Add support for threads (#216)

src/base.rs

@@ -36,7 +36,7 @@ use matrix_sdk::{
     ruma::{
         events::{
             reaction::ReactionEvent,
-            relation::Replacement,
+            relation::{Replacement, Thread},
             room::encrypted::RoomEncryptedEvent,
             room::message::{
                 OriginalRoomMessageEvent,
@@ -681,7 +681,10 @@ pub enum RoomFetchStatus {
 /// Indicates where an [EventId] lives in the [ChatStore].
 pub enum EventLocation {
     /// The [EventId] belongs to a message.
-    Message(MessageKey),
+    ///
+    /// If the first argument is [None], then it's part of the main scrollback. When [Some],
+    /// it specifies which thread it's in reply to.
+    Message(Option<OwnedEventId>, MessageKey),
 
     /// The [EventId] belongs to a reaction to the given event.
     Reaction(OwnedEventId),
@@ -689,7 +692,7 @@ pub enum EventLocation {
 
 impl EventLocation {
     fn to_message_key(&self) -> Option<&MessageKey> {
-        if let EventLocation::Message(key) = self {
+        if let EventLocation::Message(_, key) = self {
             Some(key)
         } else {
             None
@@ -741,6 +744,9 @@ pub struct RoomInfo {
     /// A map of message identifiers to a map of reaction events.
     pub reactions: HashMap<OwnedEventId, MessageReactions>,
 
+    /// A map of message identifiers to thread replies.
+    pub threads: HashMap<OwnedEventId, Messages>,
+
     /// Whether the scrollback for this room is currently being fetched.
     pub fetching: bool,
 
@@ -819,15 +825,17 @@ impl RoomInfo {
         let event_id = msg.event_id;
         let new_msgtype = msg.new_content;
 
-        let key = if let Some(EventLocation::Message(k)) = self.keys.get(&event_id) {
+        let Some(EventLocation::Message(thread, key)) = self.keys.get(&event_id) else {
-            k
-        } else {
             return;
         };
 
-        let msg = if let Some(msg) = self.messages.get_mut(key) {
+        let source = if let Some(thread) = thread {
-            msg
+            self.threads.entry(thread.clone()).or_default()
         } else {
+            &mut self.messages
+        };
+
+        let Some(msg) = source.get_mut(key) else {
             return;
         };
 
@@ -867,7 +875,7 @@ impl RoomInfo {
         let event_id = msg.event_id().to_owned();
         let key = (msg.origin_server_ts().into(), event_id.clone());
 
-        self.keys.insert(event_id, EventLocation::Message(key.clone()));
+        self.keys.insert(event_id, EventLocation::Message(None, key.clone()));
         self.messages.insert(key, msg.into());
     }
 
@@ -876,22 +884,38 @@ impl RoomInfo {
         let event_id = msg.event_id().to_owned();
         let key = (msg.origin_server_ts().into(), event_id.clone());
 
-        self.keys.insert(event_id.clone(), EventLocation::Message(key.clone()));
+        let loc = EventLocation::Message(None, key.clone());
-        self.messages.insert(key, msg.into());
+        self.keys.insert(event_id, loc);
+        self.messages.insert_message(key, msg);
+    }
 
-        // Remove any echo.
+    fn insert_thread(&mut self, msg: RoomMessageEvent, thread_root: OwnedEventId) {
-        let key = (MessageTimeStamp::LocalEcho, event_id);
+        let event_id = msg.event_id().to_owned();
-        let _ = self.messages.remove(&key);
+        let key = (msg.origin_server_ts().into(), event_id.clone());
+
+        let replies = self.threads.entry(thread_root.clone()).or_default();
+        let loc = EventLocation::Message(Some(thread_root), key.clone());
+        self.keys.insert(event_id, loc);
+        replies.insert_message(key, msg);
     }
 
     /// Insert a new message event.
     pub fn insert(&mut self, msg: RoomMessageEvent) {
         match msg {
             RoomMessageEvent::Original(OriginalRoomMessageEvent {
-                content:
+                content: RoomMessageEventContent { relates_to: Some(ref relates_to), .. },
-                    RoomMessageEventContent { relates_to: Some(Relation::Replacement(repl)), .. },
                 ..
-            }) => self.insert_edit(repl),
+            }) => {
+                match relates_to {
+                    Relation::Replacement(repl) => self.insert_edit(repl.clone()),
+                    Relation::Thread(Thread { event_id, .. }) => {
+                        let event_id = event_id.clone();
+                        self.insert_thread(msg, event_id);
+                    },
+                    Relation::Reply { .. } => self.insert_message(msg),
+                    _ => self.insert_message(msg),
+                }
+            },
             _ => self.insert_message(msg),
         }
     }
@@ -1236,8 +1260,8 @@ impl ApplicationStore for ChatStore {}
 /// Identified used to track window content.
 #[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub enum IambId {
-    /// A Matrix room.
+    /// A Matrix room, with an optional thread to show.
-    Room(OwnedRoomId),
+    Room(OwnedRoomId, Option<OwnedEventId>),
 
     /// The `:dms` window.
     DirectList,
@@ -1264,9 +1288,12 @@ pub enum IambId {
 impl Display for IambId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
-            IambId::Room(room_id) => {
+            IambId::Room(room_id, None) => {
                 write!(f, "iamb://room/{room_id}")
             },
+            IambId::Room(room_id, Some(thread)) => {
+                write!(f, "iamb://room/{room_id}/threads/{thread}")
+            },
             IambId::MemberList(room_id) => {
                 write!(f, "iamb://members/{room_id}")
             },
@@ -1328,15 +1355,27 @@ impl<'de> Visitor<'de> for IambIdVisitor {
                     return Err(E::custom("Invalid members window URL"));
                 };
 
-                let &[room_id] = path.collect::<Vec<_>>().as_slice() else {
+                match *path.collect::<Vec<_>>().as_slice() {
-                    return Err(E::custom("Invalid members window URL"));
+                    [room_id] => {
-                };
-
                         let Ok(room_id) = OwnedRoomId::try_from(room_id) else {
                             return Err(E::custom("Invalid room identifier"));
                         };
 
-                Ok(IambId::Room(room_id))
+                        Ok(IambId::Room(room_id, None))
+                    },
+                    [room_id, "threads", thread_root] => {
+                        let Ok(room_id) = OwnedRoomId::try_from(room_id) else {
+                            return Err(E::custom("Invalid room identifier"));
+                        };
+
+                        let Ok(thread_root) = OwnedEventId::try_from(thread_root) else {
+                            return Err(E::custom("Invalid thread root identifier"));
+                        };
+
+                        Ok(IambId::Room(room_id, Some(thread_root)))
+                    },
+                    _ => return Err(E::custom("Invalid members window URL")),
+                }
             },
             Some("members") => {
                 let Some(path) = url.path_segments() else {
@@ -1433,7 +1472,7 @@ pub enum IambBufferId {
     Command(CommandType),
 
     /// The message buffer or a specific message in a room.
-    Room(OwnedRoomId, RoomFocus),
+    Room(OwnedRoomId, Option<OwnedEventId>, RoomFocus),
 
