/**
 * Read pi-subagents' background-work state without importing its source.
 *
 * pi-subagents publishes its registry on a documented global symbol
 * (`Symbol.for("pi-subagents.background-work.v1")`). Reading that symbol keeps
 * this package working whether pi-subagents is bundled, installed separately, or
 * absent, and avoids importing a `.ts` file from under `node_modules`, which
 * Node refuses to type-strip.
 */

export const BACKGROUND_WORK_REGISTRY_KEY = "pi-subagents.background-work.v1";

interface BackgroundWorkItem {
	id: string;
	sessionId: string;
}

interface BackgroundWorkProvider {
	name: string;
	listActiveWork(): readonly BackgroundWorkItem[];
	reconcile?(context: { sessionId: string; nowMs: number }): void;
}

/** Returns undefined when pi-subagents is not loaded at all. */
function providers(): readonly BackgroundWorkProvider[] | undefined {
	const registry = (globalThis as Record<PropertyKey, unknown>)[Symbol.for(BACKGROUND_WORK_REGISTRY_KEY)];
	if (!registry || typeof registry !== "object") return undefined;
	const candidate = (registry as { providers?: unknown }).providers;
	if (!(candidate instanceof Map)) return undefined;
	return [...candidate.values()] as BackgroundWorkProvider[];
}

/**
 * Label every background item pi-subagents still considers active for this
 * session, as `provider:id`.
 *
 * Returns an empty array when nothing is pending. Returns undefined when the
 * registry is absent, which means "nothing is tracking work" rather than
 * "no work exists" — the caller decides what to do with that distinction.
 */
export function listPendingWorkLabels(sessionId: string, nowMs = Date.now()): string[] | undefined {
	const active = providers();
	if (!active) return undefined;

	const labels: string[] = [];
	for (const provider of active) {
		// A provider that throws must not block the orchestration loop; treat it
		// as contributing no items and keep inspecting the rest.
		try {
			provider.reconcile?.({ sessionId, nowMs });
		} catch {
			// Reconciliation is advisory.
		}
		let items: readonly BackgroundWorkItem[];
		try {
			items = provider.listActiveWork();
		} catch {
			continue;
		}
		if (!Array.isArray(items)) continue;
		for (const item of items) {
			if (!item || typeof item !== "object") continue;
			if (item.sessionId !== sessionId) continue;
			labels.push(`${provider.name}:${item.id}`);
		}
	}
	return labels;
}