feat: add onExport handler so hosts can save GeoJSON exports (#5)

* feat: add onExport handler so hosts can save GeoJSON exports

The layer export button downloads GeoJSON via an anchor element, which
works in browsers but not in desktop webviews (e.g. Tauri) that have no
download manager, so the button appears to do nothing there.

Add an optional `onExport(filename, data)` control option. When set, the
control delegates the export to it instead of triggering the browser
download, letting a host application save the file with its own dialog.
Default behavior (browser download) is unchanged when no handler is set.

* Address CodeRabbit review feedback

- Guard the host onExport callback in exportLayer with try/catch: a throwing
  host handler no longer breaks the click path. On failure we surface a notice,
  set the error state, and return null so UI feedback stays consistent.

Author: giswqs

geolibre-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "id": "maplibre-gl-overture-maps",
   "name": "MapLibre GL Overture Maps",
-  "version": "0.2.0",
+  "version": "0.3.0",
   "entry": "dist/index.js",
   "description": "Visualize Overture Maps PMTiles themes with a MapLibre control.",
   "style": "dist/style.css"

package.json

@@ -1,6 +1,6 @@
 {
   "name": "maplibre-gl-overture-maps",
-  "version": "0.2.0",
+  "version": "0.3.0",
   "description": "A MapLibre GL JS plugin for visualizing Overture Maps PMTiles themes",
   "type": "module",
   "main": "./dist/index.cjs",

src/geolibre.ts

@@ -82,7 +82,7 @@ function isOvertureMapsState(
 export const plugin: GeoLibrePlugin = {
   id: "maplibre-gl-overture-maps",
   name: "MapLibre GL Overture Maps",
-  version: "0.2.0",
+  version: "0.3.0",
   activate(app) {
     control = control ?? createControl();
     const added = app.addMapControl(control, position);

src/lib/core/OvertureMapsControl.ts

@@ -37,9 +37,15 @@ import { ensurePmtilesProtocol } from './pmtilesProtocol';
  * Default options for the OvertureMapsControl
  */
 const DEFAULT_OPTIONS: Required<
-  Omit<OvertureMapsControlOptions, 'release' | 'themeColors' | 'themeOpacity'>
+  Omit<
+    OvertureMapsControlOptions,
+    'release' | 'themeColors' | 'themeOpacity' | 'onExport'
+  >
 > &
-  Pick<OvertureMapsControlOptions, 'release' | 'themeColors' | 'themeOpacity'> = {
+  Pick<
+    OvertureMapsControlOptions,
+    'release' | 'themeColors' | 'themeOpacity' | 'onExport'
+  > = {
   collapsed: true,
   position: 'top-right',
   title: 'Overture Maps',
@@ -54,6 +60,7 @@ const DEFAULT_OPTIONS: Required<
   visibleThemes: ['buildings', 'transportation', 'places'],
   themeColors: undefined,
   themeOpacity: undefined,
+  onExport: undefined,
 };
 
 const DEFAULT_OPACITY = 0.8;
@@ -700,7 +707,23 @@ export class OvertureMapsControl implements IControl {
       return null;
     }
 
-    this._downloadGeoJSON(`overture-${theme}-${sourceLayer}.geojson`, collection);
+    const filename = `overture-${theme}-${sourceLayer}.geojson`;
+    if (this._options.onExport) {
+      // Let the host save the file (e.g. a native dialog in a desktop webview
+      // where anchor-based downloads do not work). Guard against a host
+      // handler throwing so the click path stays consistent.
+      try {
+        this._options.onExport(filename, collection);
+      } catch (error) {
+        this._notify(`Failed to export ${label}.`);
+        this._setError(
+          `Export failed (${error instanceof Error ? error.message : 'unknown error'}).`
+        );
+        return null;
+      }
+    } else {
+      this._downloadGeoJSON(filename, collection);
+    }
     const count = collection.features.length;
     this._notify(`Exported ${count} ${label} feature${count === 1 ? '' : 's'}.`);
     return collection;

src/lib/core/types.ts

@@ -1,3 +1,4 @@
+import type { FeatureCollection } from 'geojson';
 import type { Map } from 'maplibre-gl';
 import type { OvertureTheme } from './themes';
 
@@ -96,6 +97,17 @@ export interface OvertureMapsControlOptions {
    * @default 0.8 for every theme
    */
   themeOpacity?: Partial<Record<OvertureTheme, number>>;
+
+  /**
+   * Custom handler for exporting a layer to GeoJSON. When provided, it is
+   * called instead of the built-in browser download, letting a host
+   * application save the file its own way (e.g. a native save dialog in a
+   * desktop webview where anchor downloads do not work).
+   *
+   * @param filename - The suggested file name (e.g. `overture-buildings-building.geojson`)
+   * @param data - The exported FeatureCollection
+   */
+  onExport?: (filename: string, data: FeatureCollection) => void;
 }
 
 /**