frontend/lib/api.ts

import type {
  Classification,
  DocumentDetail,
  DocumentMeta,
  ExtractionResult,
  HealthInfo,
} from "./types";

// All requests go through Next's rewrite proxy to the FastAPI backend.
const BASE = "";

async function json<T>(res: Response): Promise<T> {
  if (!res.ok) {
    const text = await res.text().catch(() => "");
    throw new Error(`${res.status} ${res.statusText}: ${text}`);
  }
  return res.json() as Promise<T>;
}

export const api = {
  health: () => fetch(`${BASE}/api/health`).then((r) => json<HealthInfo>(r)),

  listDocuments: () =>
    fetch(`${BASE}/api/documents`).then((r) => json<DocumentMeta[]>(r)),

  getDocument: (id: string) =>
    fetch(`${BASE}/api/documents/${id}`).then((r) => json<DocumentDetail>(r)),

  upload: (file: File) => {
    const fd = new FormData();
    fd.append("file", file);
    return fetch(`${BASE}/api/documents`, { method: "POST", body: fd }).then(
      (r) => json<DocumentMeta>(r),
    );
  },

  deleteDocument: (id: string) =>
    fetch(`${BASE}/api/documents/${id}`, { method: "DELETE" }).then((r) =>
      json<{ ok: boolean }>(r),
    ),

  reExtract: (id: string, schema?: string, provider?: string) => {
    const q = new URLSearchParams();
    if (schema) q.set("schema", schema);
    if (provider) q.set("provider", provider);
    return fetch(`${BASE}/api/documents/${id}/extract?${q}`, {
      method: "POST",
    }).then((r) => json<ExtractionResult>(r));
  },

  reClassify: (id: string, provider?: string) => {
    const q = new URLSearchParams();
    if (provider) q.set("provider", provider);
    return fetch(`${BASE}/api/documents/${id}/classify?${q}`, {
      method: "POST",
    }).then((r) => json<Classification>(r));
  },

  reSummarize: (id: string, provider?: string) => {
    const q = new URLSearchParams();
    if (provider) q.set("provider", provider);
    return fetch(`${BASE}/api/documents/${id}/summarize?${q}`, {
      method: "POST",
    }).then((r) => json<{ summary: string }>(r));
  },

  exportUrl: (id: string, format: string) =>
    `${BASE}/api/documents/${id}/export?format=${format}`,

  schemas: () =>
    fetch(`${BASE}/api/documents/-/schemas`).then((r) =>
      json<{ schemas: string[] }>(r),
    ),
};

// --------------------------- streaming chat ---------------------------
export interface ChatStreamHandlers {
  onToken: (text: string) => void;
  onCitations: (citations: import("./types").Citation[]) => void;
  onDone: () => void;
  onError: (msg: string) => void;
}

/**
 * POST to /api/chat and parse the SSE stream manually (EventSource only
 * supports GET, so we read the response body as a stream ourselves).
 */
export async function streamChat(
  body: {
    document_id?: string | null;
    messages: { role: string; content: string }[];
    provider?: string | null;
  },
  handlers: ChatStreamHandlers,
  signal?: AbortSignal,
) {
  try {
    const res = await fetch(`${BASE}/api/chat`, {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify(body),
      signal,
    });
    if (!res.ok || !res.body) {
      throw new Error(`Chat request failed: ${res.status}`);
    }

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

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

      // SSE frames are separated by a blank line
      const frames = buffer.split("\n\n");
      buffer = frames.pop() ?? "";

      for (const frame of frames) {
        let event = "message";
        let data = "";
        for (const line of frame.split("\n")) {
          if (line.startsWith("event:")) event = line.slice(6).trim();
          else if (line.startsWith("data:")) data += line.slice(5).trim();
        }
        if (!data) continue;
        let parsed: any;
        try {
          parsed = JSON.parse(data);
        } catch {
          continue;
        }
        if (event === "token") handlers.onToken(parsed.text ?? "");
        else if (event === "citations")
          handlers.onCitations(parsed.citations ?? []);
        else if (event === "done") handlers.onDone();
        else if (event === "error") handlers.onError(parsed.message ?? "error");
      }
    }
    handlers.onDone();
  } catch (e: any) {
    if (e?.name !== "AbortError") handlers.onError(e?.message ?? String(e));
  }
}