# Data Flow: End-to-End Request Processing

This document provides a detailed walkthrough of how a user query flows through the GeoQuery system from input to visualization.

---

## Overview

```
User Query → Intent Detection → Semantic Search → SQL Generation → 
Query Execution → Result Formatting → Explanation → Map Rendering
```

**Timeline**: 2-8 seconds for typical queries

---

## Step-by-Step Walkthrough

### Example Query

**User Input**: *"Show me hospitals in Panama City"*

---

### Step 1: Frontend - User Submits Query

**Component**: `ChatPanel.tsx`

```typescript
const handleSubmit = async (message: string) => {
  // Add user message to chat
  setMessages(prev => [...prev, { role: 'user', content: message }]);
  
  // Send to backend via SSE
  const response = await fetch('http://localhost:8000/api/chat', {
    method: 'POST',
    headers: {'Content-Type': 'application/json'},
    body: JSON.stringify({ message, history })
  });
  
  // Start streaming response
  const reader = response.body.getReader();
  ...
};
```

**Request Payload**:
```json
{
  "message": "Show me hospitals in Panama City",
  "history": []
}
```

---

### Step 2: Backend - API Endpoint Receives Request

**File**: `backend/api/endpoints/chat.py`

```python
@router.post("/chat")
async def chat(request: ChatRequest):
    # Initialize executor
    executor = QueryExecutor()
    
    # Process query with streaming
    async for event in executor.process_query_stream(
        request.message, 
        request.history
    ):
        yield sse_format(event)
```

**Action**: Routes to `QueryExecutor.process_query_stream()`

---

### Step 3: Intent Detection

**Service**: `LLMGateway.detect_intent()`  
**File**: `backend/core/llm_gateway.py`

**LLM Prompt**:
```
Analyze this user query and determine the best output type.

User Query: "Show me hospitals in Panama City"

THINK STEP BY STEP:
1. What is the user asking for?
2. Does this require geographic visualization (map)?
...

Respond with ONLY ONE of these exact words:
- GENERAL_CHAT
- DATA_QUERY
- MAP_REQUEST
- SPATIAL_OP
- STAT_QUERY
```

**Gemini Response**:
```
Thinking: The user wants to SEE hospitals on a map, explicitly asks to "show"
Response: MAP_REQUEST
```

**Streaming to Frontend**:
```json
{
  "event": "intent",
  "data": {"intent": "MAP_REQUEST"}
}
```

**Frontend**: Displays intent badge in chat

---

### Step 4: Semantic Discovery

**Service**: `SemanticSearch.search_table_names()`  
**File**: `backend/core/semantic_search.py`

**Process**:
1. Convert query to embedding vector (384 dimensions)
   ```python
   query_embedding = model.encode("Show me hospitals in Panama City")
   ```

2. Calculate cosine similarity with all dataset embeddings
   ```python
   similarities = cosine_similarity(query_embedding, catalog_embeddings)
   ```

3. Return top-k matches
   ```python
   top_k_indices = np.argsort(similarities)[-15:][::-1]
   ```

**Result**:
```python
[
  "panama_healthsites_geojson",  # similarity: 0.89
  "osm_amenities",                # similarity: 0.76
  "panama_hospitals",             # similarity: 0.74
  "osm_healthcare",               # similarity: 0.71
  ...
]
```

**Streaming to Frontend**:
```json
{
  "event": "status",
  "data": {"status": "📚 Searching data catalog..."}
}
```

**Performance**: <10ms for 100+ datasets

---

### Step 5: Table Schema Retrieval

**Service**: `GeoEngine.ensure_table_loaded()`  
**File**: `backend/core/geo_engine.py`

**Process**:
1. Check if table already loaded in DuckDB
   ```python
   if "panama_healthsites_geojson" not in self.loaded_tables:
   ```

2. Load GeoJSON file
   ```python
   gdf = gpd.read_file("backend/data/osm/healthsites.geojson")
   ```

3. Register in DuckDB
   ```python
   conn.register("panama_healthsites_geojson", gdf)
   self.loaded_tables["panama_healthsites_geojson"] = gdf
   ```

**Schema Retrieved**:
```
Table: panama_healthsites_geojson
Columns: osm_id, name, amenity, operator, addr:city, geom
Row count: 986
Geometry type: Point
```

**Streaming to Frontend**:
```json
{
  "event": "status",
  "data": {"status": "💾 Loading tables: panama_healthsites_geojson..."}
}
```

