iamb/src/message/mod.rs

use std::borrow::Cow;
use std::cmp::{Ord, Ordering, PartialOrd};
use std::collections::hash_map::DefaultHasher;
use std::collections::BTreeMap;
use std::convert::TryFrom;
use std::hash::{Hash, Hasher};
use std::slice::Iter;

use chrono::{DateTime, NaiveDateTime, Utc};
use unicode_width::UnicodeWidthStr;

use matrix_sdk::ruma::{
    events::{
        room::{
            message::{
                FormattedBody,
                MessageFormat,
                MessageType,
                OriginalRoomMessageEvent,
                RedactedRoomMessageEvent,
                Relation,
                RoomMessageEvent,
                RoomMessageEventContent,
            },
            redaction::SyncRoomRedactionEvent,
        },
        Redact,
    },
    EventId,
    MilliSecondsSinceUnixEpoch,
    OwnedEventId,
    OwnedUserId,
    RoomVersionId,
    UInt,
};

use modalkit::tui::{
    style::{Modifier as StyleModifier, Style},
    symbols::line::THICK_VERTICAL,
    text::{Span, Spans, Text},
};

use modalkit::editing::{base::ViewportContext, cursor::Cursor};

use crate::{
    base::{IambResult, RoomInfo},
    config::ApplicationSettings,
    message::html::{parse_matrix_html, StyleTree},
    util::{space_span, wrapped_text},
};

mod html;
mod printer;

pub type MessageFetchResult = IambResult<(Option<String>, Vec<RoomMessageEvent>)>;
pub type MessageKey = (MessageTimeStamp, OwnedEventId);
pub type Messages = BTreeMap<MessageKey, Message>;

const fn span_static(s: &'static str) -> Span<'static> {
    Span {
        content: Cow::Borrowed(s),
        style: Style {
            fg: None,
            bg: None,
            add_modifier: StyleModifier::empty(),
            sub_modifier: StyleModifier::empty(),
        },
    }
}

const USER_GUTTER: usize = 30;
const TIME_GUTTER: usize = 12;
const READ_GUTTER: usize = 5;
const MIN_MSG_LEN: usize = 30;

const USER_GUTTER_EMPTY: &str = "                              ";
const USER_GUTTER_EMPTY_SPAN: Span<'static> = span_static(USER_GUTTER_EMPTY);

const TIME_GUTTER_EMPTY: &str = "            ";
const TIME_GUTTER_EMPTY_SPAN: Span<'static> = span_static(TIME_GUTTER_EMPTY);

#[derive(thiserror::Error, Debug)]
pub enum TimeStampIntError {
    #[error("Integer conversion error: {0}")]
    IntError(#[from] std::num::TryFromIntError),

    #[error("UInt conversion error: {0}")]
    UIntError(<UInt as TryFrom<u64>>::Error),
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum MessageTimeStamp {
    OriginServer(UInt),
    LocalEcho,
}

impl MessageTimeStamp {
    fn show(&self) -> Option<Span> {
        match self {
            MessageTimeStamp::OriginServer(ts) => {
                let time = i64::from(*ts) / 1000;
                let time = NaiveDateTime::from_timestamp_opt(time, 0)?;
                let time = DateTime::<Utc>::from_utc(time, Utc);
                let time = time.format("%T");
                let time = format!("  [{}]", time);

                Span::raw(time).into()
            },
            MessageTimeStamp::LocalEcho => None,
        }
    }

    fn is_local_echo(&self) -> bool {
        matches!(self, MessageTimeStamp::LocalEcho)
    }

    pub fn as_millis(&self) -> Option<MilliSecondsSinceUnixEpoch> {
        match self {
            MessageTimeStamp::OriginServer(ms) => MilliSecondsSinceUnixEpoch(*ms).into(),
            MessageTimeStamp::LocalEcho => None,
        }
    }
}

impl Ord for MessageTimeStamp {
    fn cmp(&self, other: &Self) -> Ordering {
        match (self, other) {
            (MessageTimeStamp::OriginServer(_), MessageTimeStamp::LocalEcho) => Ordering::Less,
            (MessageTimeStamp::OriginServer(a), MessageTimeStamp::OriginServer(b)) => a.cmp(b),
            (MessageTimeStamp::LocalEcho, MessageTimeStamp::OriginServer(_)) => Ordering::Greater,
            (MessageTimeStamp::LocalEcho, MessageTimeStamp::LocalEcho) => Ordering::Equal,
        }
    }
}

