TextForEvent.tsx

/*
Copyright 2015 - 2022 The Matrix.org Foundation C.I.C.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

import React from "react";
import {
    MatrixEvent,
    MatrixClient,
    GuestAccess,
    HistoryVisibility,
    JoinRule,
    EventType,
    MsgType,
    M_POLL_START,
    M_POLL_END,
} from "matrix-js-sdk/src/matrix";
import { KnownMembership } from "matrix-js-sdk/src/types";
import { logger } from "matrix-js-sdk/src/logger";
import { removeDirectionOverrideChars } from "matrix-js-sdk/src/utils";
import { PollStartEvent } from "matrix-js-sdk/src/extensible_events_v1/PollStartEvent";

import { _t } from "./languageHandler";
import * as Roles from "./Roles";
import { isValid3pidInvite } from "./RoomInvite";
import SettingsStore from "./settings/SettingsStore";
import { ALL_RULE_TYPES, ROOM_RULE_TYPES, SERVER_RULE_TYPES, USER_RULE_TYPES } from "./mjolnir/BanList";
import { WIDGET_LAYOUT_EVENT_TYPE } from "./stores/widgets/WidgetLayoutStore";
import { RightPanelPhases } from "./stores/right-panel/RightPanelStorePhases";
import defaultDispatcher from "./dispatcher/dispatcher";
import { RoomSettingsTab } from "./components/views/dialogs/RoomSettingsDialog";
import AccessibleButton from "./components/views/elements/AccessibleButton";
import RightPanelStore from "./stores/right-panel/RightPanelStore";
import { highlightEvent, isLocationEvent } from "./utils/EventUtils";
import { ElementCall } from "./models/Call";
import { textForVoiceBroadcastStoppedEvent, VoiceBroadcastInfoEventType } from "./voice-broadcast";
import { getSenderName } from "./utils/event/getSenderName";
import PosthogTrackers from "./PosthogTrackers.ts";

function getRoomMemberDisplayname(client: MatrixClient, event: MatrixEvent, userId = event.getSender()): string {
    const roomId = event.getRoomId();
    const member = client.getRoom(roomId)?.getMember(userId!);
    return member?.name || member?.rawDisplayName || userId || _t("common|someone");
}

function textForCallEvent(event: MatrixEvent, client: MatrixClient): () => string {
    const roomName = client.getRoom(event.getRoomId()!)?.name;
    const isSupported = client.supportsVoip();

    return isSupported
        ? () => _t("timeline|m.call|video_call_started", { roomName })
        : () => _t("timeline|m.call|video_call_started_unsupported", { roomName });
}

// These functions are frequently used just to check whether an event has
// any text to display at all. For this reason they return deferred values
// to avoid the expense of looking up translations when they're not needed.

function textForCallInviteEvent(event: MatrixEvent, client: MatrixClient): (() => string) | null {
    const senderName = getSenderName(event);
    // FIXME: Find a better way to determine this from the event?
    const isVoice = !event.getContent().offer?.sdp?.includes("m=video");
    const isSupported = client.supportsVoip();

    // This ladder could be reduced down to a couple string variables, however other languages
    // can have a hard time translating those strings. In an effort to make translations easier
    // and more accurate, we break out the string-based variables to a couple booleans.
    if (isVoice && isSupported) {
        return () => _t("timeline|m.call.invite|voice_call", { senderName });
    } else if (isVoice && !isSupported) {
        return () => _t("timeline|m.call.invite|voice_call_unsupported", { senderName });
    } else if (!isVoice && isSupported) {
        return () => _t("timeline|m.call.invite|video_call", { senderName });
    } else if (!isVoice && !isSupported) {
        return () => _t("timeline|m.call.invite|video_call_unsupported", { senderName });
    }

    return null;
}

enum Modification {
    None,
    Unset,
    Set,
    Changed,
}

function getModification(prev?: string, value?: string): Modification {
    if (prev && value && prev !== value) {
        return Modification.Changed;
    }
    if (prev && !value) {
        return Modification.Unset;
    }
    if (!prev && value) {
        return Modification.Set;
    }

