Partial solution to trucate rich text AST

truncateRichText.js

const truncateRichText = (richText, options) => {
  let characterCount = 0;

  const _truncateRich = (rich) => {
    const { children } = rich;

    const truncatedChildren = children.reduce((accumulator, node, index) => {
      if (characterCount < options.length) {
        if (isString(node)) {
          const nextCount = characterCount + node.length;
          const areAdditionalNodes = index !== children.length - 1;
          let textToTruncate;

          if (areAdditionalNodes) {
            textToTruncate = nextCount < options.length ? node : `${node}1`;
          } else {
            textToTruncate = node;
          }

          const truncatedText = truncate(textToTruncate, {
            ...options,
            length: options.length - characterCount,
          });

          characterCount = nextCount;
          accumulator.push(truncatedText);
        } else {
          accumulator.push(_truncateRich(node));
        }
      }

      return accumulator;
    }, []);

    return {
      ...rich,
      children: truncatedChildren,
    };
  };

  return isString(richText)
    ? truncate(richText, options)
    : _truncateRich(richText);
};