// 增量 SSE 解析器：网络分块可能把一个事件切成两半，必须缓冲到空行再解析。
// 浏览器的 EventSource 只支持 GET 且不能带自定义请求头，AI 对话通常用 fetch + POST，再自己解析 SSE。
// 格式参考 HTML 标准：https://html.spec.whatwg.org/multipage/server-sent-events.html

export interface SSEEvent {
  event: string; // 默认 "message"
  data: string;
  id?: string;
}

export function createSSEParser(onEvent: (e: SSEEvent) => void) {
  let buffer = "";
  return (chunk: string): void => {
    buffer += chunk.replace(/\r\n?/g, "\n");
    let sep: number;
    while ((sep = buffer.indexOf("\n\n")) >= 0) {
      const block = buffer.slice(0, sep);
      buffer = buffer.slice(sep + 2);
      const ev: SSEEvent = { event: "message", data: "" };
      const data: string[] = [];
      for (const line of block.split("\n")) {
        if (!line || line.startsWith(":")) continue; // 空行、注释（常用作心跳）
        const i = line.indexOf(":");
        const field = i < 0 ? line : line.slice(0, i);
        const value = i < 0 ? "" : line.slice(i + 1).replace(/^ /, "");
        if (field === "event") ev.event = value;
        else if (field === "data") data.push(value);
        else if (field === "id") ev.id = value;
      }
      if (data.length) {
        ev.data = data.join("\n");
        onEvent(ev);
      }
    }
  };
}

// 对话任务的状态：前端据此显示“连接中 / 生成中 / 完成 / 失败（可重试）/ 已停止”
export type ChatStatus = "idle" | "connecting" | "streaming" | "done" | "error" | "aborted";

// 服务端约定的事件：token（增量文本）、progress（任务进度）、final（结构化结果）、error
export interface FinalPayload {
  answer: string;
  citations: { id: number; title: string }[];
}

export function parseFinal(data: string): FinalPayload {
  const v = JSON.parse(data) as Partial<FinalPayload>;
  if (typeof v.answer !== "string" || !Array.isArray(v.citations)) throw new Error("final 事件格式错误");
  return { answer: v.answer, citations: v.citations };
}