    return Modification.None;
}

function textForMemberEvent(
    ev: MatrixEvent,
    client: MatrixClient,
    allowJSX: boolean,
    showHiddenEvents?: boolean,
): (() => string) | null {
    // XXX: SYJS-16 "sender is sometimes null for join messages"
    const senderName = ev.sender?.name || getRoomMemberDisplayname(client, ev);
    const targetName = ev.target?.name || getRoomMemberDisplayname(client, ev, ev.getStateKey());
    const prevContent = ev.getPrevContent();
    const content = ev.getContent();
    const reason = content.reason;

    switch (content.membership) {
        case KnownMembership.Invite: {
            const threePidContent = content.third_party_invite;
            if (threePidContent) {
                if (threePidContent.display_name) {
                    return () =>
                        _t("timeline|m.room.member|accepted_3pid_invite", {
                            targetName,
                            displayName: threePidContent.display_name,
                        });
                } else {
                    return () => _t("timeline|m.room.member|accepted_invite", { targetName });
                }
            } else {
                return () => _t("timeline|m.room.member|invite", { senderName, targetName });
            }
        }
        case KnownMembership.Ban:
            return () =>
                reason
                    ? _t("timeline|m.room.member|ban_reason", { senderName, targetName, reason })
                    : _t("timeline|m.room.member|ban", { senderName, targetName });
        case KnownMembership.Join:
            if (prevContent && prevContent.membership === KnownMembership.Join) {
                const modDisplayname = getModification(prevContent.displayname, content.displayname);
                const modAvatarUrl = getModification(prevContent.avatar_url, content.avatar_url);

                if (modDisplayname !== Modification.None && modAvatarUrl !== Modification.None) {
                    // Compromise to provide the user with more context without needing 16 translations
                    return () =>
                        _t("timeline|m.room.member|change_name_avatar", {
                            // We're taking the display namke directly from the event content here so we need
                            // to strip direction override chars which the js-sdk would normally do when
                            // calculating the display name
                            oldDisplayName: removeDirectionOverrideChars(prevContent.displayname!),
                        });
                } else if (modDisplayname === Modification.Changed) {
                    return () =>
                        _t("timeline|m.room.member|change_name", {
                            // We're taking the display name directly from the event content here so we need
                            // to strip direction override chars which the js-sdk would normally do when
                            // calculating the display name
                            oldDisplayName: removeDirectionOverrideChars(prevContent.displayname!),
                            displayName: removeDirectionOverrideChars(content.displayname!),
                        });
                } else if (modDisplayname === Modification.Set) {
                    return () =>
                        _t("timeline|m.room.member|set_name", {
                            senderName: ev.getSender(),
                            displayName: removeDirectionOverrideChars(content.displayname!),
                        });
                } else if (modDisplayname === Modification.Unset) {
                    return () =>
                        _t("timeline|m.room.member|remove_name", {
                            senderName,
                            oldDisplayName: removeDirectionOverrideChars(prevContent.displayname!),
                        });
                } else if (modAvatarUrl === Modification.Unset) {
                    return () => _t("timeline|m.room.member|remove_avatar", { senderName });
                } else if (modAvatarUrl === Modification.Changed) {
                    return () => _t("timeline|m.room.member|change_avatar", { senderName });
                } else if (modAvatarUrl === Modification.Set) {
                    return () => _t("timeline|m.room.member|set_avatar", { senderName });
                } else if (showHiddenEvents ?? SettingsStore.getValue("showHiddenEventsInTimeline")) {
                    // This is a null rejoin, it will only be visible if using 'show hidden events' (labs)
                    return () => _t("timeline|m.room.member|no_change", { senderName });
                } else {
                    return null;
                }
            } else {
                if (!ev.target) logger.warn("Join message has no target! -- " + ev.getContent().state_key);
                return () => _t("timeline|m.room.member|join", { targetName });
            }
        case KnownMembership.Leave:
            if (ev.getSender() === ev.getStateKey()) {
                if (prevContent.membership === KnownMembership.Invite) {
                    return () => _t("timeline|m.room.member|reject_invite", { targetName });
                } else {
                    return () =>
                        reason
                            ? _t("timeline|m.room.member|left_reason", { targetName, reason })
                            : _t("timeline|m.room.member|left", { targetName });
                }
            } else if (prevContent.membership === KnownMembership.Ban) {
                return () => _t("timeline|m.room.member|unban", { senderName, targetName });
            } else if (prevContent.membership === KnownMembership.Invite) {
                return () =>
                    reason
                        ? _t("timeline|m.room.member|withdrew_invite_reason", {
                              senderName,
                              targetName,
                              reason,
                          })
                        : _t("timeline|m.room.member|withdrew_invite", { senderName, targetName });
            } else if (prevContent.membership === KnownMembership.Join) {
                return () =>
                    reason
                        ? _t("timeline|m.room.member|kick_reason", {
                              senderName,
                              targetName,
                              reason,
                          })
                        : _t("timeline|m.room.member|kick", { senderName, targetName });
            } else {
                return null;
            }
    }

