satellite-provider/_docs/02_document/system-flows.md

# Satellite Provider — System Flows

## Flow Inventory

| # | Flow Name | Trigger | Primary Components | Criticality |
|---|-----------|---------|-------------------|-------------|
| F1 | Single Tile Download | HTTP GET /api/satellite/tiles/latlon | WebApi, TileDownloader, DataAccess | High |
| F2 | Region Request | HTTP POST /api/satellite/request | WebApi, RegionProcessing, TileDownloader, DataAccess | High |
| F3 | Region Processing | Queue dequeue (background) | RegionProcessing, TileDownloader, DataAccess | High |
| F4 | Route Creation | HTTP POST /api/satellite/route | WebApi, RouteManagement, DataAccess | High |
| F5 | Route Map Processing | Queue dequeue (background) | RouteManagement, RegionProcessing, TileDownloader, DataAccess | Medium |
| F6 | Status Query | HTTP GET /api/satellite/region/{id} or /route/{id} | WebApi, DataAccess | Low |
| F7 | Leaflet Tile Serving | HTTP GET /tiles/{z}/{x}/{y} | WebApi, TileService, DataAccess, FileSystem | High |
| F8 | Tile Inventory Bulk Lookup | HTTP POST /api/satellite/tiles/inventory | WebApi, TileService, DataAccess | High |

## Flow Dependencies

| Flow | Depends On | Shares Data With |
|------|-----------|-----------------|
| F1 | — | F3 (tile cache) |
| F2 | — | F3 (triggers it) |
| F3 | F2 enqueues work | F1 (shares tile cache), F5 |
| F4 | — | F5 (triggers it) |
| F5 | F4 must create route first | F3 (submits region requests) |
| F6 | F2/F4 must exist | — |
| F7 | F1 or F3 must have populated the tile (else 404) | F1, F3, F8 (shares `tiles.location_hash`) |
| F8 | — | F1, F3, F7 (shares `tiles.location_hash`) |

---

## Flow F1: Single Tile Download

### Description

Client requests a single satellite tile by geographic coordinates and zoom level. The service checks the cache (DB), downloads from Google Maps if not cached, stores it, and returns metadata.

### Preconditions

- Valid latitude, longitude, and zoom level provided
- Google Maps session token configured

### Sequence Diagram

```mermaid
sequenceDiagram
    participant Client
    participant WebApi
    participant TileService
    participant TileRepo
    participant GoogleMaps
    participant FileSystem

    Client->>WebApi: GET /api/satellite/tiles/latlon?lat&lon&zoom
    WebApi->>TileService: DownloadTileAsync(lat, lon, zoom)
    TileService->>TileRepo: FindByCoordinates(lat, lon, zoom)
    alt Tile exists in cache
        TileRepo-->>TileService: TileEntity
        TileService-->>WebApi: TileMetadata (cached)
    else Not cached
        TileService->>GoogleMaps: Download tile image
        GoogleMaps-->>TileService: JPEG bytes
        TileService->>FileSystem: Save to ./tiles/{zoom}/{x}/{y}.jpg
        TileService->>TileRepo: Insert(TileEntity)
        TileService-->>WebApi: TileMetadata (new)
    end
    WebApi-->>Client: JSON response
```

### Error Scenarios

| Error | Where | Detection | Recovery |
|-------|-------|-----------|----------|
| Google Maps timeout | Download step | HttpClient timeout | Return error to caller |
| Duplicate download race | Concurrent requests | ConcurrentDictionary check | Await existing download |
| Disk full | File save | IOException | Exception propagated, region fails |

---

## Flow F2: Region Request

### Description

Client submits a region definition (center point, size, zoom). The request is persisted and queued for asynchronous processing.

