import { randomBytes } from "node:crypto";

import { mkdir, writeFile } from "node:fs/promises";

import path from "node:path";

export const UPLOADS_DIR =

  process.env.UPLOADS_DIR ?? path.join(process.cwd(), "uploads");

export const MAX_IMAGE_BYTES = 8 * 1024 * 1024;

export const MAX_PDF_BYTES = 15 * 1024 * 1024;

const CONTENT_TYPES: Record<string, string> = {

  jpg: "image/jpeg",

  png: "image/png",

  webp: "image/webp",

  pdf: "application/pdf",

};

export function contentTypeFor(ext: string): string | null {

  return CONTENT_TYPES[ext] ?? null;

}

export const UPLOAD_NAME_RE = /^[a-f0-9]{32}\.[a-z0-9]{3,4}$/;

function sniffExt(buf: Buffer): keyof typeof CONTENT_TYPES | null {

  if (buf.length >= 3 && buf[0] === 0xff && buf[1] === 0xd8 && buf[2] === 0xff) {

    return "jpg";

  }

  if (

    buf.length >= 8 &&

    buf

      .subarray(0, 8)

      .equals(Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]))

  ) {

    return "png";

  }

  if (

    buf.length >= 12 &&

    buf.subarray(0, 4).toString("ascii") === "RIFF" &&

    buf.subarray(8, 12).toString("ascii") === "WEBP"

  ) {

    return "webp";

  }

  if (buf.length >= 4 && buf.subarray(0, 4).toString("ascii") === "%PDF") {

    return "pdf";

  }

  return null;

}

export type UploadKind = "image" | "pdf";

export async function saveUpload(file: File, kind: UploadKind): Promise<string> {

  const max = kind === "pdf" ? MAX_PDF_BYTES : MAX_IMAGE_BYTES;

  if (file.size === 0) throw new Error("Empty file.");

  if (file.size > max) {

    throw new Error(`File too large. Max ${Math.round(max / 1024 / 1024)}MB.`);

  }

  const buf = Buffer.from(await file.arrayBuffer());

  const ext = sniffExt(buf);

  const accepted =

    kind === "pdf" ? ext === "pdf" : ext === "jpg" || ext === "png" || ext === "webp";

  if (!ext || !accepted) {

    throw new Error(

      kind === "pdf"

        ? "Only PDF files are accepted."

        : "Only JPEG, PNG, or WebP images are accepted.",

    );

  }

  const name = `${randomBytes(16).toString("hex")}.${ext}`;

  await mkdir(UPLOADS_DIR, { recursive: true });

  await writeFile(path.join(UPLOADS_DIR, name), buf);

  return `/api/uploads/${name}`;

}