farmOS/modules/farm/farm_metrics/farm_metrics.module

<?php
/**
 * @file
 * Farm metrics module.
 */

/**
 * Implements hook_hook_info().
 */
function farm_metrics_hook_info() {
  $hooks['farm_metrics'] = array(
    'group' => 'farm_metrics',
  );
  return $hooks;
}

/**
 * Implements hook_permission().
 */
function farm_metrics_permission() {
  $perms = array(
    'access farm metrics' => array(
      'title' => t('Access farm metrics'),
    ),
  );
  return $perms;
}

/**
 * Implements hook_farm_access_perms().
 */
function farm_metrics_farm_access_perms($role) {
  $perms = array();

  // Access farm metrics.
  $perms[] = 'access farm metrics';

  return $perms;
}

/**
 * Implements hook_farm_info().
 */
function farm_metrics_farm_info() {
  if (user_access('access farm metrics')) {
    return array(
      'metrics' => farm_metrics(),
    );
  }
}

/**
 * Returns a sorted array of all metrics.
 */
function farm_metrics() {

  // Ask modules for metrics.
  $metrics = module_invoke_all('farm_metrics');

  // If no metrics are available, return an empty array.
  if (empty($metrics)) {
    return array();
  }

  // Make sure all metrics have defaults set.
  $defaults = array(
    'label' => '',
    'value' => '0',
    'link' => 'farm',
    'weight' => 0,
  );
  foreach ($metrics as $key => $metric) {
    $metrics[$key] = array_merge($defaults, $metric);
  }

  // Sort the metrics by weight ascending, value descending.
  $weight_index = array();
  $value_index = array();
  foreach ($metrics as $key => $row) {
    $weight_index[$key]  = $row['weight'];
    $value_index[$key] = $row['value'];
  }
  array_multisort($weight_index, SORT_ASC, $value_index, SORT_DESC, $metrics);

  // Return metrics.
  return $metrics;
}