     /// The `:dms` window.
     DirectList,
@@ -1460,17 +1499,19 @@ pub enum IambBufferId {
 impl IambBufferId {
     /// Get the identifier for the window that contains this buffer.
     pub fn to_window(&self) -> Option<IambId> {
-        match self {
+        let id = match self {
-            IambBufferId::Command(_) => None,
+            IambBufferId::Command(_) => return None,
-            IambBufferId::Room(room, _) => Some(IambId::Room(room.clone())),
+            IambBufferId::Room(room, thread, _) => IambId::Room(room.clone(), thread.clone()),
-            IambBufferId::DirectList => Some(IambId::DirectList),
+            IambBufferId::DirectList => IambId::DirectList,
-            IambBufferId::MemberList(room) => Some(IambId::MemberList(room.clone())),
+            IambBufferId::MemberList(room) => IambId::MemberList(room.clone()),
-            IambBufferId::RoomList => Some(IambId::RoomList),
+            IambBufferId::RoomList => IambId::RoomList,
-            IambBufferId::SpaceList => Some(IambId::SpaceList),
+            IambBufferId::SpaceList => IambId::SpaceList,
-            IambBufferId::VerifyList => Some(IambId::VerifyList),
+            IambBufferId::VerifyList => IambId::VerifyList,
-            IambBufferId::Welcome => Some(IambId::Welcome),
+            IambBufferId::Welcome => IambId::Welcome,
-            IambBufferId::ChatList => Some(IambId::ChatList),
+            IambBufferId::ChatList => IambId::ChatList,
-        }
+        };
+
+        Some(id)
     }
 }
 
@@ -1492,8 +1533,8 @@ impl ApplicationInfo for IambInfo {
         match content {
             IambBufferId::Command(CommandType::Command) => complete_cmdbar(text, cursor, store),
             IambBufferId::Command(CommandType::Search) => vec![],
-            IambBufferId::Room(_, RoomFocus::MessageBar) => complete_msgbar(text, cursor, store),
+            IambBufferId::Room(_, _, RoomFocus::MessageBar) => complete_msgbar(text, cursor, store),
-            IambBufferId::Room(_, RoomFocus::Scrollback) => vec![],
+            IambBufferId::Room(_, _, RoomFocus::Scrollback) => vec![],
 
             IambBufferId::DirectList => vec![],
             IambBufferId::MemberList(_) => vec![],

src/main.rs

@@ -141,14 +141,14 @@ fn config_tab_to_desc(
                     let name = user_id.to_string();
                     let room_id = worker.join_room(name.clone())?;
                     names.insert(name, room_id.clone());
-                    IambId::Room(room_id)
+                    IambId::Room(room_id, None)
                 },
-                config::WindowPath::RoomId(room_id) => IambId::Room(room_id),
+                config::WindowPath::RoomId(room_id) => IambId::Room(room_id, None),
                 config::WindowPath::AliasId(alias) => {
                     let name = alias.to_string();
                     let room_id = worker.join_room(name.clone())?;
                     names.insert(name, room_id.clone());
-                    IambId::Room(room_id)
+                    IambId::Room(room_id, None)
                 },
                 config::WindowPath::Window(id) => id,
             };
@@ -563,7 +563,7 @@ impl Application {
             HomeserverAction::CreateRoom(alias, vis, flags) => {
                 let client = &store.application.worker.client;
                 let room_id = create_room(client, alias, vis, flags).await?;
-                let room = IambId::Room(room_id);
+                let room = IambId::Room(room_id, None);
                 let target = OpenTarget::Application(room);
                 let action = WindowAction::Switch(target);
 

src/message/mod.rs

@@ -6,6 +6,7 @@ use std::collections::hash_set;
 use std::collections::BTreeMap;
 use std::convert::TryFrom;
 use std::hash::{Hash, Hasher};
+use std::ops::{Deref, DerefMut};
 
 use chrono::{DateTime, Local as LocalTz, NaiveDateTime, TimeZone};
 use comrak::{markdown_to_html, ComrakOptions};
@@ -14,6 +15,7 @@ use unicode_width::UnicodeWidthStr;
 
 use matrix_sdk::ruma::{
     events::{
+        relation::Thread,
         room::{
             encrypted::{
                 OriginalRoomEncryptedEvent,
@@ -66,7 +68,36 @@ mod html;
 mod printer;
 
 pub type MessageKey = (MessageTimeStamp, OwnedEventId);
-pub type Messages = BTreeMap<MessageKey, Message>;
+
+#[derive(Default)]
+pub struct Messages(BTreeMap<MessageKey, Message>);
+
+impl Deref for Messages {
+    type Target = BTreeMap<MessageKey, Message>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl DerefMut for Messages {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl Messages {
+    pub fn insert_message(&mut self, key: MessageKey, msg: impl Into<Message>) {
+        let event_id = key.1.clone();
+        let msg = msg.into();
+
+        self.0.insert(key, msg);
+
+        // Remove any echo.
+        let key = (MessageTimeStamp::LocalEcho, event_id);
+        let _ = self.0.remove(&key);
+    }
+}
 
 const fn span_static(s: &'static str) -> Span<'static> {
     Span {
@@ -260,33 +291,27 @@ impl MessageCursor {
         MessageCursor::default()
     }
 
-    pub fn to_key<'a>(&'a self, info: &'a RoomInfo) -> Option<&'a MessageKey> {
+    pub fn to_key<'a>(&'a self, thread: &'a Messages) -> Option<&'a MessageKey> {
         if let Some(ref key) = self.timestamp {
             Some(key)
         } else {
-            Some(info.messages.last_key_value()?.0)
+            Some(thread.last_key_value()?.0)
         }
     }
 
-    pub fn from_cursor(cursor: &Cursor, info: &RoomInfo) -> Option<Self> {
+    pub fn from_cursor(cursor: &Cursor, thread: &Messages) -> Option<Self> {
         let ev_hash = u64::try_from(cursor.get_x()).ok()?;
         let ev_term = OwnedEventId::try_from("$").ok()?;
 
         let ts_start = MessageTimeStamp::try_from(cursor.get_y()).ok()?;
         let start = (ts_start, ev_term);
-        let mut mc = None;
 
-        for ((ts, event_id), _) in info.messages.range(start..) {
+        for ((ts, event_id), _) in thread.range(&start..) {
             let mut hasher = DefaultHasher::new();
             event_id.hash(&mut hasher);
 
             if hasher.finish() == ev_hash {
-                mc = Self::from((*ts, event_id.clone())).into();
+                return Self::from((*ts, event_id.clone())).into();
-                break;
-            }
-
-            if mc.is_none() {
-                mc = Self::from((*ts, event_id.clone())).into();
             }
 
             if ts > &ts_start {
@@ -294,11 +319,15 @@ impl MessageCursor {
             }
         }
 
-        return mc;
+        // If we can't find the cursor, then go to the nearest timestamp.
+        thread
+            .range(start..)
+            .next()
+            .map(|((ts, ev), _)| Self::from((*ts, ev.clone())))
     }
 
-    pub fn to_cursor(&self, info: &RoomInfo) -> Option<Cursor> {
+    pub fn to_cursor(&self, thread: &Messages) -> Option<Cursor> {
-        let (ts, event_id) = self.to_key(info)?;
+        let (ts, event_id) = self.to_key(thread)?;
 
         let y: usize = usize::try_from(ts).ok()?;
 
@@ -652,10 +681,34 @@ impl Message {
             MessageEvent::Redacted(_) => return None,
         };
 
