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use std::{
    collections::{HashMap, VecDeque},
    sync::Arc,
};

use futures_util::future::{join_all, try_join};
use matrix_sdk::{
    Client, Room, RoomState, deserialized_responses::TimelineEvent as SdkTimelineEvent,
    room::MessagesOptions,
};
use ruma::{OwnedEventId, OwnedRoomId, OwnedUserId, UInt, push::Action};
use serde_json::Value;
use tokio::sync::{Mutex, broadcast::error::RecvError};

use crate::{
    Error, ErrorKind, EventContext, EventContextCommand, EventContextPage, EventContextSession,
    MediaId, Sender, TimelineEvent, TimelineItem,
    engine::MediaService,
    normalise::{
        MediaRegistration, MediaScope, apply_profiles, normalise_context, normalise_observed,
        resolve_replies,
    },
};

const MAX_CONTEXT_LIMIT: u16 = 50;
/// a consumer that never closes its jump views still holds at most this many
const MAX_SESSIONS: usize = 32;

/// open event contexts, oldest first, each owning the media its pages registered
#[derive(Default)]
pub(crate) struct Sessions {
    open: Mutex<VecDeque<Session>>,
}

struct Session {
    id: String,
    room_id: OwnedRoomId,
    scope: MediaScope,
}

impl Sessions {
    async fn open(
        &self,
        media: &MediaService,
        room_id: OwnedRoomId,
        registrations: Vec<MediaRegistration>,
    ) -> String {
        let scope = media.context_scope();
        let id = format!("context-{}", scope.nonce());
        let mut open = self.open.lock().await;
        media.register(&scope, registrations).await;
        open.push_back(Session {
            id: id.clone(),
            room_id,
            scope,
        });
        while open.len() > MAX_SESSIONS {
            if let Some(oldest) = open.pop_front() {
                media.release(&oldest.scope).await;
            }
        }
        id
    }

    async fn room(&self, id: &str) -> Result<OwnedRoomId, Error> {
        let open = self.open.lock().await;
        let session = open.iter().find(|session| session.id == id);
        session
            .map(|session| session.room_id.clone())
            .ok_or_else(not_open)
    }

    /// under the lock, so a page that lands after its close registers nothing
    async fn register(
        &self,
        media: &MediaService,
        id: &str,
        registrations: Vec<MediaRegistration>,
    ) -> Result<(), Error> {
        let open = self.open.lock().await;
        let session = open
            .iter()
            .find(|session| session.id == id)
            .ok_or_else(not_open)?;
        media.register(&session.scope, registrations).await;
        Ok(())
    }

    async fn close(&self, media: &MediaService, id: &str) -> Result<(), Error> {
        let mut open = self.open.lock().await;
        let index = open
            .iter()
            .position(|session| session.id == id)
            .ok_or_else(not_open)?;
        if let Some(session) = open.remove(index) {
            media.release(&session.scope).await;
        }
        Ok(())
    }

    async fn close_left(&self, media: &MediaService, client: &Client) {
        let mut open = self.open.lock().await;
        let mut kept = VecDeque::with_capacity(open.len());
        for session in open.drain(..) {
            let left = client
                .get_room(&session.room_id)
                .is_none_or(|room| matches!(room.state(), RoomState::Left | RoomState::Banned));
            if left {
                media.release(&session.scope).await;
            } else {
                kept.push_back(session);
            }
        }
        *open = kept;
    }

    /// the media service is cleared beside this, so nothing is released one by one
    pub(crate) async fn clear(&self) {
        self.open.lock().await.clear();
    }
}

fn not_open() -> Error {
    Error::new(
        ErrorKind::EventContextNotOpen,
        "event context is closed or was never opened",
    )
}

