1 AI URL with UTM tracking parameters.
+ * @param path The path segment (e.g., 'activity' or 'credits')
+ * @param email User's email for AccountChooser wrapper
+ * @param campaign The UTM campaign identifier
+ * @returns The complete URL wrapped in AccountChooser
+ */
+export function buildG1Url(
+  path: 'activity' | 'credits',
+  email: string,
+  campaign: string,
+): string {
+  const baseUrl = `${G1_AI_BASE_URL}/${path}`;
+  const params = new URLSearchParams({
+    utm_source: UTM_SOURCE,
+    utm_medium: UTM_MEDIUM,
+    utm_campaign: campaign,
+  });
+  const urlWithUtm = `${baseUrl}?${params.toString()}`;
+  return wrapInAccountChooser(email, urlWithUtm);
+}
+
+/**
+ * Extracts the G1 AI credit balance from a tier's available credits.
+ * @param tier The user tier to check
+ * @returns The credit amount as a number, 0 if eligible but empty, or null if not eligible
+ */
+export function getG1CreditBalance(
+  tier: GeminiUserTier | null | undefined,
+): number | null {
+  if (!tier?.availableCredits) {
+    return null;
+  }
+
+  const g1Credits = tier.availableCredits.filter(
+    (credit: AvailableCredits) => credit.creditType === G1_CREDIT_TYPE,
+  );
+
+  if (g1Credits.length === 0) {
+    return null;
+  }
+
+  // creditAmount is an int64 represented as string; sum all matching entries
+  return g1Credits.reduce((sum, credit) => {
+    const amount = parseInt(credit.creditAmount ?? '0', 10);
+    return sum + (isNaN(amount) ? 0 : amount);
+  }, 0);
+}
+
+export const MIN_CREDIT_BALANCE = 50;
+
+/**
+ * Determines if credits should be automatically used based on the overage strategy.
+ * @param strategy The configured overage strategy
+ * @param creditBalance The available credit balance
+ * @returns true if credits should be auto-used, false otherwise
+ */
+export function shouldAutoUseCredits(
+  strategy: OverageStrategy,
+  creditBalance: number | null,
+): boolean {
+  return (
+    strategy === 'always' &&
+    creditBalance != null &&
+    creditBalance >= MIN_CREDIT_BALANCE
+  );
+}
+
+/**
+ * Determines if the overage menu should be shown based on the strategy.
+ * @param strategy The configured overage strategy
+ * @param creditBalance The available credit balance
+ * @returns true if the menu should be shown
+ */
+export function shouldShowOverageMenu(
+  strategy: OverageStrategy,
+  creditBalance: number | null,
+): boolean {
+  return (
+    strategy === 'ask' &&
+    creditBalance != null &&
+    creditBalance >= MIN_CREDIT_BALANCE
+  );
+}
+
+/**
+ * Determines if the empty wallet menu should be shown.
+ * @param strategy The configured overage strategy
+ * @param creditBalance The available credit balance
+ * @returns true if the empty wallet menu should be shown
+ */
+export function shouldShowEmptyWalletMenu(
+  strategy: OverageStrategy,
+  creditBalance: number | null,
+): boolean {
+  return (
+    strategy !== 'never' &&
+    creditBalance != null &&
+    creditBalance < MIN_CREDIT_BALANCE
+  );
+}