import { Plugin } from 'prosemirror-state';
import { docToText } from '../serializer';

function charCount(doc: import('prosemirror-model').Node): number {
  return docToText(doc).replace(/\n/g, '').length;
}

/**
 * Enforces a character limit by rejecting transactions that grow the
 * document past it. Shrinking edits are always allowed, even while over the
 * limit (e.g. after the limit was lowered), so users can recover.
 */
export function maxLengthPlugin(getMaxLength: () => number): Plugin {
  return new Plugin({
    filterTransaction(tr, state) {
      if (!tr.docChanged) return true;
      const max = getMaxLength();
      if (!max || max <= 0) return true;
      const after = charCount(tr.doc);
      if (after <= max) return true;
      return after < charCount(state.doc);
    },
  });
}