-        if let Some(Relation::Reply { in_reply_to }) = &content.relates_to {
+        match &content.relates_to {
-            Some(in_reply_to.event_id.clone())
+            Some(Relation::Reply { in_reply_to }) => Some(in_reply_to.event_id.clone()),
-        } else {
+            Some(Relation::Thread(Thread {
-            None
+                in_reply_to: Some(in_reply_to),
+                is_falling_back: false,
+                ..
+            })) => Some(in_reply_to.event_id.clone()),
+            Some(_) | None => None,
+        }
+    }
+
+    fn thread_root(&self) -> Option<OwnedEventId> {
+        let content = match &self.event {
+            MessageEvent::EncryptedOriginal(_) => return None,
+            MessageEvent::EncryptedRedacted(_) => return None,
+            MessageEvent::Local(_, content) => content,
+            MessageEvent::Original(ev) => &ev.content,
+            MessageEvent::Redacted(_) => return None,
+        };
+
+        match &content.relates_to {
+            Some(Relation::Thread(Thread {
+                event_id,
+                in_reply_to: Some(in_reply_to),
+                is_falling_back: true,
+                ..
+            })) if event_id == &in_reply_to.event_id => Some(event_id.clone()),
+            Some(_) | None => None,
         }
     }
 
@@ -774,7 +827,10 @@ impl Message {
         let width = fmt.width();
 
         // Show the message that this one replied to, if any.
-        let reply = self.reply_to().and_then(|e| info.get_event(&e));
+        let reply = self
+            .reply_to()
+            .or_else(|| self.thread_root())
+            .and_then(|e| info.get_event(&e));
 
         if let Some(r) = &reply {
             let w = width.saturating_sub(2);
@@ -855,7 +911,22 @@ impl Message {
             }
         }
 
-        return text;
+        if let Some(thread) = info.threads.get(self.event.event_id()) {
+            // If we have threaded replies to this message, show how many.
+            let len = thread.len();
+
+            if len > 0 {
+                let style = Style::default();
+                let mut threaded = printer::TextPrinter::new(width, style, false).literal(true);
+                let len = Span::styled(len.to_string(), style.add_modifier(StyleModifier::BOLD));
+                threaded.push_str(" \u{2937} ", style);
+                threaded.push_span_nobreak(len);
+                threaded.push_str(" replies in thread", style);
+                fmt.push_text(threaded.finish(), style, &mut text);
+            }
+        }
+
+        text
     }
 
     pub fn show_msg(&self, width: usize, style: Style, hide_reply: bool) -> Text {
@@ -1058,7 +1129,7 @@ pub mod tests {
 
     #[test]
     fn test_mc_to_key() {
-        let info = mock_room();
+        let messages = mock_messages();
         let mc1 = MessageCursor::from(MSG1_KEY.clone());
         let mc2 = MessageCursor::from(MSG2_KEY.clone());
         let mc3 = MessageCursor::from(MSG3_KEY.clone());
@@ -1066,12 +1137,12 @@ pub mod tests {
         let mc5 = MessageCursor::from(MSG5_KEY.clone());
         let mc6 = MessageCursor::latest();
 
-        let k1 = mc1.to_key(&info).unwrap();
+        let k1 = mc1.to_key(&messages).unwrap();
-        let k2 = mc2.to_key(&info).unwrap();
+        let k2 = mc2.to_key(&messages).unwrap();
-        let k3 = mc3.to_key(&info).unwrap();
+        let k3 = mc3.to_key(&messages).unwrap();
-        let k4 = mc4.to_key(&info).unwrap();
+        let k4 = mc4.to_key(&messages).unwrap();
-        let k5 = mc5.to_key(&info).unwrap();
+        let k5 = mc5.to_key(&messages).unwrap();
-        let k6 = mc6.to_key(&info).unwrap();
+        let k6 = mc6.to_key(&messages).unwrap();
 
         // These should all be equal to their MSGN_KEYs.
         assert_eq!(k1, &MSG1_KEY.clone());
@@ -1084,13 +1155,13 @@ pub mod tests {
         assert_eq!(k6, &MSG1_KEY.clone());
 
         // MessageCursor::latest() fails to convert for a room w/o messages.
-        let info_empty = RoomInfo::default();
+        let messages_empty = Messages::default();
-        assert_eq!(mc6.to_key(&info_empty), None);
+        assert_eq!(mc6.to_key(&messages_empty), None);
     }
 
     #[test]
     fn test_mc_to_from_cursor() {
-        let info = mock_room();
+        let messages = mock_messages();
         let mc1 = MessageCursor::from(MSG1_KEY.clone());
         let mc2 = MessageCursor::from(MSG2_KEY.clone());
         let mc3 = MessageCursor::from(MSG3_KEY.clone());
@@ -1099,9 +1170,9 @@ pub mod tests {
         let mc6 = MessageCursor::latest();
 
         let identity = |mc: &MessageCursor| {
-            let c = mc.to_cursor(&info).unwrap();
+            let c = mc.to_cursor(&messages).unwrap();
 
-            MessageCursor::from_cursor(&c, &info).unwrap()
+            MessageCursor::from_cursor(&c, &messages).unwrap()
         };
 
         // These should all convert to a Cursor and back to the original value.

src/tests.rs

@@ -1,4 +1,4 @@
-use std::collections::{BTreeMap, HashMap};
+use std::collections::HashMap;
 use std::path::PathBuf;
 
 use matrix_sdk::ruma::{
@@ -125,17 +125,17 @@ pub fn mock_message5() -> Message {
 pub fn mock_keys() -> HashMap<OwnedEventId, EventLocation> {
     let mut keys = HashMap::new();
 
-    keys.insert(MSG1_EVID.clone(), EventLocation::Message(MSG1_KEY.clone()));
+    keys.insert(MSG1_EVID.clone(), EventLocation::Message(None, MSG1_KEY.clone()));
-    keys.insert(MSG2_EVID.clone(), EventLocation::Message(MSG2_KEY.clone()));
+    keys.insert(MSG2_EVID.clone(), EventLocation::Message(None, MSG2_KEY.clone()));
-    keys.insert(MSG3_EVID.clone(), EventLocation::Message(MSG3_KEY.clone()));
+    keys.insert(MSG3_EVID.clone(), EventLocation::Message(None, MSG3_KEY.clone()));
-    keys.insert(MSG4_EVID.clone(), EventLocation::Message(MSG4_KEY.clone()));
+    keys.insert(MSG4_EVID.clone(), EventLocation::Message(None, MSG4_KEY.clone()));
-    keys.insert(MSG5_EVID.clone(), EventLocation::Message(MSG5_KEY.clone()));
+    keys.insert(MSG5_EVID.clone(), EventLocation::Message(None, MSG5_KEY.clone()));
 
     keys
 }
 
 pub fn mock_messages() -> Messages {
-    let mut messages = BTreeMap::new();
+    let mut messages = Messages::default();
 
     messages.insert(MSG1_KEY.clone(), mock_message1());
     messages.insert(MSG2_KEY.clone(), mock_message2());
@@ -153,6 +153,7 @@ pub fn mock_room() -> RoomInfo {
 
         keys: mock_keys(),
         messages: mock_messages(),
+        threads: HashMap::default(),
 
         event_receipts: HashMap::new(),
         user_receipts: HashMap::new(),

src/windows/mod.rs

@@ -282,7 +282,7 @@ fn room_prompt(
 ) -> EditResult<Vec<(ProgramAction, ProgramContext)>, IambInfo> {
     match act {
         PromptAction::Submit => {
-            let room = IambId::Room(room_id.to_owned());
+            let room = IambId::Room(room_id.to_owned(), None);
             let open = WindowAction::Switch(OpenTarget::Application(room));
             let acts = vec![(open.into(), ctx.clone())];
 
