feat(theme): add system preference (#20)

src/app/components/calendar-year/calendar-year.scss

@@ -22,10 +22,7 @@
 	align-items: center;
 	border-radius: 4px;
 	z-index: 1000;
-
-	@media (prefers-color-scheme: dark) {
-		background-color: rgba(0, 0, 0, 0.7);
-	}
+	background-color: var(--loading-overlay-bg);
 }
 
 .loading-spinner {
@@ -37,12 +34,8 @@
 	p {
 		font-size: 16px;
 		font-weight: 500;
-		color: #333;
+		color: var(--loading-text-color);
 		margin: 0;
-
-		@media (prefers-color-scheme: dark) {
-			color: #ddd;
-		}
 	}
 }
 
@@ -63,12 +56,8 @@
 		transform: translate(-50%, -50%);
 		font-size: 20px;
 		font-weight: bold;
-		color: #333;
+		color: var(--loading-text-color);
 		pointer-events: none;
-
-		@media (prefers-color-scheme: dark) {
-			color: #ddd;
-		}
 	}
 }
 

src/app/components/dark-light-mode-button/dark-light-mode-button.html

@@ -1,21 +1,10 @@
-@if (lightMode()) {
-	<button
+<button
 	animate.enter="enter-animation"
 	mat-fab
-		color="primary"
+	[color]="effectiveTheme() === 'light' ? 'primary' : 'accent'"
 	(click)="toggleTheme()"
-		aria-label="Toggle light mode"
-	>
-		<mat-icon aria-hidden="false" aria-label="Dark mode icon" fontIcon="dark_mode"></mat-icon>
-	</button>
-} @else {
-	<button
-		animate.enter="enter-animation"
-		mat-fab
-		color="accent"
-		(click)="toggleTheme()"
-		aria-label="Toggle dark mode"
-	>
-		<mat-icon aria-hidden="false" aria-label="Light mode icon" fontIcon="light_mode"></mat-icon>
-	</button>
-}
+	[attr.aria-label]="description()"
+	[attr.title]="description()"
+>
+	<mat-icon aria-hidden="true" [fontIcon]="icon()"></mat-icon>
+</button>

src/app/components/dark-light-mode-button/dark-light-mode-button.spec.ts

@@ -1,12 +1,59 @@
 import { ComponentFixture, TestBed } from '@angular/core/testing';
 import { provideZonelessChangeDetection } from '@angular/core';
 import { DarkLightModeButton } from './dark-light-mode-button';
+import { vi } from 'vitest';
+
+class ControllableMatchMedia {
+	matches: boolean;
+	readonly media = '(prefers-color-scheme: light)';
+	onchange: ((this: MediaQueryList, event: MediaQueryListEvent) => unknown) | null = null;
+	private readonly listeners = new Set<(event: MediaQueryListEvent) => void>();
+
+	constructor(matches: boolean) {
+		this.matches = matches;
+	}
+
+	addEventListener(_type: string, listener: EventListenerOrEventListenerObject | null): void {
+		if (typeof listener === 'function') {
+			this.listeners.add(listener as (event: MediaQueryListEvent) => void);
+		}
+	}
+
+	removeEventListener(_type: string, listener: EventListenerOrEventListenerObject | null): void {
+		if (typeof listener === 'function') {
+			this.listeners.delete(listener as (event: MediaQueryListEvent) => void);
+		}
+	}
+
+	addListener(listener: (this: MediaQueryList, event: MediaQueryListEvent) => unknown): void {
+		this.listeners.add(listener);
+	}
+
+	removeListener(listener: (this: MediaQueryList, event: MediaQueryListEvent) => unknown): void {
+		this.listeners.delete(listener);
+	}
+
+	dispatchEvent(_event: Event): boolean {
+		return true;
+	}
+
+	change(matches: boolean): void {
+		this.matches = matches;
+		const event = { matches, media: this.media } as MediaQueryListEvent;
+		this.listeners.forEach((listener) => listener(event));
+		this.onchange?.call(this as unknown as MediaQueryList, event);
+	}
+}
 
 describe('DarkLightModeButton', () => {
 	let component: DarkLightModeButton;
 	let fixture: ComponentFixture<DarkLightModeButton>;
+	let mediaQuery: ControllableMatchMedia;
 
 	beforeEach(async () => {
+		mediaQuery = new ControllableMatchMedia(true);
+		vi.spyOn(window, 'matchMedia').mockReturnValue(mediaQuery as unknown as MediaQueryList);
+
 		await TestBed.configureTestingModule({
 			imports: [DarkLightModeButton],
 			providers: [provideZonelessChangeDetection()],
@@ -17,7 +64,129 @@ describe('DarkLightModeButton', () => {
 		fixture.detectChanges();
 	});
 
