import type { SessionEntry } from "../../session/session-entries";

/**
 * Slice canonical append-history for the Pi-compatible `get_entries` command.
 *
 * Delegates to the canonical `SessionManager` entry list (append order) and
 * applies only the `since` cursor — never a second history/indexing layer.
 *
 * - no `since` → all entries in append order;
 * - `since` → entries strictly after the matching durable entry;
 * - unknown `since` → throws; the caller maps it to an explicit RPC failure;
 * - always passes through the current `leafId` unchanged.
 */
export function selectRpcEntries(
	entries: readonly SessionEntry[],
	leafId: string | null,
	since?: string,
): { entries: SessionEntry[]; leafId: string | null } {
	if (since === undefined) return { entries: [...entries], leafId };
	const index = entries.findIndex(entry => entry.id === since);
	if (index === -1) throw new Error(`Unknown entries cursor: ${since}`);
	return { entries: entries.slice(index + 1), leafId };
}