diff --git a/src/components/structures/MatrixChat.tsx b/src/components/structures/MatrixChat.tsx
index 1200fcaf7a..f6848feb03 100644
--- a/src/components/structures/MatrixChat.tsx
+++ b/src/components/structures/MatrixChat.tsx
@@ -58,8 +58,8 @@ import ResizeNotifier from "../../utils/ResizeNotifier";
 import AutoDiscoveryUtils, { ValidatedServerConfig } from "../../utils/AutoDiscoveryUtils";
 import DMRoomMap from '../../utils/DMRoomMap';
 import { countRoomsWithNotif } from '../../RoomNotifs';
-import { ThemeWatcher } from "../../theme";
-import { FontWatcher } from '../../FontWatcher';
+import ThemeWatcher from "../../settings/watchers/ThemeWatcher";
+import { FontWatcher } from '../../settings/watchers/FontWatcher';
 import { storeRoomAliasInCache } from '../../RoomAliasCache';
 import { defer, IDeferred } from "../../utils/promise";
 import ToastStore from "../../stores/ToastStore";
diff --git a/src/components/views/elements/Field.tsx b/src/components/views/elements/Field.tsx
index 39ed2df9f9..771d2182ea 100644
--- a/src/components/views/elements/Field.tsx
+++ b/src/components/views/elements/Field.tsx
@@ -34,7 +34,7 @@ interface IProps extends React.InputHTMLAttributes<HTMLSelectElement | HTMLInput
     id?: string,
     // The element to create. Defaults to "input".
     // To define options for a select, use <Field><option ... /></Field>
-    element?: "input" | " select" | "textarea",
+    element?: "input" | "select" | "textarea",
     // The field's type (when used as an <input>). Defaults to "text".
     type?: string,
     // id of a <datalist> element for suggestions
diff --git a/src/components/views/settings/tabs/user/AppearanceUserSettingsTab.js b/src/components/views/settings/tabs/user/AppearanceUserSettingsTab.tsx
similarity index 73%
rename from src/components/views/settings/tabs/user/AppearanceUserSettingsTab.js
rename to src/components/views/settings/tabs/user/AppearanceUserSettingsTab.tsx
index 5b49dd0abd..702fed7b4f 100644
--- a/src/components/views/settings/tabs/user/AppearanceUserSettingsTab.js
+++ b/src/components/views/settings/tabs/user/AppearanceUserSettingsTab.tsx
@@ -20,34 +20,61 @@ import React from 'react';
 import {_t} from "../../../../../languageHandler";
 import SettingsStore, {SettingLevel} from "../../../../../settings/SettingsStore";
 import * as sdk from "../../../../../index";
-import {enumerateThemes, ThemeWatcher} from "../../../../../theme";
+import { enumerateThemes } from "../../../../../theme";
+import ThemeWatcher from "../../../../../settings/watchers/ThemeWatcher";
 import Field from "../../../elements/Field";
 import Slider from "../../../elements/Slider";
 import AccessibleButton from "../../../elements/AccessibleButton";
 import dis from "../../../../../dispatcher/dispatcher";
-import { FontWatcher } from "../../../../../FontWatcher";
+import { FontWatcher } from "../../../../../settings/watchers/FontWatcher";
+import { RecheckThemePayload } from '../../../../../dispatcher/payloads/RecheckThemePayload';
+import { Action } from '../../../../../dispatcher/actions';
+import { IValidationResult, IFieldState } from '../../../elements/Validation';
 
-export default class AppearanceUserSettingsTab extends React.Component {
-    constructor() {
-        super();
+interface IProps {
+}
+
+interface IState extends IThemeState {
+    // String displaying the current selected fontSize.
+    // Needs to be string for things like '17.' without
+    // trailing 0s.
+    fontSize: string,
+    customThemeUrl: string,
+    customThemeMessage: CustomThemeMessage,
+    useCustomFontSize: boolean,
+}
+
+export type CustomThemeMessage = {isError: boolean, text: string};
+
+interface IThemeState {
+    theme: string,
+    useSystemTheme: boolean,
+}
+
+export default class AppearanceUserSettingsTab extends React.Component<IProps, IState> {
+
+    private themeTimer: NodeJS.Timeout;
+
+    constructor(props: IProps) {
+        super(props);
 
         this.state = {
-            fontSize: SettingsStore.getValue("fontSize", null),
-            ...this._calculateThemeState(),
+            fontSize: SettingsStore.getValue("fontSize", null).toString(),
+            ...this.calculateThemeState(),
             customThemeUrl: "",
             customThemeMessage: {isError: false, text: ""},
             useCustomFontSize: SettingsStore.getValue("useCustomFontSize"),
         };
     }
 
