const API_BASE_URL =
  process.env.NEXT_PUBLIC_API_BASE_URL ?? "/backend";

const TOKEN_KEY = "huaxia_token";

export class ApiError extends Error {
  status: number;
  code: number | string | undefined;

  constructor(message: string, status: number, code?: number | string) {
    super(message);
    this.name = "ApiError";
    this.status = status;
    this.code = code;
  }
}

function authHeaders(init: RequestInit = {}, json = true): Headers {
  const token = typeof window === "undefined" ? null : localStorage.getItem(TOKEN_KEY);
  const headers = new Headers(init.headers);
  if (json) headers.set("Content-Type", "application/json");
  if (token) headers.set("Authorization", `Bearer ${token}`);
  return headers;
}

function handleUnauthorized(status: number) {
  if (status !== 401 || typeof window === "undefined") return;
  localStorage.removeItem(TOKEN_KEY);
  if (!window.location.pathname.startsWith("/login")) window.location.href = "/login";
}

/**
 * 从错误响应体里取后端给的原因（如「会话不存在或已过期」）。
 * 非 2xx 时后端返回的是 JSON（utils/response.fail），部分场景也会包成 SSE。
 */
function extractErrorMessage(body: string): string | undefined {
  const text = body.trim();
  if (!text) return undefined;
  const jsonText = text.startsWith("data:") ? text.split("\n")[0].slice(5).trim() : text;
  try {
    const payload = JSON.parse(jsonText) as { message?: string; error?: string };
    return payload?.message ?? payload?.error;
  } catch {
    return undefined;
  }
}

/**
 * 后端存在两套成功码，必须都认：
 * - utils/response.success → code 200（工作台、风控、工单等）
 * - agent/advisor_agent/protocol.agent_success → code 0（投顾 Agent 系列接口）
 * 只认 200 会把 Agent 的正常响应误判成业务失败。
 */
function isSuccessCode(code: unknown): boolean {
  return code === undefined || code === null || code === 200 || code === 0;
}

export async function apiFetch<T>(path: string, init: RequestInit = {}): Promise<T> {
  const response = await fetch(`${API_BASE_URL}${path}`, {
    ...init,
    headers: authHeaders(init),
    cache: "no-store",
  });

  const payload = await response.json().catch(() => null);
  handleUnauthorized(response.status);
  if (!response.ok || (payload && !isSuccessCode(payload.code))) {
    throw new ApiError(
      payload?.message ?? "请求失败，请稍后重试",
      response.status,
      payload?.code
    );
  }

  return (payload?.data ?? payload) as T;
}

/** multipart/form-data 提交（知识库文档上传），不能预设 Content-Type，交给浏览器带 boundary。 */
export async function apiFetchForm<T>(path: string, form: FormData, method = "POST"): Promise<T> {
  const response = await fetch(`${API_BASE_URL}${path}`, {
    method,
    headers: authHeaders({}, false),
    body: form,
    cache: "no-store",
  });
  const payload = await response.json().catch(() => null);
  handleUnauthorized(response.status);
  if (!response.ok || (payload && !isSuccessCode(payload.code))) {
    throw new ApiError(payload?.message ?? "提交失败，请稍后重试", response.status, payload?.code);
  }
  return (payload?.data ?? payload) as T;
}

/** 下载二进制/CSV 响应（审计台账导出等），返回 Blob 由调用方落盘。 */
export async function apiFetchBlob(path: string, init: RequestInit = {}): Promise<Blob> {
  const response = await fetch(`${API_BASE_URL}${path}`, {
    ...init,
    headers: authHeaders(init, false),
    cache: "no-store",
  });
  handleUnauthorized(response.status);
  if (!response.ok) throw new ApiError("导出失败，请稍后重试", response.status);
  return response.blob();
}

export function downloadBlob(blob: Blob, filename: string) {
  const url = URL.createObjectURL(blob);
  const link = document.createElement("a");
  link.href = url;
  link.download = filename;
  document.body.appendChild(link);
  link.click();
  link.remove();
  URL.revokeObjectURL(url);
}

/* ------------------------------------------------------------------ SSE */

/**
 * 后端 SSE 事件：每行形如 `data: {json}\n\n`，type 取值
 * meta / text / done / error（见 common_const SSE_EVENT_TYPE_*）。
 */
export interface SSEEvent {
  type?: string;
  content?: string;
  intent?: string;
  draft_id?: string;
  query_id?: string;
  message?: string;
  code?: number | string;
  trace_id?: string;
  [key: string]: unknown;
}