/// leaving a room closes its event contexts
pub(super) async fn close_on_leave(
    client: Client,
    media: Arc<MediaService>,
    sessions: Arc<Sessions>,
) {
    let mut info = client.room_info_notable_update_receiver();
    loop {
        match info.recv().await {
            Ok(_) | Err(RecvError::Lagged(_)) => sessions.close_left(&media, &client).await,
            Err(RecvError::Closed) => return,
        }
    }
}

pub(crate) async fn execute(
    client: Client,
    media: Arc<MediaService>,
    sessions: Arc<Sessions>,
    command: EventContextCommand,
) -> Result<crate::CommandOutput, Error> {
    let current_user_id = client.user_id().map(ToOwned::to_owned);
    let room = |room_id: &OwnedRoomId| client.get_room(room_id).ok_or_else(Error::room_unknown);
    let (context_id, token, limit, backwards) = match command {
        EventContextCommand::Fetch {
            room_id,
            event_id,
            before_limit,
            after_limit,
        } => {
            let (context, registrations, _) = capture(
                room(&room_id)?,
                current_user_id,
                event_id,
                before_limit,
                after_limit,
            )
            .await?;
            let context_id = sessions.open(&media, room_id, registrations).await;
            return Ok(crate::CommandOutput::EventContext(EventContextSession {
                context_id,
                context,
            }));
        }
        EventContextCommand::Close { context_id } => {
            sessions.close(&media, &context_id).await?;
            return Ok(crate::CommandOutput::Done);
        }
        EventContextCommand::Before {
            context_id,
            token,
            limit,
        } => (context_id, token, limit, true),
        EventContextCommand::After {
            context_id,
            token,
            limit,
        } => (context_id, token, limit, false),
    };
    if limit == 0 {
        return Err(Error::new(
            ErrorKind::Invalid,
            "context page limit must be at least 1",
        ));
    }
    validate_limit(limit)?;
    if token.is_empty() {
        return Err(Error::new(
            ErrorKind::Invalid,
            "context pagination token is empty",
        ));
    }
    let room = room(&sessions.room(&context_id).await?)?;
    let side = fetch_side(&room, Some(&token), limit, backwards).await?;
    let mut page = Assembly::new(
        &room,
        current_user_id.as_deref(),
        &side.values,
        &side.highlights,
        None,
    )
    .await;
    let events = page.take(0..side.values.len());
    sessions.register(&media, &context_id, page.media).await?;
    Ok(crate::CommandOutput::EventContextPage(EventContextPage {
        events,
        next_token: side.token,
    }))
}

pub(crate) async fn capture(
    room: Room,
    current_user_id: Option<OwnedUserId>,
    event_id: OwnedEventId,
    before_limit: u16,
    after_limit: u16,
) -> Result<(EventContext, Vec<MediaRegistration>, Vec<Value>), Error> {
    validate_limit(before_limit)?;
    validate_limit(after_limit)?;
    let raw = room
        .event_with_context(&event_id, false, UInt::from(0_u16), None)
        .await
        .map_err(|source| {
            let error = Error::from_sdk("fetching event context failed", source);
            if error
                .server
                .as_ref()
                .is_some_and(|server| server.status == 404)
            {
                Error::new(ErrorKind::EventNotFound, "event was not found")
            } else {
                error
            }
        })?;
    let (target, target_highlight) = raw
        .event
        .as_ref()
        .and_then(raw_event)
        .ok_or_else(|| Error::new(ErrorKind::EventNotFound, "event was not found"))?;
    let (before, after) = try_join(
        fetch_side(&room, raw.prev_batch_token.as_deref(), before_limit, true),
        fetch_side(&room, raw.next_batch_token.as_deref(), after_limit, false),
    )
    .await?;
    let target_index = before.values.len();
    let mut values = before.values;
    values.push(target);
    values.extend(after.values);
    let mut highlights = before.highlights;
    highlights.push(target_highlight);
    highlights.extend(after.highlights);
    let mut page = Assembly::new(
        &room,
        current_user_id.as_deref(),
        &values,
        &highlights,
        Some(target_index),
    )
    .await;
    let events_before = page.take(0..target_index);
    let event = page
        .take(target_index..target_index + 1)
        .pop()
        .ok_or_else(|| Error::new(ErrorKind::EventNotFound, "event could not be read"))?;
    let events_after = page.take(target_index + 1..values.len());
    Ok((
        EventContext {
            events_before,
            event,
            events_after,
            start_token: before.token,
            end_token: after.token,
        },
        page.media,
        values,
    ))
}

struct Side {
    /// in timeline order
    values: Vec<Value>,
    /// beside `values`, from the push actions the sdk worked out as it fetched
    highlights: Vec<bool>,
    token: Option<String>,
}

fn raw_event(event: &SdkTimelineEvent) -> Option<(Value, bool)> {
    let value = serde_json::from_str(event.raw().json().get()).ok()?;
    let highlight = event
        .push_actions()
        .is_some_and(|actions| actions.iter().any(Action::is_highlight));
    Some((value, highlight))
}

