Stock Threshold

This is what I came up with (sorry I don't know how to roll a patch yet):

In commerce_stock/includes/commerce_stock.admin.inc we can add the following to commerce_stock_admin_form() function...

function commerce_stock_admin_form($form, &$form_state) {
  //... about line 51.
  //      '#title' => t('Allow stock override for @name (@machine_name)', array('@name' => $product_type['name'], '@machine_name' => $type)),
  //    );
  //  }
  //}

  $form['stock_threshold'] = array(
    '#type' => 'fieldset',
    '#title' => t('Enable Stock Threshold'),
    '#description' => t('This sets a threshold margin from the current stock. So if 2 is inserted and the product has 6 units in stock, we can only buy 4 units.')
  );
  $form['stock_threshold']['threshold_value'] = array(
    '#type' => 'textfield',
    '#title' => t('Stock Threshold'),
    '#description' => t('Insert <strong>0</strong> to disable the threshold in stock calculations.'),
    '#default_value' => variable_get('threshold_value', 0),
    '#size' => 10,
    '#maxlength' => 2,
  );

  // Add a checkbox that requires them to say "I do", but don't show it
  //...
}

To validate the textfield as a number we modify also commerce_stock_admin_form_validate() function...

function commerce_stock_admin_form_validate($form, &$form_state) {
  if (!empty($form_state['commerce_stock']['delete_instances']) && empty($form_state['values']['confirmation'])) {
    form_set_error('confirmation', t('Please check the "I understand" checkbox to indicate you understand that all stock data in these fields will be deleted: %fields.', array('%fields' => implode(', ', $form_state['commerce_stock']['delete_instances']))));
  }

  // Validate Stock Threshold.
  $threshold = $form_state['values']['stock_threshold']['threshold_value'];
  if (!is_numeric($threshold)) {
    form_set_error('threshold_value', t('Stock Threshold must be a number.'));
  }
}

Then we can modify commerce_stock_product_check_out_of_stock() function in commerce_stock/commerce_stock.module...

function commerce_stock_product_check_out_of_stock($product_id ,$quantity, &$remaining_stock) {
  $product = commerce_product_load($product_id);
  // @todo: We shouldn't be using 'und' here should we?
  if(isset($product->commerce_stock['und'])){
    if ((isset($product->commerce_stock_override['und']) && $product->commerce_stock_override['und'][0]['value'] == 1)) {
     return FALSE;
    }

    // Check stock threshold.
    $threshold = variable_get('threshold_value', 0);

    // How many do we have for sale? Can't be less than zero.
    $remaining_stock = $product->commerce_stock['und'][0]['value'] - $threshold; // Use the threshold.
    if ($remaining_stock < 0) {
      $remaining_stock = 0;
    }
    if( ($remaining_stock < $quantity)) {
      return TRUE;
    }
    else  {
      return FALSE;
    }
  }
  else {
    return FALSE;
  }
}

This is not fully tested (for starts we can't seem to submit the configuration form correctly. After submit it always sets the value of the threshold textfield to 0), but it should work and is rather easy to implement.

Sorry, didn't read your answer before my previous comment. I will take a look, thanks :)

EDIT: After viewing the video... well, it's not the same functionality I was looking for, but gave me some ideas about Rules I will try tomorrow.

What we needed is a global parameter that stops the user from buying more products than ($stock - $threshold). That includes, validation on various forms, rules integration (the commerce_stock_product_check_out_of_stock() function is called by commerce_stock_order_has_out_of_stock() which is called in commerce_stock.rules.inc) and making the add to cart button disabled if it does not meet the requierements. Will try some other ideas. Thanks again!

Thanks for the tips!

I think the easiest way for now is doing this in the product import/update using feed tamper (php plugin) and removing the threshold in the process. As I said our thrshold is a constant in a module so it should be no problem doing this :)