add fallback behavior for showOpenFilePicker and showSaveFilePicker (#967)

## Launch Checklist

<!-- Thanks for the PR! Feel free to add or remove items from the
checklist. -->


 - [x] Briefly describe the changes in this PR.
 - [x] Link to related issues.
- [x] Include before/after visuals or gifs if this PR includes visual
changes.
 - [ ] Write tests for all new functionality.
 - [x] Add an entry to `CHANGELOG.md` under the `## main` section.

## Description

`showOpenFilePicker` and `showSaveFilePicker` are undefined on Firefox.
With this pr, Maputnik uses the old behavior as a fallback. It keeps the
naming "open" and "save" instead of "upload" and "download" to underline
that the style stays within the browser and no actual upload happens.

@zstadler Could you give it a try, please?

## Related Issue

- fixes https://github.com/maplibre/maputnik/issues/966

## Visual Changes

The "Save as" button gets hidden if `showSaveFilePicker` is not
available since it would have no use.

<table>
<tr>
<td>
Chrome
</td>
<td>
Firefox
</td>
</tr>
<tr>
<td>
<img
src="https://github.com/user-attachments/assets/cdc2cd4d-1c09-4dec-8c94-f8b0dd0c5b8e"
/>
</td>
<td>
<img
src="https://github.com/user-attachments/assets/0763ef63-6501-4cc1-977b-94753c3008ae"
/>
</td>
</tr>
</table>

CHANGELOG.md

@@ -6,7 +6,7 @@
 - Add scheme type options for vector/raster tile
 - Add `tileSize` field for raster and raster-dem tile sources
 - Update Protomaps Light gallery style to v4
-- Add support to edit local files on the file system
+- Add support to edit local files on the file system if supported by the browser
 - _...Add new stuff here..._
 
 ### 🐞 Bug fixes

src/components/ModalExport.tsx

@@ -15,6 +15,7 @@ import fieldSpecAdditional from '../libs/field-spec-additional'
 
 
 const MAPLIBRE_GL_VERSION = version;
+const showSaveFilePickerAvailable = typeof window.showSaveFilePicker === "function";
 
 
 type ModalExportInternalProps = {
@@ -86,6 +87,15 @@ class ModalExportInternal extends React.Component<ModalExportInternalProps> {
   async saveStyle() {
     const tokenStyle = this.tokenizedStyle();
 
+    // it is not guaranteed that the File System Access API is available on all
+    // browsers. If the function is not available, a fallback behavior is used.
+    if (!showSaveFilePickerAvailable) {
+      const blob = new Blob([tokenStyle], {type: "application/json;charset=utf-8"});
+      const exportName = this.exportName();
+      saveAs(blob, exportName + ".json");
+      return;
+    }
+
     let fileHandle = this.props.fileHandle;
     if (fileHandle == null) {
       fileHandle = await this.createFileHandle();
@@ -179,22 +189,18 @@ class ModalExportInternal extends React.Component<ModalExportInternalProps> {
         </div>
 
         <div className="maputnik-modal-export-buttons">
-          <InputButton
+          <InputButton onClick={this.saveStyle.bind(this)}>
-            onClick={this.saveStyle.bind(this)}
-          >
             <MdSave/>
             {t("Save")}
           </InputButton>
-          <InputButton
+          {showSaveFilePickerAvailable && (
-            onClick={this.saveStyleAs.bind(this)}
+            <InputButton onClick={this.saveStyleAs.bind(this)}>
-          >
               <MdSave/>
               {t("Save as")}
             </InputButton>
+          )}
 
-          <InputButton
+          <InputButton onClick={this.createHtml.bind(this)}>
-            onClick={this.createHtml.bind(this)}
-          >
             <MdMap/>
             {t("Create HTML")}
           </InputButton>

src/components/ModalOpen.tsx

@@ -1,6 +1,7 @@
 import React, { FormEvent } from 'react'
 import {MdFileUpload} from 'react-icons/md'
 import {MdAddCircleOutline} from 'react-icons/md'
+import FileReaderInput, { Result } from 'react-file-reader-input'
 import { Trans, WithTranslation, withTranslation } from 'react-i18next';
 
 import ModalLoading from './ModalLoading'
@@ -168,6 +169,32 @@ class ModalOpenInternal extends React.Component<ModalOpenInternalProps, ModalOpe
     return file;
   }
 
+  // it is not guaranteed that the File System Access API is available on all
+  // browsers. If the function is not available, a fallback behavior is used.
+  onFileChanged = async (_: any, files: Result[]) => {
+    const [, file] = files[0];
+    const reader = new FileReader();
+    this.clearError();
+
+    reader.readAsText(file, "UTF-8");
+    reader.onload = e => {
+      let mapStyle;
+      try {
+        mapStyle = JSON.parse(e.target?.result as string)
+      }
+      catch(err) {
+        this.setState({
+          error: (err as Error).toString()
+        });
+        return;
+      }
+      mapStyle = style.ensureStyleValidity(mapStyle)
+      this.props.onStyleOpen(mapStyle);
+      this.onOpenToggle();
+    }
+    reader.onerror = e => console.log(e.target);
+  }
+
   onOpenToggle() {
     this.setState({
       styleUrl: ""
@@ -217,10 +244,16 @@ class ModalOpenInternal extends React.Component<ModalOpenInternalProps, ModalOpe
             <h1>{t("Open local Style")}</h1>
             <p>{t("Open a local JSON style from your computer.")}</p>
             <div>
+              {typeof window.showOpenFilePicker === "function" ? (
                 <InputButton
                   className="maputnik-big-button"
                   onClick={this.onOpenFile}><MdFileUpload/> {t("Open Style")}
                 </InputButton>
+              ) : (
+                <FileReaderInput onChange={this.onFileChanged} tabIndex={-1} aria-label={t("Open Style")}>
+                  <InputButton className="maputnik-upload-button"><MdFileUpload /> {t("Open Style")}</InputButton>
+                </FileReaderInput>
+              )}
             </div>
           </section>