Add AI agent instructions for GitHub Copilot Adoption Dashboard

Author: FrankBurmo

.github/copilot-instructions.md

@@ -0,0 +1,114 @@
+# GitHub Copilot Adoption Dashboard - AI Agent Instructions
+
+## Project Overview
+
+This is a client-side React dashboard for viewing GitHub Copilot enterprise metrics via the GitHub REST API. The app is deployed to GitHub Pages and requires no backend server - all API calls happen directly from the browser to GitHub's API.
+
+**Key constraint**: GitHub Pages deployment with base path `/github-copilot-adoption-dashboard/` (set in `vite.config.ts`).
+
+## Architecture & Data Flow
+
+### Single-Page Application Structure
+- **`App.tsx`**: Monolithic component handling all logic (form state, API fetching, data processing, rendering)
+- **No component decomposition**: All UI (form, metrics cards, chart, table) lives in one 387-line component
+- **Data flow**: User input → GitHub API fetch → `processMetricsData()` → React state → render
+
+### GitHub API Integration
+```
+Endpoint: GET https://api.github.com/enterprises/{enterprise}/copilot/metrics
+Headers:
+  - Authorization: Bearer {token}
+  - Accept: application/vnd.github+json
+  - X-GitHub-Api-Version: 2022-11-28
+```
+
+Response is `DailyMetrics[]` (array of daily metrics, oldest first). The app:
+1. Takes the **last item** as the latest day's data
+2. Builds historical trend from the full array
+3. Flattens the nested structure (`editors → models → languages`) into a breakdown table
+
+### Critical Data Processing Logic
+
+**Total Seats Estimation** (line 140 in App.tsx):
+```typescript
+const estimated_total_seats = Math.round(latestDay.total_active_users * 1.2);
+```
+This is a workaround - the API doesn't provide total seats, so we estimate at 120% of active users.
+
+**Breakdown Table Sorting** (lines 127-136):
+1. Primary: Active users (descending)
+2. Secondary: Acceptance rate (descending)
+
+**Historical Data Order**: Dates are rendered left-to-right chronologically (oldest to newest) for the Chart.js line chart.
+
+## Development Workflow
+
+### Local Development
+```bash
+npm install          # Install dependencies
+npm run dev          # Start Vite dev server on localhost:5173
+```
+
+### Testing
+```bash
+npm test             # Run Vitest in watch mode
+npm run test:ui      # Launch Vitest UI
+npm run test:run     # Run tests once (CI mode)
+```
+
+**Test setup**: Vitest with `@testing-library/react`, jsdom environment (configured in `vite.config.ts`). Chart.js is mocked in tests (see `App.test.tsx` line 6).
+
+### Building & Deployment
+```bash
+npm run build        # Vite build → dist/
+npm run preview      # Preview production build locally
+```
+
+Deployment is automated via GitHub Actions. The app **must** work with the `/github-copilot-adoption-dashboard/` base path.
+
+## Project-Specific Conventions
+
+### TypeScript Patterns
+- **Interface naming**: Domain types use descriptive names (`DailyMetrics`, `CopilotIdeCodeCompletions`), not generic prefixes
+- **Array typing**: Use `Type[]` syntax (e.g., `DailyMetrics[]`), not `Array<Type>`
+- **Type safety on API responses**: Explicit `ErrorResponse` interface for error handling
+
+### React Patterns
+- **No JSX import needed**: Uses new `jsx: "react-jsx"` transform (tsconfig.json)
+- **State management**: Plain `useState` - no external state libraries
+- **Event handlers**: Inline arrow functions in JSX (e.g., `onChange={(e) => setToken(e.target.value)}`)
+- **No component composition**: Everything in `App.tsx` - if adding features, follow this pattern unless refactoring
+
+### Styling Approach
+- **No CSS modules or styled-components**: Plain CSS in `index.css` with class-based styling
+- **Layout**: CSS Grid for metrics cards (`grid-template-columns: repeat(auto-fit, minmax(250px, 1fr))`)
+- **Inline styles**: Only for the breakdown table (lines 344-375 in App.tsx)
+
+### Chart.js Configuration
+Chart.js components must be explicitly registered:
+```typescript
+ChartJS.register(CategoryScale, LinearScale, PointElement, LineElement, Title, Tooltip, Legend, Filler);
+```
+Missing this causes runtime errors. The Line chart uses custom tooltip callbacks to format dates and user counts.
+
+## Common Pitfalls & Gotchas
+
+1. **Base path for GitHub Pages**: If adding routing or asset references, account for `/github-copilot-adoption-dashboard/`
+2. **API data order**: The API returns oldest-first, but we show latest-day metrics. Don't reverse arrays unnecessarily
+3. **Sensitive data**: Tokens are in password inputs but never persisted (no localStorage/cookies)
+4. **ESLint config**: Uses flat config format (`eslint.config.js`), not legacy `.eslintrc`
+5. **Testing Chart.js**: Always mock `react-chartjs-2` in tests to avoid canvas errors
+
+## Key Files Reference
+
+- **`App.tsx`**: Single source of truth for all application logic
+- **`vite.config.ts`**: Defines base path and test configuration
+- **`package.json`**: Note the project name is `copilot-metrics-frontend` (historical)
+- **`setupTests.ts`**: Imports jest-dom matchers for Vitest
+
+## When Adding Features
+
+- **New metrics/charts**: Add to the monolithic `App.tsx` unless complexity demands refactoring
+- **New API fields**: Update the `DailyMetrics` type chain and `processMetricsData()` function
+- **Styling changes**: Prefer updating `index.css` over inline styles
+- **Tests**: Mock external dependencies (Chart.js, fetch) and test user-facing behavior