-    _calculateThemeState() {
+    private calculateThemeState(): IThemeState {
         // We have to mirror the logic from ThemeWatcher.getEffectiveTheme so we
         // show the right values for things.
 
-        const themeChoice = SettingsStore.getValueAt(SettingLevel.ACCOUNT, "theme");
-        const systemThemeExplicit = SettingsStore.getValueAt(
+        const themeChoice: string = SettingsStore.getValueAt(SettingLevel.ACCOUNT, "theme");
+        const systemThemeExplicit: boolean = SettingsStore.getValueAt(
             SettingLevel.DEVICE, "use_system_theme", null, false, true);
-        const themeExplicit = SettingsStore.getValueAt(
+        const themeExplicit: string = SettingsStore.getValueAt(
             SettingLevel.DEVICE, "theme", null, false, true);
 
         // If the user has enabled system theme matching, use that.
@@ -73,15 +100,15 @@ export default class AppearanceUserSettingsTab extends React.Component {
         };
     }
 
-    _onThemeChange = (e) => {
+    private onThemeChange(e: React.ChangeEvent<HTMLSelectElement | HTMLInputElement>): void {
         const newTheme = e.target.value;
         if (this.state.theme === newTheme) return;
 
         // doing getValue in the .catch will still return the value we failed to set,
         // so remember what the value was before we tried to set it so we can revert
-        const oldTheme = SettingsStore.getValue('theme');
+        const oldTheme: string = SettingsStore.getValue('theme');
         SettingsStore.setValue("theme", null, SettingLevel.ACCOUNT, newTheme).catch(() => {
-            dis.dispatch({action: 'recheck_theme'});
+            dis.dispatch<RecheckThemePayload>({action: Action.RecheckTheme});
             this.setState({theme: oldTheme});
         });
         this.setState({theme: newTheme});
@@ -91,23 +118,21 @@ export default class AppearanceUserSettingsTab extends React.Component {
         // XXX: The local echoed value appears to be unreliable, in particular
         // when settings custom themes(!) so adding forceTheme to override
         // the value from settings.
-        dis.dispatch({action: 'recheck_theme', forceTheme: newTheme});
+        dis.dispatch<RecheckThemePayload>({action: Action.RecheckTheme, forceTheme: newTheme});
     };
 
-    _onUseSystemThemeChanged = (checked) => {
+    private onUseSystemThemeChanged(checked: boolean) {
         this.setState({useSystemTheme: checked});
         SettingsStore.setValue("use_system_theme", null, SettingLevel.DEVICE, checked);
-        dis.dispatch({action: 'recheck_theme'});
+        dis.dispatch<RecheckThemePayload>({action: Action.RecheckTheme});
     };
 
-    _onFontSizeChanged = (size) => {
-        this.setState({fontSize: size});
+    private onFontSizeChanged(size: number) {
+        this.setState({fontSize: size.toString()});
         SettingsStore.setValue("fontSize", null, SettingLevel.DEVICE, size);
     };
 
-    _onValidateFontSize = ({value}) => {
-        console.log({value});
-
+    private async onValidateFontSize({value}: Pick<IFieldState, "value">): Promise<IValidationResult> {
         const parsedSize = parseFloat(value);
         const min = FontWatcher.MIN_SIZE;
         const max = FontWatcher.MAX_SIZE;
@@ -127,17 +152,18 @@ export default class AppearanceUserSettingsTab extends React.Component {
         return {valid: true, feedback: _t('Use between %(min)s pt and %(max)s pt', {min, max})};
     }
 
-    _onAddCustomTheme = async () => {
-        let currentThemes = SettingsStore.getValue("custom_themes");
+    private async onAddCustomTheme() {
+        let currentThemes: string[] = SettingsStore.getValue("custom_themes");
         if (!currentThemes) currentThemes = [];
         currentThemes = currentThemes.map(c => c); // cheap clone
 
