Code review improvements: Add configuration, documentation, validation, and constants to langchain-tools.js

[Copilot]

This PR addresses the code review request for server/langchain-tools.js by implementing focused improvements that enhance code quality, security, and maintainability without breaking existing functionality.

Key Improvements

🔧 Environment Configuration

Replaced hardcoded BASE_URL with configurable environment variable:

// Before
const BASE_URL = 'http://localhost:3000/api';

// After  
const BASE_URL = process.env.SWAPI_BASE_URL || 'http://localhost:3000/api';

This enables environment-specific configuration while maintaining backward compatibility.

📚 Enhanced Documentation

Added comprehensive JSDoc comments for all core functions:

/**
 * Wrapper function to capture API call details and handle errors consistently
 * @param {string} url - The API endpoint URL to call
 * @param {Object} params - Query parameters to include (default: {})
 * @returns {Promise<Object>} Object with success flag, data, and API call information
 */
async function makeApiCall(url, params = {}) {

🛡️ Input Validation & Security

Enhanced the character tool with input validation to prevent malformed data processing:

// Basic input validation
if (!Number.isInteger(id) || id <= 0) {
  return JSON.stringify({
    error: `Invalid character ID: ${id}. ID must be a positive integer.`,
    apiCall: createApiCallInfo('GET', `${BASE_URL}/characters/${id}`, {}, null, new Error('Invalid ID'))
  }, null, 2);
}

🏗️ Code Organization

Centralized hardcoded color arrays into a maintainable constant:

const SEARCH_COLORS = ['red', 'blue', 'green', 'yellow', 'brown', 'black', 'white', 'orange', 'purple', 'pink', 'blond', 'blonde', 'fair', 'dark', 'light'];

// Dynamic regex generation
const color = attributeLower.match(new RegExp(`(${SEARCH_COLORS.join('|')})`))?.[1];

✅ Test Coverage

Added comprehensive validation tests covering edge cases including negative numbers, zero, non-integers, and proper error response formatting.

Impact

• Configuration: Now supports environment-specific deployments
• Documentation: Self-documenting code improves developer experience
• Security: Input validation prevents potential issues from malformed data
• Maintainability: Centralized constants reduce code duplication
• Testing: All 63 tests pass with new validation coverage

Backward Compatibility

All changes maintain full backward compatibility with existing functionality. No breaking changes were introduced.

Fixes #68.

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