    return null;
}

function textForTopicEvent(ev: MatrixEvent): (() => string) | null {
    const senderDisplayName = ev.sender && ev.sender.name ? ev.sender.name : ev.getSender();
    return () =>
        _t("timeline|m.room.topic", {
            senderDisplayName,
            topic: ev.getContent().topic,
        });
}

function textForRoomAvatarEvent(ev: MatrixEvent): (() => string) | null {
    const senderDisplayName = ev?.sender?.name || ev.getSender();
    return () => _t("timeline|m.room.avatar|changed", { senderDisplayName });
}

function textForRoomNameEvent(ev: MatrixEvent): (() => string) | null {
    const senderDisplayName = ev.sender && ev.sender.name ? ev.sender.name : ev.getSender();

    if (!ev.getContent().name || ev.getContent().name.trim().length === 0) {
        return () => _t("timeline|m.room.name|remove", { senderDisplayName });
    }
    if (ev.getPrevContent().name) {
        return () =>
            _t("timeline|m.room.name|change", {
                senderDisplayName,
                oldRoomName: ev.getPrevContent().name,
                newRoomName: ev.getContent().name,
            });
    }
    return () =>
        _t("timeline|m.room.name|set", {
            senderDisplayName,
            roomName: ev.getContent().name,
        });
}

function textForTombstoneEvent(ev: MatrixEvent): (() => string) | null {
    const senderDisplayName = ev.sender && ev.sender.name ? ev.sender.name : ev.getSender();
    return () => _t("timeline|m.room.tombstone", { senderDisplayName });
}

const onViewJoinRuleSettingsClick = (): void => {
    defaultDispatcher.dispatch({
        action: "open_room_settings",
        initial_tab_id: RoomSettingsTab.Security,
    });
};

function textForJoinRulesEvent(ev: MatrixEvent, client: MatrixClient, allowJSX: boolean): () => Renderable {
    const senderDisplayName = ev.sender && ev.sender.name ? ev.sender.name : ev.getSender();
    switch (ev.getContent().join_rule) {
        case JoinRule.Public:
            return () =>
                _t("timeline|m.room.join_rules|public", {
                    senderDisplayName,
                });
        case JoinRule.Invite:
            return () =>
                _t("timeline|m.room.join_rules|invite", {
                    senderDisplayName,
                });
        case JoinRule.Knock:
            return () => _t("timeline|m.room.join_rules|knock", { senderDisplayName });
        case JoinRule.Restricted:
            if (allowJSX) {
                return () => (
                    <span>
                        {_t(
                            "timeline|m.room.join_rules|restricted_settings",
                            {
                                senderDisplayName,
                            },
                            {
                                a: (sub) => (
                                    <AccessibleButton kind="link_inline" onClick={onViewJoinRuleSettingsClick}>
                                        {sub}
                                    </AccessibleButton>
                                ),
                            },
                        )}
                    </span>
                );
            }

            return () => _t("timeline|m.room.join_rules|restricted", { senderDisplayName });
        default:
            // The spec supports "knock" and "private", however nothing implements these.
            return () =>
                _t("timeline|m.room.join_rules|unknown", {
                    senderDisplayName,
                    rule: ev.getContent().join_rule,
                });
    }
}

function textForGuestAccessEvent(ev: MatrixEvent): (() => string) | null {
    const senderDisplayName = ev.sender && ev.sender.name ? ev.sender.name : ev.getSender();
    switch (ev.getContent().guest_access) {
        case GuestAccess.CanJoin:
            return () => _t("timeline|m.room.guest_access|can_join", { senderDisplayName });
        case GuestAccess.Forbidden:
            return () => _t("timeline|m.room.guest_access|forbidden", { senderDisplayName });
        default:
            // There's no other options we can expect, however just for safety's sake we'll do this.
            return () =>
                _t("timeline|m.room.guest_access|unknown", {
                    senderDisplayName,
                    rule: ev.getContent().guest_access,
                });
    }
}