### Preconditions

- Valid region parameters (lat, lon, size_meters, zoom_level)

### Sequence Diagram

```mermaid
sequenceDiagram
    participant Client
    participant WebApi
    participant RegionService
    participant RegionRepo
    participant Queue

    Client->>WebApi: POST /api/satellite/request {lat, lon, size, zoom}
    WebApi->>RegionService: CreateRegionRequest(dto)
    RegionService->>RegionRepo: Insert(RegionEntity status=pending)
    RegionRepo-->>RegionService: region_id
    RegionService->>Queue: Enqueue(region_id)
    RegionService-->>WebApi: region_id
    WebApi-->>Client: 200 OK {region_id}
```

### Error Scenarios

| Error | Where | Detection | Recovery |
|-------|-------|-----------|----------|
| Queue full | Enqueue step | Channel at capacity | Return 503 / reject request |
| DB insert failure | Persist step | Exception | Return 500 |

---

## Flow F3: Region Processing (Background)

### Description

Background service dequeues region IDs, calculates tile grid, downloads all tiles (with concurrency control), optionally stitches them, and produces output files (CSV, summary, stitched image).

### Preconditions

- Region exists in DB with status "pending"
- Google Maps session token configured

### Sequence Diagram

```mermaid
sequenceDiagram
    participant Queue
    participant RegionProcessor
    participant RegionService
    participant TileService
    participant GoogleMaps
    participant RegionRepo
    participant FileSystem

    Queue->>RegionProcessor: Dequeue region_id
    RegionProcessor->>RegionRepo: GetById(region_id)
    RegionProcessor->>RegionRepo: UpdateStatus(processing)
    loop For each tile in grid
        RegionProcessor->>TileService: DownloadTileAsync(lat, lon, zoom)
        TileService->>GoogleMaps: Download (if not cached)
    end
    RegionProcessor->>FileSystem: Write CSV (tile manifest)
    RegionProcessor->>FileSystem: Write summary file
    opt stitch_tiles = true
        RegionProcessor->>FileSystem: Stitch tiles into composite image
    end
    RegionProcessor->>RegionRepo: UpdateStatus(completed, file paths)
```

### Data Flow

| Step | From | To | Data | Format |
|------|------|----|------|--------|
| 1 | Queue | RegionProcessor | region_id | int |
| 2 | RegionProcessor | TileService | lat, lon, zoom per tile | method call |
| 3 | TileService | FileSystem | JPEG image | file |
| 4 | RegionProcessor | FileSystem | tile manifest | CSV |
| 5 | RegionProcessor | FileSystem | region summary | TXT |
| 6 | RegionProcessor | FileSystem | composite image | JPEG |

### Error Scenarios

| Error | Where | Detection | Recovery |
|-------|-------|-----------|----------|
| Tile download failure | Per-tile loop | Exception from TileService | Log, continue with remaining tiles |
| All tiles fail | After loop | Zero tiles downloaded | Mark region as "failed" |
| Stitch failure | Image processing | ImageSharp exception | Mark region failed, tiles still available |

---

## Flow F4: Route Creation

### Description

Client submits a route (ordered waypoints + optional geofence polygons). The service interpolates intermediate points every ~200m and persists the full point set.

### Preconditions

- At least 2 waypoints provided
- Valid geofence polygons (if provided)

### Sequence Diagram

```mermaid
sequenceDiagram
    participant Client
    participant WebApi
    participant RouteService
    participant RouteRepo
    participant GeoUtils

    Client->>WebApi: POST /api/satellite/route {points, geofences, options}
    WebApi->>RouteService: CreateRoute(request)
    RouteService->>GeoUtils: Interpolate points between waypoints
    GeoUtils-->>RouteService: All points (original + intermediate)
    RouteService->>RouteRepo: InsertRoute(RouteEntity)
    RouteService->>RouteRepo: InsertPoints(RoutePointEntities)
    RouteService-->>WebApi: RouteResponse
    WebApi-->>Client: 200 OK {route_id, total_points, total_distance}
```

### Error Scenarios

| Error | Where | Detection | Recovery |
|-------|-------|-----------|----------|
| Invalid points (< 2) | Validation | Count check | Return 400 |
| DB insert failure | Persist step | Exception | Return 500 |

---

## Flow F5: Route Map Processing (Background)

### Description

When a route requests map tiles (`request_maps = true`), a background service creates region requests for each route point, optionally filtered by geofence, then waits for all regions to complete and produces a ZIP archive.

