feat: new search experience (#58)

Reviewed-on: #58

crates/chat/src/search.rs

@@ -0,0 +1,133 @@
+use std::cmp::Reverse;
+use std::collections::BTreeMap;
+use std::sync::Arc;
+
+use common::EventExt;
+use nostr_sdk::prelude::*;
+
+/// A chat message kept in memory for content search.
+#[derive(Debug, Clone)]
+pub struct SearchMessage {
+    /// ID of the room the message belongs to
+    pub room: u64,
+    /// Author of the message
+    pub author: PublicKey,
+    /// The content of the message
+    pub content: Arc<str>,
+    /// When the message was created
+    pub created_at: Timestamp,
+}
+
+#[derive(Debug)]
+struct IndexedMessage {
+    message: SearchMessage,
+    /// Lowercase content so repeated searches don't re-allocate per message
+    normalized: Arc<str>,
+}
+
+/// In-memory index of chat message rumors, keyed by room and rumor id.
+#[derive(Debug, Default)]
+pub struct MessageSearchIndex(BTreeMap<u64, BTreeMap<EventId, Arc<IndexedMessage>>>);
+
+impl MessageSearchIndex {
+    /// Index a rumor for search, ignoring reactions and empty content.
+    pub fn insert(&mut self, rumor: &UnsignedEvent) {
+        if !is_chat(rumor.kind) || rumor.content.trim().is_empty() {
+            return;
+        }
+
+        let Some(id) = rumor.id else { return };
+
+        let indexed = Arc::new(IndexedMessage {
+            message: SearchMessage {
+                room: rumor.uniq_id(),
+                author: rumor.pubkey,
+                content: rumor.content.as_str().into(),
+                created_at: rumor.created_at,
+            },
+            normalized: rumor.content.to_lowercase().into(),
+        });
+
+        self.0
+            .entry(rumor.uniq_id())
+            .or_default()
+            .entry(id)
+            .or_insert(indexed);
+    }
+
+    /// Find messages whose content contains all of the terms, newest first.
+    pub fn search(&self, terms: &[String], limit: usize) -> Vec<SearchMessage> {
+        let mut matches: Vec<&Arc<IndexedMessage>> = self
+            .0
+            .values()
+            .flat_map(|messages| messages.values())
+            .filter(|indexed| terms.iter().all(|term| indexed.normalized.contains(term)))
+            .collect();
+
+        matches.sort_by_key(|indexed| Reverse(indexed.message.created_at));
+        matches.truncate(limit);
+
+        matches
+            .into_iter()
+            .map(|indexed| indexed.message.clone())
+            .collect()
+    }
+
+    /// Drop all indexed messages.
+    pub fn clear(&mut self) {
+        self.0.clear();
+    }
+}
+
+fn is_chat(kind: Kind) -> bool {
+    kind == Kind::PrivateDirectMessage || kind == Kind::Custom(15)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn rumor(kind: Kind, content: &str, created_at: u64) -> UnsignedEvent {
+        let sender = Keys::generate();
+        let peer = Keys::generate().public_key();
+
+        let mut rumor = EventBuilder::new(kind, content)
+            .tag(Tag::public_key(peer))
+            .finalize_unsigned(sender.public_key());
+        rumor.ensure_id();
+        rumor.created_at = Timestamp::from(created_at);
+        rumor
+    }
+
+    #[test]
+    fn search_matches_all_terms_newest_first_and_deduplicates() {
+        let mut index = MessageSearchIndex::default();
+        let first = rumor(Kind::PrivateDirectMessage, "Hello ALICE", 10);
+        let second = rumor(Kind::PrivateDirectMessage, "hello again", 20);
+        let reaction = rumor(Kind::Reaction, "hello world", 30);
+
+        index.insert(&first);
+        index.insert(&first);
+        index.insert(&second);
+        index.insert(&reaction);
+
+        let hits = index.search(&["hello".to_owned()], 10);
+        assert_eq!(hits.len(), 2);
+        assert_eq!(&*hits[0].content, "hello again");
+        assert_eq!(hits[0].created_at, Timestamp::from(20));
+
+        let hits = index.search(&["hello".to_owned(), "again".to_owned()], 10);
+        assert_eq!(hits.len(), 1);
+
+        let hits = index.search(&["hello".to_owned()], 1);
+        assert_eq!(hits.len(), 1);
+    }
+
+    #[test]
+    fn empty_content_is_not_indexed() {
+        let mut index = MessageSearchIndex::default();
+        index.insert(&rumor(Kind::PrivateDirectMessage, "   ", 10));
+
+        assert!(index.search(&["hello".to_owned()], 10).is_empty());
+    }
+}