function textForServerACLEvent(ev: MatrixEvent): (() => string) | null {
    const senderDisplayName = ev.sender && ev.sender.name ? ev.sender.name : ev.getSender();
    const prevContent = ev.getPrevContent();
    const current = ev.getContent();
    const prev = {
        deny: Array.isArray(prevContent.deny) ? prevContent.deny : [],
        allow: Array.isArray(prevContent.allow) ? prevContent.allow : [],
        allow_ip_literals: prevContent.allow_ip_literals !== false,
    };

    let getText: () => string;
    if (prev.deny.length === 0 && prev.allow.length === 0) {
        getText = () => _t("timeline|m.room.server_acl|set", { senderDisplayName });
    } else {
        getText = () => _t("timeline|m.room.server_acl|changed", { senderDisplayName });
    }

    if (!Array.isArray(current.allow)) {
        current.allow = [];
    }

    // If we know for sure everyone is banned, mark the room as obliterated
    if (current.allow.length === 0) {
        return () => getText() + " " + _t("timeline|m.room.server_acl|all_servers_banned");
    }

    return getText;
}

function textForMessageEvent(ev: MatrixEvent, client: MatrixClient): (() => string) | null {
    if (isLocationEvent(ev)) {
        return textForLocationEvent(ev);
    }

    return () => {
        const senderDisplayName = ev.sender && ev.sender.name ? ev.sender.name : ev.getSender();
        let message = ev.getContent().body;
        if (ev.isRedacted()) {
            message = textForRedactedPollAndMessageEvent(ev, client);
        }

        if (ev.getContent().msgtype === MsgType.Emote) {
            message = "* " + senderDisplayName + " " + message;
        } else if (ev.getContent().msgtype === MsgType.Image) {
            message = _t("timeline|m.image|sent", { senderDisplayName });
        } else if (ev.getType() == EventType.Sticker) {
            message = _t("timeline|m.sticker", { senderDisplayName });
        } else {
            // in this case, parse it as a plain text message
            message = senderDisplayName + ": " + message;
        }
        return message;
    };
}

function textForCanonicalAliasEvent(ev: MatrixEvent): (() => string) | null {
    const senderName = getSenderName(ev);
    const oldAlias = ev.getPrevContent().alias;
    const oldAltAliases = ev.getPrevContent().alt_aliases || [];
    const newAlias = ev.getContent().alias;
    const newAltAliases = ev.getContent().alt_aliases || [];
    const removedAltAliases = oldAltAliases.filter((alias: string) => !newAltAliases.includes(alias));
    const addedAltAliases = newAltAliases.filter((alias: string) => !oldAltAliases.includes(alias));

    if (!removedAltAliases.length && !addedAltAliases.length) {
        if (newAlias) {
            return () =>
                _t("timeline|m.room.canonical_alias|set", {
                    senderName,
                    address: ev.getContent().alias,
                });
        } else if (oldAlias) {
            return () =>
                _t("timeline|m.room.canonical_alias|removed", {
                    senderName,
                });
        }
    } else if (newAlias === oldAlias) {
        if (addedAltAliases.length && !removedAltAliases.length) {
            return () =>
                _t("timeline|m.room.canonical_alias|alt_added", {
                    senderName,
                    addresses: addedAltAliases.join(", "),
                    count: addedAltAliases.length,
                });
        }
        if (removedAltAliases.length && !addedAltAliases.length) {
            return () =>
                _t("timeline|m.room.canonical_alias|alt_removed", {
                    senderName,
                    addresses: removedAltAliases.join(", "),
                    count: removedAltAliases.length,
                });
        }
        if (removedAltAliases.length && addedAltAliases.length) {
            return () =>
                _t("timeline|m.room.canonical_alias|changed_alternative", {
                    senderName,
                });
        }
    } else {
        // both alias and alt_aliases where modified
        return () =>
            _t("timeline|m.room.canonical_alias|changed_main_and_alternative", {
                senderName,
            });
    }
    // in case there is no difference between the two events,
    // say something as we can't simply hide the tile from here
    return () =>
        _t("timeline|m.room.canonical_alias|changed", {
            senderName,
        });
}