### Preconditions

- Route exists with `request_maps = true`
- Route points already interpolated and persisted

### Sequence Diagram

```mermaid
sequenceDiagram
    participant RouteProcessor
    participant RouteRepo
    participant RegionService
    participant Queue
    participant RegionProcessor
    participant FileSystem

    RouteProcessor->>RouteRepo: GetRouteWithPoints(route_id)
    loop For each route point
        RouteProcessor->>RouteProcessor: Check geofence (point-in-polygon)
        opt Point inside geofence (or no geofence)
            RouteProcessor->>RegionService: CreateRegionRequest(point)
            RegionService->>Queue: Enqueue(region_id)
        end
    end
    RouteProcessor->>RouteProcessor: Wait for all regions to complete
    opt create_tiles_zip = true
        RouteProcessor->>FileSystem: Create ZIP of all tiles (max 50MB)
        RouteProcessor->>RouteRepo: Update tiles_zip_path
    end
```

### Error Scenarios

| Error | Where | Detection | Recovery |
|-------|-------|-----------|----------|
| Region processing timeout | Wait loop | Polling timeout | Mark route partially complete |
| ZIP exceeds 50MB | ZIP creation | Size check during write | Truncate or skip |
| Geofence calculation error | Point-in-polygon | Exception | Include point (fail-open) |

---

## Flow F6: Status Query

### Description

Client polls for the status of a region or route by ID. Returns current processing state and output file paths when complete.

### Sequence Diagram

```mermaid
sequenceDiagram
    participant Client
    participant WebApi
    participant DataAccess

    Client->>WebApi: GET /api/satellite/region/{id}
    WebApi->>DataAccess: GetRegionById(id)
    DataAccess-->>WebApi: RegionEntity (status, file paths)
    WebApi-->>Client: JSON {status, files}
```

---

## Flow F7: Leaflet Tile Serving (added AZ-310, rewired AZ-505)

### Description

Leaflet (or any HTTP/2-capable client) requests a single tile body by slippy `(z, x, y)`. The handler resolves the most-recent variant across sources/flights by `location_hash` and streams the JPEG body back. AZ-505 rewired the lookup predicate from `(tile_zoom, tile_x, tile_y)` to `location_hash = Uuidv5(TileNamespace, "{z}/{x}/{y}")` so the read hits the `tiles_leaflet_path` covering index as an `Index Only Scan`; the selection rule (`captured_at DESC, updated_at DESC, id DESC LIMIT 1`) is unchanged from AZ-484 / AZ-503-foundation. Kestrel runs `Http1AndHttp2` over TLS (`https://+:8080` in dev) so ALPN multiplexes many concurrent leaflet requests on a single TLS connection.

### Sequence Diagram

```mermaid
sequenceDiagram
    participant Client
    participant Kestrel
    participant ServeTile
    participant TileService
    participant TileRepo
    participant FileSystem

    Client->>Kestrel: GET /tiles/{z}/{x}/{y} (HTTP/2 via TLS+ALPN)
    Kestrel->>ServeTile: route match
    ServeTile->>TileService: GetOrDownloadTileAsync(z, x, y)
    TileService->>TileRepo: GetByTileCoordinatesAsync(z, x, y)
    Note over TileRepo: WHERE location_hash = $1<br/>ORDER BY captured_at DESC, updated_at DESC, id DESC<br/>LIMIT 1<br/>Index Only Scan: tiles_leaflet_path
    alt Cached
        TileRepo-->>TileService: TileEntity
        TileService->>FileSystem: read file_path
        FileSystem-->>TileService: JPEG bytes
        TileService-->>ServeTile: TileBytes (file_path, ETag, Cache-Control)
        ServeTile-->>Client: 200 OK, JPEG body
    else Miss
        TileService->>TileService: download via GoogleMapsDownloaderV2
        Note over TileService: persists row + on-disk path, falls through to ServeTile
        TileService-->>ServeTile: TileBytes
        ServeTile-->>Client: 200 OK, JPEG body
    end
```