/** 一次 SSE 请求聚合后的结果。 */
export interface SSESummary {
  /** 所有 text 事件拼接出的完整回答。 */
  text: string;
  intent?: string;
  draftId?: string;
  queryId?: string;
  traceId?: string;
  /** error 事件里的提示文案。 */
  error?: string;
  /** error 事件里的后端错误码（如投顾 Agent 的 40001 / 40030 / 50001）。 */
  errorCode?: number | string;
  /** 客服 Agent 命中的知识来源（裸 JSON 响应里的 sources）。 */
  sources?: unknown[];
}

/**
 * 读取 /advisor-agent/chat/stream 的完整响应并聚合成一条结果。
 *
 * 后端目前是「SSE 包装的整包输出」：所有分支都先 await 完整结果，再一次性 yield
 * meta → text → done，text 只有一个且内容是完整回答（见 api/routers/advisor_agent.py）。
 * 所以这里按非流式处理——读完整个响应再渲染，避免为了不存在的增量做无用功。
 *
 * 将来后端改成真增量（把 llm_client 的 astream 分片 yield text）时，
 * 改回 response.body.getReader() 增量解析即可，这里的事件类型契约不用动。
 */
export async function readSSE(
  path: string,
  body: unknown,
  signal?: AbortSignal
): Promise<SSESummary> {
  const response = await fetch(`${API_BASE_URL}${path}`, {
    method: "POST",
    headers: authHeaders({ headers: { Accept: "text/event-stream" } }),
    body: JSON.stringify(body),
    cache: "no-store",
    signal,
  });

  handleUnauthorized(response.status);
  if (!response.ok) {
    const body = await response.text();
    throw new ApiError(
      extractErrorMessage(body) ?? "请求失败，请稍后重试",
      response.status
    );
  }

  const summary: SSESummary = { text: "" };
  const raw = await response.text();

  for (const block of raw.split("\n\n")) {
    const line = block.split("\n").find((item) => item.startsWith("data:"));
    if (!line) continue;
    const data = line.slice(5).trim();
    if (!data || data === "[DONE]") continue;

    let event: SSEEvent;
    try {
      event = JSON.parse(data) as SSEEvent;
    } catch {
      continue; /* 忽略心跳与非 JSON 块 */
    }

    const record = event as Record<string, unknown>;
    const type = typeof record.type === "string" ? record.type : undefined;

    if (type === "text") {
      summary.text += (record.content as string) ?? "";
    } else if (type === "meta") {
      summary.intent = record.intent as string | undefined;
      summary.draftId = record.draft_id as string | undefined;
      summary.queryId = record.query_id as string | undefined;
      summary.traceId = record.trace_id as string | undefined;
    } else if (type === "done") {
      if (record.draft_id) summary.draftId = record.draft_id as string;
      if (record.query_id) summary.queryId = record.query_id as string;
    } else if (type === "error") {
      summary.error = (record.message as string) ?? "助手返回错误，请稍后重试";
      /*
       * 投顾 Agent 的失败也走 SSE（agent_failure），不是 HTTP 4xx，
       * 错误码和 trace_id 只在事件体里，取出来才能给「下一步怎么做」的提示和排查线索。
       */
      if (typeof record.code === "number" || typeof record.code === "string") {
        summary.errorCode = record.code;
      }
      if (typeof record.trace_id === "string") summary.traceId = record.trace_id;
    } else if (!type) {
      /*
       * 无 type 的响应——客服 Agent / 客户 Agent 不用事件包装，直接 dump 业务对象：
       * service/customer_agent/chat.py → {answer, sources, intent, rewritten_query, trace_id}
       * 另兼容 success() 包装的 {code, message, data}（取值时自动下钻一层 data）。
       * 旧实现只认 type=text，导致这两个 Agent 的回复恒为空串（聊天框永远回「暂时没有找到合适的回答」）。
       */
      const node =
        record.data && typeof record.data === "object"
          ? (record.data as Record<string, unknown>)
          : record;
      const answer = node.answer ?? node.content ?? node.summary;
      if (typeof answer === "string" && answer) {
        summary.text += answer;
      } else if (typeof record.message === "string" && record.message) {
        summary.error = record.message;
        if (typeof record.code === "number" || typeof record.code === "string") {
          summary.errorCode = record.code;
        }
      }
      if (typeof node.intent === "string") summary.intent = node.intent;
      if (typeof node.query_id === "string") summary.queryId = node.query_id;
      const trace = node.trace_id ?? record.trace_id;
      if (typeof trace === "string") summary.traceId = trace;
      if (Array.isArray(node.sources)) summary.sources = node.sources;
    }
  }

  return summary;
}