// SPDX-FileCopyrightText: 2025-2026 Kat Suricata <https://KatSuricata.com/>
// SPDX-License-Identifier: (CC-BY-4.0+ OR Apache-2.0+)

/**
 * Mode selection for the site. `src/app.html` holds the same two literals in a
 * small script that runs before the first paint. Change both places together.
 */

/** The root element attribute that selects a mode. */
export const SCHEME_ATTRIBUTE = 'data-scheme';

/** The localStorage key that holds a saved mode. */
export const SCHEME_STORAGE_KEY = 'digitalrust-scheme';

export type Scheme = 'dark' | 'safe-mode';

export const schemes: readonly Scheme[] = ['dark', 'safe-mode'];

export function isScheme(value: unknown): value is Scheme {
	return value === 'dark' || value === 'safe-mode';
}

/** The saved mode, or null when the reader saved none. */
export function savedScheme(): Scheme | null {
	try {
		const value = localStorage.getItem(SCHEME_STORAGE_KEY);
		return isScheme(value) ? value : null;
	} catch {
		/* A blocked storage call means no saved mode. */
		return null;
	}
}

/** The platform preference. The dark theme is the default when the platform gives no preference. */
export function platformScheme(): Scheme {
	return window.matchMedia('(prefers-color-scheme: light)').matches ? 'safe-mode' : 'dark';
}

/** The mode on screen now: a saved preference first, then the platform preference. */
export function activeScheme(): Scheme {
	return savedScheme() ?? platformScheme();
}

/** Saves a mode and applies it to the root element. */
export function applyScheme(scheme: Scheme): void {
	try {
		localStorage.setItem(SCHEME_STORAGE_KEY, scheme);
	} catch {
		/* A blocked storage call keeps the mode for this page only. */
	}
	document.documentElement.setAttribute(SCHEME_ATTRIBUTE, scheme);
}