-        if (this._themeTimer) {
-            clearTimeout(this._themeTimer);
+        if (this.themeTimer) {
+            clearTimeout(this.themeTimer);
         }
 
         try {
             const r = await fetch(this.state.customThemeUrl);
+            // XXX: need some schema for this
             const themeInfo = await r.json();
             if (!themeInfo || typeof(themeInfo['name']) !== 'string' || typeof(themeInfo['colors']) !== 'object') {
                 this.setState({customThemeMessage: {text: _t("Invalid theme schema."), isError: true}});
@@ -153,42 +179,32 @@ export default class AppearanceUserSettingsTab extends React.Component {
         await SettingsStore.setValue("custom_themes", null, SettingLevel.ACCOUNT, currentThemes);
         this.setState({customThemeUrl: "", customThemeMessage: {text: _t("Theme added!"), isError: false}});
 
-        this._themeTimer = setTimeout(() => {
+        this.themeTimer = setTimeout(() => {
             this.setState({customThemeMessage: {text: "", isError: false}});
         }, 3000);
     };
 
-    _onCustomThemeChange = (e) => {
+    private onCustomThemeChange(e: React.ChangeEvent<HTMLSelectElement | HTMLInputElement>) {
         this.setState({customThemeUrl: e.target.value});
     };
 
-    render() {
-        return (
-            <div className="mx_SettingsTab">
-                <div className="mx_SettingsTab_heading">{_t("Appearance")}</div>
-                {this._renderThemeSection()}
-                {SettingsStore.isFeatureEnabled("feature_font_scaling") ? this._renderFontSection() : null}
-            </div>
-        );
-    }
-
-    _renderThemeSection() {
+    private renderThemeSection() {
         const SettingsFlag = sdk.getComponent("views.elements.SettingsFlag");
         const LabelledToggleSwitch = sdk.getComponent("views.elements.LabelledToggleSwitch");
 
         const themeWatcher = new ThemeWatcher();
-        let systemThemeSection;
+        let systemThemeSection: JSX.Element;
         if (themeWatcher.isSystemThemeSupported()) {
             systemThemeSection = <div>
                 <LabelledToggleSwitch
                     value={this.state.useSystemTheme}
                     label={SettingsStore.getDisplayName("use_system_theme")}
-                    onChange={this._onUseSystemThemeChanged}
+                    onChange={this.onUseSystemThemeChanged}
                 />
             </div>;
         }
 
-        let customThemeForm;
+        let customThemeForm: JSX.Element;
         if (SettingsStore.isFeatureEnabled("feature_custom_themes")) {
             let messageElement = null;
             if (this.state.customThemeMessage.text) {
@@ -200,17 +216,17 @@ export default class AppearanceUserSettingsTab extends React.Component {
             }
             customThemeForm = (
                 <div className='mx_SettingsTab_section'>
-                    <form onSubmit={this._onAddCustomTheme}>
+                    <form onSubmit={this.onAddCustomTheme}>
                         <Field
                             label={_t("Custom theme URL")}
                             type='text'
                             id='mx_GeneralUserSettingsTab_customThemeInput'
                             autoComplete="off"
-                            onChange={this._onCustomThemeChange}
+                            onChange={this.onCustomThemeChange}
                             value={this.state.customThemeUrl}
                         />
                         <AccessibleButton
-                            onClick={this._onAddCustomTheme}
+                            onClick={this.onAddCustomTheme}
                             type="submit" kind="primary_sm"
                             disabled={!this.state.customThemeUrl.trim()}
                         >{_t("Add theme")}</AccessibleButton>
@@ -220,7 +236,8 @@ export default class AppearanceUserSettingsTab extends React.Component {
             );
         }
 