@@ -661,7 +661,7 @@ impl WindowOps<IambInfo> for IambWindow {
 impl Window<IambInfo> for IambWindow {
     fn id(&self) -> IambId {
         match self {
-            IambWindow::Room(room) => IambId::Room(room.id().to_owned()),
+            IambWindow::Room(room) => IambId::Room(room.id().to_owned(), room.thread().cloned()),
             IambWindow::DirectList(_) => IambId::DirectList,
             IambWindow::MemberList(_, room_id, _) => IambId::MemberList(room_id.clone()),
             IambWindow::RoomList(_) => IambId::RoomList,
@@ -724,9 +724,9 @@ impl Window<IambInfo> for IambWindow {
 
     fn open(id: IambId, store: &mut ProgramStore) -> IambResult<Self> {
         match id {
-            IambId::Room(room_id) => {
+            IambId::Room(room_id, thread) => {
                 let (room, name, tags) = store.application.worker.get_room(room_id)?;
-                let room = RoomState::new(room, name, tags, store);
+                let room = RoomState::new(room, thread, name, tags, store);
 
                 store.application.need_load.insert(room.id().to_owned(), Need::MEMBERS);
                 return Ok(room.into());
@@ -775,7 +775,7 @@ impl Window<IambInfo> for IambWindow {
         let ChatStore { names, worker, .. } = &mut store.application;
 
         if let Some(room) = names.get_mut(&name) {
-            let id = IambId::Room(room.clone());
+            let id = IambId::Room(room.clone(), None);
 
             IambWindow::open(id, store)
         } else {
@@ -783,7 +783,7 @@ impl Window<IambInfo> for IambWindow {
             names.insert(name, room_id.clone());
 
             let (room, name, tags) = store.application.worker.get_room(room_id)?;
-            let room = RoomState::new(room, name, tags, store);
+            let room = RoomState::new(room, None, name, tags, store);
 
             store.application.need_load.insert(room.id().to_owned(), Need::MEMBERS);
             Ok(room.into())

src/windows/room/chat.rs

@@ -24,10 +24,12 @@ use matrix_sdk::{
             MessageType,
             OriginalRoomMessageEvent,
             Relation,
+            ReplyWithinThread,
             RoomMessageEventContent,
             TextMessageEventContent,
         },
         EventId,
+        OwnedEventId,
         OwnedRoomId,
         RoomId,
     },
@@ -70,6 +72,7 @@ use modalkit::prelude::*;
 
 use crate::base::{
     DownloadFlags,
+    EventLocation,
     IambAction,
     IambBufferId,
     IambError,
@@ -106,10 +109,10 @@ pub struct ChatState {
 }
 
 impl ChatState {
-    pub fn new(room: MatrixRoom, store: &mut ProgramStore) -> Self {
+    pub fn new(room: MatrixRoom, thread: Option<OwnedEventId>, store: &mut ProgramStore) -> Self {
         let room_id = room.room_id().to_owned();
-        let scrollback = ScrollbackState::new(room_id.clone());
+        let scrollback = ScrollbackState::new(room_id.clone(), thread.clone());
-        let id = IambBufferId::Room(room_id.clone(), RoomFocus::MessageBar);
+        let id = IambBufferId::Room(room_id.clone(), thread, RoomFocus::MessageBar);
         let ebuf = store.load_buffer(id);
         let tbox = TextBoxState::new(ebuf);
 
@@ -129,6 +132,10 @@ impl ChatState {
         }
     }
 
+    pub fn thread(&self) -> Option<&OwnedEventId> {
+        self.scrollback.thread()
+    }
+
     fn get_joined(&self, worker: &Requester) -> Result<MatrixRoom, IambError> {
         let Some(room) = worker.client.get_room(self.id()) else {
             return Err(IambError::NotJoined);
@@ -141,6 +148,29 @@ impl ChatState {
         }
     }
 
+    fn get_thread_last<'a>(
+        &self,
+        thread_root: &OwnedEventId,
+        info: &'a RoomInfo,
+    ) -> Option<&'a OriginalRoomMessageEvent> {
+        let last = info.threads.get(thread_root).and_then(|t| Some(t.last_key_value()?.1));
+
+        let msg = if let Some(last) = last {
+            &last.event
+        } else if let EventLocation::Message(_, key) = info.keys.get(thread_root)? {
+            let msg = info.messages.get(key)?;
+            &msg.event
+        } else {
+            return None;
+        };
+
+        if let MessageEvent::Original(ev) = &msg {
+            Some(ev)
+        } else {
+            None
+        }
+    }
+
     fn get_reply_to<'a>(&self, info: &'a RoomInfo) -> Option<&'a OriginalRoomMessageEvent> {
         let key = self.reply_to.as_ref()?;
         let msg = info.messages.get(key)?;
@@ -485,8 +515,15 @@ impl ChatState {
                     )));
 
                     show_echo = false;
+                } else if let Some(thread_root) = self.scrollback.thread() {
+                    if let Some(m) = self.get_reply_to(info) {
+                        msg = msg.make_for_thread(m, ReplyWithinThread::Yes, AddMentions::No);
+                    } else if let Some(m) = self.get_thread_last(thread_root, info) {
+                        msg = msg.make_for_thread(m, ReplyWithinThread::No, AddMentions::No);
+                    } else {
+                        // Internal state is wonky?
+                    }
                 } else if let Some(m) = self.get_reply_to(info) {
-                    // XXX: Switch to RoomMessageEventContent::reply() once it's stable?
                     msg = msg.make_reply_to(m, ForwardThread::Yes, AddMentions::No);
                 }
 
@@ -560,7 +597,8 @@ impl ChatState {
             let key = (MessageTimeStamp::LocalEcho, event_id.clone());
             let msg = MessageEvent::Local(event_id, msg.into());
             let msg = Message::new(msg, user, MessageTimeStamp::LocalEcho);
-            info.messages.insert(key, msg);
+            let thread = self.scrollback.get_thread_mut(info);
+            thread.insert(key, msg);
         }
 
         // Jump to the end of the scrollback to show the message.
@@ -627,12 +665,14 @@ impl WindowOps<IambInfo> for ChatState {
     fn dup(&self, store: &mut ProgramStore) -> Self {
         // XXX: I want each WindowSlot to have its own shared buffer, instead of each Room; need to
         // find a good way to pass that info here so that it can be part of the content id.
-        let id = IambBufferId::Room(self.room_id.clone(), RoomFocus::MessageBar);
+        let room_id = self.room_id.clone();
+        let thread = self.thread().cloned();
+        let id = IambBufferId::Room(room_id.clone(), thread, RoomFocus::MessageBar);
         let ebuf = store.load_buffer(id);
         let tbox = TextBoxState::new(ebuf);
 
