feat: polish message attachment downloads

src/components/messageStream/utils/downloadFile.ts

@@ -0,0 +1,78 @@
+type SaveFilePicker = (options?: {
+  suggestedName?: string;
+  types?: Array<{
+    description?: string;
+    accept: Record<string, string[]>;
+  }>;
+}) => Promise<{
+  createWritable: () => Promise<{
+    write: (data: Blob) => Promise<void>;
+    close: () => Promise<void>;
+  }>;
+}>;
+
+type NavigatorWithFileShare = Navigator & {
+  canShare?: (data: { files?: File[] }) => boolean;
+  share?: (data: { files?: File[]; title?: string }) => Promise<void>;
+};
+
+type WindowWithSavePicker = Window & {
+  showSaveFilePicker?: SaveFilePicker;
+};
+
+export async function downloadFile(url: string, filename: string) {
+  const res = await fetch(url, { credentials: "include" });
+  if (!res.ok) throw new Error(await res.text());
+
+  const blob = await res.blob();
+  const safeName = filename || "download";
+
+  if (window.isSecureContext) {
+    const picker = (window as WindowWithSavePicker).showSaveFilePicker;
+    if (picker) {
+      const handle = await picker({
+        suggestedName: safeName,
+        types: blob.type
+          ? [
+              {
+                description: "File",
+                accept: { [blob.type]: [extensionFromName(safeName)] },
+              },
+            ]
+          : undefined,
+      });
+      const writable = await handle.createWritable();
+      await writable.write(blob);
+      await writable.close();
+      return;
+    }
+  }
+
+  const file = new File([blob], safeName, {
+    type: blob.type || "application/octet-stream",
+  });
+  const nav = navigator as NavigatorWithFileShare;
+  if (nav.canShare?.({ files: [file] }) && nav.share) {
+    await nav.share({ files: [file], title: safeName });
+    return;
+  }
+
+  const objectUrl = URL.createObjectURL(blob);
+  triggerDownload(objectUrl, safeName);
+  window.setTimeout(() => URL.revokeObjectURL(objectUrl), 30_000);
+}
+
+function triggerDownload(url: string, filename: string) {
+  const a = document.createElement("a");
+  a.href = url;
+  a.download = filename;
+  a.style.display = "none";
+  document.body.append(a);
+  a.click();
+  a.remove();
+}
+
+function extensionFromName(filename: string) {
+  const match = /\.[^.]+$/.exec(filename);
+  return match?.[0] || ".bin";
+}