feat: support importing emails from .zip archives

lib/eml-import.ts

@@ -0,0 +1,48 @@
+export interface ImportableEmail {
+  name: string;
+  blob: Blob;
+}
+
+const EMAIL_MIME = "message/rfc822";
+
+function isEmlName(name: string): boolean {
+  return /\.eml$/i.test(name);
+}
+
+function isZipName(name: string): boolean {
+  return /\.zip$/i.test(name);
+}
+
+async function extractEmlsFromZip(file: File): Promise<ImportableEmail[]> {
+  const { default: JSZip } = await import("jszip");
+  const zip = await JSZip.loadAsync(await file.arrayBuffer());
+  const out: ImportableEmail[] = [];
+  const entries = Object.values(zip.files);
+  for (const entry of entries) {
+    if (entry.dir) continue;
+    if (!isEmlName(entry.name)) continue;
+    const data = await entry.async("arraybuffer");
+    out.push({
+      name: entry.name.split(/[\\/]/).pop() || entry.name,
+      blob: new Blob([data], { type: EMAIL_MIME }),
+    });
+  }
+  return out;
+}
+
+export async function expandImportableEmails(
+  files: File[],
+): Promise<ImportableEmail[]> {
+  const out: ImportableEmail[] = [];
+  for (const file of files) {
+    if (isZipName(file.name) || file.type === "application/zip") {
+      out.push(...(await extractEmlsFromZip(file)));
+      continue;
+    }
+    const blob = new Blob([await file.arrayBuffer()], { type: EMAIL_MIME });
+    out.push({ name: file.name, blob });
+  }
+  return out;
+}
+
+export const EML_IMPORT_ACCEPT = ".eml,.zip,message/rfc822,application/zip";