async fn fetch_side(
    room: &Room,
    token: Option<&str>,
    limit: u16,
    backwards: bool,
) -> Result<Side, Error> {
    let Some(token) = token else {
        return Ok(Side {
            values: Vec::new(),
            highlights: Vec::new(),
            token: None,
        });
    };
    if limit == 0 {
        return Ok(Side {
            values: Vec::new(),
            highlights: Vec::new(),
            token: Some(token.to_owned()),
        });
    }
    let mut options = if backwards {
        MessagesOptions::backward()
    } else {
        MessagesOptions::forward()
    };
    options = options.from(token);
    options.limit = UInt::from(limit);
    let messages = room
        .messages(options)
        .await
        .map_err(|source| Error::from_sdk("fetching event context events failed", source))?;
    let mut events: Vec<_> = messages.chunk.iter().filter_map(raw_event).collect();
    if backwards {
        events.reverse();
    }
    let (values, highlights) = events.into_iter().unzip();
    Ok(Side {
        values,
        highlights,
        token: messages.end,
    })
}

/// a window of raw events normalised together, so relations inside it land on their targets
struct Assembly {
    items: Vec<(usize, TimelineItem)>,
    media: Vec<MediaRegistration>,
}

impl Assembly {
    async fn new(
        room: &Room,
        current_user_id: Option<&ruma::UserId>,
        values: &[Value],
        highlights: &[bool],
        keep: Option<usize>,
    ) -> Self {
        let page = normalise_context(values, keep, current_user_id, room.room_id());
        let mut items = page.items;
        for (index, item) in &mut items {
            if let TimelineItem::Event(event) = item {
                event.highlight = highlights[*index];
            }
        }
        let mut media = page.media;
        let mut targets: HashMap<OwnedEventId, TimelineEvent> = HashMap::new();
        let mut missing = Vec::new();
        for (_, item) in &items {
            if let TimelineItem::Event(event) = item
                && let Some(event_id) = &event.event_id
            {
                targets.insert(event_id.clone(), (**event).clone());
            }
        }
        for event in events(&mut items) {
            if let Some(reply) = &event.reply_to
                && !targets.contains_key(&reply.event_id)
                && !missing.contains(&reply.event_id)
            {
                missing.push(reply.event_id.clone());
            }
        }
        let fetched = join_all(
            missing
                .into_iter()
                .map(|event_id| fetch_reply(room, current_user_id, event_id)),
        )
        .await;
        for (event, registrations) in fetched.into_iter().flatten() {
            media.extend(registrations);
            if let Some(event_id) = event.event_id.clone() {
                targets.insert(event_id, event);
            }
        }
        let profiles = profiles(
            room,
            items
                .iter()
                .filter_map(|(_, item)| match item {
                    TimelineItem::Event(event) => Some(&event.sender.user_id),
                    _ => None,
                })
                .chain(targets.values().map(|event| &event.sender.user_id)),
        )
        .await;
        apply_profiles(targets.values_mut(), &profiles);
        apply_profiles(events(&mut items), &profiles);
        resolve_replies(events(&mut items), &targets);
        Self { items, media }
    }

    /// the items that came from raw events in `range`
    fn take(&mut self, range: std::ops::Range<usize>) -> Vec<TimelineItem> {
        let (taken, kept) = std::mem::take(&mut self.items)
            .into_iter()
            .partition(|(index, _)| range.contains(index));
        self.items = kept;
        taken.into_iter().map(|(_, item)| item).collect()
    }
}

fn events(items: &mut [(usize, TimelineItem)]) -> impl Iterator<Item = &mut TimelineEvent> {
    items.iter_mut().filter_map(|(_, item)| match item {
        TimelineItem::Event(event) => Some(&mut **event),
        _ => None,
    })
}

async fn fetch_reply(
    room: &Room,
    current_user_id: Option<&ruma::UserId>,
    event_id: OwnedEventId,
) -> Option<(TimelineEvent, Vec<MediaRegistration>)> {
    let event = room
        .load_or_fetch_event(&event_id, None)
        .await
        .inspect_err(|error| tracing::debug!(%event_id, %error, "fetching a reply target failed"))
        .ok()?;
    let value: Value = serde_json::from_str(event.raw().json().get()).ok()?;
    let identity = format!("{}\n{event_id}", room.room_id());
    match normalise_observed(&value, current_user_id, &identity)? {
        (TimelineItem::Event(event), media) => Some((*event, media)),
        _ => None,
    }
}