impl PartialOrd for MessageTimeStamp {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        self.cmp(other).into()
    }
}

impl From<MilliSecondsSinceUnixEpoch> for MessageTimeStamp {
    fn from(millis: MilliSecondsSinceUnixEpoch) -> Self {
        MessageTimeStamp::OriginServer(millis.0)
    }
}

impl TryFrom<&MessageTimeStamp> for usize {
    type Error = TimeStampIntError;

    fn try_from(ts: &MessageTimeStamp) -> Result<Self, Self::Error> {
        let n = match ts {
            MessageTimeStamp::LocalEcho => 0,
            MessageTimeStamp::OriginServer(u) => usize::try_from(u64::from(*u))?,
        };

        Ok(n)
    }
}

impl TryFrom<usize> for MessageTimeStamp {
    type Error = TimeStampIntError;

    fn try_from(u: usize) -> Result<Self, Self::Error> {
        if u == 0 {
            Ok(MessageTimeStamp::LocalEcho)
        } else {
            let n = u64::try_from(u)?;
            let n = UInt::try_from(n).map_err(TimeStampIntError::UIntError)?;

            Ok(MessageTimeStamp::OriginServer(n))
        }
    }
}

#[derive(Clone, Debug, Default, Eq, PartialEq)]
pub struct MessageCursor {
    /// When timestamp is None, the corner is determined by moving backwards from
    /// the most recently received message.
    pub timestamp: Option<MessageKey>,

    /// A row within the [Text] representation of a [Message].
    pub text_row: usize,
}

impl MessageCursor {
    pub fn new(timestamp: MessageKey, text_row: usize) -> Self {
        MessageCursor { timestamp: Some(timestamp), text_row }
    }

    /// Get a cursor that refers to the most recent message.
    pub fn latest() -> Self {
        MessageCursor::default()
    }

    pub fn to_key<'a>(&'a self, info: &'a RoomInfo) -> Option<&'a MessageKey> {
        if let Some(ref key) = self.timestamp {
            Some(key)
        } else {
            Some(info.messages.last_key_value()?.0)
        }
    }

    pub fn from_cursor(cursor: &Cursor, info: &RoomInfo) -> 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..) {
            let mut hasher = DefaultHasher::new();
            event_id.hash(&mut hasher);

            if hasher.finish() == ev_hash {
                mc = Self::from((*ts, event_id.clone())).into();
                break;
            }

            if mc.is_none() {
                mc = Self::from((*ts, event_id.clone())).into();
            }

            if ts > &ts_start {
                break;
            }
        }

        return mc;
    }

    pub fn to_cursor(&self, info: &RoomInfo) -> Option<Cursor> {
        let (ts, event_id) = self.to_key(info)?;

        let y: usize = usize::try_from(ts).ok()?;

        let mut hasher = DefaultHasher::new();
        event_id.hash(&mut hasher);
        let x = usize::try_from(hasher.finish()).ok()?;

        Cursor::new(y, x).into()
    }
}

impl From<Option<MessageKey>> for MessageCursor {
    fn from(key: Option<MessageKey>) -> Self {
        MessageCursor { timestamp: key, text_row: 0 }
    }
}

impl From<MessageKey> for MessageCursor {
    fn from(key: MessageKey) -> Self {
        MessageCursor { timestamp: Some(key), text_row: 0 }
    }
}

impl Ord for MessageCursor {
    fn cmp(&self, other: &Self) -> Ordering {
        match (&self.timestamp, &other.timestamp) {
            (None, None) => self.text_row.cmp(&other.text_row),
            (None, Some(_)) => Ordering::Greater,
            (Some(_), None) => Ordering::Less,
            (Some(st), Some(ot)) => {
                let pcmp = st.cmp(ot);
                let tcmp = self.text_row.cmp(&other.text_row);

                pcmp.then(tcmp)
            },
        }
    }
}

impl PartialOrd for MessageCursor {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        self.cmp(other).into()
    }
}

