import type { StorageLocation } from "yt-dlp-transcript-common/lib/storageLocations";

// WHERE A MOVE IS GOING, as the two panels that start one can say it.
//
// A destination is EITHER a configured location, named by its id, OR a root the
// operator typed. The difference is not cosmetic: for a location the client
// sends the ID AND NOTHING ELSE, and the root is looked up on the server, from
// the same settings.json /storage writes. A form that posted the root alongside
// the id would be a second copy of a fact that already has one home, and the
// copy the server trusted would be the one the browser held when the page was
// rendered — stale the moment a re-point moved the location somewhere else.
//
// NOT IN EITHER ACTIONS FILE, for the reason lib/relocationJob.ts and
// lib/queueForSlugs.ts are not either: both carry "use server", where every
// non-type export is a server action. A shared resolver cannot live in one.
export type MoveDestination =
  { kind: "location"; locationId: string } | { kind: "custom"; root: string };

export type ResolvedDestination = { root: string } | { error: string };

// The root, or the sentence explaining why there is not one. Pure: the caller
// hands it `getSettings().storage.locations`, so this is unit-testable and has
// no opinion about which process is asking.
export function resolveMoveDestination(
  dest: MoveDestination,
  locations: readonly StorageLocation[],
): ResolvedDestination {
  if (dest.kind === "custom") {
    const root = dest.root.trim();
    return root ? { root } : { error: "Enter a destination root." };
  }
  const id = dest.locationId.trim();
  const found = locations.find((l) => l.id === id);
  if (!found) {
    return {
      error:
        `No storage location "${id}" is configured. ` +
        `Add it on /storage, or choose a different destination.`,
    };
  }
  return { root: found.root };
}