-        const themes = Object.entries(enumerateThemes())
+        // XXX: replace any type here
+        const themes = Object.entries<any>(enumerateThemes())
             .map(p => ({id: p[0], name: p[1]})); // convert pairs to objects for code readability
         const builtInThemes = themes.filter(p => !p.id.startsWith("custom-"));
         const customThemes = themes.filter(p => !builtInThemes.includes(p))
@@ -232,7 +249,7 @@ export default class AppearanceUserSettingsTab extends React.Component {
                 {systemThemeSection}
                 <Field
                     id="theme" label={_t("Theme")} element="select"
-                    value={this.state.theme} onChange={this._onThemeChange}
+                    value={this.state.theme} onChange={this.onThemeChange}
                     disabled={this.state.useSystemTheme}
                 >
                     {orderedThemes.map(theme => {
@@ -245,7 +262,7 @@ export default class AppearanceUserSettingsTab extends React.Component {
         );
     }
 
-    _renderFontSection() {
+    private renderFontSection() {
         const SettingsFlag = sdk.getComponent("views.elements.SettingsFlag");
         return <div className="mx_SettingsTab_section mx_AppearanceUserSettingsTab_fontScaling">
             <span className="mx_SettingsTab_subheading">{_t("Font size")}</span>
@@ -253,9 +270,9 @@ export default class AppearanceUserSettingsTab extends React.Component {
                 <div className="mx_AppearanceUserSettingsTab_fontSlider_smallText">Aa</div>
                 <Slider
                     values={[13, 15, 16, 18, 20]}
-                    value={this.state.fontSize}
-                    onSelectionChange={this._onFontSizeChanged}
-                    displayFunc={value => {}}
+                    value={parseInt(this.state.fontSize, 10)}
+                    onSelectionChange={this.onFontSizeChanged}
+                    displayFunc={value => ""}
                     disabled={this.state.useCustomFontSize}
                 />
                 <div className="mx_AppearanceUserSettingsTab_fontSlider_largeText">Aa</div>
@@ -263,7 +280,7 @@ export default class AppearanceUserSettingsTab extends React.Component {
             <SettingsFlag
                 name="useCustomFontSize"
                 level={SettingLevel.ACCOUNT}
-                onChange={(checked)=> this.setState({useCustomFontSize: checked})}
+                onChange={(checked) => this.setState({useCustomFontSize: checked})}
             />
             <Field
                 type="text"
@@ -272,10 +289,20 @@ export default class AppearanceUserSettingsTab extends React.Component {
                 placeholder={this.state.fontSize.toString()}
                 value={this.state.fontSize.toString()}
                 id="font_size_field"
-                onValidate={this._onValidateFontSize}
+                onValidate={this.onValidateFontSize}
                 onChange={(value) => this.setState({fontSize: value.target.value})}
                 disabled={!this.state.useCustomFontSize}
             />
         </div>;
     }
+
+    render() {
+        return (
+            <div className="mx_SettingsTab">
+                <div className="mx_SettingsTab_heading">{_t("Appearance")}</div>
+                {this.renderThemeSection()}
+                {SettingsStore.isFeatureEnabled("feature_font_scaling") ? this.renderFontSection() : null}
+            </div>
+        );
+    }
 }
diff --git a/src/dispatcher/actions.ts b/src/dispatcher/actions.ts
index 8b1be1c54e..ba72daa00d 100644
--- a/src/dispatcher/actions.ts
+++ b/src/dispatcher/actions.ts
@@ -43,5 +43,10 @@ export enum Action {
      * Sets the current tooltip. Should be use with ViewTooltipPayload.
      */
     ViewTooltip = "view_tooltip",
+
+    /**
+     *  Forces the theme to reload. No additional payload information required.
+     */
+    RecheckTheme = "recheck_theme",
 }
 
diff --git a/src/dispatcher/payloads/RecheckThemePayload.ts b/src/dispatcher/payloads/RecheckThemePayload.ts
new file mode 100644
index 0000000000..06f7012049
--- /dev/null
+++ b/src/dispatcher/payloads/RecheckThemePayload.ts
@@ -0,0 +1,27 @@
+/*
+Copyright 2020 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 { ActionPayload } from "../payloads";
+import { Action } from "../actions";
+
+export interface RecheckThemePayload extends ActionPayload {
+    action: Action.RecheckTheme,
+
+    /**
+     * Optionally specify the exact theme which is to be loaded.
+     */
+    forceTheme?: string;
+}
diff --git a/src/FontWatcher.js b/src/settings/watchers/FontWatcher.ts
similarity index 51%
rename from src/FontWatcher.js
rename to src/settings/watchers/FontWatcher.ts
index 006df202ad..dce9e77e9e 100644
--- a/src/FontWatcher.js
+++ b/src/settings/watchers/FontWatcher.ts
@@ -14,38 +14,42 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import dis from './dispatcher/dispatcher';
-import SettingsStore, {SettingLevel} from './settings/SettingsStore';
+import dis from '../../dispatcher/dispatcher';
+import SettingsStore, {SettingLevel} from '../SettingsStore';
+import IWatcher from "./Watcher";
+import { toPx } from '../../utils/units';
 