function textForThreePidInviteEvent(event: MatrixEvent): (() => string) | null {
    const senderName = getSenderName(event);

    if (!isValid3pidInvite(event)) {
        return () =>
            _t("timeline|m.room.third_party_invite|revoked", {
                senderName,
                targetDisplayName: event.getPrevContent().display_name || _t("common|someone"),
            });
    }

    return () =>
        _t("timeline|m.room.third_party_invite|sent", {
            senderName,
            targetDisplayName: event.getContent().display_name,
        });
}

function textForHistoryVisibilityEvent(event: MatrixEvent): (() => string) | null {
    const senderName = getSenderName(event);
    switch (event.getContent().history_visibility) {
        case HistoryVisibility.Invited:
            return () => _t("timeline|m.room.history_visibility|invited", { senderName });
        case HistoryVisibility.Joined:
            return () =>
                _t("timeline|m.room.history_visibility|joined", {
                    senderName,
                });
        case HistoryVisibility.Shared:
            return () => _t("timeline|m.room.history_visibility|shared", { senderName });
        case HistoryVisibility.WorldReadable:
            return () => _t("timeline|m.room.history_visibility|world_readable", { senderName });
        default:
            return () =>
                _t("timeline|m.room.history_visibility|unknown", {
                    senderName,
                    visibility: event.getContent().history_visibility,
                });
    }
}

// Currently will only display a change if a user's power level is changed
function textForPowerEvent(event: MatrixEvent, client: MatrixClient): (() => string) | null {
    const senderName = getSenderName(event);
    if (!event.getPrevContent()?.users || !event.getContent()?.users) {
        return null;
    }
    const previousUserDefault: number = event.getPrevContent().users_default || 0;
    const currentUserDefault: number = event.getContent().users_default || 0;
    // Construct set of userIds
    const users: string[] = [];
    Object.keys(event.getContent().users).forEach((userId) => {
        if (users.indexOf(userId) === -1) users.push(userId);
    });
    Object.keys(event.getPrevContent().users).forEach((userId) => {
        if (users.indexOf(userId) === -1) users.push(userId);
    });

    const diffs: {
        userId: string;
        name: string;
        from: number;
        to: number;
    }[] = [];
    users.forEach((userId) => {
        // Previous power level
        let from: number = event.getPrevContent().users[userId];
        if (!Number.isInteger(from)) {
            from = previousUserDefault;
        }
        // Current power level
        let to = event.getContent().users[userId];
        if (!Number.isInteger(to)) {
            to = currentUserDefault;
        }
        if (from === previousUserDefault && to === currentUserDefault) {
            return;
        }
        if (to !== from) {
            const name = getRoomMemberDisplayname(client, event, userId);
            diffs.push({ userId, name, from, to });
        }
    });
    if (!diffs.length) {
        return null;
    }

    // XXX: This is also surely broken for i18n
    return () =>
        _t("timeline|m.room.power_levels|changed", {
            senderName,
            powerLevelDiffText: diffs
                .map((diff) =>
                    _t("timeline|m.room.power_levels|user_from_to", {
                        userId: diff.name,
                        fromPowerLevel: Roles.textualPowerLevel(diff.from, previousUserDefault),
                        toPowerLevel: Roles.textualPowerLevel(diff.to, currentUserDefault),
                    }),
                )
                .join(", "),
        });
}

const onPinnedMessagesClick = (): void => {
    PosthogTrackers.trackInteraction("PinnedMessageStateEventClick");
    RightPanelStore.instance.setCard({ phase: RightPanelPhases.PinnedMessages }, false);
};

function textForPinnedEvent(event: MatrixEvent, client: MatrixClient, allowJSX: boolean): (() => Renderable) | null {
    if (!SettingsStore.getValue("feature_pinning")) return null;
    const senderName = getSenderName(event);
    const roomId = event.getRoomId()!;

    const pinned = event.getContent<{ pinned: string[] }>().pinned ?? [];
    const previouslyPinned: string[] = event.getPrevContent().pinned ?? [];
    const newlyPinned = pinned.filter((item) => previouslyPinned.indexOf(item) < 0);
    const newlyUnpinned = previouslyPinned.filter((item) => pinned.indexOf(item) < 0);

