/**
 * 演示专用的假 SSE 流。
 *
 * `useAiChat` 要求 `request` 返回一个 `Response`，真实的实现由后端提供。
 * 这里用 ReadableStream 按内置协议逐条吐出事件，让文档站无需后端也能跑通
 * 流式对话的完整链路。
 *
 * 内置协议的事件名与载荷字段（见 `parseDefaultEvent` / `extractText` 等）：
 * - `thinking`    载荷取 `thought` / `thinking` / `reasoning`
 * - `answer`      载荷取 `answer` / `text` / `content`
 * - `tool-status` 载荷取 `text` / `message` / `status`
 * - `citation`    载荷为引用对象
 * - `done`        载荷可带 `conversationId` 与 `duration`
 */

/** 单条 SSE 事件。 */
interface MockEvent {
	event: string;
	data: Record<string, unknown>;
}

/** 每个事件之间的间隔，模拟真实的流式节奏。 */
const STEP_DELAY = 420;

function buildEvents(question: string): MockEvent[] {
	return [
		{ event: "thinking", data: { thought: `先理解问题：「${question}」` } },
		{ event: "thinking", data: { thought: "然后确认需要的数据口径与时间范围。" } },
		{ event: "tool-status", data: { text: "正在查询数据" } },
		{ event: "answer", data: { text: "根据当前口径，" } },
		{ event: "answer", data: { text: `关于「${question}」的结论如下：` } },
		{ event: "answer", data: { text: "\n\n- 近 30 天整体**环比上升 12%**" } },
		{ event: "answer", data: { text: "\n- 其中移动端贡献了主要增量" } },
		{ event: "citation", data: { source: "分析中心", dataDomain: "订单域", timeRange: "近 30 天" } },
		{ event: "done", data: { conversationId: "demo-conversation", duration: STEP_DELAY * 9 } }
	];
}

function sleep(ms: number): Promise<void> {
	return new Promise(resolve => setTimeout(resolve, ms));
}

/**
 * 生成一段假的流式回复。
 *
 * @param question 用户提问，会回显在回答里
 * @param signal   取消信号，用户点「停止」时中断
 */
export function createMockReply(question: string, signal?: AbortSignal): Response {
	const encoder = new TextEncoder();
	const events = buildEvents(question);
	let index = 0;

	const stream = new ReadableStream<Uint8Array>({
		async pull(controller) {
			if (signal?.aborted) {
				controller.error(new DOMException("已停止生成", "AbortError"));
				return;
			}
			if (index >= events.length) {
				controller.close();
				return;
			}
			const item = events[index];
			index += 1;
			controller.enqueue(encoder.encode(`event: ${item.event}\ndata: ${JSON.stringify(item.data)}\n\n`));
			await sleep(STEP_DELAY);
		}
	});

	return new Response(stream, {
		headers: { "Content-Type": "text/event-stream" }
	});
}

/** 构造一条用于静态展示的消息。 */
export function createMessage(
	id: number,
	role: "user" | "assistant",
	content: string,
	extra: Partial<{ thinkingList: Array<{ id: number; content: string }>; citationList: unknown[] }> = {}
) {
	return {
		id,
		role,
		content,
		thinkingList: extra.thinkingList ?? [],
		citationList: extra.citationList ?? [],
		createdAt: Date.now() - (10 - id) * 60_000,
		statusText: "",
		duration: role === "assistant" ? 2400 : undefined
	};
}