// Generated by scripts/sync-shared.mjs from shared/client/main-session.ts. Do not edit this copy; edit the shared source and run "node scripts/sync-shared.mjs".
/**
 * Main-view Session derivation for the multi-instance Client Session model.
 *
 * The Client Session Controller carries no global "current" selection: view
 * selection belongs to the workspace UI, which owns the main-area reference and
 * publishes it through the catalog's per-source ownership counts
 * (`SessionSummary.retainedBy.mainView`). A plugin that needs the Session the
 * main view shows derives it from that marker instead of the removed
 * `SessionListState.current` field.
 *
 * The marker describes view ownership, not authority. It is the right input for
 * presentation and for deciding which view a navigation targets; it is not a
 * business fallback, because source counts never imply visibility or success.
 * @module dsh-web/shared/main-session
 */

/** The catalog row subset this helper reads (a `SessionSummary` projection). */
export interface MainViewOwnedRow<Id extends string = string> {
  /** Catalog row identity. */
  readonly id: Id
  /** Per-source local ownership counts; absent rows are never owned. */
  readonly retainedBy?: Readonly<Partial<Record<string, number>>> | undefined
}

/**
 * Resolve the Session the main view currently shows.
 *
 * Reads the catalog's rows rather than a per-id retain-info source: ownership
 * counts ride the list snapshot, so this neither allocates observers nor opens
 * history, and a subscription to the list still fires when the selection moves.
 * @param byId - the session catalog's rows (`SessionListState.byId`), when available.
 * @returns the main-view session id, or undefined when the main view shows none.
 */
export function mainViewSessionId<Id extends string>(
  byId: Readonly<Record<Id, MainViewOwnedRow<Id> | undefined>> | undefined | null,
): Id | undefined {
  if (byId === undefined || byId === null) return undefined
  for (const row of Object.values<MainViewOwnedRow<Id> | undefined>(byId)) {
    if (row !== undefined && (row.retainedBy?.mainView ?? 0) > 0) return row.id
  }
  return undefined
}