    if (newlyPinned.length === 1 && newlyUnpinned.length === 0) {
        // A single message was pinned, include a link to that message.
        if (allowJSX) {
            const messageId = newlyPinned.pop()!;

            return () => (
                <span>
                    {_t(
                        "timeline|m.room.pinned_events|pinned_link",
                        { senderName },
                        {
                            a: (sub) => (
                                <AccessibleButton
                                    kind="link_inline"
                                    onClick={() => {
                                        PosthogTrackers.trackInteraction("PinnedMessageStateEventClick");
                                        highlightEvent(roomId, messageId);
                                    }}
                                >
                                    {sub}
                                </AccessibleButton>
                            ),
                            b: (sub) => (
                                <AccessibleButton kind="link_inline" onClick={onPinnedMessagesClick}>
                                    {sub}
                                </AccessibleButton>
                            ),
                        },
                    )}
                </span>
            );
        }

        return () => _t("timeline|m.room.pinned_events|pinned", { senderName });
    }

    if (newlyUnpinned.length === 1 && newlyPinned.length === 0) {
        // A single message was unpinned, include a link to that message.
        if (allowJSX) {
            const messageId = newlyUnpinned.pop()!;

            return () => (
                <span>
                    {_t(
                        "timeline|m.room.pinned_events|unpinned_link",
                        { senderName },
                        {
                            a: (sub) => (
                                <AccessibleButton
                                    kind="link_inline"
                                    onClick={() => {
                                        PosthogTrackers.trackInteraction("PinnedMessageStateEventClick");
                                        highlightEvent(roomId, messageId);
                                    }}
                                >
                                    {sub}
                                </AccessibleButton>
                            ),
                            b: (sub) => (
                                <AccessibleButton kind="link_inline" onClick={onPinnedMessagesClick}>
                                    {sub}
                                </AccessibleButton>
                            ),
                        },
                    )}
                </span>
            );
        }

        return () => _t("timeline|m.room.pinned_events|unpinned", { senderName });
    }

    if (allowJSX) {
        return () => (
            <span>
                {_t(
                    "timeline|m.room.pinned_events|changed_link",
                    { senderName },
                    {
                        a: (sub) => (
                            <AccessibleButton kind="link_inline" onClick={onPinnedMessagesClick}>
                                {sub}
                            </AccessibleButton>
                        ),
                    },
                )}
            </span>
        );
    }

    return () => _t("timeline|m.room.pinned_events|changed", { senderName });
}

function textForWidgetEvent(event: MatrixEvent): (() => string) | null {
    const senderName = getSenderName(event);
    const { name: prevName, type: prevType, url: prevUrl } = event.getPrevContent();
    const { name, type, url } = event.getContent() || {};

    let widgetName = name || prevName || type || prevType || "";
    // Apply sentence case to widget name
    if (widgetName && widgetName.length > 0) {
        widgetName = widgetName[0].toUpperCase() + widgetName.slice(1);
    }

    // If the widget was removed, its content should be {}, but this is sufficiently
    // equivalent to that condition.
    if (url) {
        if (prevUrl) {
            return () =>
                _t("timeline|m.widget|modified", {
                    widgetName,
                    senderName,
                });
        } else {
            return () =>
                _t("timeline|m.widget|added", {
                    widgetName,
                    senderName,
                });
        }
    } else {
        return () =>
            _t("timeline|m.widget|removed", {
                widgetName,
                senderName,
            });
    }
}

function textForWidgetLayoutEvent(event: MatrixEvent): (() => string) | null {
    const senderName = getSenderName(event);
    return () => _t("timeline|io.element.widgets.layout", { senderName });
}

function textForMjolnirEvent(event: MatrixEvent): (() => string) | null {
    const senderName = getSenderName(event);
    const { entity: prevEntity } = event.getPrevContent();
    const { entity, recommendation, reason } = event.getContent();

    // Rule removed
    if (!entity) {
        if (USER_RULE_TYPES.includes(event.getType())) {
            return () => _t("timeline|mjolnir|removed_rule_users", { senderName, glob: prevEntity });
        } else if (ROOM_RULE_TYPES.includes(event.getType())) {
            return () => _t("timeline|mjolnir|removed_rule_rooms", { senderName, glob: prevEntity });
        } else if (SERVER_RULE_TYPES.includes(event.getType())) {
            return () =>
                _t("timeline|mjolnir|removed_rule_servers", {
                    senderName,
                    glob: prevEntity,
                });
        }