/// under lazy-loaded members a sender may be unknown locally, and `get_member` fetches the
/// member list once for the room when it is
async fn profiles<'a>(
    room: &Room,
    user_ids: impl Iterator<Item = &'a OwnedUserId>,
) -> HashMap<OwnedUserId, Sender> {
    let mut unique: Vec<&OwnedUserId> = user_ids.collect();
    unique.sort();
    unique.dedup();
    join_all(unique.into_iter().map(|user_id| async move {
        let member = room.get_member(user_id).await.ok().flatten()?;
        Some((
            user_id.clone(),
            Sender {
                user_id: user_id.clone(),
                display_name: member.display_name().map(str::to_owned),
                avatar: member.avatar_url().map(MediaId::plain),
                name_ambiguous: member.name_ambiguous(),
            },
        ))
    }))
    .await
    .into_iter()
    .flatten()
    .collect()
}

fn validate_limit(limit: u16) -> Result<(), Error> {
    if limit > MAX_CONTEXT_LIMIT {
        Err(Error::new(ErrorKind::Invalid, "context limit exceeds 50"))
    } else {
        Ok(())
    }
}

1	use std::{
2	collections::{HashMap, VecDeque},
3	sync::Arc,
4	};
5
6	use futures_util::future::{join_all, try_join};
7	use matrix_sdk::{
8	Client, Room, RoomState, deserialized_responses::TimelineEvent as SdkTimelineEvent,
9	room::MessagesOptions,
10	};
11	use ruma::{OwnedEventId, OwnedRoomId, OwnedUserId, UInt, push::Action};
12	use serde_json::Value;
13	use tokio::sync::{Mutex, broadcast::error::RecvError};
14
15	use crate::{
16	Error, ErrorKind, EventContext, EventContextCommand, EventContextPage, EventContextSession,
17	MediaId, Sender, TimelineEvent, TimelineItem,
18	engine::MediaService,
19	normalise::{
20	MediaRegistration, MediaScope, apply_profiles, normalise_context, normalise_observed,
21	resolve_replies,
22	},
23	};
24
25	const MAX_CONTEXT_LIMIT: u16 = 50;
26	/// a consumer that never closes its jump views still holds at most this many
27	const MAX_SESSIONS: usize = 32;
28
29	/// open event contexts, oldest first, each owning the media its pages registered
30	#[derive(Default)]
31	pub(crate) struct Sessions {
32	open: Mutex<VecDeque<Session>>,
33	}
34
35	struct Session {
36	id: String,
37	room_id: OwnedRoomId,
38	scope: MediaScope,
39	}
40
41	impl Sessions {
42	async fn open(
43	&self,
44	media: &MediaService,
45	room_id: OwnedRoomId,
46	registrations: Vec<MediaRegistration>,
47	) -> String {
48	let scope = media.context_scope();
49	let id = format!("context-{}", scope.nonce());
50	let mut open = self.open.lock().await;
51	media.register(&scope, registrations).await;
52	open.push_back(Session {
53	id: id.clone(),
54	room_id,
55	scope,
56	});
57	while open.len() > MAX_SESSIONS {
58	if let Some(oldest) = open.pop_front() {
59	media.release(&oldest.scope).await;
60	}
61	}
62	id
63	}
64
65	async fn room(&self, id: &str) -> Result<OwnedRoomId, Error> {
66	let open = self.open.lock().await;
67	let session = open.iter().find(\|session\| session.id == id);
68	session
69	.map(\|session\| session.room_id.clone())
70	.ok_or_else(not_open)
71	}
72
73	/// under the lock, so a page that lands after its close registers nothing
74	async fn register(
75	&self,
76	media: &MediaService,
77	id: &str,
78	registrations: Vec<MediaRegistration>,
79	) -> Result<(), Error> {
80	let open = self.open.lock().await;
81	let session = open
82	.iter()
83	.find(\|session\| session.id == id)
84	.ok_or_else(not_open)?;
85	media.register(&session.scope, registrations).await;
86	Ok(())
87	}
88
89	async fn close(&self, media: &MediaService, id: &str) -> Result<(), Error> {
90	let mut open = self.open.lock().await;
91	let index = open
92	.iter()
93	.position(\|session\| session.id == id)
94	.ok_or_else(not_open)?;
