feat: implement initial download method

src/download.ts

@@ -1 +1,41 @@
-export function downloadObject(cid: string) {}
+import { getActivePortals } from "#portal.js";
+import { ErrTuple } from "#types.js";
+import { decodeCid, getVerifiableStream } from "@lumeweb/libportal";
+
+const NO_PORTALS_ERROR = [null, "no active portals"] as ErrTuple;
+
+export async function downloadObject(cid: string): Promise<ErrTuple> {
+  const activePortals = getActivePortals();
+
+  if (!activePortals.size) {
+    return NO_PORTALS_ERROR;
+  }
+
+  for (const portal of activePortals) {
+    if (!(await portal.isLoggedIn())) {
+      try {
+        await portal.register();
+      } catch {
+        continue;
+      }
+
+      await portal.login();
+    }
+
+    let stream, proof;
+
+    try {
+      stream = await portal.downloadFile(cid);
+      proof = await portal.downloadProof(cid);
+    } catch {
+      continue;
+    }
+
+    return [
+      await getVerifiableStream(decodeCid(cid).hash, proof, stream),
+      null,
+    ];
+  }
+
+  return NO_PORTALS_ERROR;
+}