import type { AiRequestBody } from "@/lib/ai/types";
import { decodeHexByteEscapes } from "@/lib/ai/decode-text";

function emitText(text: string, onUpdate: (text: string) => void) {
  onUpdate(decodeHexByteEscapes(text));
}

function parseApiError(text: string, status: number): string {
  const trimmed = text.trim();
  if (
    trimmed.startsWith("<!DOCTYPE") ||
    trimmed.startsWith("<html") ||
    trimmed.includes("<title>404")
  ) {
    return `AI 接口未到达后端 (${status})。请确认 Nginx 反代到 3130 且包含 /api/ 路径。`;
  }
  return trimmed.slice(0, 800) || `AI 请求失败 (${status})`;
}

export async function streamAiCompletion(
  body: AiRequestBody,
  onUpdate: (text: string) => void,
): Promise<string> {
  const res = await fetch("/api/ai", {
    method: "POST",
    cache: "no-store",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify(body),
  });

  if (!res.ok) {
    throw new Error(parseApiError(await res.text(), res.status));
  }

  if (!res.body) {
    throw new Error("AI 响应为空");
  }

  const reader = res.body.getReader();
  const decoder = new TextDecoder();
  let text = "";

  while (true) {
    const { done, value } = await reader.read();
    if (done) {
      break;
    }
    text += decoder.decode(value, { stream: true });
    emitText(text, onUpdate);
  }

  text += decoder.decode();
  emitText(text, onUpdate);

  if (!text.trim()) {
    throw new Error("AI 返回内容为空，请检查模型配置或稍后重试");
  }

  return decodeHexByteEscapes(text);
}