# SimpleFinanceDash - Product Requirements Document

## 1. Overview

SimpleFinanceDash is a self-hosted personal budget dashboard web application. It replaces a manual spreadsheet-based budget tracker with a proper application, enabling future extensibility (sharing, automations, summaries). The application replicates a monthly budget tracking workflow with support for bills, variable expenses, debts, savings, and investments.

## 2. Goals

- Provide a clean, pastel-themed budget dashboard that mirrors the existing spreadsheet workflow
- Self-hosted, lightweight single-binary deployment
- Support for German and English (i18n)
- Solid foundation for future features (sharing, automation, customization)

## 3. Users

- **MVP**: Single-user accounts, isolated data per user
- **Future**: Shared/household budgets, multi-user collaboration

## 4. Tech Stack

| Layer       | Technology                                      |
|-------------|------------------------------------------------|
| Frontend    | React + Vite + TypeScript + Tailwind CSS + shadcn/ui |
| Backend     | Go (standard library + router of choice)        |
| Database    | PostgreSQL                                      |
| Auth        | Local username/password + OIDC (e.g. Authentik) |
| Deployment  | Single binary (embedded SPA) + Docker Compose   |
| API         | REST (JSON)                                     |

## 5. Architecture

### 5.1 Single Binary

The Go backend embeds the built React SPA using `embed.FS`. A single Docker image contains everything. PostgreSQL runs as a separate service in `compose.yml`.

### 5.2 Project Structure (proposed)

```
SimpleFinanceDash/
  backend/
    cmd/server/         # main entrypoint
    internal/
      api/              # HTTP handlers / routes
      auth/             # local auth + OIDC
      db/               # database access (queries, migrations)
      models/           # domain types
      i18n/             # translations
    migrations/         # SQL migration files
  frontend/
    src/
      components/       # React components (shadcn/ui based)
      pages/            # route-level pages
      hooks/            # custom hooks
      lib/              # utilities, API client
      i18n/             # translation files (de, en)
  compose.yml
  Dockerfile
  PRD.md
```

## 6. Data Model

### 6.1 Core Entities

**User**
- id (UUID)
- email
- password_hash (nullable, empty for OIDC-only users)
- oidc_subject (nullable)
- display_name
- preferred_locale (de | en)
- created_at, updated_at

**Category**
- id (UUID)
- user_id (FK)
- name
- type: enum(bill, variable_expense, debt, saving, investment, income)
- icon (optional, for future use)
- sort_order
- created_at, updated_at

Categories are global per user and reused across budget periods.

**Budget**
- id (UUID)
- user_id (FK)
- name (e.g. "Oktober 2025")
- start_date
- end_date
- currency (default: EUR)
- carryover_amount (manually set or pulled from previous budget)
- created_at, updated_at

**BudgetItem**
- id (UUID)
- budget_id (FK)
- category_id (FK)
- budgeted_amount (planned)
- actual_amount (spent/received)
- notes (optional)
- created_at, updated_at

Each BudgetItem represents one category's row within a monthly budget (e.g. "Strom & Heizung" with budget 65.00, actual 65.00).

### 6.2 Relationships

```
User 1--* Category
User 1--* Budget
Budget 1--* BudgetItem
Category 1--* BudgetItem
```

### 6.3 Derived Values (computed, not stored)

- **Available amount** = carryover + sum(income actuals) - sum(bill actuals) - sum(expense actuals) - sum(debt actuals) - sum(saving actuals) - sum(investment actuals)
- **Budget vs Actual per type** = aggregated from BudgetItems
- **Remaining per category** = budgeted - actual

## 7. Features (MVP)

### 7.1 Authentication

- **Local auth**: Email + password registration/login with bcrypt hashing
- **OIDC**: Connect to external identity providers (e.g. Authentik). Strongly encouraged over local auth in the UI
- **Session management**: HTTP-only cookies with JWT or server-side sessions

### 7.2 Budget Setup

- Create a new monthly budget period (start date, end date, currency, carryover)
- Option to copy categories/budgeted amounts from a previous month
- Edit or delete existing budgets

### 7.3 Dashboard View

Replicates the spreadsheet layout as a single-page dashboard for the selected budget:

**Top Section - Financial Overview**
- Carryover, Income, Bills, Expenses, Debts, Savings, Investments
- Budget vs Actual columns
- Available balance with donut chart

**Bills Tracker**
- Table of bill categories with Budget and Actual columns
- Inline editing of actual amounts

**Variable Expenses Summary**
- Table with Budget, Actual, Remaining columns
- Bar chart: Budget vs Actual per category

**Expense Breakdown**
- Pie chart showing distribution across expense categories

**Debt Tracker**
- Table of debt categories with Budget and Actual columns

### 7.4 Category Management

- CRUD for categories per user
- Category types: bill, variable_expense, debt, saving, investment, income
- Categories persist across budgets