95	if let Some(session) = open.remove(index) {
96	media.release(&session.scope).await;
97	}
98	Ok(())
99	}
100
101	async fn close_left(&self, media: &MediaService, client: &Client) {
102	let mut open = self.open.lock().await;
103	let mut kept = VecDeque::with_capacity(open.len());
104	for session in open.drain(..) {
105	let left = client
106	.get_room(&session.room_id)
107	.is_none_or(\|room\| matches!(room.state(), RoomState::Left \| RoomState::Banned));
108	if left {
109	media.release(&session.scope).await;
110	} else {
111	kept.push_back(session);
112	}
113	}
114	*open = kept;
115	}
116
117	/// the media service is cleared beside this, so nothing is released one by one
118	pub(crate) async fn clear(&self) {
119	self.open.lock().await.clear();
120	}
121	}
122
123	fn not_open() -> Error {
124	Error::new(
125	ErrorKind::EventContextNotOpen,
126	"event context is closed or was never opened",
127	)
128	}
129
130	/// leaving a room closes its event contexts
131	pub(super) async fn close_on_leave(
132	client: Client,
133	media: Arc<MediaService>,
134	sessions: Arc<Sessions>,
135	) {
136	let mut info = client.room_info_notable_update_receiver();
137	loop {
138	match info.recv().await {
139	Ok(_) \| Err(RecvError::Lagged(_)) => sessions.close_left(&media, &client).await,
140	Err(RecvError::Closed) => return,
141	}
142	}
143	}
144
145	pub(crate) async fn execute(
146	client: Client,
147	media: Arc<MediaService>,
148	sessions: Arc<Sessions>,
149	command: EventContextCommand,
150	) -> Result<crate::CommandOutput, Error> {
151	let current_user_id = client.user_id().map(ToOwned::to_owned);
152	let room = \|room_id: &OwnedRoomId\| client.get_room(room_id).ok_or_else(Error::room_unknown);
153	let (context_id, token, limit, backwards) = match command {
154	EventContextCommand::Fetch {
155	room_id,
156	event_id,
157	before_limit,
158	after_limit,
159	} => {
160	let (context, registrations, _) = capture(
161	room(&room_id)?,
162	current_user_id,
163	event_id,
164	before_limit,
165	after_limit,
166	)
167	.await?;
168	let context_id = sessions.open(&media, room_id, registrations).await;
169	return Ok(crate::CommandOutput::EventContext(EventContextSession {
170	context_id,
171	context,
172	}));
173	}
174	EventContextCommand::Close { context_id } => {
175	sessions.close(&media, &context_id).await?;
176	return Ok(crate::CommandOutput::Done);
177	}
178	EventContextCommand::Before {
179	context_id,
180	token,
181	limit,
182	} => (context_id, token, limit, true),
183	EventContextCommand::After {
184	context_id,
185	token,
186	limit,
187	} => (context_id, token, limit, false),
188	};
189	if limit == 0 {
190	return Err(Error::new(
191	ErrorKind::Invalid,
192	"context page limit must be at least 1",
193	));
194	}
195	validate_limit(limit)?;
196	if token.is_empty() {
197	return Err(Error::new(
198	ErrorKind::Invalid,
199	"context pagination token is empty",
200	));
201	}
202	let room = room(&sessions.room(&context_id).await?)?;
203	let side = fetch_side(&room, Some(&token), limit, backwards).await?;
204	let mut page = Assembly::new(
205	&room,
206	current_user_id.as_deref(),
207	&side.values,
208	&side.highlights,
209	None,
210	)
211	.await;
212	let events = page.take(0..side.values.len());
213	sessions.register(&media, &context_id, page.media).await?;
214	Ok(crate::CommandOutput::EventContextPage(EventContextPage {
215	events,
216	next_token: side.token,
217	}))
218	}
219
220	pub(crate) async fn capture(
221	room: Room,
222	current_user_id: Option<OwnedUserId>,
223	event_id: OwnedEventId,
224	before_limit: u16,
225	after_limit: u16,
226	) -> Result<(EventContext, Vec<MediaRegistration>, Vec<Value>), Error> {
227	validate_limit(before_limit)?;
228	validate_limit(after_limit)?;
229	let raw = room