-export class FontWatcher {
-    static MIN_SIZE = 13;
-    static MAX_SIZE = 20;
+export class FontWatcher implements IWatcher {
+    public static readonly MIN_SIZE = 13;
+    public static readonly MAX_SIZE = 20;
+
+    private dispatcherRef: string;
 
     constructor() {
-        this._dispatcherRef = null;
+        this.dispatcherRef = null;
     }
 
-    start() {
-        this._setRootFontSize(SettingsStore.getValue("fontSize"));
-        this._dispatcherRef = dis.register(this._onAction);
+    public start() {
+        this.setRootFontSize(SettingsStore.getValue("fontSize"));
+        this.dispatcherRef = dis.register(this.onAction);
     }
 
-    stop() {
-        dis.unregister(this._dispatcherRef);
+    public stop() {
+        dis.unregister(this.dispatcherRef);
     }
 
-    _onAction = (payload) => {
+    private onAction = (payload) => {
         if (payload.action === 'update-font-size') {
-            this._setRootFontSize(payload.size);
+            this.setRootFontSize(payload.size);
         }
     };
 
-    _setRootFontSize = (size) => {
+    private setRootFontSize = (size) => {
         const fontSize = Math.max(Math.min(FontWatcher.MAX_SIZE, size), FontWatcher.MIN_SIZE);
 
