/**
 * Validates a numeric input string.
 *
 * Allowed characters: digits 0-9, a single decimal point, a leading minus sign.
 * Returns an object with:
 *   isValid  {boolean} - true when the string represents a well-formed number
 *   value    {number|null} - parsed numeric value, or null when invalid
 *   sanitized {string} - trimmed input string
 */
function validateNumericInput(input) {
  var str = String(input).trim();
  var result = { isValid: false, value: null, sanitized: str };

  if (str === '') {
    return result;
  }

  // Reject characters other than digits, decimal point, and minus sign
  if (/[^0-9.\-]/.test(str)) {
    return result;
  }

  // Minus sign is only valid as the very first character
  var minusCount = (str.match(/-/g) || []).length;
  if (minusCount > 1 || (minusCount === 1 && str.charAt(0) !== '-')) {
    return result;
  }

  // Only one decimal point is allowed
  if ((str.match(/\./g) || []).length > 1) {
    return result;
  }

  // A bare '-' or '.' is not a valid number
  if (str === '-' || str === '.') {
    return result;
  }

  var parsed = parseFloat(str);
  if (isNaN(parsed)) {
    return result;
  }

  result.isValid = true;
  result.value = parsed;
  return result;
}