230	.event_with_context(&event_id, false, UInt::from(0_u16), None)
231	.await
232	.map_err(\|source\| {
233	let error = Error::from_sdk("fetching event context failed", source);
234	if error
235	.server
236	.as_ref()
237	.is_some_and(\|server\| server.status == 404)
238	{
239	Error::new(ErrorKind::EventNotFound, "event was not found")
240	} else {
241	error
242	}
243	})?;
244	let (target, target_highlight) = raw
245	.event
246	.as_ref()
247	.and_then(raw_event)
248	.ok_or_else(\|\| Error::new(ErrorKind::EventNotFound, "event was not found"))?;
249	let (before, after) = try_join(
250	fetch_side(&room, raw.prev_batch_token.as_deref(), before_limit, true),
251	fetch_side(&room, raw.next_batch_token.as_deref(), after_limit, false),
252	)
253	.await?;
254	let target_index = before.values.len();
255	let mut values = before.values;
256	values.push(target);
257	values.extend(after.values);
258	let mut highlights = before.highlights;
259	highlights.push(target_highlight);
260	highlights.extend(after.highlights);
261	let mut page = Assembly::new(
262	&room,
263	current_user_id.as_deref(),
264	&values,
265	&highlights,
266	Some(target_index),
267	)
268	.await;
269	let events_before = page.take(0..target_index);
270	let event = page
271	.take(target_index..target_index + 1)
272	.pop()
273	.ok_or_else(\|\| Error::new(ErrorKind::EventNotFound, "event could not be read"))?;
274	let events_after = page.take(target_index + 1..values.len());
275	Ok((
276	EventContext {
277	events_before,
278	event,
279	events_after,
280	start_token: before.token,
281	end_token: after.token,
282	},
283	page.media,
284	values,
285	))
286	}
287
288	struct Side {
289	/// in timeline order
290	values: Vec<Value>,
291	/// beside `values`, from the push actions the sdk worked out as it fetched
292	highlights: Vec<bool>,
293	token: Option<String>,
294	}
295
296	fn raw_event(event: &SdkTimelineEvent) -> Option<(Value, bool)> {
297	let value = serde_json::from_str(event.raw().json().get()).ok()?;
298	let highlight = event
299	.push_actions()
300	.is_some_and(\|actions\| actions.iter().any(Action::is_highlight));
301	Some((value, highlight))
302	}
303
304	async fn fetch_side(
305	room: &Room,
306	token: Option<&str>,
307	limit: u16,
308	backwards: bool,
309	) -> Result<Side, Error> {
310	let Some(token) = token else {
311	return Ok(Side {
312	values: Vec::new(),
313	highlights: Vec::new(),
314	token: None,
315	});
316	};
317	if limit == 0 {
318	return Ok(Side {
319	values: Vec::new(),
320	highlights: Vec::new(),
321	token: Some(token.to_owned()),
322	});
323	}
324	let mut options = if backwards {
325	MessagesOptions::backward()
326	} else {
327	MessagesOptions::forward()
328	};
329	options = options.from(token);
330	options.limit = UInt::from(limit);
331	let messages = room
332	.messages(options)
333	.await
334	.map_err(\|source\| Error::from_sdk("fetching event context events failed", source))?;
335	let mut events: Vec<_> = messages.chunk.iter().filter_map(raw_event).collect();
336	if backwards {
337	events.reverse();
338	}
339	let (values, highlights) = events.into_iter().unzip();
340	Ok(Side {
341	values,
342	highlights,
343	token: messages.end,
344	})
345	}
346
347	/// a window of raw events normalised together, so relations inside it land on their targets
348	struct Assembly {
349	items: Vec<(usize, TimelineItem)>,
350	media: Vec<MediaRegistration>,
351	}
352
353	impl Assembly {
354	async fn new(
355	room: &Room,
356	current_user_id: Option<&ruma::UserId>,
357	values: &[Value],
358	highlights: &[bool],
359	keep: Option<usize>,
360	) -> Self {
361	let page = normalise_context(values, keep, current_user_id, room.room_id());
362	let mut items = page.items;
363	for (index, item) in &mut items {
