<?php

define('WEBFORM_CALCULATOR_REGEX', '/\{\w+\}/');

/**
 * Implements of hook_webform_component_info().
 */
function webform_calculator_webform_component_info() {
  $components = array();

  $components['formula'] = array(
    'label' => t('Formula'),
    'description' => t('Computes values of other fields.'),
    'features' => array(
      'required' => FALSE,
    ),
    'file' => 'components/formula.inc',
    'conditional_type' => 'numeric',
  );

  return $components;
}

/**
 * Implements hook_webform_submission_presave().
 */
function webform_calculator_webform_submission_presave($node, &$submission) {
  foreach ($node->webform['components'] as $component) {
    if ($component['type'] == 'formula') {
      $submission->data[$component['cid']][0] = webform_calculator_replace_formula_values($component, $node, $submission);
    }
  }
}

/**
 * Evaluate math formula.
 *
 * @param $formula
 *   Mathematical formula (without tokens).
 * @param int $precision
 *   Round precision.
 *
 * @return float
 *   Calculated value for given formula.
 */
function webform_calculator_eval($formula, $precision = 1) {
  eval("\$result = $formula;");
  return round($result, $precision);
}

/**
 * Implements hook_theme().
 */
function webform_calculator_theme() {
  return array(webform_component_invoke('formula', 'theme'));
}

/**
 * Get list of component names inside formula.
 *
 * @param $formula
 *   Formula to be searched in (with tokens).
 *
 * @return array
 *   Names of components that are used in formula as tokens.
 */
function webform_calculator_get_components_from_formula($formula) {
  $components = array();
  if (preg_match_all(WEBFORM_CALCULATOR_REGEX, $formula, $matches)) {
    foreach ((array)$matches[0] as $match) {
      $components[] = str_replace(array('{', '}'), array('', ''), $match);
    }
  }
  return $components;
}

/**
 * Replace tokens in formula with values of components and evaluate formula.
 *
 * @param $formula_component
 *   Formula compont.
 * @param $webform_node
 *   Webform's node.
 * @param $submission
 *   Webform submission.
 *
 * @return float|int
 *   Value of evaluated formula.
 */
function webform_calculator_replace_formula_values($formula_component, $webform_node, $submission) {
  $formula = $formula_component['value'];
  $components_from_formula = webform_calculator_get_components_from_formula($formula);

  // Get webform components keyed by form key.
  $components_by_key = array();
  foreach ($webform_node->webform['components'] as $component) {
    $components_by_key[$component['form_key']] = $component;
  }

  foreach ($components_from_formula as $component_key) {
    if (isset($components_by_key[$component_key])) {
      $component = $components_by_key[$component_key];
      $values = $submission->data[$component['cid']];
      $sum = 0;
      foreach ($values as $value) {
        $sum += $value;
      }
      $formula = str_replace('{' . $component_key . '}', '(' . $sum . ')', $formula);
    }
  }

  try  {
    webform_calculator_validate_php($formula);
    return webform_calculator_eval($formula, $formula_component['extra']['precision']);
  }
  catch (Exception $e) {
    watchdog_exception('webform_calculator', $e);
    return 0;
  }
}

/**
 * Validate if code that will be used with eval is secure and valid.
 *
 * @param $code
 *   PHP code to check.
 *
 * @return bool
 *   TRUE if code is valid, FALSE otherwise.
 *
 * @throws Exception
 */
function webform_calculator_validate_php($code) {
  $allowed_tokens = array(T_LNUMBER, T_DNUMBER, T_WHITESPACE);
  $allowed_chars = array('+', '-', '*', '/', '(', ')', '%');

  $tokens = token_get_all('<?php ' . $code);
  // Remove opening php tag.
  array_shift($tokens);

  foreach ($tokens as $token) {
    // Checking for allowed characters.
    if (is_string($token)) {
      if (!in_array($token, $allowed_chars)) {
        throw new Exception(t('Disallowed character %char was used.', array('%char' => $token)));
      }
      continue;
    }
    // Checking for allowed tokens.
    if (!in_array($token[0], $allowed_tokens)) {
      throw new Exception(t('Using %token is disallowed.', array('%token' => token_name($token[0]))));
    }
  }

  // Check PHP syntax.
  ob_start();
  if (@eval("\$return_array = $code;") === FALSE) {
    throw new Exception(t('Error occurred while parsing code.'));
  }
  else {
    ob_end_clean();
    return TRUE;
  }
}

/**
 * Implements hook_form_builder_element_types().
 * @param string $form_type
 * @param int $form_id
 * @return array
 */
function webform_calculator_form_builder_element_types($form_type, $form_id) {
  if ($form_type == 'webform') {
    drupal_add_css(drupal_get_path('module', 'webform_calculator') . '/formula.css');
    $fields = array(
      'formula' => array(
        'title' => t('Formula'),
        'weight' => -30,
        'properties' => array(
          'title',
          'value',
          'description',
          'field_prefix',
          'field_suffix',
          'hidden',
          'size',
          'title_display',
          'error_message',
          'precision',
        ),
      ),
    );
    if (function_exists('_form_builder_webform_default')) {
      $fields['formula']['default'] = _form_builder_webform_default('formula', array(), array('name' => t('New formula')));
    }

    return $fields;
  }
}

/**
 * Implements hook_form_builder_preview_alter().
 */
function webform_calculator_form_builder_preview_alter(&$element, $form_type, $form_id) {
  if ($form_type == 'webform' && $element['#webform_component']['type'] == 'formula') {
    $element['#attributes']['placeholder'] = $element['#webform_component']['value'];
  }
}