feat: add group discovery and group preview (#59)

Reviewed-on: #59

crates/nip29/src/utils.rs

@@ -0,0 +1,60 @@
+use std::collections::HashSet;
+use std::collections::hash_map::DefaultHasher;
+use std::hash::{Hash, Hasher};
+
+use nostr_sdk::prelude::*;
+
+use crate::{GroupId, GroupKey};
+
+const LIST_SUBSCRIPTION: &str = "nip29-list";
+const FORK_SUBSCRIPTION: &str = "nip29-forks";
+const GROUP_PREFIX: &str = "grp-";
+const BROWSE_PREFIX: &str = "brw-";
+const PAGE_PREFIX: &str = "pg-";
+
+pub(crate) fn list_subscription_id() -> SubscriptionId {
+    SubscriptionId::new(LIST_SUBSCRIPTION)
+}
+
+pub(crate) fn fork_subscription_id() -> SubscriptionId {
+    SubscriptionId::new(FORK_SUBSCRIPTION)
+}
+
+pub(crate) fn subscription_id(key: &GroupKey) -> SubscriptionId {
+    SubscriptionId::new(format!("{GROUP_PREFIX}{:08x}", key.uniq_id() as u32))
+}
+
+pub(crate) fn browse_subscription(relay: &RelayUrl) -> SubscriptionId {
+    let mut hasher = DefaultHasher::new();
+    relay.hash(&mut hasher);
+
+    SubscriptionId::new(format!("{BROWSE_PREFIX}{:08x}", hasher.finish() as u32))
+}
+
+pub(crate) fn page_subscription(key: &GroupKey) -> SubscriptionId {
+    SubscriptionId::new(format!("{PAGE_PREFIX}{:08x}", key.uniq_id() as u32))
+}
+
+pub(crate) fn is_page(id: &SubscriptionId) -> bool {
+    id.as_str().starts_with(PAGE_PREFIX)
+}
+
+pub(crate) fn is_own_subscription(id: &SubscriptionId) -> bool {
+    let id = id.as_str();
+    id == LIST_SUBSCRIPTION
+        || id == FORK_SUBSCRIPTION
+        || id.starts_with(GROUP_PREFIX)
+        || id.starts_with(BROWSE_PREFIX)
+        || id.starts_with(PAGE_PREFIX)
+}
+
+pub(crate) fn parse_members(event: &Event) -> Option<(GroupId, Timestamp, usize)> {
+    if event.kind != Kind::GroupMembers {
+        return None;
+    }
+
+    let id = GroupId::new(event.tags.identifier()?).ok()?;
+    let members = event.tags.public_keys().collect::<HashSet<_>>().len();
+
+    Some((id, event.created_at, members))
+}