/**
 * The native `.num` document file: a ZIP container around the same JSON the
 * `.json` export writes (json.ts), so it's smaller on disk and leaves room
 * for more parts later (images, attachments) without changing the format.
 *
 * Layout, modelled on OpenDocument:
 *   mimetype        "application/x-numolus", stored uncompressed as the
 *                   first entry, so a file sniffer can identify the format
 *                   from a fixed offset
 *   meta.json       { format, formatVersion, created (ISO 8601) }
 *   document.json   the document, exactly as `serializeDocument()` writes it
 *
 * Reading only needs `document.json`; `mimetype` is checked when present so
 * a random ZIP renamed to `.num` fails with a clear message.
 */
import { strFromU8, strToU8, unzipSync, zipSync } from 'fflate';

export const NUM_MIMETYPE = 'application/x-numolus';
export const NUM_FORMAT_VERSION = 1;

export class NumFileError extends Error {}

export function packNum(documentJson: string, now: Date = new Date()): Uint8Array {
  const meta = { format: 'numolus', formatVersion: NUM_FORMAT_VERSION, created: now.toISOString() };
  return zipSync({
    mimetype: [strToU8(NUM_MIMETYPE), { level: 0 }],
    'meta.json': strToU8(JSON.stringify(meta, null, 2)),
    'document.json': strToU8(documentJson),
  });
}

/** The `document.json` text inside a `.num` file. */
export function unpackNum(bytes: Uint8Array): string {
  let files: Record<string, Uint8Array>;
  try {
    files = unzipSync(bytes);
  } catch {
    throw new NumFileError('Keine gültige .num-Datei (kein ZIP-Archiv).');
  }
  const mimetype = files.mimetype ? strFromU8(files.mimetype).trim() : null;
  if (mimetype !== null && mimetype !== NUM_MIMETYPE) {
    throw new NumFileError(`Keine numolus-Datei (Typ "${mimetype}").`);
  }
  const doc = files['document.json'];
  if (!doc) throw new NumFileError('Die .num-Datei enthält kein document.json.');
  const meta = files['meta.json'] ? safeJson(strFromU8(files['meta.json'])) : null;
  const version = meta && typeof meta === 'object' ? (meta as { formatVersion?: unknown }).formatVersion : undefined;
  if (typeof version === 'number' && version > NUM_FORMAT_VERSION) {
    throw new NumFileError(
      `Die Datei stammt aus einer neueren numolus-Version (Format ${version}); bitte die App aktualisieren.`,
    );
  }
  return strFromU8(doc);
}

function safeJson(text: string): unknown {
  try {
    return JSON.parse(text);
  } catch {
    return null;
  }
}