/**
 * Pure helpers for pairing-lifecycle status transitions. Extracted so
 * the rules are unit-testable without spinning up Baileys / Postgres.
 *
 * Key invariant the tests guard:
 *   - A failed or abandoned pair MUST NOT leave the row stuck in
 *     `pending`. It transitions to `unpaired` so the operator can see
 *     the account on the list with a Re-pair affordance.
 *   - Successful pairing transitions to `connected` (set by the
 *     session-manager on the `open` event — not this helper's job).
 *   - Auto-reconnect for transient drops only applies to accounts
 *     that have been linked at least once (`lastConnectedAt` set).
 */

export type AccountStatus =
  | "pending"
  | "unpaired"
  | "connected"
  | "disconnected"
  | "logged_out"
  | "banned";

export interface PairCloseInput {
  /** Status of the account row at the moment the close event fires. */
  current: AccountStatus;
  /** Did Baileys signal a logged-out close (vs an ephemeral close)? */
  loggedOut: boolean;
  /** Was it the post-pair "restart required" close (status 515)? */
  restartRequired?: boolean;
}

export type StatusUpdate = {
  next: AccountStatus;
  /** Wipe the cached QR PNG when the pair window closes. */
  clearQrPng: boolean;
} | null;

/**
 * Decide the status transition when the Baileys session closes during
 * a pairing attempt.
 *
 * - logged_out close → terminal: `logged_out`.
 * - restart-required close → null (this is a SUCCESS signal that triggers
 *   a reconnect; the row stays in its current state until `open` fires).
 * - ephemeral close (refs exhausted, network blip, etc.) → park as
 *   `unpaired` so the row stays visible and the user can retry.
 */
export function decideOnPairClose({ current, loggedOut, restartRequired }: PairCloseInput): StatusUpdate {
  if (loggedOut) {
    return { next: "logged_out", clearQrPng: true };
  }
  if (restartRequired) {
    // Post-pair-success reconnect — the next `open` event finishes the
    // job. Don't touch DB state and don't tear the listener down.
    return null;
  }
  // Whatever transient state we were in (most often `pending`), park
  // the row as `unpaired` — anything else hides it from the operator.
  return { next: "unpaired", clearQrPng: true };
}

/** Whether the session-manager should auto-reconnect after a non-loggedOut close. */
export function shouldAutoReconnect(args: {
  loggedOut: boolean;
  restartRequired?: boolean;
  /** True if the account row has `last_connected_at` set (has been linked before). */
  hasEverConnected: boolean;
}): boolean {
  if (args.loggedOut) return false;
  // Status 515 is the post-pair-success reconnect — always do it,
  // regardless of whether the account has ever connected before.
  if (args.restartRequired) return true;
  return args.hasEverConnected;
}

/** Decide what happens when the 5-min pair-window timeout fires. */
export function decideOnPairTimeout({ current }: { current: AccountStatus }): StatusUpdate | null {
  // Only the still-pending rows need cleanup. Anything else has already
  // moved on (connected, unpaired by an earlier close, etc.).
  if (current !== "pending") return null;
  return { next: "unpaired", clearQrPng: true };
}

/**
 * Decide how the pair-handler should react to a `close` event delivered
 * to its listener. Three outcomes:
 *
 *   - "ignore-leaked-close": the new attempt is still warming up and
 *     we're seeing the OLD session's tail close. Do nothing — don't
 *     emit timeout to the UI, don't touch the DB row.
 *   - "post-pair-restart": status-515 close from a successful scan.
 *     The session-manager will reconnect; we keep the listener alive
 *     and wait for the subsequent `open` event.
 *   - "treat-as-timeout": a real ephemeral close on a live attempt
 *     (refs exhausted, etc.). Park the row as `unpaired` and push
 *     `session.timeout` to the UI.
 *
 * Captures the regression where, after the user pulled up a QR and
 * navigated back, clicking Pair again would instantly flash "Pairing
 * timed out" because the await on stop() returned before
 * sessionManager.handleEvent finished broadcasting the old session's
 * close — and the new listener was already attached.
 */
export type PairListenerCloseDecision =
  | "ignore-leaked-close"
  | "post-pair-restart"
  | "treat-as-timeout";

export function decidePairListenerOnClose(input: {
  warmingUp: boolean;
  restartRequired?: boolean;
}): PairListenerCloseDecision {
  if (input.warmingUp) return "ignore-leaked-close";
  if (input.restartRequired) return "post-pair-restart";
  return "treat-as-timeout";
}