-        if (fontSize != size) {
+        if (fontSize !== size) {
             SettingsStore.setValue("fontSize", null, SettingLevel.Device, fontSize);
         }
-        document.querySelector(":root").style.fontSize = fontSize + "px";
+        (<HTMLElement>document.querySelector(":root")).style.fontSize = toPx(fontSize);
     };
 }
diff --git a/src/settings/watchers/ThemeWatcher.ts b/src/settings/watchers/ThemeWatcher.ts
new file mode 100644
index 0000000000..ce0db881c0
--- /dev/null
+++ b/src/settings/watchers/ThemeWatcher.ts
@@ -0,0 +1,138 @@
+/*
+Copyright 2019 Michael Telatynski <7t3chguy@gmail.com>
+Copyright 2019, 2020 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 SettingsStore, { SettingLevel } from '../SettingsStore';
+import dis from '../../dispatcher/dispatcher';
+import { Action } from '../../dispatcher/actions';
+import ThemeController from "../controllers/ThemeController";
+import { setTheme } from "../../theme";
+import { ActionPayload } from '../../dispatcher/payloads';
+
+export default class ThemeWatcher {
+    // XXX: I think this is unused.
+    static _instance = null;
+
+    private themeWatchRef: string;
+    private systemThemeWatchRef: string;
+    private dispatcherRef: string;
+
+    private preferDark: MediaQueryList;
+    private preferLight: MediaQueryList;
+
+    private currentTheme: string;
+
+    constructor() {
+        this.themeWatchRef = null;
+        this.systemThemeWatchRef = null;
+        this.dispatcherRef = null;
+
+        // we have both here as each may either match or not match, so by having both
+        // we can get the tristate of dark/light/unsupported
+        this.preferDark = (<any>global).matchMedia("(prefers-color-scheme: dark)");
+        this.preferLight = (<any>global).matchMedia("(prefers-color-scheme: light)");
+
+        this.currentTheme = this.getEffectiveTheme();
+    }
+
+    public start() {
+        this.themeWatchRef = SettingsStore.watchSetting("theme", null, this.onChange);
+        this.systemThemeWatchRef = SettingsStore.watchSetting("use_system_theme", null, this.onChange);
+        if (this.preferDark.addEventListener) {
+            this.preferDark.addEventListener('change', this.onChange);
+            this.preferLight.addEventListener('change', this.onChange);
+        }
+        this.dispatcherRef = dis.register(this.onAction);
+    }
+
+    public stop() {
+        if (this.preferDark.addEventListener) {
+            this.preferDark.removeEventListener('change', this.onChange);
+            this.preferLight.removeEventListener('change', this.onChange);
+        }
+        SettingsStore.unwatchSetting(this.systemThemeWatchRef);
+        SettingsStore.unwatchSetting(this.themeWatchRef);
+        dis.unregister(this.dispatcherRef);
+    }
+
+    private onChange = () => {
+        this.recheck();
+    };
+
+    private onAction = (payload: ActionPayload) => {
+        if (payload.action === Action.RecheckTheme) {
+            // XXX forceTheme
+            this.recheck(payload.forceTheme);
+        }
+    };
+
+    // XXX: forceTheme param added here as local echo appears to be unreliable
+    // https://github.com/vector-im/riot-web/issues/11443
+    public recheck(forceTheme?: string) {
+        const oldTheme = this.currentTheme;
+        this.currentTheme = forceTheme === undefined ? this.getEffectiveTheme() : forceTheme;
+        if (oldTheme !== this.currentTheme) {
+            setTheme(this.currentTheme);
+        }
+    }
+
+    public getEffectiveTheme(): string {
+        // Dev note: Much of this logic is replicated in the AppearanceUserSettingsTab
+
+        // XXX: checking the isLight flag here makes checking it in the ThemeController
+        // itself completely redundant since we just override the result here and we're
+        // now effectively just using the ThemeController as a place to store the static
+        // variable. The system theme setting probably ought to have an equivalent
+        // controller that honours the same flag, although probablt better would be to
+        // have the theme logic in one place rather than split between however many
+        // different places.
+        if (ThemeController.isLogin) return 'light';
+
+        // If the user has specifically enabled the system matching option (excluding default),
+        // then use that over anything else. We pick the lowest possible level for the setting
+        // to ensure the ordering otherwise works.
+        const systemThemeExplicit = SettingsStore.getValueAt(
+            SettingLevel.DEVICE, "use_system_theme", null, false, true);
+        if (systemThemeExplicit) {
+            console.log("returning explicit system theme");
+            if (this.preferDark.matches) return 'dark';
+            if (this.preferLight.matches) return 'light';
+        }
+
+        // If the user has specifically enabled the theme (without the system matching option being
+        // enabled specifically and excluding the default), use that theme. We pick the lowest possible
+        // level for the setting to ensure the ordering otherwise works.
+        const themeExplicit = SettingsStore.getValueAt(
+            SettingLevel.DEVICE, "theme", null, false, true);
+        if (themeExplicit) {
+            console.log("returning explicit theme: " + themeExplicit);
+            return themeExplicit;
+        }
+
+        // If the user hasn't really made a preference in either direction, assume the defaults of the
+        // settings and use those.
+        if (SettingsStore.getValue('use_system_theme')) {
+            if (this.preferDark.matches) return 'dark';
+            if (this.preferLight.matches) return 'light';
+        }
+        console.log("returning theme value");
+        return SettingsStore.getValue('theme');
+    }
+
+    public isSystemThemeSupported() {
+        return this.preferDark.matches || this.preferLight.matches;
+    }
+}
diff --git a/src/settings/watchers/Watcher.ts b/src/settings/watchers/Watcher.ts
new file mode 100644
index 0000000000..a9f6f3f2c8
--- /dev/null
+++ b/src/settings/watchers/Watcher.ts
@@ -0,0 +1,20 @@
+/*
+Copyright 2020 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.
+*/
+
+export default interface IWatcher {
+    start(): void
+    stop(): void
+}
\ No newline at end of file
diff --git a/src/theme.js b/src/theme.js
index 72b6e93443..ccb753d601 100644
--- a/src/theme.js
+++ b/src/theme.js
@@ -19,114 +19,8 @@ import {_t} from "./languageHandler";
 
