nip19: add a few utils for getting filters and relays

A few utility functions for getting filters and relays from nip19
objects. We will use this for finding notes on other relays.

src/main.rs

@@ -65,6 +65,38 @@ fn render_note<'a>(_app_ctx: &Context, note: &'a Note) -> Vec<u8> {
         .into()
 }
 
+fn nip19_to_filters(nip19: &Nip19) -> Result<Vec<Filter>, Error> {
+    match nip19 {
+        Nip19::Event(ev) => {
+            let mut filters = vec![Filter::new().id(ev.event_id).limit(1)];
+            if let Some(author) = ev.author {
+                filters.push(Filter::new().author(author).kind(Kind::Metadata).limit(1))
+            }
+            Ok(filters)
+        }
+        Nip19::EventId(evid) => Ok(vec![Filter::new().id(*evid).limit(1)]),
+        Nip19::Profile(prof) => Ok(vec![Filter::new()
+            .author(prof.public_key)
+            .kind(Kind::Metadata)
+            .limit(1)]),
+        Nip19::Pubkey(pk) => Ok(vec![Filter::new()
+            .author(*pk)
+            .kind(Kind::Metadata)
+            .limit(1)]),
+        Nip19::Secret(_sec) => Err(Error::InvalidNip19),
+    }
+}
+
+fn nip19_relays(nip19: &Nip19) -> Vec<String> {
+    let mut relays: Vec<String> = vec![];
+    match nip19 {
+        Nip19::Event(ev) => relays.extend(ev.relays.clone()),
+        Nip19::Profile(p) => relays.extend(p.relays.clone()),
+        _ => (),
+    }
+    relays
+}
+
 async fn serve(
     ctx: &Context,
     r: Request<hyper::body::Incoming>,