        // Unknown type. We'll say something, but we shouldn't end up here.
        return () => _t("timeline|mjolnir|removed_rule", { senderName, glob: prevEntity });
    }

    // Invalid rule
    if (!recommendation || !reason) return () => _t("timeline|mjolnir|updated_invalid_rule", { senderName });

    // Rule updated
    if (entity === prevEntity) {
        if (USER_RULE_TYPES.includes(event.getType())) {
            return () =>
                _t("timeline|mjolnir|updated_rule_users", {
                    senderName,
                    glob: entity,
                    reason,
                });
        } else if (ROOM_RULE_TYPES.includes(event.getType())) {
            return () =>
                _t("timeline|mjolnir|updated_rule_rooms", {
                    senderName,
                    glob: entity,
                    reason,
                });
        } else if (SERVER_RULE_TYPES.includes(event.getType())) {
            return () =>
                _t("timeline|mjolnir|updated_rule_servers", {
                    senderName,
                    glob: entity,
                    reason,
                });
        }

        // Unknown type. We'll say something but we shouldn't end up here.
        return () =>
            _t("timeline|mjolnir|updated_rule", {
                senderName,
                glob: entity,
                reason,
            });
    }

    // New rule
    if (!prevEntity) {
        if (USER_RULE_TYPES.includes(event.getType())) {
            return () =>
                _t("timeline|mjolnir|created_rule_users", {
                    senderName,
                    glob: entity,
                    reason,
                });
        } else if (ROOM_RULE_TYPES.includes(event.getType())) {
            return () =>
                _t("timeline|mjolnir|created_rule_rooms", {
                    senderName,
                    glob: entity,
                    reason,
                });
        } else if (SERVER_RULE_TYPES.includes(event.getType())) {
            return () =>
                _t("timeline|mjolnir|created_rule_servers", {
                    senderName,
                    glob: entity,
                    reason,
                });
        }

        // Unknown type. We'll say something but we shouldn't end up here.
        return () =>
            _t("timeline|mjolnir|created_rule", {
                senderName,
                glob: entity,
                reason,
            });
    }

    // else the entity !== prevEntity - count as a removal & add
    if (USER_RULE_TYPES.includes(event.getType())) {
        return () =>
            _t("timeline|mjolnir|changed_rule_users", { senderName, oldGlob: prevEntity, newGlob: entity, reason });
    } else if (ROOM_RULE_TYPES.includes(event.getType())) {
        return () =>
            _t("timeline|mjolnir|changed_rule_rooms", { senderName, oldGlob: prevEntity, newGlob: entity, reason });
    } else if (SERVER_RULE_TYPES.includes(event.getType())) {
        return () =>
            _t("timeline|mjolnir|changed_rule_servers", { senderName, oldGlob: prevEntity, newGlob: entity, reason });
    }

    // Unknown type. We'll say something but we shouldn't end up here.
    return () =>
        _t("timeline|mjolnir|changed_rule_glob", {
            senderName,
            oldGlob: prevEntity,
            newGlob: entity,
            reason,
        });
}

export function textForLocationEvent(event: MatrixEvent): () => string {
    return () =>
        _t("timeline|m.location|full", {
            senderName: getSenderName(event),
        });
}

function textForRedactedPollAndMessageEvent(ev: MatrixEvent, client: MatrixClient): string {
    let message = _t("timeline|self_redaction");
    const unsigned = ev.getUnsigned();
    const redactedBecauseUserId = unsigned?.redacted_because?.sender;
    if (redactedBecauseUserId && redactedBecauseUserId !== ev.getSender()) {
        const room = client.getRoom(ev.getRoomId());
        const sender = room?.getMember(redactedBecauseUserId);
        message = _t("timeline|redaction", {
            name: sender?.name || redactedBecauseUserId,
        });
    }

    return message;
}

function textForPollStartEvent(event: MatrixEvent, client: MatrixClient): (() => string) | null {
    return () => {
        let message = "";

        if (event.isRedacted()) {
            message = textForRedactedPollAndMessageEvent(event, client);
            const senderDisplayName = event.sender?.name ?? event.getSender();
            message = senderDisplayName + ": " + message;
        } else {
            message = _t("timeline|m.poll.start", {
                senderName: getSenderName(event),
                pollQuestion: (event.unstableExtensibleEvent as PollStartEvent)?.question?.text,
            });
        }

