feat(export): adapt DataExportSection for platform-specific file handling

Integrate PlatformServiceFactory to provide platform-specific data export:
- Add platform-specific file saving for Capacitor and other platforms
- Use web download mechanism only in web platform
- Conditionally show platform-specific save instructions
- Add iOS/Android detection for targeted guidance
- Update success messages based on platform context
- Improve download link visibility logic for web platform

This change ensures proper file handling across web, mobile, and desktop
platforms while maintaining a consistent user experience.

src/components/DataExportSection.vue

@@ -1,3 +1,17 @@
+/**
+ * Data Export Section Component
+ * 
+ * Provides UI and functionality for exporting user data and backing up identifier seeds.
+ * Includes buttons for seed backup and database export, with platform-specific download instructions.
+ * 
+ * @component
+ * @displayName DataExportSection
+ * @example
+ * ```vue
+ * <DataExportSection :active-did="currentDid" />
+ * ```
+ */
+
 <template>
   <div
     id="sectionDataExport"
@@ -28,17 +42,17 @@
     >
       If no download happened yet, click again here to download now.
     </a>
-    <div class="mt-4">
+    <div class="mt-4" v-if="showPlatformInstructions">
       <p>
         After the download, you can save the file in your preferred storage
         location.
       </p>
       <ul>
-        <li class="list-disc list-outside ml-4">
+        <li v-if="platformService.isCapacitor() && isIOS" class="list-disc list-outside ml-4">
           On iOS: Choose "More..." and select a place in iCloud, or go "Back"
           and save to another location.
         </li>
-        <li class="list-disc list-outside ml-4">
+        <li v-if="platformService.isCapacitor() && !isIOS" class="list-disc list-outside ml-4">
           On Android: Choose "Open" and then share
           <font-awesome icon="share-nodes" class="fa-fw" />
           to your prefered place.
@@ -53,38 +67,106 @@ import { Component, Prop, Vue } from "vue-facing-decorator";
 import { NotificationIface } from "../constants/app";
 import { db } from "../db/index";
 import { logger } from "../utils/logger";
+import { PlatformServiceFactory } from "../services/PlatformServiceFactory";
+import { PlatformService } from "../services/PlatformService";
 
+/**
+ * @vue-component
+ * Data Export Section Component
+ * Handles database export and seed backup functionality with platform-specific behavior
+ */
 @Component
 export default class DataExportSection extends Vue {
+  /**
+   * Notification function injected by Vue
+   * Used to show success/error messages to the user
+   */
   $notify!: (notification: NotificationIface, timeout?: number) => void;
 
+  /**
+   * Active DID (Decentralized Identifier) of the user
+   * Controls visibility of seed backup option
+   * @required
+   */
   @Prop({ required: true }) readonly activeDid!: string;
+
+  /**
+   * URL for the database export download
+   * Created and revoked dynamically during export process
+   * Only used in web platform
+   */
   downloadUrl = "";
 
+  /**
+   * Platform service instance for platform-specific operations
+   */
+  private platformService: PlatformService = PlatformServiceFactory.getInstance();
+
+  /**
+   * Whether the current platform is iOS
+   */
+  private get isIOS(): boolean {
+    return /iPad|iPhone|iPod/.test(navigator.userAgent);
+  }
+
+  /**
+   * Whether to show platform-specific instructions
+   */
+  private get showPlatformInstructions(): boolean {
+    return this.platformService.isCapacitor();
+  }
+
+  /**
+   * Lifecycle hook to clean up resources
+   * Revokes object URL when component is unmounted (web platform only)
+   */
   beforeUnmount() {
-    if (this.downloadUrl) {
+    if (this.downloadUrl && this.platformService.isWeb()) {
       URL.revokeObjectURL(this.downloadUrl);
     }
   }
 
+  /**
+   * Exports the database to a JSON file
+   * Uses platform-specific methods for saving the exported data
+   * Shows success/error notifications to user
+   * 
+   * @throws {Error} If export fails
+   * @emits {Notification} Success or error notification
+   */
   public async exportDatabase() {
     try {
       const blob = await db.export({ prettyJson: true });
+      const fileName = `${db.name}-backup.json`;
+
+      if (this.platformService.isWeb()) {
+        // Web platform: Use download link
         this.downloadUrl = URL.createObjectURL(blob);
         const downloadAnchor = this.$refs.downloadLink as HTMLAnchorElement;
         downloadAnchor.href = this.downloadUrl;
-      downloadAnchor.download = `${db.name}-backup.json`;
+        downloadAnchor.download = fileName;
         downloadAnchor.click();
+        setTimeout(() => URL.revokeObjectURL(this.downloadUrl), 1000);
+      } else if (this.platformService.isCapacitor()) {
+        // Capacitor platform: Write to app directory
+        const content = await blob.text();
+        await this.platformService.writeFile(fileName, content);
+      } else {
+        // Other platforms: Use platform service
+        await this.platformService.writeFile(fileName, await blob.text());
+      }
+
       this.$notify(
         {
           group: "alert",
           type: "success",
-          title: "Download Started",
+          title: "Export Successful",
-          text: "See your downloads directory for the backup. It is in the Dexie format.",
+          text: this.platformService.isWeb()
+            ? "See your downloads directory for the backup. It is in the Dexie format."
+            : "The backup has been saved to your device.",
         },
         -1,
       );
-      setTimeout(() => URL.revokeObjectURL(this.downloadUrl), 1000);
     } catch (error) {
       logger.error("Export Error:", error);
       this.$notify(
@@ -99,15 +181,23 @@ export default class DataExportSection extends Vue {
     }
   }
 
+  /**
+   * Computes class names for the initial download button
+   * @returns Object with 'hidden' class when download is in progress (web platform only)
+   */
   public computedStartDownloadLinkClassNames() {
     return {
-      hidden: this.downloadUrl,
+      hidden: this.downloadUrl && this.platformService.isWeb(),
     };
   }
 
+  /**
+   * Computes class names for the secondary download link
+   * @returns Object with 'hidden' class when no download is available or not on web platform
+   */
   public computedDownloadLinkClassNames() {
     return {
-      hidden: !this.downloadUrl,
+      hidden: !this.downloadUrl || !this.platformService.isWeb(),
     };
   }
 }