// 不自动运行（依赖 vue，需要 npm install 后用 vitest 运行 useChatStream.test.ts）
// Vue 3 组合式函数：POST + 流式读取、状态机、停止生成、断线后带 Last-Event-ID 重试。
import { ref, shallowRef, readonly, onScopeDispose } from "vue";
import { createSSEParser, parseFinal, type ChatStatus, type FinalPayload } from "./sse.ts";

export interface ChatOptions {
  url: string;
  fetchImpl?: typeof fetch;
  maxRetries?: number;
}

export function useChatStream(opts: ChatOptions) {
  const status = ref<ChatStatus>("idle");
  const text = ref("");
  const progress = ref("");
  const final = shallowRef<FinalPayload | null>(null);
  const error = ref("");
  let controller: AbortController | null = null;
  let lastEventId: string | undefined;
  const doFetch = opts.fetchImpl ?? fetch;

  async function send(question: string, attempt = 0): Promise<void> {
    if (attempt === 0) {
      controller?.abort(); // 新问题：取消上一次的生成
      text.value = "";
      final.value = null;
      error.value = "";
      lastEventId = undefined;
    }
    controller = new AbortController();
    status.value = "connecting";
    try {
      const resp = await doFetch(opts.url, {
        method: "POST",
        headers: { "Content-Type": "application/json", ...(lastEventId ? { "Last-Event-ID": lastEventId } : {}) },
        body: JSON.stringify({ question }),
        signal: controller.signal,
      });
      if (!resp.ok || !resp.body) throw new Error(`HTTP ${resp.status}`);
      status.value = "streaming";
      const feed = createSSEParser((e) => {
        if (e.id) lastEventId = e.id; // 记录进度，断线重连时服务端从这里继续
        if (e.event === "token") text.value += e.data;
        else if (e.event === "progress") progress.value = JSON.parse(e.data).step;
        else if (e.event === "final") final.value = parseFinal(e.data);
        else if (e.event === "error") throw new Error(e.data);
      });
      const reader = resp.body.pipeThrough(new TextDecoderStream()).getReader();
      for (;;) {
        const { value, done } = await reader.read();
        if (done) break;
        feed(value);
      }
      status.value = final.value ? "done" : "error";
      if (!final.value) error.value = "连接提前结束";
    } catch (e) {
      if ((e as Error).name === "AbortError") {
        status.value = "aborted";
        return;
      }
      if (attempt < (opts.maxRetries ?? 2)) {
        await new Promise((r) => setTimeout(r, 300 * 2 ** attempt));
        return send(question, attempt + 1);
      }
      status.value = "error";
      error.value = (e as Error).message;
    }
  }

  function stop() {
    controller?.abort();
  }

  onScopeDispose(stop); // 组件卸载时停止，避免泄漏和继续计费

  return {
    status: readonly(status),
    text: readonly(text),
    progress: readonly(progress),
    final,
    error: readonly(error),
    send,
    stop,
  };
}