import { createRouter } from '../../create-router';
import { mkdir } from 'node:fs/promises';
import { join } from 'node:path';
import { getTmpAttachmentsDir, getAttachmentsDir } from '@@/data-path';
import { writeAtomic } from '@@/write-atomic';

const MAX_FILE_SIZE = 5 * 1024 * 1024; // 5 MB
/** PDFs never enter a prompt whole — the agent reads them from disk — so the ceiling is storage, not context. */
const PDF_MAX_FILE_SIZE = 25 * 1024 * 1024; // 25 MB

export const uploadRouter = createRouter();

uploadRouter.post('/', async (ctx) => {
  const user = ctx.get('user');
  const body = ctx.get('body') as Record<string, unknown>;

  const file = body.file as File | null;
  const sessionId = (body.sessionId as string) || null;

  if (!file || !(file instanceof File)) {
    return ctx.json({ error: 'file is required' }, 400);
  }

  // Images and PDFs. The two are handled very differently downstream and it is worth knowing which is
  // which here: an image travels to the model as base64 in the message, while a PDF is left on disk and
  // the agent is told where it is, because reading a document is something its own tools already do well
  // (page ranges, extraction) and a 10 MB base64 blob in a prompt is not.
  const isImage = file.type.startsWith('image/');
  const isPdf = file.type === 'application/pdf' || file.name.toLowerCase().endsWith('.pdf');
  if (!isImage && !isPdf) {
    return ctx.json({ error: 'Only images and PDFs are allowed' }, 400);
  }

  // A PDF is allowed to be bigger: 5 MB is a generous photo and a small report. The agent reads it from
  // disk in page ranges, so size costs storage rather than context.
  const limit = isPdf ? PDF_MAX_FILE_SIZE : MAX_FILE_SIZE;
  if (file.size > limit) {
    return ctx.json({ error: `File exceeds ${Math.round(limit / 1024 / 1024)} MB limit` }, 400);
  }

  try {
    const buffer = Buffer.from(await file.arrayBuffer());
    const ext = file.name.split('.').pop() || 'png';
    const filename = `${crypto.randomUUID()}.${ext}`;

    let saveDir: string;
    if (sessionId) {
      saveDir = getAttachmentsDir(user.email, sessionId);
    } else {
      saveDir = getTmpAttachmentsDir(user.email);
    }

    await writeAtomic(join(saveDir, filename), buffer);

    // Only an image gets a data URL. Building one for a PDF would mean carrying megabytes through the
    // browser for a preview nothing renders.
    const dataUrl = isImage ? `data:${file.type};base64,${buffer.toString('base64')}` : '';

    return ctx.json({
      filename: file.name,
      dataUrl,
      attachmentId: filename,
      kind: isPdf ? 'pdf' : 'image',
    });
  } catch (err) {
    const message = err instanceof Error ? err.message : 'Upload failed';
    return ctx.json({ error: message }, 500);
  }
});