#[derive(Clone)]
pub enum MessageEvent {
    Original(Box<OriginalRoomMessageEvent>),
    Redacted(Box<RedactedRoomMessageEvent>),
    Local(OwnedEventId, Box<RoomMessageEventContent>),
}

impl MessageEvent {
    pub fn event_id(&self) -> &EventId {
        match self {
            MessageEvent::Original(ev) => ev.event_id.as_ref(),
            MessageEvent::Redacted(ev) => ev.event_id.as_ref(),
            MessageEvent::Local(event_id, _) => event_id.as_ref(),
        }
    }

    pub fn body(&self) -> Cow<'_, str> {
        match self {
            MessageEvent::Original(ev) => body_cow_content(&ev.content),
            MessageEvent::Redacted(ev) => {
                let reason = ev
                    .unsigned
                    .redacted_because
                    .as_ref()
                    .and_then(|e| e.as_original())
                    .and_then(|r| r.content.reason.as_ref());

                if let Some(r) = reason {
                    Cow::Owned(format!("[Redacted: {:?}]", r))
                } else {
                    Cow::Borrowed("[Redacted]")
                }
            },
            MessageEvent::Local(_, content) => body_cow_content(content),
        }
    }

    pub fn html(&self) -> Option<StyleTree> {
        let content = match self {
            MessageEvent::Original(ev) => &ev.content,
            MessageEvent::Redacted(_) => return None,
            MessageEvent::Local(_, content) => content,
        };

        if let MessageType::Text(content) = &content.msgtype {
            if let Some(FormattedBody { format: MessageFormat::Html, body }) = &content.formatted {
                Some(parse_matrix_html(body.as_str()))
            } else {
                None
            }
        } else {
            None
        }
    }

    pub fn redact(&mut self, redaction: SyncRoomRedactionEvent, version: &RoomVersionId) {
        match self {
            MessageEvent::Redacted(_) => return,
            MessageEvent::Local(_, _) => return,
            MessageEvent::Original(ev) => {
                let redacted = ev.clone().redact(redaction, version);
                *self = MessageEvent::Redacted(Box::new(redacted));
            },
        }
    }
}

fn body_cow_content(content: &RoomMessageEventContent) -> Cow<'_, str> {
    let s = match &content.msgtype {
        MessageType::Text(content) => content.body.as_str(),
        MessageType::VerificationRequest(_) => "[Verification Request]",
        MessageType::Emote(content) => content.body.as_ref(),
        MessageType::Notice(content) => content.body.as_str(),
        MessageType::ServerNotice(content) => content.body.as_str(),

        MessageType::Audio(content) => {
            return Cow::Owned(format!("[Attached Audio: {}]", content.body));
        },
        MessageType::File(content) => {
            return Cow::Owned(format!("[Attached File: {}]", content.body));
        },
        MessageType::Image(content) => {
            return Cow::Owned(format!("[Attached Image: {}]", content.body));
        },
        MessageType::Video(content) => {
            return Cow::Owned(format!("[Attached Video: {}]", content.body));
        },
        _ => {
            return Cow::Owned(format!("[Unknown message type: {:?}]", content.msgtype()));
        },
    };

    Cow::Borrowed(s)
}

enum MessageColumns {
    /// Four columns: sender, message, timestamp, read receipts.
    Four,

    /// Three columns: sender, message, timestamp.
    Three,

    /// Two columns: sender, message.
    Two,

    /// One column: message with sender on line before the message.
    One,
}

struct MessageFormatter<'a> {
    settings: &'a ApplicationSettings,
    cols: MessageColumns,
    fill: usize,
    user: Option<Span<'a>>,
    time: Option<Span<'a>>,
    read: Iter<'a, OwnedUserId>,
}

impl<'a> MessageFormatter<'a> {
    fn width(&self) -> usize {
        self.fill
    }

    #[inline]
    fn push_spans(&mut self, spans: Spans<'a>, style: Style, text: &mut Text<'a>) {
        match self.cols {
            MessageColumns::Four => {
                let settings = self.settings;
                let user = self.user.take().unwrap_or(USER_GUTTER_EMPTY_SPAN);
                let time = self.time.take().unwrap_or(TIME_GUTTER_EMPTY_SPAN);

                let mut line = vec![user];
                line.extend(spans.0);
                line.push(time);