### Error Handling

| Failure | Detection | Handling |
|---------|-----------|----------|
| Tile not present and downloader rejects (404 from Google Maps) | `TileService.GetOrDownloadTileAsync` propagates the downloader's `HttpRequestException` | Returns 500; `ServeTile` does NOT translate this to 404 because the predicate matched (path-traversal cases below 404 earlier in routing) |
| Path traversal in `/tiles/...` segment | ASP.NET Core route binding | `400`/`404` before the handler runs (covered by SEC-02) |

---

## Flow F8: Tile Inventory Bulk Lookup (added AZ-505)

### Description

Programmatic clients (httpx `http2=True`, .NET `HttpClient`, onboard cross-repo callers) post a batch of up to 5000 `(z, x, y)` triples (Form A) or up to 5000 pre-computed `location_hash` UUIDs (Form B) and get one inventory entry per input slot, in the same order. Each entry says whether the cell is present and — when present — the most-recent row's `id`, `capturedAt`, `source`, `flightId`, and `resolutionMPerPx`. No tile bodies are returned; the caller subsequently fetches bodies via F7. This is the read-half of the bulk-list contract that the onboard `gps-denied-onboard` workspace consumes to decide which Google-Maps cells it needs and which UAV variants are already on the server.

### Sequence Diagram

```mermaid
sequenceDiagram
    participant Client
    participant Kestrel
    participant GetTilesInventory
    participant TileService
    participant TileRepo

    Client->>Kestrel: POST /api/satellite/tiles/inventory (JWT, Form A or B)
    Kestrel->>GetTilesInventory: route match
    GetTilesInventory->>GetTilesInventory: XOR check (both/neither populated → 400)
    GetTilesInventory->>GetTilesInventory: cap check (count > 5000 → 400)
    GetTilesInventory->>TileService: GetInventoryAsync(request)
    Note over TileService: Form A: compute location_hash per coord<br/>via Uuidv5.LocationHashForTile<br/>Form B: echo caller-supplied hashes
    TileService->>TileRepo: GetTilesByLocationHashesAsync(hashes)
    Note over TileRepo: NpgsqlCommand:<br/>SELECT DISTINCT ON (location_hash) ...<br/>WHERE location_hash = ANY($1::uuid[])<br/>ORDER BY location_hash, captured_at DESC, updated_at DESC, id DESC<br/>(bypasses Dapper IEnumerable expansion)
    TileRepo-->>TileService: IReadOnlyDictionary<Guid, TileEntity>
    TileService->>TileService: shape into TileInventoryEntry[] in request order
    TileService-->>GetTilesInventory: TileInventoryResponse
    GetTilesInventory-->>Client: 200 OK, JSON (results in input order)
```

### Validation Surface

| Input | Detection | Response |
|-------|-----------|----------|
| Both `tiles` and `locationHashes` populated | Handler XOR check | 400 + ProblemDetails (`tile-inventory.md` Inv-1) |
| Neither populated | Handler XOR check | 400 + ProblemDetails |
| `count > 5000` (`TileInventoryLimits.MaxEntriesPerRequest`) | Handler cap check | 400 + ProblemDetails (Inv-7) |
| No `Authorization: Bearer …` header | `.RequireAuthorization()` | 401 before handler runs |

### Performance

p95 ≤ 1000 ms for 2500-coord batches (AZ-505 AC-4). Cycle-6 measured: p95=66ms — well under budget. The covering index (`tiles_leaflet_path`) supplies the leading `location_hash` lookup; the projection's columns beyond the INCLUDE list (`id`, `captured_at`, `flight_id`, ...) trigger a bounded heap fetch which is documented and accepted per the AZ-505 NFR.