         ChatState {
-            room_id: self.room_id.clone(),
+            room_id,
             room: self.room.clone(),
 
             tbox,
@@ -688,8 +728,10 @@ impl Editable<ProgramContext, ProgramStore, IambInfo> for ChatState {
 
         match delegate!(self, w => w.editor_command(act, ctx, store)) {
             res @ Ok(_) => res,
-            Err(EditError::WrongBuffer(IambBufferId::Room(room_id, focus)))
+            Err(EditError::WrongBuffer(IambBufferId::Room(room_id, thread, focus)))
-                if room_id == self.room_id && act.is_switchable(ctx) =>
+                if room_id == self.room_id &&
+                    thread.as_ref() == self.thread() &&
+                    act.is_switchable(ctx) =>
             {
                 // Switch focus.
                 self.focus = focus;
@@ -807,7 +849,7 @@ impl Promptable<ProgramContext, ProgramStore, IambInfo> for ChatState {
         store: &mut ProgramStore,
     ) -> EditResult<Vec<(ProgramAction, ProgramContext)>, IambInfo> {
         if let RoomFocus::Scrollback = self.focus {
-            return Ok(vec![]);
+            return self.scrollback.prompt(act, ctx, store);
         }
 
         match act {

src/windows/room/mod.rs

@@ -6,6 +6,7 @@ use matrix_sdk::{
             room::{name::RoomNameEventContent, topic::RoomTopicEventContent},
             tag::{TagInfo, Tags},
         },
+        OwnedEventId,
         RoomId,
     },
     DisplayName,
@@ -90,6 +91,7 @@ impl From<SpaceState> for RoomState {
 impl RoomState {
     pub fn new(
         room: MatrixRoom,
+        thread: Option<OwnedEventId>,
         name: DisplayName,
         tags: Option<Tags>,
         store: &mut ProgramStore,
@@ -102,7 +104,14 @@ impl RoomState {
         if room.is_space() {
             SpaceState::new(room).into()
         } else {
-            ChatState::new(room, store).into()
+            ChatState::new(room, thread, store).into()
+        }
+    }
+
+    pub fn thread(&self) -> Option<&OwnedEventId> {
+        match self {
+            RoomState::Chat(chat) => chat.thread(),
+            RoomState::Space(_) => None,
         }
     }
 
@@ -293,7 +302,15 @@ impl RoomState {
     pub fn get_title(&self, store: &mut ProgramStore) -> Line {
         let title = store.application.get_room_title(self.id());
         let style = Style::default().add_modifier(StyleModifier::BOLD);
-        let mut spans = vec![Span::styled(title, style)];
+        let mut spans = vec![];
+
+        if let RoomState::Chat(chat) = self {
+            if chat.thread().is_some() {
+                spans.push("Thread in ".into());
+            }
+        }
+
+        spans.push(Span::styled(title, style));
 
         match self.room().topic() {
             Some(desc) if !desc.is_empty() => {

src/windows/room/scrollback.rs

@@ -3,7 +3,7 @@
 use ratatui_image::Image;
 use regex::Regex;
 
-use matrix_sdk::ruma::OwnedRoomId;
+use matrix_sdk::ruma::{OwnedEventId, OwnedRoomId};
 
 use modalkit_ratatui::{ScrollActions, TerminalCursor, WindowOps};
 use ratatui::{
@@ -29,6 +29,7 @@ use modalkit::actions::{
     Scrollable,
     Searchable,
     SelectionAction,
+    WindowAction,
 };
 use modalkit::editing::{
     completion::CompletionList,
@@ -44,11 +45,13 @@ use modalkit::prelude::*;
 use crate::{
     base::{
         IambBufferId,
+        IambId,
         IambInfo,
         IambResult,
         Need,
         ProgramContext,
         ProgramStore,
+        RoomFetchStatus,
         RoomFocus,
         RoomInfo,
     },
@@ -56,9 +59,9 @@ use crate::{
     message::{Message, MessageCursor, MessageKey, Messages},
 };
 
-fn nth_key_before(pos: MessageKey, n: usize, info: &RoomInfo) -> MessageKey {
+fn nth_key_before(pos: MessageKey, n: usize, thread: &Messages) -> MessageKey {
     let mut end = &pos;
-    let iter = info.messages.range(..=&pos).rev().enumerate();
+    let iter = thread.range(..=&pos).rev().enumerate();
 
     for (i, (key, _)) in iter {
         end = key;
@@ -71,13 +74,13 @@ fn nth_key_before(pos: MessageKey, n: usize, info: &RoomInfo) -> MessageKey {
     end.clone()
 }
 
-fn nth_before(pos: MessageKey, n: usize, info: &RoomInfo) -> MessageCursor {
+fn nth_before(pos: MessageKey, n: usize, thread: &Messages) -> MessageCursor {
-    nth_key_before(pos, n, info).into()
+    nth_key_before(pos, n, thread).into()
 }
 
-fn nth_key_after(pos: MessageKey, n: usize, info: &RoomInfo) -> MessageKey {
+fn nth_key_after(pos: MessageKey, n: usize, thread: &Messages) -> MessageKey {
     let mut end = &pos;
-    let iter = info.messages.range(&pos..).enumerate();
+    let iter = thread.range(&pos..).enumerate();
 
     for (i, (key, _)) in iter {
         end = key;
@@ -90,12 +93,12 @@ fn nth_key_after(pos: MessageKey, n: usize, info: &RoomInfo) -> MessageKey {
     end.clone()
 }
 
-fn nth_after(pos: MessageKey, n: usize, info: &RoomInfo) -> MessageCursor {
+fn nth_after(pos: MessageKey, n: usize, thread: &Messages) -> MessageCursor {
-    nth_key_after(pos, n, info).into()
+    nth_key_after(pos, n, thread).into()
 }
 
-fn prevmsg<'a>(key: &MessageKey, info: &'a RoomInfo) -> Option<&'a Message> {
+fn prevmsg<'a>(key: &MessageKey, thread: &'a Messages) -> Option<&'a Message> {
-    info.messages.range(..key).next_back().map(|(_, v)| v)
+    thread.range(..key).next_back().map(|(_, v)| v)
 }
 
 pub struct ScrollbackState {
@@ -105,6 +108,9 @@ pub struct ScrollbackState {
     /// The buffer identifier used for saving marks, etc.
     id: IambBufferId,
 
+    /// The currently focused thread in this room.
+    thread: Option<OwnedEventId>,
+
     /// The currently selected message in the scrollback.
     cursor: MessageCursor,
 
@@ -122,8 +128,8 @@ pub struct ScrollbackState {
 }
 
 impl ScrollbackState {
-    pub fn new(room_id: OwnedRoomId) -> ScrollbackState {
+    pub fn new(room_id: OwnedRoomId, thread: Option<OwnedEventId>) -> ScrollbackState {
-        let id = IambBufferId::Room(room_id.to_owned(), RoomFocus::Scrollback);
+        let id = IambBufferId::Room(room_id.to_owned(), thread.clone(), RoomFocus::Scrollback);
         let cursor = MessageCursor::default();
         let viewctx = ViewportContext::default();
         let jumped = HistoryList::default();
@@ -132,6 +138,7 @@ impl ScrollbackState {
         ScrollbackState {
             room_id,
             id,
+            thread,
             cursor,
             viewctx,
             jumped,
@@ -152,7 +159,7 @@ impl ScrollbackState {
         self.cursor
             .timestamp
             .clone()
-            .or_else(|| info.messages.last_key_value().map(|kv| kv.0.clone()))
+            .or_else(|| self.get_thread(info).last_key_value().map(|kv| kv.0.clone()))
     }
 
     pub fn get_mut<'a>(&mut self, messages: &'a mut Messages) -> Option<&'a mut Message> {
@@ -163,26 +170,80 @@ impl ScrollbackState {
         }
     }
 
