localstorage.ts

const appName = "AppName";

export type LocalStorage = {
    theme: "dark" | "light"
    items: Array<Item>
}

export type Item = {
    id: string
}

type StorageType<T> = T extends keyof LocalStorage ? LocalStorage[T] : never;

export const SetStorageValue = (value: Partial<LocalStorage>): void => {
	if (!localStorage) throw new Error("Cannot access localStorage");

    const storage = localStorage.getItem(appName);

    if (storage == null) {
        localStorage.setItem(appName, JSON.stringify(value));
        return;
    }

    const parsedStorage = JSON.parse(storage);

    localStorage.setItem(appName, JSON.stringify({ ...parsedStorage, ...value }));

    return;
}

export function GetStorageValue<T extends keyof LocalStorage>(value: T): StorageType<T> | null {
	if (!localStorage) return null;

	const storageObject = JSON.parse(localStorage.getItem(appName) || "{}") as LocalStorage;

	return storageObject[value] as StorageType<T>;
}