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/**
* Robust JSON parser for LLM outputs
* Handles common issues like:
* - Missing opening/closing braces
* - Markdown code blocks
* - Extra text before/after JSON
* - Escaped quotes
* - Trailing commas
*/
export class JsonParser {
/**
* Extract and parse JSON from potentially messy LLM output
* @param {string} text - Raw text from LLM
* @param {object} options - Parsing options
* @returns {object} Parsed JSON object
*/
static parse(text, options = {}) {
const {
debug = false,
expectArray = false,
expectObject = true,
repairAttempts = true
} = options;
if (debug) {
console.log("\nRAW LLM OUTPUT:");
console.log("-".repeat(70));
console.log(text);
console.log("-".repeat(70) + "\n");
}
// Step 1: Clean the text
let cleaned = this.cleanText(text, debug);
// Step 2: Extract JSON
let extracted = this.extractJson(cleaned, expectArray, expectObject, debug);
// Step 3: Attempt to parse
try {
const parsed = JSON.parse(extracted);
if (debug) console.log("Successfully parsed JSON\n");
return parsed;
} catch (firstError) {
if (debug) {
console.log("First parse attempt failed:", firstError.message);
}
if (!repairAttempts) {
throw new Error(`JSON parse failed: ${firstError.message}\n\nExtracted text:\n${extracted}`);
}
// Step 4: Attempt repairs
return this.attemptRepairs(extracted, debug);
}
}
/**
* Clean text from common LLM artifacts
*/
static cleanText(text, debug = false) {
let cleaned = text;
// Remove markdown code blocks
cleaned = cleaned.replace(/```json\s*/gi, '');
cleaned = cleaned.replace(/```\s*/g, '');
// Remove common prefixes
cleaned = cleaned.replace(/^(Here's the plan:|JSON output:|Plan:|Output:)\s*/i, '');
// Trim whitespace
cleaned = cleaned.trim();
if (debug && cleaned !== text) {
console.log("Cleaned text (removed markdown/prefixes)\n");
}
return cleaned;
}
/**
* Extract JSON from text (handles text before/after JSON)
*/
static extractJson(text, expectArray = false, expectObject = true, debug = false) {
// Try to find JSON boundaries
const startChar = expectArray ? '[' : '{';
const endChar = expectArray ? ']' : '}';
const startIdx = text.indexOf(startChar);
const lastIdx = text.lastIndexOf(endChar);
if (startIdx === -1 || lastIdx === -1 || startIdx >= lastIdx) {
if (debug) {
console.log(`Could not find valid ${startChar}...${endChar} boundaries`);
console.log(`Start index: ${startIdx}, End index: ${lastIdx}`);
}
// Maybe it's missing braces - try to add them
if (expectObject && !text.trim().startsWith('{')) {
const withBraces = '{' + text.trim() + '}';
if (debug) console.log("Added missing opening brace");
return withBraces;
}
return text;
}
const extracted = text.substring(startIdx, lastIdx + 1);
if (debug && extracted !== text) {
console.log("Extracted JSON from surrounding text:");
console.log(extracted.substring(0, 100) + (extracted.length > 100 ? '...' : ''));
console.log();
}
return extracted;
}
/**
* Attempt various repair strategies
*/
static attemptRepairs(jsonString, debug = false) {
const repairs = [
// Repair 1: Remove trailing commas
(str) => {
const fixed = str.replace(/,(\s*[}\]])/g, '$1');
if (debug && fixed !== str) console.log("Repair 1: Removed trailing commas");
return fixed;
},
// Repair 2: Fix missing quotes around property names
(str) => {
const fixed = str.replace(/([{,]\s*)([a-zA-Z_][a-zA-Z0-9_]*)\s*:/g, '$1"$2":');
if (debug && fixed !== str) console.log("Repair 2: Added quotes around property names");
return fixed;
},
// Repair 3: Fix single quotes to double quotes
(str) => {
const fixed = str.replace(/'/g, '"');
if (debug && fixed !== str) console.log("Repair 3: Converted single quotes to double quotes");
