/**
 * Browser-side API client.
 * All calls go through /api/proxy/* — token added server-side.
 */

import type {
  AskRequest,
  AskResponse,
  AskSmartRequest,
  AskSmartResponse,
  AskSmartStreamEvent,
  CreateDocumentRequest,
  DocumentContentResponse,
  DocumentMeta,
  DocumentsListResponse,
  HealthResponse,
  PingResponse,
  ReindexResponse,
} from "./types";

const PROXY = "/api/proxy";

class ApiError extends Error {
  status: number;
  body: unknown;
  constructor(status: number, message: string, body?: unknown) {
    super(message);
    this.status = status;
    this.body = body;
  }
}

async function request<T>(path: string, init?: RequestInit): Promise<T> {
  const url = path ? `${PROXY}/${path}` : PROXY;
  const res = await fetch(url, {
    ...init,
    headers: {
      "Content-Type": "application/json",
      ...(init?.headers || {}),
    },
  });
  const text = await res.text();
  let data: unknown;
  try {
    data = text ? JSON.parse(text) : null;
  } catch {
    data = text;
  }
  if (!res.ok) {
    const msg =
      typeof data === "object" && data && "detail" in data
        ? String((data as { detail: unknown }).detail)
        : `HTTP ${res.status}`;
    throw new ApiError(res.status, msg, data);
  }
  return data as T;
}

export { ApiError };

// ─── Health & Ops ─────────────────────────────────────────────────
export const api = {
  health: () => request<HealthResponse>(""),
  ping: () => request<PingResponse>("ping"),

  reindex: (force_full = false, rebuild_anchors = false) =>
    request<ReindexResponse>("reindex", {
      method: "POST",
      body: JSON.stringify({ force_full, rebuild_anchors }),
    }),

  // ─── Documents ───────────────────────────────────────────────────
  listDocuments: () => request<DocumentsListResponse>("documents"),
  getDocument: (doc_id: string) => request<DocumentMeta>(`documents/${doc_id}`),
  getDocumentContent: (doc_id: string) =>
    request<DocumentContentResponse>(`documents/${doc_id}/content`),
  createDocument: (req: CreateDocumentRequest) =>
    request<DocumentMeta>("documents", {
      method: "POST",
      body: JSON.stringify(req),
    }),
  deleteDocument: (doc_id: string) =>
    request<{ status: string; doc_id: string }>(`documents/${doc_id}`, {
      method: "DELETE",
    }),

  // ─── Inference ───────────────────────────────────────────────────
  askSmart: (req: AskSmartRequest, signal?: AbortSignal) =>
    request<AskSmartResponse>("ask_smart", {
      method: "POST",
      body: JSON.stringify(req),
      signal,
    }),

  /**
   * Doc-scoped inference (retrieval bypass) — used when the user pins a
   * conversation to a single doc.
   */
  ask: (req: AskRequest, signal?: AbortSignal) =>
    request<AskResponse>("ask", {
      method: "POST",
      body: JSON.stringify(req),
      signal,
    }),

  /**
   * Streaming variant of /ask_smart. Emits SSE events; caller receives a
   * sequence of typed events via the `onEvent` callback. Resolves when the
   * stream closes (after `done`/`rejected`/`error`).
   */
  askSmartStream: async (
    req: AskSmartRequest,
    onEvent: (e: AskSmartStreamEvent) => void,
    signal?: AbortSignal
  ): Promise<void> => {
    const res = await fetch(`${PROXY}/ask_smart`, {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        Accept: "text/event-stream",
      },
      body: JSON.stringify({ ...req, stream: true }),
      signal,
    });
    if (!res.ok || !res.body) {
      const text = await res.text().catch(() => "");
      throw new ApiError(res.status, `stream HTTP ${res.status}`, text);
    }
    // Fallback: backend didn't honour stream=true (old deploy / proxy buffering).
    // Parse the body as JSON and emit a single equivalent event.
    const ct = res.headers.get("content-type") || "";
    if (!ct.includes("text/event-stream")) {
      const data = await res.json().catch(() => null);
      if (!data) {
        throw new ApiError(res.status, "non-SSE response could not be parsed");
      }
      if (data._grounding_status === "rejected_low_similarity") {
        onEvent({ event: "rejected", data });
      } else {
        onEvent({ event: "done", data });
      }
      return;
    }
    const reader = res.body.getReader();
    const decoder = new TextDecoder("utf-8");
    let buffer = "";
    let sawAny = false;
    while (true) {
      const { done, value } = await reader.read();
      if (done) break;
      buffer += decoder.decode(value, { stream: true });
      let sep: number;
      while ((sep = buffer.indexOf("\n\n")) !== -1) {
        const frame = buffer.slice(0, sep);
        buffer = buffer.slice(sep + 2);
        const parsed = parseSSE(frame);
        if (parsed) {
          sawAny = true;
          onEvent(parsed);
        }
      }
    }
    if (!sawAny) {
      throw new ApiError(0, "stream closed with no events received");
    }
  },
};

function parseSSE(frame: string): AskSmartStreamEvent | null {
  let event = "message";
  let dataLines: string[] = [];
  for (const line of frame.split("\n")) {
    if (line.startsWith("event:")) event = line.slice(6).trim();
    else if (line.startsWith("data:")) dataLines.push(line.slice(5).trim());
  }
  if (dataLines.length === 0) return null;
  try {
    const data = JSON.parse(dataLines.join("\n"));
    return { event, data } as AskSmartStreamEvent;
  } catch {
    return null;
  }
}