                // Show read receipts.
                let user_char =
                    |user: &'a OwnedUserId| -> Span<'a> { settings.get_user_char_span(user) };

                let a = self.read.next().map(user_char).unwrap_or_else(|| Span::raw(" "));
                let b = self.read.next().map(user_char).unwrap_or_else(|| Span::raw(" "));
                let c = self.read.next().map(user_char).unwrap_or_else(|| Span::raw(" "));

                line.push(Span::raw(" "));
                line.push(c);
                line.push(b);
                line.push(a);
                line.push(Span::raw(" "));

                text.lines.push(Spans(line))
            },
            MessageColumns::Three => {
                let user = self.user.take().unwrap_or(USER_GUTTER_EMPTY_SPAN);
                let time = self.time.take().unwrap_or_else(|| Span::from(""));

                let mut line = vec![user];
                line.extend(spans.0);
                line.push(time);

                text.lines.push(Spans(line))
            },
            MessageColumns::Two => {
                let user = self.user.take().unwrap_or(USER_GUTTER_EMPTY_SPAN);
                let mut line = vec![user];
                line.extend(spans.0);

                text.lines.push(Spans(line));
            },
            MessageColumns::One => {
                if let Some(user) = self.user.take() {
                    text.lines.push(Spans(vec![user]));
                }

                let leading = space_span(2, style);
                let mut line = vec![leading];
                line.extend(spans.0);

                text.lines.push(Spans(line));
            },
        }
    }

    fn push_text(&mut self, append: Text<'a>, style: Style, text: &mut Text<'a>) {
        for line in append.lines.into_iter() {
            self.push_spans(line, style, text);
        }
    }
}

pub struct Message {
    pub event: MessageEvent,
    pub sender: OwnedUserId,
    pub timestamp: MessageTimeStamp,
    pub downloaded: bool,
    pub html: Option<StyleTree>,
}

impl Message {
    pub fn new(event: MessageEvent, sender: OwnedUserId, timestamp: MessageTimeStamp) -> Self {
        let html = event.html();
        let downloaded = false;

        Message { event, sender, timestamp, downloaded, html }
    }

    pub fn reply_to(&self) -> Option<OwnedEventId> {
        let content = match &self.event {
            MessageEvent::Local(_, content) => content,
            MessageEvent::Original(ev) => &ev.content,
            MessageEvent::Redacted(_) => return None,
        };

        if let Some(Relation::Reply { in_reply_to }) = &content.relates_to {
            Some(in_reply_to.event_id.clone())
        } else {
            None
        }
    }

    fn get_render_style(&self, selected: bool) -> Style {
        let mut style = Style::default();

        if selected {
            style = style.add_modifier(StyleModifier::REVERSED)
        }

        if self.timestamp.is_local_echo() {
            style = style.add_modifier(StyleModifier::ITALIC);
        }

        return style;
    }

    fn get_render_format<'a>(
        &'a self,
        prev: Option<&Message>,
        width: usize,
        info: &'a RoomInfo,
        settings: &'a ApplicationSettings,
    ) -> MessageFormatter<'a> {
        if USER_GUTTER + TIME_GUTTER + READ_GUTTER + MIN_MSG_LEN <= width &&
            settings.tunables.read_receipt_display
        {
            let cols = MessageColumns::Four;
            let fill = width - USER_GUTTER - TIME_GUTTER - READ_GUTTER;
            let user = self.show_sender(prev, true, settings);
            let time = self.timestamp.show();
            let read = match info.receipts.get(self.event.event_id()) {
                Some(read) => read.iter(),
                None => [].iter(),
            };

            MessageFormatter { settings, cols, fill, user, time, read }
        } else if USER_GUTTER + TIME_GUTTER + MIN_MSG_LEN <= width {
            let cols = MessageColumns::Three;
            let fill = width - USER_GUTTER - TIME_GUTTER;
            let user = self.show_sender(prev, true, settings);
            let time = self.timestamp.show();
            let read = [].iter();

            MessageFormatter { settings, cols, fill, user, time, read }
        } else if USER_GUTTER + MIN_MSG_LEN <= width {
            let cols = MessageColumns::Two;
            let fill = width - USER_GUTTER;
            let user = self.show_sender(prev, true, settings);
            let time = None;
            let read = [].iter();

            MessageFormatter { settings, cols, fill, user, time, read }
        } else {
            let cols = MessageColumns::One;
            let fill = width.saturating_sub(2);
            let user = self.show_sender(prev, false, settings);
            let time = None;
            let read = [].iter();