        return message;
    };
}

function textForPollEndEvent(event: MatrixEvent): (() => string) | null {
    return () =>
        _t("timeline|m.poll.end|sender_ended", {
            senderName: getSenderName(event),
        });
}

type Renderable = string | React.ReactNode | null;

interface IHandlers {
    [type: string]: (
        ev: MatrixEvent,
        client: MatrixClient,
        allowJSX: boolean,
        showHiddenEvents?: boolean,
    ) => (() => Renderable) | null;
}

const handlers: IHandlers = {
    [EventType.RoomMessage]: textForMessageEvent,
    [EventType.Sticker]: textForMessageEvent,
    [EventType.CallInvite]: textForCallInviteEvent,
    [M_POLL_START.name]: textForPollStartEvent,
    [M_POLL_END.name]: textForPollEndEvent,
    [M_POLL_START.altName]: textForPollStartEvent,
    [M_POLL_END.altName]: textForPollEndEvent,
};

const stateHandlers: IHandlers = {
    [EventType.RoomCanonicalAlias]: textForCanonicalAliasEvent,
    [EventType.RoomName]: textForRoomNameEvent,
    [EventType.RoomTopic]: textForTopicEvent,
    [EventType.RoomMember]: textForMemberEvent,
    [EventType.RoomAvatar]: textForRoomAvatarEvent,
    [EventType.RoomThirdPartyInvite]: textForThreePidInviteEvent,
    [EventType.RoomHistoryVisibility]: textForHistoryVisibilityEvent,
    [EventType.RoomPowerLevels]: textForPowerEvent,
    [EventType.RoomPinnedEvents]: textForPinnedEvent,
    [EventType.RoomServerAcl]: textForServerACLEvent,
    [EventType.RoomTombstone]: textForTombstoneEvent,
    [EventType.RoomJoinRules]: textForJoinRulesEvent,
    [EventType.RoomGuestAccess]: textForGuestAccessEvent,

    // TODO: Enable support for m.widget event type (https://github.com/vector-im/element-web/issues/13111)
    "im.vector.modular.widgets": textForWidgetEvent,
    [WIDGET_LAYOUT_EVENT_TYPE]: textForWidgetLayoutEvent,
    [VoiceBroadcastInfoEventType]: textForVoiceBroadcastStoppedEvent,
};

// Add all the Mjolnir stuff to the renderer
for (const evType of ALL_RULE_TYPES) {
    stateHandlers[evType] = textForMjolnirEvent;
}

// Add both stable and unstable m.call events
for (const evType of ElementCall.CALL_EVENT_TYPE.names) {
    stateHandlers[evType] = textForCallEvent;
}

/**
 * Determines whether the given event has text to display.
 *
 * @param client The Matrix Client instance for the logged-in user
 * @param ev The event
 * @param showHiddenEvents An optional cached setting value for showHiddenEventsInTimeline
 *     to avoid hitting the settings store
 */
export function hasText(ev: MatrixEvent, client: MatrixClient, showHiddenEvents?: boolean): boolean {
    const handler = (ev.isState() ? stateHandlers : handlers)[ev.getType()];
    return Boolean(handler?.(ev, client, false, showHiddenEvents));
}

/**
 * Gets the textual content of the given event.
 *
 * @param ev The event
 * @param client The Matrix Client instance for the logged-in user
 * @param allowJSX Whether to output rich JSX content
 * @param showHiddenEvents An optional cached setting value for showHiddenEventsInTimeline
 *     to avoid hitting the settings store
 */
export function textForEvent(ev: MatrixEvent, client: MatrixClient): string;
export function textForEvent(
    ev: MatrixEvent,
    client: MatrixClient,
    allowJSX: true,
    showHiddenEvents?: boolean,
): string | React.ReactNode;
export function textForEvent(
    ev: MatrixEvent,
    client: MatrixClient,
    allowJSX = false,
    showHiddenEvents?: boolean,
): string | React.ReactNode {
    const handler = (ev.isState() ? stateHandlers : handlers)[ev.getType()];
    return handler?.(ev, client, allowJSX, showHiddenEvents)?.() || "";
}