import { sessionMatchesSubject } from "./chat-profile-picker-model";
import type { ChatSession } from "./home-types";
import { isUnsavedEmptyConsultation } from "./session-list-filter";

/** A list row is metadata, never authority to erase an opened transcript.
 * A complete refresh of one person drops that person's rows the server no
 * longer returns, and leaves every other person untouched. */
export function mergeSubjectSessionRows(
  current: readonly ChatSession[],
  incoming: readonly ChatSession[],
  options?: { readonly subjectId?: string; readonly complete?: boolean },
): ChatSession[] {
  const incomingIds = new Set(incoming.map((session) => session.id));
  const subjectId = options?.subjectId;
  const base = options?.complete && subjectId
    ? current.filter((session) => incomingIds.has(session.id)
      || !sessionMatchesSubject(session, subjectId)
      || isUnsavedEmptyConsultation(session))
    : current;
  const rows = new Map(base.map((session) => [session.id, session]));
  for (const row of incoming) {
    const existing = rows.get(row.id);
    rows.set(row.id, existing?.messagesHydrated
      ? { ...existing, ...row, messages: existing.messages, messagesHydrated: true }
      : row);
  }
  return [...rows.values()];
}