# Frontend Component Architecture

Overview of GeoQuery's React components and their interactions.

---

## Component Hierarchy

```
App (Next.js Layout)
└── Main Page
    ├── ChatPanel
    │   ├── MessageList
    │   ├── InputForm
    │   └── CitationLinks
    ├── MapViewer
    │   ├── LeafletMap
    │   ├── LayerControl
    │   │   ├── SortableLayerItem (draggable)
    │   │   └── LayerSettings
    │   └── EmptyState
    └── DataExplorer
        ├── ResultsTable
        └── ExportButton
```

---

## Core Components

### ChatPanel (`components/ChatPanel.tsx`)

Main conversational interface with streaming support.

**Props**:
```typescript
interface ChatPanelProps {
  onLayerAdd: (layer: MapLayer) => void;
}
```

**State**:
```typescript
const [messages, setMessages] = useState<Message[]>([]);
const [isLoading, setIsLoading] = useState(false);
const [currentThought, setCurrentThought] = useState<string>('');
```

**Key Features**:
- SSE (Server-Sent Events) for streaming
- Real-time thought process display
- Markdown rendering
- Citation link generation
- Layer reference chips

**SSE Implementation**:
```typescript
const response = await fetch('/api/chat', {
  method: 'POST',
  headers: {'Content-Type': 'application/json'},
  body: JSON.stringify({message, history})
});

const reader = response.body.getReader();
const decoder = new TextDecoder();

while (true) {
  const {value, done} = await reader.read();
  if (done) break;
  
  const chunk = decoder.decode(value);
  // Process SSE events...
}
```

**Event Handling**:
- `status`: Updates loading status
- `intent`: Shows detected intent
- `chunk`: Streams text incrementally
- `result`: Adds map layer and displays data

---

### MapViewer (`components/MapViewer.tsx`)

Interactive Leaflet map with layer management.

**Props**:
```typescript
interface MapViewerProps {
  layers: MapLayer[];
  onLayerUpdate: (id: string, updates: Partial<MapLayer>) => void;
  onLayerRemove: (id: string) => void;
  onLayerReorder: (fromIndex: number, toIndex: number) => void;
}
```

**Layer Model**:
```typescript
interface MapLayer {
  id: string;
  name: string;
  data: GeoJSON.FeatureCollection;
  visible: boolean;
  style: {
    color: string;
    fillColor: string;
    fillOpacity: number;
    weight: number;
  };
  choropleth?: {
    enabled: boolean;
    column: string;
    palette: string;
    scale: 'linear' | 'log';
    min?: number;
    max?: number;
  };
  pointMarker?: {
    icon: string;
    style: 'icon' | 'circle';
    color: string;
    size: number;
  };
}
```

**Key Features:**
- Layer visibility toggle
- Style customization (color, opacity, weight)
- Drag-and-drop layer reordering
- Auto-fit bounds to new layers
- Choropleth visualization
- Point rendering modes (icon vs circle)

**Point Rendering Logic**:
```typescript
const pointToLayer = (feature: any, latlng: L.LatLng) => {
  if (layer.pointMarker?.style === "circle") {
    // Simple circle for large datasets
    return L.circleMarker(latlng, {
      radius: 5,
      fillColor: layer.pointMarker.color,
      color: '#ffffff',
      weight: 2,
      opacity: 1,
      fillOpacity: 0.7
    });
  }
  
  // Emoji icon for POI
  return L.marker(latlng, {
    icon: L.divIcon({
      html: `<div style="font-size: 32px">${layer.pointMarker.icon}</div>`,
      className: 'custom-emoji-marker',
      iconSize: [32, 32]
    })
  });
};
```

**Choropleth Implementation**:
```typescript
// Calculate color based on value
const fillColor = getChoroplethColor(
  feature.properties[choropleth.column],
  choropleth.min,
  choropleth.max,
  choropleth.palette,
  choropleth.scale
);
```

---

### DataExplorer (`components/DataExplorer.tsx`)

Tabular data view with export capabilities.