 export const DEFAULT_THEME = "light";
 import Tinter from "./Tinter";
-import dis from "./dispatcher/dispatcher";
-import SettingsStore, {SettingLevel} from "./settings/SettingsStore";
-import ThemeController from "./settings/controllers/ThemeController";
-
-export class ThemeWatcher {
-    static _instance = null;
-
-    constructor() {
-        this._themeWatchRef = null;
-        this._systemThemeWatchRef = null;
-        this._dispatcherRef = null;
-
-        // we have both here as each may either match or not match, so by having both
-        // we can get the tristate of dark/light/unsupported
-        this._preferDark = global.matchMedia("(prefers-color-scheme: dark)");
-        this._preferLight = global.matchMedia("(prefers-color-scheme: light)");
-
-        this._currentTheme = this.getEffectiveTheme();
-    }
-
-    start() {
-        this._themeWatchRef = SettingsStore.watchSetting("theme", null, this._onChange);
-        this._systemThemeWatchRef = SettingsStore.watchSetting("use_system_theme", null, this._onChange);
-        if (this._preferDark.addEventListener) {
-            this._preferDark.addEventListener('change', this._onChange);
-            this._preferLight.addEventListener('change', this._onChange);
-        }
-        this._dispatcherRef = dis.register(this._onAction);
-    }
-
-    stop() {
-        if (this._preferDark.addEventListener) {
-            this._preferDark.removeEventListener('change', this._onChange);
-            this._preferLight.removeEventListener('change', this._onChange);
-        }
-        SettingsStore.unwatchSetting(this._systemThemeWatchRef);
-        SettingsStore.unwatchSetting(this._themeWatchRef);
-        dis.unregister(this._dispatcherRef);
-    }
-
-    _onChange = () => {
-        this.recheck();
-    };
-
-    _onAction = (payload) => {
-        if (payload.action === 'recheck_theme') {
-            // XXX forceTheme
-            this.recheck(payload.forceTheme);
-        }
-    };
-
-    // XXX: forceTheme param added here as local echo appears to be unreliable
-    // https://github.com/vector-im/riot-web/issues/11443
-    recheck(forceTheme) {
-        const oldTheme = this._currentTheme;
-        this._currentTheme = forceTheme === undefined ? this.getEffectiveTheme() : forceTheme;
-        if (oldTheme !== this._currentTheme) {
-            setTheme(this._currentTheme);
-        }
-    }
-
-    getEffectiveTheme() {
-        // Dev note: Much of this logic is replicated in the AppearanceUserSettingsTab
-
-        // XXX: checking the isLight flag here makes checking it in the ThemeController
-        // itself completely redundant since we just override the result here and we're
-        // now effectively just using the ThemeController as a place to store the static
-        // variable. The system theme setting probably ought to have an equivalent
-        // controller that honours the same flag, although probablt better would be to
-        // have the theme logic in one place rather than split between however many
-        // different places.
-        if (ThemeController.isLogin) return 'light';
-
-        // If the user has specifically enabled the system matching option (excluding default),
-        // then use that over anything else. We pick the lowest possible level for the setting
-        // to ensure the ordering otherwise works.
-        const systemThemeExplicit = SettingsStore.getValueAt(
-            SettingLevel.DEVICE, "use_system_theme", null, false, true);
-        if (systemThemeExplicit) {
-            console.log("returning explicit system theme");
-            if (this._preferDark.matches) return 'dark';
-            if (this._preferLight.matches) return 'light';
-        }
-
-        // If the user has specifically enabled the theme (without the system matching option being
-        // enabled specifically and excluding the default), use that theme. We pick the lowest possible
-        // level for the setting to ensure the ordering otherwise works.
-        const themeExplicit = SettingsStore.getValueAt(
-            SettingLevel.DEVICE, "theme", null, false, true);
-        if (themeExplicit) {
-            console.log("returning explicit theme: " + themeExplicit);
-            return themeExplicit;
-        }
-
-        // If the user hasn't really made a preference in either direction, assume the defaults of the
-        // settings and use those.
-        if (SettingsStore.getValue('use_system_theme')) {
-            if (this._preferDark.matches) return 'dark';
-            if (this._preferLight.matches) return 'light';
-        }
-        console.log("returning theme value");
-        return SettingsStore.getValue('theme');
-    }
-
-    isSystemThemeSupported() {
-        return this._preferDark.matches || this._preferLight.matches;
-    }
-}
+import SettingsStore from "./settings/SettingsStore";
+import ThemeWatcher from "./settings/watchers/ThemeWatcher";
 
 export function enumerateThemes() {
     const BUILTIN_THEMES = {