return fixed;
},
// Repair 4: Add missing closing braces
(str) => {
const openBraces = (str.match(/{/g) || []).length;
const closeBraces = (str.match(/}/g) || []).length;
if (openBraces > closeBraces) {
const fixed = str + '}'.repeat(openBraces - closeBraces);
if (debug) console.log(`Repair 4: Added ${openBraces - closeBraces} missing closing brace(s)`);
return fixed;
}
return str;
},
// Repair 5: Add missing closing brackets
(str) => {
const openBrackets = (str.match(/\[/g) || []).length;
const closeBrackets = (str.match(/]/g) || []).length;
if (openBrackets > closeBrackets) {
const fixed = str + ']'.repeat(openBrackets - closeBrackets);
if (debug) console.log(`Repair 5: Added ${openBrackets - closeBrackets} missing closing bracket(s)`);
return fixed;
}
return str;
},
// Repair 6: Fix escaped quotes that shouldn't be escaped
(str) => {
const fixed = str.replace(/\\"/g, '"');
if (debug && fixed !== str) console.log("Repair 6: Fixed escaped quotes");
return fixed;
},
// Repair 7: Remove control characters
(str) => {
// eslint-disable-next-line no-control-regex
const fixed = str.replace(/[\x00-\x1F\x7F]/g, '');
if (debug && fixed !== str) console.log("Repair 7: Removed control characters");
return fixed;
}
];
let current = jsonString;
// Try each repair in sequence
for (const repair of repairs) {
current = repair(current);
}
// Try parsing after all repairs
try {
const parsed = JSON.parse(current);
if (debug) console.log("Successfully parsed after repairs\n");
return parsed;
} catch (error) {
// Last resort: try to extract just the atoms array if it's there
const atomsMatch = current.match(/"atoms"\s*:\s*(\[[\s\S]*\])/);
if (atomsMatch) {
try {
const atomsOnly = { atoms: JSON.parse(atomsMatch[1]) };
if (debug) console.log("Extracted and parsed atoms array\n");
return atomsOnly;
} catch (innerError) {
// Fall through to final error
}
}
// If all repairs fail, throw detailed error
throw new Error(
`JSON parse failed after all repair attempts.\n\n` +
`Original error: ${error.message}\n\n` +
`Attempted repairs:\n${current.substring(0, 500)}${current.length > 500 ? '...' : ''}\n\n` +
`Tip: Check if the LLM is following the JSON schema correctly.`
);
}
}
/**
* Validate parsed plan structure
*/
static validatePlan(plan, debug = false) {
if (!plan || typeof plan !== 'object') {
throw new Error('Plan must be an object');
}
if (!Array.isArray(plan.atoms)) {
throw new Error('Plan must have an "atoms" array');
}
if (plan.atoms.length === 0) {
throw new Error('Plan must have at least one atom');
}
for (const atom of plan.atoms) {
if (typeof atom.id !== 'number') {
throw new Error(`Atom missing or invalid id: ${JSON.stringify(atom)}`);
}
if (!atom.kind || !['tool', 'decision', 'final'].includes(atom.kind)) {
throw new Error(`Atom ${atom.id} has invalid kind: ${atom.kind}`);
}
if (!atom.name || typeof atom.name !== 'string') {
throw new Error(`Atom ${atom.id} missing or invalid name`);
}
if (atom.dependsOn && !Array.isArray(atom.dependsOn)) {
throw new Error(`Atom ${atom.id} dependsOn must be an array`);
}
}
if (debug) {
console.log(`Plan structure validated: ${plan.atoms.length} atoms\n`);
}
return true;
}
/**
* Pretty print plan for debugging
*/
static prettyPrint(plan) {
console.log("\nPLAN STRUCTURE:");
console.log("=".repeat(70));
for (const atom of plan.atoms) {
const deps = atom.dependsOn && atom.dependsOn.length > 0
? ` (depends on: ${atom.dependsOn.join(', ')})`
: '';
console.log(` ${atom.id}. [${atom.kind}] ${atom.name}${deps}`);
if (atom.input && Object.keys(atom.input).length > 0) {
console.log(` Input: ${JSON.stringify(atom.input)}`);
}
}
console.log("=".repeat(70) + "\n");
}
} |