const isTripleBacktick = (text: string, index: number): boolean =>
  (index >= 2 && text.substring(index - 2, index + 1) === "```") ||
  (index >= 1 && text.substring(index - 1, index + 2) === "```") ||
  (index <= text.length - 3 && text.substring(index, index + 3) === "```");

const countDollarPairs = (text: string): number => {
  let dollarPairs = 0;
  let inInlineCode = false;
  for (let i = 0; i < text.length - 1; i += 1) {
    if (text[i] === "`" && !isTripleBacktick(text, i)) {
      inInlineCode = !inInlineCode;
    }
    if (!inInlineCode && text[i] === "$" && text[i + 1] === "$") {
      dollarPairs += 1;
      i += 1;
    }
  }
  return dollarPairs;
};

const addClosingKatex = (text: string): string => {
  const firstDollarIndex = text.indexOf("$$");
  const hasNewlineAfterStart = firstDollarIndex !== -1 && text.indexOf("\n", firstDollarIndex) !== -1;
  if (hasNewlineAfterStart && !text.endsWith("\n")) return `${text}\n$$`;
  return `${text}$$`;
};

export const handleIncompleteBlockKatex = (text: string): string => {
  const dollarPairs = countDollarPairs(text);
  if (dollarPairs % 2 === 0) return text;
  return addClosingKatex(text);
};