import { json, error } from '@sveltejs/kit';
import { getPersonalityById, replacePersonalityBinary } from '$lib/server/db.js';
import { verifySession, SESSION_COOKIE } from '$lib/server/session.js';
import { FILE_SIZE } from '$lib/prs.js';

const NAME_OFFSET = 0x0e;
const NAME_LEN    = 12;
const CH_COUNT_OFFSET = 0x0d;

function readPrsName(bytes) {
  let name = '';
  for (let i = 0; i < NAME_LEN; i++) {
    if (bytes[NAME_OFFSET + i] === 0) break;
    name += String.fromCharCode(bytes[NAME_OFFSET + i]);
  }
  return name.trim();
}

export async function POST({ request, cookies }) {
  const session = verifySession(cookies.get(SESSION_COOKIE));
  if (!session) throw error(401, 'Unauthorized');

  const body = await request.json().catch(() => null);
  if (!body?.id || !body?.data) throw error(400, 'Missing id or data');

  const record = getPersonalityById(body.id);
  if (!record) throw error(404, 'Personality not found');
  if (record.deleted_at) throw error(400, 'Cannot replace binary of a deleted personality');

  const bytes = new Uint8Array(body.data);
  if (bytes.length !== FILE_SIZE) {
    throw error(400, `Invalid file size: expected ${FILE_SIZE} bytes, got ${bytes.length}`);
  }

  const newPrsName     = readPrsName(bytes);
  const newChannelCount = bytes[CH_COUNT_OFFSET];

  // Preview mode — return diff without saving
  if (body.preview) {
    return json({
      preview: true,
      current: {
        prs_name:      record.prs_name ?? '',
        channel_count: record.channel_count
      },
      incoming: {
        prs_name:      newPrsName,
        channel_count: newChannelCount
      }
    });
  }

  // Commit — replace the binary
  replacePersonalityBinary(body.id, {
    data:          Buffer.from(bytes),
    prs_name:      newPrsName,
    channel_count: newChannelCount
  });

  return json({ success: true, prs_name: newPrsName, channel_count: newChannelCount });
}