+	afterEach(() => {
+		vi.restoreAllMocks();
+		document.body.classList.remove('light-mode', 'dark-mode');
+	});
+
 	it('should create', () => {
 		expect(component).toBeTruthy();
 	});
+
+	it('starts in System and resolves its initial appearance from the browser preference', () => {
+		const button = fixture.nativeElement.querySelector('button') as HTMLButtonElement;
+		const icon = button.querySelector('mat-icon');
+
+		expect(icon?.getAttribute('data-mat-icon-name')).toBe('brightness_auto');
+		expect(button.getAttribute('aria-label')).toBe(
+			'Theme: System (currently Light). Switch to Light theme',
+		);
+		expect(button.getAttribute('title')).toBe(
+			'Theme: System (currently Light). Switch to Light theme',
+		);
+		expect(document.body.classList.contains('light-mode')).toBe(true);
+		expect(document.body.classList.contains('dark-mode')).toBe(false);
+	});
+
+	it('cycles System to Light to Dark and wraps back to System', () => {
+		const button = fixture.nativeElement.querySelector('button') as HTMLButtonElement;
+
+		button.click();
+		fixture.detectChanges();
+		expect(button.querySelector('mat-icon')?.getAttribute('data-mat-icon-name')).toBe(
+			'light_mode',
+		);
+		expect(button.getAttribute('aria-label')).toBe(
+			'Theme: Light (currently Light). Switch to Dark theme',
+		);
+		expect(button.getAttribute('title')).toBe(
+			'Theme: Light (currently Light). Switch to Dark theme',
+		);
+		expect(document.body.classList.contains('light-mode')).toBe(true);
+		expect(document.body.classList.contains('dark-mode')).toBe(false);
+
+		button.click();
+		fixture.detectChanges();
+		expect(button.querySelector('mat-icon')?.getAttribute('data-mat-icon-name')).toBe(
+			'dark_mode',
+		);
+		expect(button.getAttribute('aria-label')).toBe(
+			'Theme: Dark (currently Dark). Switch to System theme',
+		);
+		expect(button.getAttribute('title')).toBe(
+			'Theme: Dark (currently Dark). Switch to System theme',
+		);
+		expect(document.body.classList.contains('light-mode')).toBe(false);
+		expect(document.body.classList.contains('dark-mode')).toBe(true);
+
+		button.click();
+		fixture.detectChanges();
+		expect(button.querySelector('mat-icon')?.getAttribute('data-mat-icon-name')).toBe(
+			'brightness_auto',
+		);
+		expect(button.getAttribute('aria-label')).toBe(
+			'Theme: System (currently Light). Switch to Light theme',
+		);
+		expect(button.getAttribute('title')).toBe(
+			'Theme: System (currently Light). Switch to Light theme',
+		);
+		expect(document.body.classList.contains('light-mode')).toBe(true);
+		expect(document.body.classList.contains('dark-mode')).toBe(false);
+	});
+
+	it('follows live browser changes while System is selected', () => {
+		const button = fixture.nativeElement.querySelector('button') as HTMLButtonElement;
+
+		mediaQuery.change(false);
+		fixture.detectChanges();
+		expect(button.getAttribute('aria-label')).toBe(
+			'Theme: System (currently Dark). Switch to Light theme',
+		);
+		expect(document.body.classList.contains('light-mode')).toBe(false);
+		expect(document.body.classList.contains('dark-mode')).toBe(true);
+		expect(document.body.classList.contains('light-mode')).not.toBe(
+			document.body.classList.contains('dark-mode'),
+		);
+
+		mediaQuery.change(true);
+		fixture.detectChanges();
+		expect(button.getAttribute('aria-label')).toBe(
+			'Theme: System (currently Light). Switch to Light theme',
+		);
+		expect(document.body.classList.contains('light-mode')).toBe(true);
+		expect(document.body.classList.contains('dark-mode')).toBe(false);
+	});
+
+	it('keeps explicit modes fixed and uses the latest browser value when returning to System', () => {
+		const button = fixture.nativeElement.querySelector('button') as HTMLButtonElement;
+
+		button.click();
+		fixture.detectChanges();
+		mediaQuery.change(false);
+		fixture.detectChanges();
+		expect(button.getAttribute('aria-label')).toBe(
+			'Theme: Light (currently Light). Switch to Dark theme',
+		);
+		expect(document.body.classList.contains('light-mode')).toBe(true);
+		expect(document.body.classList.contains('dark-mode')).toBe(false);
+
+		button.click();
+		fixture.detectChanges();
+		mediaQuery.change(true);
+		fixture.detectChanges();
+		expect(button.getAttribute('aria-label')).toBe(
+			'Theme: Dark (currently Dark). Switch to System theme',
+		);
+		expect(document.body.classList.contains('light-mode')).toBe(false);
+		expect(document.body.classList.contains('dark-mode')).toBe(true);
+
+		mediaQuery.change(false);
+		button.click();
+		fixture.detectChanges();
+		expect(button.getAttribute('aria-label')).toBe(
+			'Theme: System (currently Dark). Switch to Light theme',
+		);
+		expect(document.body.classList.contains('light-mode')).toBe(false);
+		expect(document.body.classList.contains('dark-mode')).toBe(true);
+	});
 });

src/app/components/dark-light-mode-button/dark-light-mode-button.ts

@@ -1,21 +1,35 @@
-import { Component } from '@angular/core';
-import { ThemeService } from '../../services/theme-service';
+import { Component, computed, inject } from '@angular/core';
+import { EffectiveTheme, ThemePreference, ThemeService } from '../../services/theme-service';
 import { MatIcon } from '@angular/material/icon';
+import { MatFabButton } from '@angular/material/button';
 