            MessageFormatter { settings, cols, fill, user, time, read }
        }
    }

    pub fn show<'a>(
        &'a self,
        prev: Option<&Message>,
        selected: bool,
        vwctx: &ViewportContext<MessageCursor>,
        info: &'a RoomInfo,
        settings: &'a ApplicationSettings,
    ) -> Text<'a> {
        let width = vwctx.get_width();

        let style = self.get_render_style(selected);
        let mut fmt = self.get_render_format(prev, width, info, settings);
        let mut text = Text { lines: vec![] };
        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));

        if let Some(r) = &reply {
            let w = width.saturating_sub(2);
            let mut replied = r.show_msg(w, style, true);
            let mut sender = r.sender_span(settings);
            let sender_width = UnicodeWidthStr::width(sender.content.as_ref());
            let trailing = w.saturating_sub(sender_width + 1);

            sender.style = sender.style.patch(style);

            fmt.push_spans(
                Spans(vec![
                    Span::styled(" ", style),
                    Span::styled(THICK_VERTICAL, style),
                    sender,
                    Span::styled(":", style),
                    space_span(trailing, style),
                ]),
                style,
                &mut text,
            );

            for line in replied.lines.iter_mut() {
                line.0.insert(0, Span::styled(THICK_VERTICAL, style));
                line.0.insert(0, Span::styled(" ", style));
            }

            fmt.push_text(replied, style, &mut text);
        }

        // Now show the message contents, and the inlined reply if we couldn't find it above.
        let msg = self.show_msg(width, style, reply.is_some());
        fmt.push_text(msg, style, &mut text);

        if text.lines.is_empty() {
            // If there was nothing in the body, just show an empty message.
            fmt.push_spans(space_span(width, style).into(), style, &mut text);
        }

        return text;
    }

    pub fn show_msg(&self, width: usize, style: Style, hide_reply: bool) -> Text {
        if let Some(html) = &self.html {
            html.to_text(width, style, hide_reply)
        } else {
            let mut msg = self.event.body();

            if self.downloaded {
                msg.to_mut().push_str(" \u{2705}");
            }

            wrapped_text(msg, width, style)
        }
    }

    fn sender_span(&self, settings: &ApplicationSettings) -> Span {
        settings.get_user_span(self.sender.as_ref())
    }

    fn show_sender(
        &self,
        prev: Option<&Message>,
        align_right: bool,
        settings: &ApplicationSettings,
    ) -> Option<Span> {
        let user = if matches!(prev, Some(prev) if self.sender == prev.sender) {
            return None;
        } else {
            self.sender_span(settings)
        };

        let Span { content, style } = user;
        let stop = content.len().min(28);
        let s = &content[..stop];

        let sender = if align_right {
            format!("{: >width$}  ", s, width = 28)
        } else {
            format!("{: <width$}  ", s, width = 28)
        };

        Span::styled(sender, style).into()
    }
}

impl From<OriginalRoomMessageEvent> for Message {
    fn from(event: OriginalRoomMessageEvent) -> Self {
        let timestamp = event.origin_server_ts.into();
        let user_id = event.sender.clone();
        let content = MessageEvent::Original(event.into());

        Message::new(content, user_id, timestamp)
    }
}

impl From<RedactedRoomMessageEvent> for Message {
    fn from(event: RedactedRoomMessageEvent) -> Self {
        let timestamp = event.origin_server_ts.into();
        let user_id = event.sender.clone();
        let content = MessageEvent::Redacted(event.into());

        Message::new(content, user_id, timestamp)
    }
}

impl From<RoomMessageEvent> for Message {
    fn from(event: RoomMessageEvent) -> Self {
        match event {
            RoomMessageEvent::Original(ev) => ev.into(),
            RoomMessageEvent::Redacted(ev) => ev.into(),
        }
    }
}

impl ToString for Message {
    fn to_string(&self) -> String {
        self.event.body().into_owned()
    }
}

#[cfg(test)]
pub mod tests {
    use super::*;
    use crate::tests::*;

    #[test]
    fn test_mc_cmp() {
        let mc1 = MessageCursor::from(MSG1_KEY.clone());
        let mc2 = MessageCursor::from(MSG2_KEY.clone());
        let mc3 = MessageCursor::from(MSG3_KEY.clone());
        let mc4 = MessageCursor::from(MSG4_KEY.clone());
        let mc5 = MessageCursor::from(MSG5_KEY.clone());

        // Everything is equal to itself.
        assert_eq!(mc1.cmp(&mc1), Ordering::Equal);
        assert_eq!(mc2.cmp(&mc2), Ordering::Equal);
        assert_eq!(mc3.cmp(&mc3), Ordering::Equal);
        assert_eq!(mc4.cmp(&mc4), Ordering::Equal);
        assert_eq!(mc5.cmp(&mc5), Ordering::Equal);