### 7.5 Internationalization (i18n)

- German (de) and English (en)
- User preference stored in profile
- All UI labels, messages, and formatting (date, currency) localized

### 7.6 Charts

- **Donut chart**: Available balance vs spent
- **Bar chart**: Budget vs Actual per variable expense category
- **Pie chart**: Expense breakdown by category
- Library: Recharts or similar React-compatible charting library

## 8. UI / Design

### 8.1 Color Scheme

Pastel color palette inspired by the reference screenshots:
- Soft blues, pinks, yellows, greens, lavenders
- Light backgrounds with subtle section dividers
- shadcn/ui components with custom pastel theme tokens

### 8.2 Layout

- Left sidebar or top nav for navigation (Dashboard, Categories, Settings)
- Main content area with the dashboard sections stacked vertically
- Responsive but desktop-first (primary use case)

### 8.3 Future: Customization

- Architecture should support theming (CSS variables / Tailwind config)
- Not implemented in MVP, but color tokens should be centralized for easy swapping later

## 9. API Endpoints (MVP)

### Auth
| Method | Path                  | Description              |
|--------|-----------------------|--------------------------|
| POST   | /api/auth/register    | Local registration       |
| POST   | /api/auth/login       | Local login              |
| POST   | /api/auth/logout      | Logout                   |
| GET    | /api/auth/oidc        | Initiate OIDC flow       |
| GET    | /api/auth/oidc/callback | OIDC callback          |
| GET    | /api/auth/me          | Get current user         |

### Categories
| Method | Path                       | Description           |
|--------|----------------------------|-----------------------|
| GET    | /api/categories            | List user categories  |
| POST   | /api/categories            | Create category       |
| PUT    | /api/categories/:id        | Update category       |
| DELETE | /api/categories/:id        | Delete category       |

### Budgets
| Method | Path                              | Description                    |
|--------|-----------------------------------|--------------------------------|
| GET    | /api/budgets                      | List user budgets              |
| POST   | /api/budgets                      | Create budget                  |
| GET    | /api/budgets/:id                  | Get budget with items + totals |
| PUT    | /api/budgets/:id                  | Update budget                  |
| DELETE | /api/budgets/:id                  | Delete budget                  |
| POST   | /api/budgets/:id/copy-from/:srcId | Copy items from another budget |

### Budget Items
| Method | Path                              | Description         |
|--------|-----------------------------------|---------------------|
| POST   | /api/budgets/:id/items            | Create budget item  |
| PUT    | /api/budgets/:id/items/:itemId    | Update budget item  |
| DELETE | /api/budgets/:id/items/:itemId    | Delete budget item  |

### User Settings
| Method | Path                  | Description           |
|--------|-----------------------|-----------------------|
| GET    | /api/settings         | Get user settings     |
| PUT    | /api/settings         | Update user settings  |

## 10. Deployment

### compose.yml

```yaml
services:
  app:
    build: .
    ports:
      - "8080:8080"
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/simplefinancedash?sslmode=disable
      - OIDC_ISSUER=https://auth.example.com
      - OIDC_CLIENT_ID=simplefinancedash
      - OIDC_CLIENT_SECRET=secret
      - SESSION_SECRET=change-me
    depends_on:
      db:
        condition: service_healthy

  db:
    image: postgres:16-alpine
    volumes:
      - pgdata:/var/lib/postgresql/data
    environment:
      - POSTGRES_USER=user
      - POSTGRES_PASSWORD=pass
      - POSTGRES_DB=simplefinancedash
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U user -d simplefinancedash"]
      interval: 5s
      timeout: 5s
      retries: 5

volumes:
  pgdata:
```

### Dockerfile

Multi-stage build:
1. Node stage: build React SPA
2. Go stage: embed SPA, compile binary
3. Final stage: minimal image (distroless or alpine) with single binary

## 11. Testing

### Backend (Go)
- Unit tests for business logic and handlers
- Integration tests against a test PostgreSQL instance (testcontainers)
- API endpoint tests with httptest

### Frontend (React)
- Component tests with Vitest + React Testing Library
- Page-level integration tests

### E2E
- Playwright for critical user flows (login, create budget, edit items, view dashboard)

## 12. Non-Goals (MVP)

These are explicitly out of scope for v1 but should be kept in mind architecturally:

- CSV / bank import
- Recurring / automated transactions
- Shared / household budgets
- Custom themes / color picker
- GraphQL API
- PDF / CSV export
- Weekly / yearly views
- Mobile app

## 13. Future Considerations

- **Customization engine**: User-defined colors, layout preferences, category icons
- **Sharing**: Invite users to a shared budget (household mode)
- **Automations**: Recurring transactions, auto-carryover between months
- **Summaries**: Monthly/yearly reports with trends
- **GraphQL**: For flexible dashboard queries and aggregations
- **Import/Export**: CSV import from banks, PDF/CSV export of reports