import type { QueueItem, QueueStatus } from './encounterLifecycle';

// Preference tiers for what to preview after a close (design §3.5).
const TIERS: QueueStatus[][] = [
  ['in-progress', 'onleave'], // resume what you're juggling
  ['triaged', 'arrived'],     // ready to see
  ['scheduled'],              // later today
];

/** Smartest next item to PREVIEW (not enter) after closing `closedKey`. Undefined nothing left to pick. */
export const nextCandidateKey = (items: QueueItem[], closedKey: string): string | undefined => {
  const pool = items.filter((i) => i.key !== closedKey);
  for (const tier of TIERS) {
    const hit = pool.find((i) => tier.includes(i.status));
    if (hit) return hit.key;
  }
  return undefined;
};

/** What the overview's selection should become when the queue or the active encounter changes. */
export type SelectionOutcome =
  | { kind: 'keep' }
  | { kind: 'clear' }
  | { kind: 'select'; key: string };

/**
 * THE ACTIVE ENCOUNTER IS NEVER "STALE SELECTION", EVEN WHEN IT IS NOT ON TODAY'S QUEUE.
 *
 * The overview renders the workspace only while `selectedKey === active.item.key`. So re-selecting the
 * queue's first item whenever the selection is not a queue row **unmounts the open visit** - and an active
 * encounter that is not a queue row is a real state, not an edge case: stagnant-draft nag opens
 * a visit whose note has been waiting for days, which is precisely the visit that is NOT on today's board.
 *
 * Extracted rather than left inline because it is load-bearing and invisible: with the guard missing,
 * the nag's wiring lands, the active slot fills, and the workspace never appears - the button reads as dead
 * for a second reason, which is the failure exists to remove.
 *
 * @param activeKey the key of the ACTIVE encounter, if there is one.
 */
export const selectionAfterQueueChange = (
  items: QueueItem[],
  selectedKey: string | undefined,
  activeKey: string | undefined,
): SelectionOutcome => {
  if (activeKey !== undefined && selectedKey === activeKey) return { kind: 'keep' };
  if (items.length === 0) return { kind: 'clear' };
  if (items.some((i) => i.key === selectedKey)) return { kind: 'keep' };
  // Prefer a visit already under way - resuming beats starting.
  const first = items.find((i) => i.status === 'in-progress') ?? items[0];
  return { kind: 'select', key: first.key };
};