Support outcode & gps search

server-rs/src/routes/postcodes.rs

@@ -28,6 +28,12 @@ pub struct PostcodesResponse {
     features: Vec<Map<String, Value>>,
 }
 
+#[derive(Deserialize)]
+pub struct NearestPostcodeParams {
+    lat: f64,
+    lng: f64,
+}
+
 #[derive(Deserialize)]
 pub struct PostcodeParams {
     bounds: Option<String>,
@@ -311,6 +317,45 @@ pub async fn get_postcodes(
     Ok(Json(response))
 }
 
+/// Find the nearest postcode to a given lat/lng coordinate.
+pub async fn get_nearest_postcode(
+    State(shared): State<Arc<SharedState>>,
+    Query(params): Query<NearestPostcodeParams>,
+) -> Result<Json<Value>, StatusCode> {
+    let state = shared.load_state();
+    let postcode_data = &state.postcode_data;
+
+    let query_lat = params.lat as f32;
+    let query_lng = params.lng as f32;
+    let cos_lat = (query_lat as f64).to_radians().cos() as f32;
+
+    let mut best_idx: Option<usize> = None;
+    let mut best_dist_sq = f32::MAX;
+
+    for (idx, &(pc_lat, pc_lon)) in postcode_data.centroids.iter().enumerate() {
+        let dlat = pc_lat - query_lat;
+        let dlon = (pc_lon - query_lng) * cos_lat;
+        let dist_sq = dlat * dlat + dlon * dlon;
+        if dist_sq < best_dist_sq {
+            best_dist_sq = dist_sq;
+            best_idx = Some(idx);
+        }
+    }
+
+    let idx = best_idx.ok_or(StatusCode::NOT_FOUND)?;
+    let (lat, lon) = postcode_data.centroids[idx];
+    let geometry = postcode_data.geometries[idx].clone();
+    let postcode = &postcode_data.postcodes[idx];
+
+    info!(postcode = %postcode, "GET /api/nearest-postcode");
+    Ok(Json(serde_json::json!({
+        "postcode": postcode,
+        "latitude": lat as f64,
+        "longitude": lon as f64,
+        "geometry": geometry,
+    })))
+}
+
 /// Look up a single postcode and return its centroid coordinates and geometry.
 pub async fn get_postcode_lookup(
     State(shared): State<Arc<SharedState>>,