# Top-Level Application Architecture

## Tech Stack Recommendations

### Frontend
- **Framework**: React 18 + TypeScript
- **Styling**: CSS-in-JS (styled-components or vanilla-extract) or Tailwind CSS
- **Terminal**: xterm.js
- **Real-Time**: Yjs + y-websocket (CRDT collaboration)
- **Build Tool**: Vite
- **Fonts**: IBM Plex Sans + IBM Plex Mono (Google Fonts or self-hosted)
- **State Management**: Zustand or React Context (keep it simple)

### Backend
- **Language**: Go
- **Kubernetes Client**: kubernetes/client-go
- **WebSockets**: gorilla/websocket
- **CRDT Backend**: Redis (single-node) or y-leveldb/y-mongodb (multi-node)
- **Build/Deployment**: Docker, Kubernetes

## Project Structure

```
krates/
├── client/                     # Frontend application
│   ├── src/
│   │   ├── components/        # React components
│   │   │   ├── canvas/       # Canvas and world layer
│   │   │   │   ├── WorldLayer.tsx
│   │   │   │   ├── GridOverlay.tsx
│   │   │   │   └── Minimap.tsx
│   │   │   ├── krate/        # Krate and windows
│   │   │   │   ├── Krate.tsx
│   │   │   │   ├── KrateHeader.tsx
│   │   │   │   ├── DetailWindow.tsx
│   │   │   │   └── CollectionWindow.tsx
│   │   │   ├── Spotlight.tsx
│   │   │   ├── TopBar.tsx
│   │   │   ├── AdminDrawer.tsx
│   │   │   ├── ShellTerminal.tsx  # xterm.js wrapper
│   │   │   └── LogsViewer.tsx
│   │   ├── hooks/            # Custom React hooks
│   │   │   ├── useCanvas.ts
│   │   │   ├── useSpotlight.ts
│   │   │   ├── useWebSocket.ts
│   │   │   └── useKubernetes.ts
│   │   ├── state/            # State management
│   │   │   ├── canvasStore.ts
│   │   │   ├── krateStore.ts
│   │   │   └── spotlightStore.ts
│   │   ├── utils/
│   │   │   ├── fuzzy.ts      # Fuzzy search algorithm
│   │   │   ├── crdt.ts       # Yjs setup
│   │   │   ├── keyboard.ts   # Keyboard handling
│   │   │   └── math.ts       # Canvas math helpers
│   │   ├── App.tsx
│   │   └── main.tsx
│   ├── public/               # Static assets
│   └── package.json
│
├── server/                    # Backend service
│   ├── cmd/
│   │   └── server/
│   │       └── main.go
│   ├── internal/
│   │   ├── api/             # HTTP endpoints
│   │   │   ├── handlers/
│   │   │   └── routes.go
│   │   ├── ws/              # WebSocket handlers
│   │   │   ├── shell.go
│   │   │   ├── logs.go
│   │   │   └── watch.go
│   │   ├── k8s/             # Kubernetes client wrappers
│   │   │   ├── client.go
│   │   │   ├── resources.go
│   │   │   └── watch.go
│   │   ├── crdt/            # Yjs integration
│   │   │   └── provider.go
│   │   └── auth/            # Authentication/authorization
│   │       └── token.go
│   ├── pkg/                 # Reusable packages
│   └── go.mod
│
├── design/                   # This folder
│   ├── canvas.md
│   ├── spotlight.md
│   ├── krate.md
│   ├── detail-window.md
│   ├── top-bar.md
│   ├── admin-drawer.md
│   ├── minimap.md
│   ├── backend.md
│   └── architecture.md
│
└── README.md
```

## State Management Strategy

### Global State (Zustand)
```typescript
// canvasStore.ts
interface CanvasState {
  camX: number;
  camY: number;
  zoom: number;
  flying: boolean;
  dragging: boolean;
  collapsed: boolean;
  spacePanning: boolean;
}

// krateStore.ts
interface KrateStore {
  krates: Map<string, Krate>;
  selectedKrateId: string | null;
}

// spotlightStore.ts
interface SpotlightStore {
  open: boolean;
  query: string;
  filterType: string | null;
  sel: number;
  navigated: boolean;
}

// userStore.ts
interface UserStore {
  currentUser: User;
  presence: Map<string, UserPresence>;
}
```

