/**
 * message-queue extension — owns the per-conversation steering message queue
 * (state + surface + drain-and-clear). Plugs into the kernel host via a
 * manifest + activate(host); the session-orchestrator drains it via the
 * `messageQueueHandle` service. Does NOT touch the turn loop.
 */
import type { Extension, HostAPI, Manifest } from "@dispatch/kernel";
import type { SurfaceContext, SurfaceProvider } from "@dispatch/surface-registry";
import { surfaceRegistryHandle } from "@dispatch/surface-registry";
import type { SurfaceSpec } from "@dispatch/ui-contract";
import { buildQueueSpec, MESSAGE_QUEUE_SURFACE_ID } from "./pure.js";
import { createMessageQueueService, messageQueueHandle } from "./service.js";

export const manifest: Manifest = {
	id: "message-queue",
	name: "Message Queue",
	version: "0.0.0",
	apiVersion: "^0.1.0",
	trust: "bundled",
	activation: "eager",
	dependsOn: ["surface-registry"],
	capabilities: {},
	contributes: {
		services: ["message-queue"],
	},
};

export function activate(host: HostAPI): void {
	const registry = host.getService(surfaceRegistryHandle);

	const subscribers = new Set<() => void>();

	const service = createMessageQueueService({
		id: () => crypto.randomUUID(),
		now: () => Date.now(),
		notify: () => {
			for (const sub of subscribers) {
				sub();
			}
		},
		logger: host.logger,
	});

	host.provideService(messageQueueHandle, service);

	function getSpec(context?: SurfaceContext): SurfaceSpec {
		const convId = context?.conversationId;
		const messages = convId === undefined ? [] : service.getQueue(convId);
		return buildQueueSpec(messages);
	}

	function invoke(_actionId: string, _payload?: unknown, _context?: SurfaceContext): void {
		// The message-queue surface is read-only: a client renders the queue and
		// the session-orchestrator drains it. No client-facing actions.
	}

	const provider: SurfaceProvider = {
		catalogEntry: {
			id: MESSAGE_QUEUE_SURFACE_ID,
			region: "side",
			title: "Message Queue",
			scope: "conversation",
		},
		getSpec,
		invoke,
		subscribe(onChange) {
			subscribers.add(onChange);
			return () => {
				subscribers.delete(onChange);
			};
		},
	};

	registry.register(provider);

	host.logger.info("message-queue: registered");
}

export const extension: Extension = {
	manifest,
	activate,
};