---

### Step 6: SQL Generation

**Service**: `LLMGateway.generate_analytical_sql()`  
**File**: `backend/core/llm_gateway.py`

**Prompt to Gemini**:
```
You are a DuckDB SQL expert. Generate a valid DuckDB SQL query.

Table: panama_healthsites_geojson
Columns: osm_id, name, amenity, operator, addr:city, geom
Row count: 986

User Request: "Show me hospitals in Panama City"

Rules:
1. Return ONLY the SQL query
2. ALWAYS include 'geom' for map visualization
3. Use ILIKE for case-insensitive matching
4. Use ST_Intersects for spatial filtering
...

Generate SQL:
```

**Gemini Thinking** (streamed):
```
"I need to:
1. Filter for amenity='hospital'
2. Filter for Panama City (district name is 'Panamá')
3. Use spatial intersection with admin boundaries
4. Include geometry for map rendering"
```

**Gemini Response**:
```sql
SELECT 
  name, 
  amenity, 
  operator,
  geom 
FROM panama_healthsites_geojson 
WHERE amenity = 'hospital' 
  AND ST_Intersects(
    geom, 
    (SELECT geom FROM pan_admin2 WHERE adm2_name = 'Panamá')
  )
```

**Streaming to Frontend**:
```json
{
  "event": "chunk",
  "data": {"type": "thought", "content": "I need to filter for hospitals..."}
}
```

**Performance**: ~1 second for SQL generation

---

### Step 7: Query Execution

**Service**: `GeoEngine.execute_spatial_query()`  
**File**: `backend/core/geo_engine.py`

**Execution**:
```python
try:
    result = conn.execute(sql).fetchdf()
    geojson = json.loads(result.to_json())
except Exception as e:
    # Try SQL correction
    corrected_sql = await llm.correct_sql(query, sql, str(e), schema)
    result = conn.execute(corrected_sql).fetchdf()
```

**Result**:
```python
# GeoDataFrame with 45 rows
   name                      amenity   operator              geom
0  Hospital Santo Tomás      hospital  MINSA       POINT(...)
1  Hospital del Niño         hospital  CSS         POINT(...)
...
```

**Convert to GeoJSON**:
```json
{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {"type": "Point", "coordinates": [-79.5, 8.98]},
      "properties": {"name": "Hospital Santo Tomás", "amenity": "hospital"}
    },
    ...
  ]
}
```

**Streaming to Frontend**:
```json
{
  "event": "status",
  "data": {"status": "✅ Found 45 results"}
}
```

**Performance**: 100ms - 2s depending on data size

---

### Step 8: Result Formatting

**Service**: `ResponseFormatter.format_geojson_layer()`  
**File**: `backend/services/response_formatter.py`

**Layer Name Generation**:
```python
layer_info = await llm.generate_layer_name(query, sql)
# Returns: {"name": "Hospitals in Panama City", "emoji": "🏥", "pointStyle": "icon"}
```

**GeoJSON Enhancement**:
```python
geojson["properties"] = {
    "layer_id": "abc123",
    "layer_name": "Hospitals in Panama City",
    "style": {
        "color": "#E63946",
        "fillColor": "#E63946",
        "opacity": 0.8,
        "fillOpacity": 0.4
    },
    "pointMarker": {
        "icon": "🏥",
        "style": "icon",
        "color": "#E63946",
        "size": 32
    },
    "choropleth": {"enabled": false}
}
```

**Auto-Detection**:
- Detects geometry type (Point)
- Checks for numeric columns (none meaningful)
- Configures point marker style based on `pointStyle: "icon"`

---

### Step 9: Explanation Generation

**Service**: `LLMGateway.stream_explanation()`  
**File**: `backend/core/llm_gateway.py`

**Prompt to Gemini**:
```
Explain the results of this data query to the user.

User Question: "Show me hospitals in Panama City"
SQL Query: SELECT name, amenity, geom FROM ... WHERE amenity='hospital'...
Data Result Summary: Found 45 features (Points)

Instructions:
1. Keep response concise
2. Only describe ACTUAL data returned
3. Cite data source
4. Speak as GeoQuery
```

**Gemini Response** (streamed):
```
"I have located 45 hospitals within Panama City district.

The map displays each hospital as a 🏥 icon. You can click on any 
marker to see details including the hospital name and operator.

**Key facilities include**:
- Hospital Santo Tomás (MINSA)
- Hospital del Niño (CSS)
- Hospital Punta Pacifica (Private)

Source: Healthcare facility data from OpenStreetMap via Healthsites.io"
```

**Streaming to Frontend**:
```json
{
  "event": "chunk",
  "data": {"type": "text", "content": "I have located 45 hospitals..."}
}
```