        // Local echo is always greater than an origin server timestamp.
        assert_eq!(mc1.cmp(&mc2), Ordering::Greater);
        assert_eq!(mc1.cmp(&mc3), Ordering::Greater);
        assert_eq!(mc1.cmp(&mc4), Ordering::Greater);
        assert_eq!(mc1.cmp(&mc5), Ordering::Greater);

        // mc2 is the smallest timestamp.
        assert_eq!(mc2.cmp(&mc1), Ordering::Less);
        assert_eq!(mc2.cmp(&mc3), Ordering::Less);
        assert_eq!(mc2.cmp(&mc4), Ordering::Less);
        assert_eq!(mc2.cmp(&mc5), Ordering::Less);

        // mc3 should be less than mc4 because of its event ID.
        assert_eq!(mc3.cmp(&mc1), Ordering::Less);
        assert_eq!(mc3.cmp(&mc2), Ordering::Greater);
        assert_eq!(mc3.cmp(&mc4), Ordering::Less);
        assert_eq!(mc3.cmp(&mc5), Ordering::Less);

        // mc4 should be greater than mc3 because of its event ID.
        assert_eq!(mc4.cmp(&mc1), Ordering::Less);
        assert_eq!(mc4.cmp(&mc2), Ordering::Greater);
        assert_eq!(mc4.cmp(&mc3), Ordering::Greater);
        assert_eq!(mc4.cmp(&mc5), Ordering::Less);

        // mc5 is the greatest OriginServer timestamp.
        assert_eq!(mc5.cmp(&mc1), Ordering::Less);
        assert_eq!(mc5.cmp(&mc2), Ordering::Greater);
        assert_eq!(mc5.cmp(&mc3), Ordering::Greater);
        assert_eq!(mc5.cmp(&mc4), Ordering::Greater);
    }

    #[test]
    fn test_mc_to_key() {
        let info = mock_room();
        let mc1 = MessageCursor::from(MSG1_KEY.clone());
        let mc2 = MessageCursor::from(MSG2_KEY.clone());
        let mc3 = MessageCursor::from(MSG3_KEY.clone());
        let mc4 = MessageCursor::from(MSG4_KEY.clone());
        let mc5 = MessageCursor::from(MSG5_KEY.clone());
        let mc6 = MessageCursor::latest();

        let k1 = mc1.to_key(&info).unwrap();
        let k2 = mc2.to_key(&info).unwrap();
        let k3 = mc3.to_key(&info).unwrap();
        let k4 = mc4.to_key(&info).unwrap();
        let k5 = mc5.to_key(&info).unwrap();
        let k6 = mc6.to_key(&info).unwrap();

        // These should all be equal to their MSGN_KEYs.
        assert_eq!(k1, &MSG1_KEY.clone());
        assert_eq!(k2, &MSG2_KEY.clone());
        assert_eq!(k3, &MSG3_KEY.clone());
        assert_eq!(k4, &MSG4_KEY.clone());
        assert_eq!(k5, &MSG5_KEY.clone());

        // MessageCursor::latest() turns into the largest key (our local echo message).
        assert_eq!(k6, &MSG1_KEY.clone());

        // MessageCursor::latest() fails to convert for a room w/o messages.
        let info_empty = RoomInfo::default();
        assert_eq!(mc6.to_key(&info_empty), None);
    }

    #[test]
    fn test_mc_to_from_cursor() {
        let info = mock_room();
        let mc1 = MessageCursor::from(MSG1_KEY.clone());
        let mc2 = MessageCursor::from(MSG2_KEY.clone());
        let mc3 = MessageCursor::from(MSG3_KEY.clone());
        let mc4 = MessageCursor::from(MSG4_KEY.clone());
        let mc5 = MessageCursor::from(MSG5_KEY.clone());
        let mc6 = MessageCursor::latest();

        let identity = |mc: &MessageCursor| {
            let c = mc.to_cursor(&info).unwrap();

            MessageCursor::from_cursor(&c, &info).unwrap()
        };

        // These should all convert to a Cursor and back to the original value.
        assert_eq!(identity(&mc1), mc1);
        assert_eq!(identity(&mc2), mc2);
        assert_eq!(identity(&mc3), mc3);
        assert_eq!(identity(&mc4), mc4);
        assert_eq!(identity(&mc5), mc5);

        // MessageCursor::latest() should point at the most recent message after conversion.
        assert_eq!(identity(&mc6), mc1);
    }
}