364	if let TimelineItem::Event(event) = item {
365	event.highlight = highlights[*index];
366	}
367	}
368	let mut media = page.media;
369	let mut targets: HashMap<OwnedEventId, TimelineEvent> = HashMap::new();
370	let mut missing = Vec::new();
371	for (_, item) in &items {
372	if let TimelineItem::Event(event) = item
373	&& let Some(event_id) = &event.event_id
374	{
375	targets.insert(event_id.clone(), (**event).clone());
376	}
377	}
378	for event in events(&mut items) {
379	if let Some(reply) = &event.reply_to
380	&& !targets.contains_key(&reply.event_id)
381	&& !missing.contains(&reply.event_id)
382	{
383	missing.push(reply.event_id.clone());
384	}
385	}
386	let fetched = join_all(
387	missing
388	.into_iter()
389	.map(\|event_id\| fetch_reply(room, current_user_id, event_id)),
390	)
391	.await;
392	for (event, registrations) in fetched.into_iter().flatten() {
393	media.extend(registrations);
394	if let Some(event_id) = event.event_id.clone() {
395	targets.insert(event_id, event);
396	}
397	}
398	let profiles = profiles(
399	room,
400	items
401	.iter()
402	.filter_map(\|(_, item)\| match item {
403	TimelineItem::Event(event) => Some(&event.sender.user_id),
404	_ => None,
405	})
406	.chain(targets.values().map(\|event\| &event.sender.user_id)),
407	)
408	.await;
409	apply_profiles(targets.values_mut(), &profiles);
410	apply_profiles(events(&mut items), &profiles);
411	resolve_replies(events(&mut items), &targets);
412	Self { items, media }
413	}
414
415	/// the items that came from raw events in `range`
416	fn take(&mut self, range: std::ops::Range<usize>) -> Vec<TimelineItem> {
417	let (taken, kept) = std::mem::take(&mut self.items)
418	.into_iter()
419	.partition(\|(index, _)\| range.contains(index));
420	self.items = kept;
421	taken.into_iter().map(\|(_, item)\| item).collect()
422	}
423	}
424
425	fn events(items: &mut [(usize, TimelineItem)]) -> impl Iterator<Item = &mut TimelineEvent> {
426	items.iter_mut().filter_map(\|(_, item)\| match item {
427	TimelineItem::Event(event) => Some(&mut **event),
428	_ => None,
429	})
430	}
431
432	async fn fetch_reply(
433	room: &Room,
434	current_user_id: Option<&ruma::UserId>,
435	event_id: OwnedEventId,
436	) -> Option<(TimelineEvent, Vec<MediaRegistration>)> {
437	let event = room
438	.load_or_fetch_event(&event_id, None)
439	.await
440	.inspect_err(\|error\| tracing::debug!(%event_id, %error, "fetching a reply target failed"))
441	.ok()?;
442	let value: Value = serde_json::from_str(event.raw().json().get()).ok()?;
443	let identity = format!("{}\n{event_id}", room.room_id());
444	match normalise_observed(&value, current_user_id, &identity)? {
445	(TimelineItem::Event(event), media) => Some((*event, media)),
446	_ => None,
447	}
448	}
449
450	/// under lazy-loaded members a sender may be unknown locally, and `get_member` fetches the
451	/// member list once for the room when it is
452	async fn profiles<'a>(
453	room: &Room,
454	user_ids: impl Iterator<Item = &'a OwnedUserId>,
455	) -> HashMap<OwnedUserId, Sender> {
456	let mut unique: Vec<&OwnedUserId> = user_ids.collect();
457	unique.sort();
458	unique.dedup();
459	join_all(unique.into_iter().map(\|user_id\| async move {
460	let member = room.get_member(user_id).await.ok().flatten()?;
461	Some((
462	user_id.clone(),
463	Sender {
464	user_id: user_id.clone(),
465	display_name: member.display_name().map(str::to_owned),
466	avatar: member.avatar_url().map(MediaId::plain),
467	name_ambiguous: member.name_ambiguous(),
468	},
469	))
470	}))
471	.await
472	.into_iter()
473	.flatten()
474	.collect()
475	}
476
477	fn validate_limit(limit: u16) -> Result<(), Error> {
478	if limit > MAX_CONTEXT_LIMIT {
479	Err(Error::new(ErrorKind::Invalid, "context limit exceeds 50"))
480	} else {
481	Ok(())
482	}
483	}