**Props**:
```typescript
interface DataExplorerProps {
  data: any[];
  visible: boolean;
}
```

**Features**:
- Responsive table
- Column sorting
- CSV export
- Pagination for large datasets

---

## Sub-Components

### SortableLayerItem

Draggable layer control item using `@dnd-kit`.

**Features**:
- Drag handle with visual feedback
- Layer visibility toggle
- Settings expansion
- Style controls (color pickers, sliders)
- Remove layer button

**Drag-and-Drop**:
```typescript
const {
  attributes,
  listeners,
  setNodeRef,
  transform,
  transition
} = useSortable({ id: layer.id });

const style = {
  transform: CSS.Transform.toString(transform),
  transition
};
```

### AutoFitBounds

Utility component that auto-zooms map to new layers.

```typescript
function AutoFitBounds({ layers }: { layers: MapLayer[] }) {
  const map = useMap();
  
  useEffect(() => {
    if (layers.length > prevLayersLength.current) {
      const latestLayer = layers[layers.length - 1];
      const bounds = L.geoJSON(latestLayer.data).getBounds();
      if (bounds.isValid()) {
        map.fitBounds(bounds, { padding: [50, 50] });
      }
    }
  }, [layers]);
  
  return null;
}
```

---

## State Management

### Global State (Main Page)

```typescript
const [layers, setLayers] = useState<MapLayer[]>([]);

const handleLayerAdd = (geojson: GeoJSON.FeatureCollection) => {
  const newLayer: MapLayer = {
    id: geojson.properties.layer_id,
    name: geojson.properties.layer_name,
    data: geojson,
    visible: true,
    style: geojson.properties.style,
    choropleth: geojson.properties.choropleth,
    pointMarker: geojson.properties.pointMarker
  };
  
  setLayers(prev => [...prev, newLayer]);
};
```

### Layer Updates

```typescript
const handleLayerUpdate = (id: string, updates: Partial<MapLayer>) => {
  setLayers(prev => prev.map(layer =>
    layer.id === id ? { ...layer, ...updates } : layer
  ));
};
```

---

## Styling & Theming

### Global Styles (`app/globals.css`)

- Tailwind CSS for utility-first styling
- Custom CSS variables for theming
- Leaflet overrides for custom markers

### Color Palettes

```typescript
const COLOR_PALETTES = {
  viridis: ['#440154', '#482878', ... '#fde725'],
  blues: ['#f7fbff', ... '#08306b'],
  reds: ['#fff5f0', ... '#67000d']
};
```

---

## Performance Optimizations

### React Optimizations

1. **Memoization**:
   ```typescript
   const MemoizedGeoJSON = React.memo(GeoJSON);
   ```

2. **Key Management**:
   ```typescript
   key={layer.id + JSON.stringify(layer.style)}
   ```

3. **Lazy Loading**:
   - Components loaded on-demand
   - Map tiles loaded progressively

### Leaflet Optimizations

1. **Circle Markers for Large Datasets**:
   - Use `L.circleMarker` instead of `L.divIcon` for >500 points
   - Significantly faster rendering

2. **Layer Virtualization**:
   - Only render visible layers
   - Remove offscreen features

---

## Responsive Design

### Breakpoints

- **Mobile** (<640px): Stacked layout
- **Tablet** (640-1024px): Sidebar collapses
- **Desktop** (>1024px): Full sidebar

### Mobile Adaptations

- Layer legend becomes bottom sheet
- Map controls repositioned
- Touch-friendly drag handles

---

## Accessibility

- **Keyboard Navigation**: Tab through controls
- **Screen Readers**: ARIA labels on interactive elements
- **Color Contrast**: WCAG AA compliant
- **Focus Indicators**: Visible focus states

---

## Icons & Assets

- **Lucide React**: Icon library for UI elements
- **Leaflet Markers**: Default and custom markers
- **Emoji Icons**: Unicode emojis for POI markers

---

## Next Steps

- **Backend Services**: [../backend/CORE_SERVICES.md](../backend/CORE_SERVICES.md)
- **API Reference**: [../backend/API_ENDPOINTS.md](../backend/API_ENDPOINTS.md)
- **Data Flow**: [../DATA_FLOW.md](../DATA_FLOW.md)