 @Component({
 	selector: 'app-dark-light-mode-button',
-	imports: [MatIcon],
+	imports: [MatFabButton, MatIcon],
 	templateUrl: './dark-light-mode-button.html',
 	styleUrl: './dark-light-mode-button.scss',
 })
 export class DarkLightModeButton {
-	constructor(private themeService: ThemeService) {}
-
-	lightMode(): boolean {
-		return this.themeService.isLightMode();
-	}
+	private readonly themeService = inject(ThemeService);
+	readonly themePreference = this.themeService.themePreference;
+	readonly effectiveTheme = this.themeService.effectiveTheme;
+	readonly icon = computed(() => {
+		const preference = this.themePreference();
+		return preference === 'system' ? 'brightness_auto' : `${preference}_mode`;
+	});
+	readonly description = computed(() => {
+		const preference = this.themePreference();
+		const selected = this.preferenceLabel(preference);
+		const effective = this.preferenceLabel(this.effectiveTheme());
+		const next = this.preferenceLabel(this.themeService.nextThemePreference());
+		return `Theme: ${selected} (currently ${effective}). Switch to ${next} theme`;
+	});
 
 	toggleTheme(): void {
 		this.themeService.toggleTheme();
 	}
+
+	private preferenceLabel(preference: ThemePreference | EffectiveTheme): string {
+		return preference.charAt(0).toUpperCase() + preference.slice(1);
+	}
 }

src/app/services/theme-service.ts

@@ -1,20 +1,51 @@
-import { Injectable, signal } from '@angular/core';
+import { computed, Injectable, signal } from '@angular/core';
+
+export type ThemePreference = 'system' | 'light' | 'dark';
+export type EffectiveTheme = 'light' | 'dark';
 
 @Injectable({ providedIn: 'root' })
 export class ThemeService {
-	private lightModeMedia = window.matchMedia('(prefers-color-scheme: light)');
-	isLightMode = signal(this.lightModeMedia.matches);
+	private readonly lightModeMedia = window.matchMedia('(prefers-color-scheme: light)');
+	private readonly systemIsLight = signal(this.lightModeMedia.matches);
+	private readonly selectedPreference = signal<ThemePreference>('system');
+	readonly themePreference = this.selectedPreference.asReadonly();
+	readonly effectiveTheme = computed<EffectiveTheme>(() => {
+		const preference = this.selectedPreference();
+		return preference === 'system' ? (this.systemIsLight() ? 'light' : 'dark') : preference;
+	});
+	readonly isLightMode = computed(() => this.effectiveTheme() === 'light');
+	readonly nextThemePreference = computed(() => this.nextPreference(this.selectedPreference()));
 
 	constructor() {
-		this.toggleTheme(this.isLightMode());
+		this.applyEffectiveTheme();
 		this.lightModeMedia.addEventListener('change', (e) => {
-			this.isLightMode.set(e.matches);
+			this.systemIsLight.set(e.matches);
+			if (this.selectedPreference() === 'system') {
+				this.applyEffectiveTheme();
+			}
 		});
 	}
 
-	toggleTheme(forceLight?: boolean) {
-		const isLight = forceLight ?? !this.isLightMode();
-		this.isLightMode.set(isLight);
+	setThemePreference(preference: ThemePreference): void {
+		this.selectedPreference.set(preference);
+		this.applyEffectiveTheme();
+	}
+
+	toggleTheme(forceLight?: boolean): void {
+		if (forceLight !== undefined) {
+			this.setThemePreference(forceLight ? 'light' : 'dark');
+			return;
+		}
+
+		this.setThemePreference(this.nextThemePreference());
+	}
+
+	private nextPreference(preference: ThemePreference): ThemePreference {
+		return preference === 'system' ? 'light' : preference === 'light' ? 'dark' : 'system';
+	}
+
+	private applyEffectiveTheme(): void {
+		const isLight = this.effectiveTheme() === 'light';
 		document.body.classList.toggle('light-mode', isLight);
 		document.body.classList.toggle('dark-mode', !isLight);
 	}

src/styles.scss

@@ -34,6 +34,8 @@ html {
 	--rtt-bg: #99ff87;
 	--cp-bg: #eca0ff;
 	--other-bg: #ff9b9b;
+	--loading-overlay-bg: rgba(255, 255, 255, 0.9);
+	--loading-text-color: #333;
 }
 
 .dark-mode {
@@ -52,6 +54,8 @@ html {
 	--rtt-bg: #468149;
 	--cp-bg: #703e79;
 	--other-bg: #9b3939;
+	--loading-overlay-bg: rgba(0, 0, 0, 0.7);
+	--loading-text-color: #ddd;
 }
 
 body {