+    pub fn thread(&self) -> Option<&OwnedEventId> {
+        self.thread.as_ref()
+    }
+
+    pub fn get_thread<'a>(&self, info: &'a RoomInfo) -> &'a Messages {
+        if let Some(thread_root) = self.thread.as_ref() {
+            info.threads.get(thread_root).unwrap_or(&info.messages)
+        } else {
+            &info.messages
+        }
+    }
+
+    pub fn get_thread_mut<'a>(&self, info: &'a mut RoomInfo) -> &'a mut Messages {
+        if let Some(thread_root) = self.thread.as_ref() {
+            info.threads.get_mut(thread_root).unwrap_or(&mut info.messages)
+        } else {
+            &mut info.messages
+        }
+    }
+
     pub fn messages<'a>(
         &self,
         range: EditRange<MessageCursor>,
         info: &'a RoomInfo,
     ) -> impl Iterator<Item = (&'a MessageKey, &'a Message)> {
-        let start = range.start.to_key(info);
+        let thread = self.get_thread(info);
-        let end = range.end.to_key(info);
+        let start = range.start.to_key(thread);
+        let end = range.end.to_key(thread);
 
         let (start, end) = if let (Some(start), Some(end)) = (start, end) {
             (start, end)
-        } else if let Some((last, _)) = info.messages.last_key_value() {
+        } else if let Some((last, _)) = thread.last_key_value() {
             (last, last)
         } else {
-            return info.messages.range(..);
+            return thread.range(..);
         };
 
         if range.inclusive {
-            info.messages.range(start..=end)
+            thread.range(start..=end)
         } else {
-            info.messages.range(start..end)
+            thread.range(start..end)
+        }
+    }
+
+    fn need_more_messages(&self, info: &RoomInfo) -> bool {
+        match info.fetch_id {
+            // Don't fetch if we've already hit the end of history.
+            RoomFetchStatus::Done => return false,
+            // Fetch at least once if we're viewing a room.
+            RoomFetchStatus::NotStarted => return true,
+            _ => {},
+        }
+
+        let first_key = self.get_thread(info).first_key_value().map(|(k, _)| k);
+        let at_top = first_key == self.viewctx.corner.timestamp.as_ref();
+
+        match (at_top, self.thread.as_ref()) {
+            (false, _) => {
+                // Not scrolled to top, don't fetch.
+                false
+            },
+            (true, None) => {
+                // Scrolled to top in non-thread, fetch.
+                true
+            },
+            (true, Some(thread_root)) => {
+                // Scrolled to top in thread, fetch until we have the thread root.
+                //
+                // Typically, if the user has entered a thread view, we should already have fetched
+                // all the way back to the thread root, but it is technically possible via :threads
+                // or when restoring a thread view in the layout at startup to not have the message
+                // yet.
+                !info.keys.contains_key(thread_root)
+            },
         }
     }
 
@@ -193,7 +254,8 @@ impl ScrollbackState {
         info: &RoomInfo,
         settings: &ApplicationSettings,
     ) {
-        let selidx = if let Some(key) = self.cursor.to_key(info) {
+        let thread = self.get_thread(info);
+        let selidx = if let Some(key) = self.cursor.to_key(thread) {
             key
         } else {
             return;
@@ -207,9 +269,9 @@ impl ScrollbackState {
                 let mut lines = 0;
                 let target = self.viewctx.get_height() / 2;
 
-                for (key, item) in info.messages.range(..=&idx).rev() {
+                for (key, item) in thread.range(..=&idx).rev() {
                     let sel = selidx == key;
-                    let prev = prevmsg(key, info);
+                    let prev = prevmsg(key, thread);
                     let len = item.show(prev, sel, &self.viewctx, info, settings).lines.len();
 
                     if key == &idx {
@@ -230,9 +292,9 @@ impl ScrollbackState {
                 let mut lines = 0;
                 let target = self.viewctx.get_height();
 
-                for (key, item) in info.messages.range(..=&idx).rev() {
+                for (key, item) in thread.range(..=&idx).rev() {
                     let sel = key == selidx;
-                    let prev = prevmsg(key, info);
+                    let prev = prevmsg(key, thread);
                     let len = item.show(prev, sel, &self.viewctx, info, settings).lines.len();
 
                     lines += len;
@@ -248,8 +310,18 @@ impl ScrollbackState {
         }
     }
 
+    fn jump_changed(&mut self) -> bool {
+        self.jumped.current() != &self.cursor
+    }
+
+    fn push_jump(&mut self) {
+        self.jumped.push(self.cursor.clone());
+    }
+
     fn shift_cursor(&mut self, info: &RoomInfo, settings: &ApplicationSettings) {
-        let last_key = if let Some(k) = info.messages.last_key_value() {
+        let thread = self.get_thread(info);
+
+        let last_key = if let Some(k) = thread.last_key_value() {
             k.0
         } else {
             return;
@@ -266,9 +338,9 @@ impl ScrollbackState {
         let mut lines = 0;
 
         let cursor_key = self.cursor.timestamp.as_ref().unwrap_or(last_key);
-        let mut prev = prevmsg(cursor_key, info);
+        let mut prev = prevmsg(cursor_key, thread);
 
-        for (idx, item) in info.messages.range(corner_key.clone()..) {
+        for (idx, item) in thread.range(corner_key.clone()..) {
             if idx == cursor_key {
                 // Cursor is already within the viewport.
                 break;
@@ -317,7 +389,7 @@ impl ScrollbackState {
             MoveType::BufferLineOffset => None,
             MoveType::BufferLinePercent => None,
             MoveType::BufferPos(MovePosition::Beginning) => {
-                let start = info.messages.first_key_value()?.0.clone();
+                let start = self.get_thread(info).first_key_value()?.0.clone();
 
                 Some(start.into())
             },
@@ -330,9 +402,11 @@ impl ScrollbackState {
             MoveType::ParagraphBegin(dir) |
             MoveType::SectionBegin(dir) |
             MoveType::SectionEnd(dir) => {
+                let thread = self.get_thread(info);
+
                 match dir {
-                    MoveDir1D::Previous => nth_before(pos, count, info).into(),
+                    MoveDir1D::Previous => nth_before(pos, count, thread).into(),
-                    MoveDir1D::Next => nth_after(pos, count, info).into(),
+                    MoveDir1D::Next => nth_after(pos, count, thread).into(),
                 }
             },
             MoveType::ViewportPos(MovePosition::Beginning) => {
@@ -381,12 +455,14 @@ impl ScrollbackState {
             RangeType::XmlTag => None,
 
             RangeType::Buffer => {
-                let start = info.messages.first_key_value()?.0.clone();
+                let thread = self.get_thread(info);
-                let end = info.messages.last_key_value()?.0.clone();
+                let start = thread.first_key_value()?.0.clone();
+                let end = thread.last_key_value()?.0.clone();
 
                 Some(EditRange::inclusive(start.into(), end.into(), TargetShape::LineWise))
             },
             RangeType::Line | RangeType::Paragraph | RangeType::Sentence => {
+                let thread = self.get_thread(info);
                 let count = ctx.resolve(count);
 
                 if count == 0 {
@@ -395,7 +471,7 @@ impl ScrollbackState {
 
                 let mut end = &pos;
 
-                for (i, (key, _)) in info.messages.range(&pos..).enumerate() {
+                for (i, (key, _)) in thread.range(&pos..).enumerate() {
                     if i >= count {
                         break;
                     }
@@ -420,9 +496,10 @@ impl ScrollbackState {
         mut count: usize,
         info: &RoomInfo,
     ) -> Option<MessageCursor> {
+        let thread = self.get_thread(info);
         let mut mc = None;
 
-        for (key, msg) in info.messages.range(&start..) {
+        for (key, msg) in thread.range(&start..) {
             if count == 0 {
                 break;
             }
@@ -447,9 +524,10 @@ impl ScrollbackState {
         mut count: usize,
         info: &RoomInfo,
     ) -> (Option<MessageCursor>, bool) {
+        let thread = self.get_thread(info);
         let mut mc = None;
 
