// The channel page's address-bar keys. The page opens over any page (`?chan=`, the shell's), so its own
// keys are the shell's too: no module owns them, a page switch clears them with `chan`, and the page
// under it writes none of ITS keys while the channel stands over it — the address names only what the
// screen shows. The watch state is not here: it is an account preference that follows every channel
// (`channelShow`).
export const CHANNEL_PAGE_KEYS = ["chtab", "chsort", "chtypes"] as const;

export type ChannelTab = "videos" | "about";
type ChannelContentTypes = {
  includeNormal: boolean;
  includeShorts: boolean;
  includeLive: boolean;
};
export type ChannelPageView = { tab: ChannelTab; sort: string; types: ChannelContentTypes };

const DEFAULT_SORT = "newest";
// The content types as letters: n(ormal) s(horts) l(ive); "none" for an empty choice.
const TYPE_LETTERS: [keyof ChannelContentTypes, string][] = [
  ["includeNormal", "n"],
  ["includeShorts", "s"],
  ["includeLive", "l"],
];

/** The address-bar delta for the channel page's view; `null` clears every key (the page closed). The
 *  content types are always written: a page opened fresh takes them from the feed, so a link without
 *  them would reopen with whatever the feed of the browser opening it holds. */
export function channelPageParamUpdates(v: ChannelPageView | null): Record<string, string | null> {
  if (v == null) return { chtab: null, chsort: null, chtypes: null };
  const letters = TYPE_LETTERS.filter(([k]) => v.types[k])
    .map(([, l]) => l)
    .join("");
  return {
    chtab: v.tab === "about" ? "about" : null,
    chsort: v.sort && v.sort !== DEFAULT_SORT ? v.sort : null,
    chtypes: letters || "none",
  };
}

/** The view a channel page's address names; what it leaves out comes from `fresh` (the defaults of a
 *  page opened without a link: the videos tab, newest first, the feed's content types). */
export function channelPageViewFrom(
  params: URLSearchParams,
  fresh: ChannelPageView,
): ChannelPageView {
  const raw = params.get("chtypes");
  const types =
    raw == null
      ? fresh.types
      : (Object.fromEntries(
          TYPE_LETTERS.map(([k, l]) => [k, raw !== "none" && raw.includes(l)]),
        ) as ChannelContentTypes);
  return {
    tab: params.get("chtab") === "about" ? "about" : fresh.tab,
    sort: params.get("chsort") || fresh.sort,
    types,
  };
}