Partial Json Parser

gistfile1.txt

/**
 * Partial JSON parser for streaming LLM responses.
 * Extracts the "response" field from incomplete JSON as it streams in.
 * 
 * Expected format (wrapped in markdown code fences):
 * ```json
 * {"response": "...", "language": "...", "suggestedCasetas": [...], "suggestedMenus": [...]}
 * ```
 */

/**
 * Extract the response text from a partial JSON string.
 * Handles the markdown code fence wrapper and incomplete JSON.
 */
export function extractResponseFromPartialJson(partialText: string): string | null {
  // Remove markdown code fences if present
  let json = partialText;
  
  // Strip ```json prefix
  const jsonStart = json.indexOf('```json');
  if (jsonStart !== -1) {
    json = json.substring(jsonStart + 7);
  }
  
  // Strip trailing ``` if present
  const jsonEnd = json.lastIndexOf('```');
  if (jsonEnd !== -1) {
    json = json.substring(0, jsonEnd);
  }
  
  json = json.trim();
  
  if (!json) return null;
  
  // Find the "response" field
  const responseKeyIndex = json.indexOf('"response"');
  if (responseKeyIndex === -1) return null;
  
  // Find the colon after "response"
  const colonIndex = json.indexOf(':', responseKeyIndex + 10);
  if (colonIndex === -1) return null;
  
  // Find the opening quote of the value
  const valueStart = json.indexOf('"', colonIndex);
  if (valueStart === -1) return null;
  
  // Extract the string value, handling escape sequences
  let result = '';
  let i = valueStart + 1;
  let escaped = false;
  
  while (i < json.length) {
    const char = json[i];
    
    if (escaped) {
      // Handle escape sequences
      switch (char) {
        case 'n': result += '\n'; break;
        case 'r': result += '\r'; break;
        case 't': result += '\t'; break;
        case '"': result += '"'; break;
        case '\\': result += '\\'; break;
        case '/': result += '/'; break;
        case 'b': result += '\b'; break;
        case 'f': result += '\f'; break;
        case 'u':
          // Unicode escape \uXXXX
          if (i + 4 < json.length) {
            const hex = json.substring(i + 1, i + 5);
            const code = parseInt(hex, 16);
            if (!isNaN(code)) {
              result += String.fromCharCode(code);
              i += 4;
            }
          }
          break;
        default:
          // Unknown escape, just add the char
          result += char;
      }
      escaped = false;
    } else if (char === '\\') {
      escaped = true;
    } else if (char === '"') {
      // End of string value - this is the complete response
      break;
    } else {
      result += char;
    }
    
    i++;
  }
  
  return result;
}

/**
 * Try to parse complete JSON and extract structured data.
 * Returns null if JSON is not complete/valid.
 */
export interface ParsedResponse {
  response: string;
  language?: string;
  suggestedCasetas?: Array<{ id: string; name: string; number: string }>;
  suggestedMenus?: Array<{ id: string; name: string; price?: string; casetaId?: string }>;
}

export function tryParseCompleteJson(text: string): ParsedResponse | null {
  // Remove markdown code fences
  let json = text;
  
  const jsonStart = json.indexOf('```json');
  if (jsonStart !== -1) {
    json = json.substring(jsonStart + 7);
  }
  
  const jsonEnd = json.lastIndexOf('```');
  if (jsonEnd !== -1) {
    json = json.substring(0, jsonEnd);
  }
  
  json = json.trim();
  
  if (!json) return null;
  
  try {
    const parsed = JSON.parse(json);
    if (typeof parsed.response === 'string') {
      return {
        response: parsed.response,
        language: parsed.language,
        suggestedCasetas: parsed.suggestedCasetas,
        suggestedMenus: parsed.suggestedMenus,
      };
    }
  } catch {
    // JSON not complete yet
  }
  
  return null;
}