-        for (key, msg) in info.messages.range(..&end).rev() {
+        for (key, msg) in thread.range(..&end).rev() {
             if count == 0 {
                 break;
             }
@@ -487,6 +565,7 @@ impl WindowOps<IambInfo> for ScrollbackState {
         ScrollbackState {
             room_id: self.room_id.clone(),
             id: self.id.clone(),
+            thread: self.thread.clone(),
             cursor: self.cursor.clone(),
             viewctx: self.viewctx.clone(),
             jumped: self.jumped.clone(),
@@ -535,7 +614,8 @@ impl EditorActions<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
         store: &mut ProgramStore,
     ) -> EditResult<EditInfo, IambInfo> {
         let info = store.application.rooms.get_or_default(self.room_id.clone());
-        let key = if let Some(k) = self.cursor.to_key(info) {
+        let thread = self.get_thread(info);
+        let key = if let Some(k) = self.cursor.to_key(thread) {
             k.clone()
         } else {
             let msg = "No messages to select.";
@@ -546,7 +626,7 @@ impl EditorActions<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
         match operation {
             EditAction::Motion => {
                 if motion.is_jumping() {
-                    self.jumped.push(self.cursor.clone());
+                    self.push_jump();
                 }
 
                 let pos = match motion {
@@ -564,9 +644,10 @@ impl EditorActions<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
                     EditTarget::CharJump(mark) | EditTarget::LineJump(mark) => {
                         let mark = ctx.resolve(mark);
                         let cursor = store.cursors.get_mark(self.id.clone(), mark)?;
+                        let thread = self.get_thread(info);
 
-                        if let mc @ Some(_) = MessageCursor::from_cursor(&cursor, info) {
+                        if let Some(mc) = MessageCursor::from_cursor(&cursor, thread) {
-                            mc
+                            Some(mc)
                         } else {
                             let msg = "Failed to restore mark";
                             let err = EditError::Failure(msg.into());
@@ -642,8 +723,9 @@ impl EditorActions<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
                     EditTarget::CharJump(mark) | EditTarget::LineJump(mark) => {
                         let mark = ctx.resolve(mark);
                         let cursor = store.cursors.get_mark(self.id.clone(), mark)?;
+                        let thread = self.get_thread(info);
 
-                        if let Some(c) = MessageCursor::from_cursor(&cursor, info) {
+                        if let Some(c) = MessageCursor::from_cursor(&cursor, thread) {
                             self._range_to(c).into()
                         } else {
                             let msg = "Failed to restore mark";
@@ -739,8 +821,9 @@ impl EditorActions<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
         store: &mut ProgramStore,
     ) -> EditResult<EditInfo, IambInfo> {
         let info = store.application.get_room_info(self.room_id.clone());
+        let thread = self.get_thread(info);
 
-        if let Some(cursor) = self.cursor.to_cursor(info) {
+        if let Some(cursor) = self.cursor.to_cursor(thread) {
             store.cursors.set_mark(self.id.clone(), name, cursor);
 
             Ok(None)
@@ -814,11 +897,13 @@ impl EditorActions<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
                 let ngroup = store.cursors.get_group(self.id.clone(), &reg)?;
 
                 // Lists don't have groups; override current position.
-                if self.jumped.current() != &self.cursor {
+                if self.jump_changed() {
-                    self.jumped.push(self.cursor.clone());
+                    self.push_jump();
                 }
 
-                if let Some(mc) = MessageCursor::from_cursor(ngroup.leader.cursor(), info) {
+                let thread = self.get_thread(info);
+
+                if let Some(mc) = MessageCursor::from_cursor(ngroup.leader.cursor(), thread) {
                     self.cursor = mc;
 
                     Ok(None)
@@ -831,9 +916,10 @@ impl EditorActions<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
             },
             CursorAction::Save(_) => {
                 let reg = ctx.get_register().unwrap_or(Register::UnnamedCursorGroup);
+                let thread = self.get_thread(info);
 
                 // Lists don't have groups; override any previously saved group.
-                let cursor = self.cursor.to_cursor(info).ok_or_else(|| {
+                let cursor = self.cursor.to_cursor(thread).ok_or_else(|| {
                     let msg = "Cannot save position in message history";
                     EditError::Failure(msg.into())
                 })?;
@@ -892,14 +978,14 @@ impl Jumpable<ProgramContext, IambInfo> for ScrollbackState {
                 let msg = "No changes to jump to within the list";
                 let err = UIError::Failure(msg.into());
 
-                return Err(err);
+                Err(err)
             },
             PositionList::JumpList => {
                 let (len, pos) = match dir {
                     MoveDir1D::Previous => {
-                        if self.jumped.future_len() == 0 && *self.jumped.current() != self.cursor {
+                        if self.jumped.future_len() == 0 && self.jump_changed() {
                             // Push current position if this is the first jump backwards.
-                            self.jumped.push(self.cursor.clone());
+                            self.push_jump();
                         }
 
                         let plen = self.jumped.past_len();
@@ -919,7 +1005,7 @@ impl Jumpable<ProgramContext, IambInfo> for ScrollbackState {
                     self.cursor = pos.clone();
                 }
 
-                return Ok(count.saturating_sub(len));
+                Ok(count.saturating_sub(len))
             },
         }
     }
@@ -929,48 +1015,42 @@ impl Promptable<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
     fn prompt(
         &mut self,
         act: &PromptAction,
-        _: &ProgramContext,
+        ctx: &ProgramContext,
         store: &mut ProgramStore,
     ) -> EditResult<Vec<(Action<IambInfo>, ProgramContext)>, IambInfo> {
         let info = store.application.get_room_info(self.room_id.clone());
+        let thread = self.get_thread(info);
 
-        let _ = if let Some(key) = self.cursor.to_key(info) {
+        let Some(key) = self.cursor.to_key(thread) else {
-            key
-        } else {
             let msg = "No message currently selected";
             let err = EditError::Failure(msg.into());
-
             return Err(err);
         };
 
         match act {
             PromptAction::Submit => {
-                // XXX: I'm not sure exactly what to do here yet. I think I want this to display a
+                if self.thread.is_some() {
-                // pop-over ListState with actions that can then be submitted:
+                    let msg =
-                //
+                        "You are already in a thread. Use :reply to reply to a specific message.";
-                // - Create a reply
+                    let err = EditError::Failure(msg.into());
-                // - Edit a message
+                    Err(err)
-                // - Redact a message
+                } else {
-                // - React to a message
+                    let root = key.1.clone();
-                // - Report a message
+                    let room_id = self.room_id.clone();
-                // - Download an attachment
+                    let id = IambId::Room(room_id, Some(root));
-                //
+                    let open = WindowAction::Switch(OpenTarget::Application(id));
-                // Each of these should correspond to a command that a user can run. For example,
+                    Ok(vec![(open.into(), ctx.clone())])
-                // running `:reply` when hovering over a message should be equivalent to opening
+                }
-                // the pop-up and selecting "Reply To This Message".
-                return Ok(vec![]);
             },
             PromptAction::Abort(..) => {
                 let msg = "Cannot abort a message.";
                 let err = EditError::Failure(msg.into());
-
+                Err(err)
-                return Err(err);
             },
             PromptAction::Recall(..) => {
                 let msg = "Cannot recall previous messages.";
                 let err = EditError::Failure(msg.into());
-
+                Err(err)
-                return Err(err);
             },
         }
     }
@@ -988,8 +1068,9 @@ impl ScrollActions<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
         let info = store.application.rooms.get_or_default(self.room_id.clone());
         let settings = &store.application.settings;
         let mut corner = self.viewctx.corner.clone();
+        let thread = self.get_thread(info);
 
