import { useAppStore } from "../store/useAppStore";
import { markSessionRead } from "./api";

/**
 * Session read cursor (Android 协同 B3/D4) — the consumer side of the per-session
 * unread count. Two write paths, both landing on the same single cursor:
 *
 *   - opening a session (this end)      → POST /sessions/{id}/read
 *   - the `session_read` frame (other ends) → clears the badge locally only
 *
 * The store's `clearUnread` zeroes the badge; the network cannot fail the badge,
 * because `GET /sessions` is the eventual truth (a failed POST simply means the
 * dot comes back on the next list load).
 */

/** Which session does a `session_read` frame address? The payload's own
 *  `sessionId` wins when present (a frame may scope itself in the body, like the
 *  streaming frames), else the envelope's. "" means unattributable: the caller
 *  must then leave every badge alone rather than guess, since clearing the wrong
 *  session's badge would hide messages the user has not seen. */
export function sessionReadTarget(
  envelopeSessionId: string | undefined,
  r: Record<string, unknown> | null
): string {
  const payload = typeof r?.sessionId === "string" ? r.sessionId : "";
  return payload || envelopeSessionId || "";
}

/** Mark a session read because the user just opened it (called once its first
 *  page of history has landed, so the cursor never passes messages that were
 *  never rendered). Zeroes the badge immediately — the list must not show a stale
 *  dot for the conversation on screen — and pushes the cursor so every other end
 *  converges. A session this end already reads as read is skipped entirely: the
 *  WS frame (or this very call) may have cleared it first, and switching back and
 *  forth must not fire a request per render. */
export function markSessionOpenedRead(sessionId: string): void {
  if (!sessionId) return;
  const { sessions, clearUnread } = useAppStore.getState();
  if (!(sessions[sessionId]?.unreadCount ?? 0)) return;
  clearUnread(sessionId);
  void markSessionRead(sessionId).catch(() => {
    // Best effort: the server cursor stays where it was until the next attempt,
    // and the next GET /sessions reports it as truth.
  });
}