feat: NIP-87 federation discovery

Author: tvolk131

assets/icons/search.svg

@@ -1,10 +1,16 @@
-use std::collections::BTreeMap;
+use std::collections::{BTreeMap, BTreeSet};
 use std::fmt::Debug;
+use std::str::FromStr;
 use std::time::Duration;
 
+use fedimint_core::config::FederationId;
+use fedimint_core::invite_code::InviteCode;
 use iced::Subscription;
 use nostr_relay_pool::RelayStatus;
-use nostr_sdk::Url;
+use nostr_sdk::{Alphabet, EventSource, Filter, Kind, PublicKey, SingleLetterTag, TagKind, Url};
+
+const D_TAG: TagKind = TagKind::SingleLetter(SingleLetterTag::lowercase(Alphabet::D));
+const U_TAG: TagKind = TagKind::SingleLetter(SingleLetterTag::lowercase(Alphabet::U));
 
 #[derive(Default, Debug, Clone, PartialEq, Eq)]
 pub struct NostrState {
@@ -69,6 +75,60 @@ impl NostrModule {
         )
     }
 
+    /// Fetches recommendations for Fedimint federations.
+    /// For every federation, this function returns a tuple containing the set of nostr npubs of
+    /// users who have recommended the federation, and the set of all invite codes that have been
+    /// provided for the federation. All federations returned are guaranteed to contain at least
+    /// one nostr npub and one invite code.
+    pub async fn find_federations(
+        &self,
+    ) -> Result<
+        BTreeMap<FederationId, (BTreeSet<PublicKey>, BTreeSet<InviteCode>)>,
+        nostr_sdk::client::Error,
+    > {
+        let fedimint_recommendation_events = self
+            .client
+            .get_events_of(
+                vec![Filter::new()
+                    .kind(Kind::Custom(38_000))
+                    .custom_tag(SingleLetterTag::lowercase(Alphabet::K), vec!["38173"])
+                    .custom_tag(SingleLetterTag::lowercase(Alphabet::N), vec!["mainnet"])],
+                EventSource::both(None),
+            )
+            .await?;
+
+        let mut federations = BTreeMap::new();
+
+        for recommendation_event in &fedimint_recommendation_events {
+            for d_tag in recommendation_event.get_tags_content(D_TAG) {
+                let Ok(federation_id) = FederationId::from_str(d_tag) else {
+                    continue;
+                };
+
+                let (recommenders, invite_codes) = federations
+                    .entry(federation_id)
+                    .or_insert_with(|| (BTreeSet::new(), BTreeSet::new()));
+
+                recommenders.insert(recommendation_event.pubkey);
+
+                for u_tag in recommendation_event.get_tags_content(U_TAG) {
+                    if let Ok(invite_code) = InviteCode::from_str(u_tag) {
+                        if invite_code.federation_id() == federation_id {
+                            invite_codes.insert(invite_code);
+                        }
+                    }
+                }
+            }
+        }
+
+        // It's possible for a user to recommend a federation without providing any invite codes.
+        // If a federation has no recommendations that include any invite codes, we don't want to
+        // include it in the list of federations since it's not possible to join it.
+        federations.retain(|_, (_, invite_codes)| !invite_codes.is_empty());
+
+        Ok(federations)
+    }
+
     /// Fetches the current state of the Nostr SDK client.
     /// Note: This is async because it's grabbing read locks
     /// on the relay `RwLock`s. No network requests are made.