langchain-core/src/utils/json.ts

export function parseJsonMarkdown(s: string, parser = parsePartialJson) {
  // eslint-disable-next-line no-param-reassign
  s = s.trim();
  const match = /```(json)?(.*)```/s.exec(s);
  if (!match) {
    return parser(s);
  } else {
    return parser(match[2]);
  }
}

// Adapted from https://github.com/KillianLucas/open-interpreter/blob/main/interpreter/core/llm/utils/parse_partial_json.py
// MIT License
export function parsePartialJson(s: string) {
  // If the input is undefined, return null to indicate failure.
  if (typeof s === "undefined") {
    return null;
  }

  // Attempt to parse the string as-is.
  try {
    return JSON.parse(s);
  } catch (error) {
    // Pass
  }

  // Initialize variables.
  let new_s = "";
  const stack = [];
  let isInsideString = false;
  let escaped = false;

  // Process each character in the string one at a time.
  for (let char of s) {
    if (isInsideString) {
      if (char === '"' && !escaped) {
        isInsideString = false;
      } else if (char === "\n" && !escaped) {
        char = "\\n"; // Replace the newline character with the escape sequence.
      } else if (char === "\\") {
        escaped = !escaped;
      } else {
        escaped = false;
      }
    } else {
      if (char === '"') {
        isInsideString = true;
        escaped = false;
      } else if (char === "{") {
        stack.push("}");
      } else if (char === "[") {
        stack.push("]");
      } else if (char === "}" || char === "]") {
        if (stack && stack[stack.length - 1] === char) {
          stack.pop();
        } else {
          // Mismatched closing character; the input is malformed.
          return null;
        }
      }
    }

    // Append the processed character to the new string.
    new_s += char;
  }

  // If we're still inside a string at the end of processing,
  // we need to close the string.
  if (isInsideString) {
    new_s += '"';
  }

  // Close any remaining open structures in the reverse order that they were opened.
  for (let i = stack.length - 1; i >= 0; i -= 1) {
    new_s += stack[i];
  }

  // Attempt to parse the modified string as JSON.
  try {
    return JSON.parse(new_s);
  } catch (error) {
    // If we still can't parse the string as JSON, return null to indicate failure.
    return null;
  }
}