element-web/src/settings/WatchManager.ts

/*
Copyright 2019-2024 New Vector Ltd.

SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
Please see LICENSE files in the repository root for full details.
*/

import { SettingLevel } from "./SettingLevel";

export type CallbackFn = (changedInRoomId: string | null, atLevel: SettingLevel, newValAtLevel: any) => void;

const IRRELEVANT_ROOM: string | null = null;

/**
 * Generalized management class for dealing with watchers on a per-handler (per-level)
 * basis without duplicating code. Handlers are expected to push updates through this
 * class, which are then proxied outwards to any applicable watchers.
 */
export class WatchManager {
    private watchers = new Map<string, Map<string | null, CallbackFn[]>>(); // settingName -> roomId -> CallbackFn[]

    // Proxy for handlers to delegate changes to this manager
    public watchSetting(settingName: string, roomId: string | null, cb: CallbackFn): void {
        if (!this.watchers.has(settingName)) this.watchers.set(settingName, new Map());
        if (!this.watchers.get(settingName)!.has(roomId)) this.watchers.get(settingName)!.set(roomId, []);
        this.watchers.get(settingName)!.get(roomId)!.push(cb);
    }

    // Proxy for handlers to delegate changes to this manager
    public unwatchSetting(cb: CallbackFn): void {
        this.watchers.forEach((map) => {
            map.forEach((callbacks) => {
                let idx: number;
                while ((idx = callbacks.indexOf(cb)) !== -1) {
                    callbacks.splice(idx, 1);
                }
            });
        });
    }

    public notifyUpdate(
        settingName: string,
        inRoomId: string | null,
        atLevel: SettingLevel,
        newValueAtLevel: any,
    ): void {
        // Dev note: We could avoid raising changes for ultimately inconsequential changes, but
        // we also don't have a reliable way to get the old value of a setting. Instead, we'll just
        // let it fall through regardless and let the receiver dedupe if they want to.

        if (!this.watchers.has(settingName)) return;

        const roomWatchers = this.watchers.get(settingName)!;
        const callbacks: CallbackFn[] = [];

        if (inRoomId !== null && roomWatchers.has(inRoomId)) {
            callbacks.push(...roomWatchers.get(inRoomId)!);
        }

        if (!inRoomId) {
            // Fire updates to all the individual room watchers too, as they probably care about the change higher up.
            callbacks.push(...Array.from(roomWatchers.values()).flat(1));
        } else if (roomWatchers.has(IRRELEVANT_ROOM)) {
            callbacks.push(...roomWatchers.get(IRRELEVANT_ROOM)!);
        }

        for (const callback of callbacks) {
            callback(inRoomId, atLevel, newValueAtLevel);
        }
    }
}