-        let last_key = if let Some(k) = info.messages.last_key_value() {
+        let last_key = if let Some(k) = thread.last_key_value() {
             k.0
         } else {
             return Ok(None);
@@ -1008,11 +1089,11 @@ impl ScrollActions<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
 
         match dir {
             MoveDir2D::Up => {
-                let first_key = info.messages.first_key_value().map(|f| f.0.clone());
+                let first_key = thread.first_key_value().map(|f| f.0.clone());
 
-                for (key, item) in info.messages.range(..=&corner_key).rev() {
+                for (key, item) in thread.range(..=&corner_key).rev() {
                     let sel = key == cursor_key;
-                    let prev = prevmsg(key, info);
+                    let prev = prevmsg(key, thread);
                     let txt = item.show(prev, sel, &self.viewctx, info, settings);
                     let len = txt.height().max(1);
                     let max = len.saturating_sub(1);
@@ -1037,9 +1118,9 @@ impl ScrollActions<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
                 }
             },
             MoveDir2D::Down => {
-                let mut prev = prevmsg(&corner_key, info);
+                let mut prev = prevmsg(&corner_key, thread);
 
-                for (key, item) in info.messages.range(&corner_key..) {
+                for (key, item) in thread.range(&corner_key..) {
                     let sel = key == cursor_key;
                     let txt = item.show(prev, sel, &self.viewctx, info, settings);
                     let len = txt.height().max(1);
@@ -1101,8 +1182,9 @@ impl ScrollActions<ProgramContext, ProgramStore, IambInfo> for ScrollbackState {
             Axis::Vertical => {
                 let info = store.application.rooms.get_or_default(self.room_id.clone());
                 let settings = &store.application.settings;
+                let thread = self.get_thread(info);
 
-                if let Some(key) = self.cursor.to_key(info).cloned() {
+                if let Some(key) = self.cursor.to_key(thread).cloned() {
                     self.scrollview(key, pos, info, settings);
                 }
 
@@ -1237,14 +1319,18 @@ impl<'a> StatefulWidget for Scrollback<'a> {
             state.viewctx.corner = state.cursor.clone();
         }
 
+        let thread = state.get_thread(info);
+
         let cursor = &state.cursor;
-        let cursor_key = if let Some(k) = cursor.to_key(info) {
+        let cursor_key = if let Some(k) = cursor.to_key(thread) {
             k
         } else {
+            if state.need_more_messages(info) {
                 self.store
                     .application
                     .need_load
                     .insert(state.room_id.to_owned(), Need::MESSAGES);
+            }
             return;
         };
 
@@ -1252,16 +1338,16 @@ impl<'a> StatefulWidget for Scrollback<'a> {
         let corner_key = if let Some(k) = &corner.timestamp {
             k.clone()
         } else {
-            nth_key_before(cursor_key.clone(), height, info)
+            nth_key_before(cursor_key.clone(), height, thread)
         };
 
         let foc = self.focused || cursor.timestamp.is_some();
         let full = std::mem::take(&mut state.show_full_on_redraw) || cursor.timestamp.is_none();
         let mut lines = vec![];
         let mut sawit = false;
-        let mut prev = prevmsg(&corner_key, info);
+        let mut prev = prevmsg(&corner_key, thread);
 
-        for (key, item) in info.messages.range(&corner_key..) {
+        for (key, item) in thread.range(&corner_key..) {
             let sel = key == cursor_key;
             let txt = item.show(prev, foc && sel, &state.viewctx, info, settings);
 
@@ -1338,14 +1424,13 @@ impl<'a> StatefulWidget for Scrollback<'a> {
             state.cursor.timestamp.is_none()
         {
             // If the cursor is at the last message, then update the read marker.
-            if let Some((k, _)) = info.messages.last_key_value() {
+            if let Some((k, _)) = thread.last_key_value() {
                 info.set_receipt(settings.profile.user_id.clone(), k.1.clone());
             }
         }
 
         // Check whether we should load older messages for this room.
-        let first_key = info.messages.first_key_value().map(|(k, _)| k.clone());
+        if state.need_more_messages(info) {
-        if first_key == state.viewctx.corner.timestamp {
             // If the top of the screen is the older message, load more.
             self.store
                 .application
@@ -1364,7 +1449,7 @@ mod tests {
     async fn test_search_messages() {
         let room_id = TEST_ROOM1_ID.clone();
         let mut store = mock_store().await;
-        let mut scrollback = ScrollbackState::new(room_id.clone());
+        let mut scrollback = ScrollbackState::new(room_id.clone(), None);
         let ctx = ProgramContext::default();
 
         let next = MoveDirMod::Exact(MoveDir1D::Next);
@@ -1418,7 +1503,7 @@ mod tests {
     #[tokio::test]
     async fn test_movement() {
         let mut store = mock_store().await;
-        let mut scrollback = ScrollbackState::new(TEST_ROOM1_ID.clone());
+        let mut scrollback = ScrollbackState::new(TEST_ROOM1_ID.clone(), None);
         let ctx = ProgramContext::default();
 
         let prev = |n: usize| EditTarget::Motion(MoveType::Line(MoveDir1D::Previous), n.into());
@@ -1452,7 +1537,7 @@ mod tests {
     #[tokio::test]
     async fn test_dirscroll() {
         let mut store = mock_store().await;
-        let mut scrollback = ScrollbackState::new(TEST_ROOM1_ID.clone());
+        let mut scrollback = ScrollbackState::new(TEST_ROOM1_ID.clone(), None);
         let ctx = ProgramContext::default();
 
         let prev = MoveDir2D::Up;
@@ -1603,7 +1688,7 @@ mod tests {
     #[tokio::test]
     async fn test_cursorpos() {
         let mut store = mock_store().await;
-        let mut scrollback = ScrollbackState::new(TEST_ROOM1_ID.clone());
+        let mut scrollback = ScrollbackState::new(TEST_ROOM1_ID.clone(), None);
         let ctx = ProgramContext::default();
 
         // Skip rendering typing notices.

src/windows/room/space.rs

@@ -39,7 +39,7 @@ pub struct SpaceState {
 impl SpaceState {
     pub fn new(room: MatrixRoom) -> Self {
         let room_id = room.room_id().to_owned();
-        let content = IambBufferId::Room(room_id.clone(), RoomFocus::Scrollback);
+        let content = IambBufferId::Room(room_id.clone(), None, RoomFocus::Scrollback);
         let list = ListState::new(content, vec![]);
         let last_fetch = None;
 

src/worker.rs

@@ -409,7 +409,7 @@ fn members_insert(
 ) {
     if let Ok(members) = res {
         let ChatStore { rooms, .. } = &mut store.application;
-        let info = rooms.get_or_default(room_id.clone());
+        let info = rooms.get_or_default(room_id);
 
         for member in members {
             let user_id = member.user_id();
@@ -1069,12 +1069,20 @@ impl ClientWorker {
 
                     match info.keys.get(redacts) {
                         None => return,
-                        Some(EventLocation::Message(key)) => {
+                        Some(EventLocation::Message(None, key)) => {
                             if let Some(msg) = info.messages.get_mut(key) {
                                 let ev = SyncRoomRedactionEvent::Original(ev);
                                 msg.redact(ev, room_version);
                             }
                         },
+                        Some(EventLocation::Message(Some(root), key)) => {
+                            if let Some(thread) = info.threads.get_mut(root) {
+                                if let Some(msg) = thread.get_mut(key) {
+                                    let ev = SyncRoomRedactionEvent::Original(ev);
+                                    msg.redact(ev, room_version);
+                                }
+                            }
+                        },
                         Some(EventLocation::Reaction(event_id)) => {
                             if let Some(reactions) = info.reactions.get_mut(event_id) {
                                 reactions.remove(redacts);