paseo/packages/app/src/utils/split-markdown-blocks.ts

function getFenceDelimiter(line: string) {
  const match = /^( {0,3})(`{3,}|~{3,})/.exec(line);
  return match?.[2] ?? null;
}

export function splitMarkdownBlocks(text: string): string[] {
  if (text.length === 0) {
    return [];
  }

  const blocks: string[] = [];
  let currentLines: string[] = [];
  let activeFenceCharacter: "`" | "~" | null = null;
  let activeFenceLength = 0;
  let sawBlockSeparator = false;

  for (const line of text.split("\n")) {
    const isBlankLine = line.trim().length === 0;

    if (!activeFenceCharacter && isBlankLine) {
      if (currentLines.length > 0) {
        sawBlockSeparator = true;
      }
      continue;
    }

    if (!activeFenceCharacter && sawBlockSeparator) {
      blocks.push(currentLines.join("\n"));
      currentLines = [];
      sawBlockSeparator = false;
    }

    currentLines.push(line);

    const fenceDelimiter = getFenceDelimiter(line);
    if (!fenceDelimiter) {
      continue;
    }

    if (!activeFenceCharacter) {
      activeFenceCharacter = fenceDelimiter[0] as "`" | "~";
      activeFenceLength = fenceDelimiter.length;
      continue;
    }

    if (fenceDelimiter[0] === activeFenceCharacter && fenceDelimiter.length >= activeFenceLength) {
      activeFenceCharacter = null;
      activeFenceLength = 0;
    }
  }

  if (currentLines.length > 0) {
    blocks.push(currentLines.join("\n"));
  }

  return blocks.filter((block) => block.length > 0);
}