**Performance**: ~1-2 seconds for explanation

---

### Step 10: Final Result Event

**Event Sent**:
```json
{
  "event": "result",
  "data": {
    "response": "I have located 45 hospitals within Panama City...",
    "sql_query": "SELECT name, amenity, geom FROM ...",
    "geojson": { /* GeoJSON with 45 features */ },
    "chart_data": null,
    "raw_data": [ /* 45 rows of data */ ],
    "data_citations": [
      "Healthcare facility data from OpenStreetMap via Healthsites.io"
    ]
  }
}
```

---

### Step 11: Frontend - Map Rendering

**Component**: `MapViewer.tsx`

**Process**:
1. Receive GeoJSON from result event
2. Create new MapLayer
   ```typescript
   const newLayer: MapLayer = {
     id: geojson.properties.layer_id,
     name: geojson.properties.layer_name,
     data: geojson,
     visible: true,
     style: geojson.properties.style,
     pointMarker: geojson.properties.pointMarker
   };
   ```

3. Render with Leaflet
   ```typescript
   <GeoJSON
     data={layer.data}
     pointToLayer={(feature, latlng) => {
       if (layer.pointMarker?.style === "icon") {
         return L.marker(latlng, {
           icon: L.divIcon({
             html: `<div style="font-size: 32px">${layer.pointMarker.icon}</div>`
           })
         });
       }
     }}
   />
   ```

4. Auto-fit bounds to show all hospitals
5. Display layer in legend panel

**Result**: Interactive map with 45 hospital markers (🏥 icons)

---

## Performance Breakdown

| Step | Service | Time | Async |
|------|---------|------|-------|
| 1. Frontend Submit | - | <10ms | - |
| 2. API Routing | FastAPI | <5ms | - |
| 3. Intent Detection | Gemini | ~500ms | ✓ |
| 4. Semantic Search | SentenceTransformer | <10ms | ✓ |
| 5. Schema Loading | DuckDB | 50-200ms | - |
| 6. SQL Generation | Gemini | ~1s | ✓ Streamed |
| 7. Query Execution | DuckDB | 100ms-2s | - |
| 8. Formatting | Python | 10-50ms | - |
| 9. Explanation | Gemini | ~1s | ✓ Streamed |
| 10. Frontend Render | Leaflet | 50-200ms | - |

**Total**: 2-5 seconds (perception: faster due to streaming)

---

## Error Handling Flow

### SQL Execution Failure

```
SQL Error → Extract Error Message → Send to LLM → Generate Corrected SQL → 
Retry Execution → If Still Fails → Return Error to User
```

**Example**:
```python
try:
    result = execute_query(sql)
except Exception as e:
    # Error: column "hospitals" does not exist
    corrected_sql = await llm.correct_sql(query, sql, str(e), schema)
    # LLM fixes: hospitals → panama_healthsites_geojson
    result = execute_query(corrected_sql)
```

### Data Unavailable

```
LLM Realizes Data Missing → Returns Special Marker → 
System Detects Marker → Returns Helpful Error Message
```

**Example**:
```sql
-- ERROR: DATA_UNAVAILABLE
-- Requested: crime statistics
-- Available: admin boundaries, hospitals, schools
```

---

## Streaming Architecture

**Benefits of SSE (Server-Sent Events)**:
1. **Progressive Disclosure**: User sees thinking process
2. **Faster Perceived Performance**: Content streams in
3. **Transparency**: Shows "why" behind answers
4. **Simple Protocol**: HTTP-based, works everywhere

**Event Types**:
- `status`: Processing updates ("🔍 Searching...", "⚡ Executing...")
- `intent`: Detected intent category
- `chunk`: Streamed content (thought or text)
- `result`: Final payload with all data

---

## Complex Query Flow

For queries requiring multiple steps (e.g., "Compare hospital density with school density by province"):

1. **Complexity Detection**: QueryPlanner identifies multi-dataset query
2. **Step Decomposition**: Break into atomic steps
   - Step 1: Count hospitals per province
   - Step 2: Count schools per province
   - Step 3: Calculate ratios
3. **Parallel Execution**: Execute independent steps concurrently
4. **Result Combination**: Merge results for final answer
5. **Unified Explanation**: LLM explains combined analysis

See `backend/core/query_planner.py` for implementation.

---

## Next Steps

- **Backend Services**: [backend/CORE_SERVICES.md](backend/CORE_SERVICES.md)
- **API Reference**: [backend/API_ENDPOINTS.md](backend/API_ENDPOINTS.md)
- **Frontend Components**: [frontend/COMPONENTS.md](frontend/COMPONENTS.md)