### Collection State (Per-Window)
```typescript
// stored in krate.windows[].state or separate map
interface CollectionState {
  search: string;
  view: 'list' | 'tree';
  sel: number;
}
```

## WebSocket Architecture

### Connection Setup
```
1. Connect to /ws/sync (CRDT + awareness)
2. Connect to /ws/watch (resource updates)
3. On-demand connections:
   - /ws/shell (when shell window opened)
   - /ws/logs (when logs window opened)
```

### Message Format
```
// CRDT sync
{
  type: 'sync',
  payload: Uint8Array  // Yjs update encoded
}

// Awareness presence
{
  type: 'awareness',
  updates: UserPresence[]
}

// Resource watch
{
  type: 'resource',
  action: 'add' | 'update' | 'delete',
  kind: string,         // 'Pod', 'Deployment', etc.
  resource: K8sObject
}

// Shell output
{
  type: 'shell:output',
  data: string          // stdout/stderr
}

// Shell input
{
  type: 'shell:input',
  data: string          // keypresses, etc.
}
```

## Build & Deployment

### Development
```
# Frontend
cd client
npm install
npm run dev  # Vite dev server

# Backend
cd server
go run cmd/server/main.go
```

### Production
```
# Backend
cd server
go build -o krates-server
./krates-server --config config.yaml

# Frontend
cd client
npm run build
# Serve static files with nginx or similar
```

### Docker
```dockerfile
# Backend Dockerfile
FROM golang:1.21-alpine
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN go build -o /krates ./cmd/server
CMD ["/krates"]

# Frontend Dockerfile
FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .
RUN npm run build
CMD ["npm", "start"]
```

## Performance Optimization

### Frontend
1. **Virtualization**: Don't render off-screen krates if world is large
2. **Debounce**: 16ms debouncing on all frequent events
3. **Web Workers**: Fuzzy search in worker for large datasets
4. **Memoization**: Reuse expensive calculations (transforms, layouts)
5. **CSS optimization**: Use transforms, avoid layout thrashing

### Backend
1. **Caching**: Cache static resource lists (with watch for updates)
2. **Connection pooling**: Reuse k8s API connections
3. **Rate limiting**: Per-user limits on WebSocket connections
4. **Compression**: WebSocket message compression
5. **Batching**: Batch resource updates when possible

## Testing Strategy

### Unit Tests
- Fuzzy search algorithm
- Coordinate transformations
- CRDT conflict resolution
- WebSocket message formatting

### Integration Tests
- Kubernetes API integration
- WebSocket connection lifecycle
- Multi-user presence sync

### E2E Tests
- User flows: search → spotlight → krate creation
- Multi-user: user A creates krate, user B sees it
- Drag/drop and resize interactions

## Security Checklist

### Authentication
- [ ] JWT or session-based auth on all WebSocket connections
- [ ] Token validation on every message
- [ ] Expire inactive sessions

### Authorization
- [ ] Namespace-level RBAC enforcement
- [ ] Block access to unauthorized resources
- [ ] Audit logging

### Data Protection
- [ ] Never log sensitive data (especially decoded secrets)
- [ ] Sanitize user inputs
- [ ] Escape HTML in text display
- [ ] CSP headers on frontend

### Network
- [ ] TLS/HTTPS for all connections
- [ ] WSS for WebSocket connections
- [ ] Origin validation on WebSocket upgrade

## Future Enhancements (Backlog)

### Already Identified
- Tile layout presets (logs hero, split, grid)
- Port-forwarding window
- Events window
- Diff view (compare YAMLs)
- Multi-cluster support

### Additional Ideas
- Keyboard shortcuts customization
- Workspace presets (save/restore layouts)
- Annotations/markers on canvas
- Shared annotations (multi-user notes)
- History/undo stack
- Keyboard macro recording
- Export workspace (screenshots, layouts)