import type { NextFunction, Request, Response } from "express";
import { v4 as uuid } from "uuid";
import { API_PREFIX, MAX_WHITEBOARD_BODY_BYTES } from "../constants.js";

/**
 * T-167 — route-scoped body parser for `PUT /pages/:id/whiteboard`.
 *
 * A canvas save is a single JSON document (the whole canvas), and a large
 * board (the 2,000-object render/perf gate) can exceed the global 256 KB JSON
 * ceiling. This mirrors `csv-import-body.ts`: it buffers ONLY the canvas-save
 * route (everything else falls through to the 256 KB parser), 413s past
 * `MAX_WHITEBOARD_BODY_BYTES`, and sets `req.body` + `req._body = true` so the
 * downstream global parser skips. It must be registered BEFORE the
 * `app.useBodyParser("json", …)` calls (main.ts + integration helper).
 */

const CANVAS_SAVE_PATH = new RegExp(
  `^/${API_PREFIX.replace(/\//g, "\\/")}/pages/[^/]+/whiteboard$`,
);

function envelope(req: Request, res: Response, code: string, status: number, message: string): void {
  const requestId = (req.headers["x-request-id"] as string | undefined) ?? uuid();
  req.id = requestId;
  res.setHeader("x-request-id", requestId);
  res.status(status).json({ error: { code, message, requestId } });
}

export function whiteboardBodyParser(req: Request, res: Response, next: NextFunction): void {
  if (req.method !== "PUT" || !CANVAS_SAVE_PATH.test(req.path)) {
    next();
    return;
  }
  // Fast path: a declared Content-Length over the cap 413s without buffering.
  const declared = Number(req.headers["content-length"] ?? 0);
  if (declared > MAX_WHITEBOARD_BODY_BYTES) {
    req.resume();
    envelope(req, res, "PAYLOAD_TOO_LARGE", 413, `Whiteboard canvas exceeds the ${MAX_WHITEBOARD_BODY_BYTES} byte limit.`);
    return;
  }
  const chunks: Buffer[] = [];
  let size = 0;
  let done = false;
  const finish = (err?: unknown): void => {
    if (done) return;
    done = true;
    if (err) {
      next(err);
      return;
    }
    const raw = Buffer.concat(chunks);
    req.rawBody = raw;
    try {
      req.body = raw.length > 0 ? JSON.parse(raw.toString("utf8")) : null;
    } catch {
      envelope(req, res, "VALIDATION_ERROR", 400, "Request body must be valid JSON.");
      return;
    }
    (req as unknown as Record<string, unknown>)._body = true; // stop the downstream 256 KB parser
    next();
  };
  req.on("data", (chunk: Buffer) => {
    size += chunk.length;
    if (size > MAX_WHITEBOARD_BODY_BYTES) {
      done = true;
      req.resume();
      envelope(req, res, "PAYLOAD_TOO_LARGE", 413, `Whiteboard canvas exceeds the ${MAX_WHITEBOARD_BODY_BYTES} byte limit.`);
      return;
    }
    chunks.push(chunk);
  });
  req.on("end", () => finish());
  req.on("error", (err) => finish(err));
}