BudgetSync

BudgetSync is a mobile app that replaces a manual Excel budgeting workflow with an automated, AI-powered system. It:

• Imports credit card statements (TD and Amex CSV formats) via expo-document-picker and parses them with the xlsx library
• Auto-categorizes transactions using AI — sends all transactions in one call and returns a structured JSON response with category, subcategory, and confidence
• Suggests monthly projected budgets based on the last 3 months of actual spending, with AI-generated explanations for each suggestion
• Syncs to a personal Google Sheet matching an existing tracker layout with income, expense categories, projected vs actual columns, and monthly balance summaries
• Supports 9 expense categories: Essentials, Transportation, Food, Entertainment, Personal Care, Gifts & Donations, Loans, Savings, Legal — each with projected and actual tracking

I was managing a detailed monthly budget in Excel — tracking projected vs actual spend across 9 categories, syncing credit card statements manually, and running the same calculations every month. The process worked but was tedious. BudgetSync automates the repetitive parts while keeping full data ownership: everything syncs to a personal Google Sheet I control, with no third-party data sharing.

• Provider-agnostic AI client: single askAI(prompt) function that routes to Claude (claude-sonnet-4-20250514), GPT-4o, or Gemini 1.5 Flash based on user preference — each with different API formats and response schemas
• Google OAuth without a backend: implemented Google Sheets authentication using expo-auth-session with scopes for Sheets, Drive, email, and profile — access token stored securely in expo-secure-store
• CSV parsing across card formats: TD and Amex use different column layouts (TD: Date/Description/Debit/Credit, Amex: Date/Description/Amount) — normalized to a common transaction schema using the xlsx library
• Secure credential storage: API keys, OAuth tokens, spreadsheet ID, salary, and fixed costs all stored in expo-secure-store with typed key constants, surviving app restarts
• File-based routing with expo-router: 6-tab navigation (Home, New Month, Import, Review, Sync, Settings) mirroring the Next.js App Router pattern in a React Native context

Completed: App shell, 6-tab navigation, Settings screen (AI provider selector, Google OAuth, budget preferences, danger zone), AI abstraction layer, secure credential storage, Google Cloud project setup (Sheets API + Drive API enabled, OAuth consent screen configured).

In progress: Local data storage layer (lib/storage.ts), Home screen with income/expense cards and progress bars, New Month setup with AI suggestions, CSV import and AI categorization flow, Google Sheets sync.