improves handling of user data

src/lib/user/index.ts

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+export * from './preferences';
+export * from './progress';

src/lib/user/preferences.ts

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+import type { UserPreferences } from '$lib/types';
+import clamp from 'just-clamp';
+import { persisted } from 'svelte-local-storage-store';
+
+const _default_user_preferences = { playback_rate: 1, volume: 1 } satisfies UserPreferences;
+const _user_preferences = persisted<UserPreferences>('USER_PREFERENCE', _default_user_preferences);
+
+export const user_preferences = {
+	subscribe: _user_preferences.subscribe,
+	set: {
+		playback_rate: (value: number) => {
+			const playback_rate = clamp(value, 0.5, 5);
+			return _user_preferences.update((prefs) => ({ ...prefs, playback_rate }));
+		},
+		volume: (value: number) => {
+			const volume = clamp(value, 0, 1);
+			return _user_preferences.update((prefs) => ({ ...prefs, volume }));
+		},
+	},
+	clear: () => _user_preferences.set(_default_user_preferences),
+};

src/lib/user/progress.ts

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+import { episode_audio, episode_progress } from '$lib/audio';
+import type { UserProgress } from '$lib/types';
+import { get_pathname_from_url } from '$lib/utility/get-pathname-from-url';
+import { info } from '$lib/utility/package/log';
+import { persisted } from 'svelte-local-storage-store';
+import { get } from 'svelte/store';
+
+const _default_user_progress = {} satisfies UserProgress;
+const _user_progress = persisted<UserProgress>('USER_PROGRESS', _default_user_progress);
+
+const save = () => {
+	const audio = get(episode_audio);
+	if (!audio?.src) return;
+
+	info('saving progress: ', audio.src);
+
+	const pathname = get_pathname_from_url(audio.src);
+	const current_time = get(episode_progress).current_time;
+	_user_progress.update((prev) => ({ ...prev, [pathname]: current_time }));
+};
+
+export const user_progress = {
+	subscribe: _user_progress.subscribe,
+	get: (src: string) => get(_user_progress)[get_pathname_from_url(src)],
+	save,
+	clear: () => _user_progress.set(_default_user_progress),
+};