/app/code/core/Mage/Weee/Model/Observer.php

<?php
/**
 * Magento
 *
 * NOTICE OF LICENSE
 *
 * This source file is subject to the Open Software License (OSL 3.0)
 * that is bundled with this package in the file LICENSE.txt.
 * It is also available through the world-wide-web at this URL:
 * http://opensource.org/licenses/osl-3.0.php
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to license@magentocommerce.com so we can send you a copy immediately.
 *
 * DISCLAIMER
 *
 * Do not edit or add to this file if you wish to upgrade Magento to newer
 * versions in the future. If you wish to customize Magento for your
 * needs please refer to http://www.magentocommerce.com for more information.
 *
 * @category    Mage
 * @package     Mage_Weee
 * @copyright   Copyright (c) 2012 Magento Inc. (http://www.magentocommerce.com)
 * @license     http://opensource.org/licenses/osl-3.0.php  Open Software License (OSL 3.0)
 */

class Mage_Weee_Model_Observer extends Mage_Core_Model_Abstract
{
    /**
     * Assign custom renderer for product create/edit form weee attribute element
     *
     * @param Varien_Event_Observer $observer
     * @return  Mage_Weee_Model_Observer
     */
    public function setWeeeRendererInForm(Varien_Event_Observer $observer)
    {
        //adminhtml_catalog_product_edit_prepare_form

        $form = $observer->getEvent()->getForm();
//        $product = $observer->getEvent()->getProduct();

        $attributes = Mage::getSingleton('weee/tax')->getWeeeAttributeCodes(true);
        foreach ($attributes as $code) {
            if ($weeeTax = $form->getElement($code)) {
                $weeeTax->setRenderer(
                    Mage::app()->getLayout()->createBlock('weee/renderer_weee_tax')
                );
            }
        }

        return $this;
    }

    /**
     * Exclude WEEE attributes from standard form generation
     *
     * @param Varien_Event_Observer $observer
     * @return  Mage_Weee_Model_Observer
     */
    public function updateExcludedFieldList(Varien_Event_Observer $observer)
    {
        //adminhtml_catalog_product_form_prepare_excluded_field_list

        $block      = $observer->getEvent()->getObject();
        $list       = $block->getFormExcludedFieldList();
        $attributes = Mage::getSingleton('weee/tax')->getWeeeAttributeCodes(true);
        $list       = array_merge($list, array_values($attributes));

        $block->setFormExcludedFieldList($list);

        return $this;
    }

    /**
     * Add additional price calculation to select object which is using for select indexed data
     *
     * @param   Varien_Event_Observer $observer
     * @return  Mage_Weee_Model_Observer
     */
    public function prepareCatalogIndexSelect(Varien_Event_Observer $observer)
    {
        $storeId = (int)$observer->getEvent()->getStoreId();
        if (!Mage::helper('weee')->isEnabled($storeId)) {
            return $this;
        }

        switch(Mage::helper('weee')->getListPriceDisplayType()) {
            case Mage_Weee_Model_Tax::DISPLAY_EXCL_DESCR_INCL:
            case Mage_Weee_Model_Tax::DISPLAY_EXCL:
                return $this;
        }

        /** @var $select Varien_Db_Select */
        $select = $observer->getEvent()->getSelect();
        $table  = $observer->getEvent()->getTable();

        $websiteId       = (int)Mage::app()->getStore($storeId)->getWebsiteId();
        $customerGroupId = (int)Mage::getSingleton('customer/session')->getCustomerGroupId();

        $response               = $observer->getEvent()->getResponseObject();
        $additionalCalculations = $response->getAdditionalCalculations();

        $attributes = Mage::getSingleton('weee/tax')->getWeeeAttributeCodes();

        if ($attributes && Mage::helper('weee')->isDiscounted()) {
            $joinConditions = array(
                "discount_percent.entity_id = {$table}.entity_id",
                $select->getAdapter()->quoteInto('discount_percent.website_id = ?', $websiteId),
                $select->getAdapter()->quoteInto('discount_percent.customer_group_id = ?', $customerGroupId)
            );
            $tableWeeDiscount = Mage::getSingleton('weee/tax')->getResource()->getTable('weee/discount');
            $select->joinLeft(
                array('discount_percent' => $tableWeeDiscount),
                implode(' AND ', $joinConditions),
                array()
            );
        }
        $checkDiscountField = $select->getAdapter()->getCheckSql(
            'discount_percent.value IS NULL', 0, 'discount_percent.value');
        foreach ($attributes as $attribute) {
            $fieldAlias = sprintf('weee_%s_table.value', $attribute);
            $checkAdditionalCalculation = $select->getAdapter()->getCheckSql("{$fieldAlias} IS NULL", 0, $fieldAlias);
            if (Mage::helper('weee')->isDiscounted()) {
                $additionalCalculations[] = sprintf('+(%s*(1-(%s/100)))', $checkAdditionalCalculation, $checkDiscountField);
            } else {
                $additionalCalculations[] = "+($checkAdditionalCalculation)";
            }
        }
        $response->setAdditionalCalculations($additionalCalculations);

        /** @var $rateRequest Varien_Object */
        $rateRequest = Mage::getSingleton('tax/calculation')->getRateRequest();

        $attributes  = Mage::getSingleton('weee/tax')->getWeeeTaxAttributeCodes();
        foreach ($attributes as $attribute) {
            $attributeId = (int)Mage::getSingleton('eav/entity_attribute')
                ->getIdByCode(Mage_Catalog_Model_Product::ENTITY, $attribute);
            $tableAlias  = sprintf('weee_%s_table', $attribute);
            $quotedTableAlias = $select->getAdapter()->quoteTableAs($tableAlias, null);
            $attributeSelect  = $this->_getSelect();
            $attributeSelect
                ->from(array($tableAlias => Mage::getSingleton('weee/tax')->getResource()->getTable('weee/tax')))
                ->where("{$quotedTableAlias}.attribute_id = ?", $attributeId)
                ->where("{$quotedTableAlias}.website_id IN(?)", array($websiteId, 0))
                ->where("{$quotedTableAlias}.country = ?", $rateRequest->getCountryId())
                ->where("{$quotedTableAlias}.state IN(?)", array($rateRequest->getRegionId(), '*'));

            $order = array(
                sprintf('%s.state %s', $tableAlias, Varien_Db_Select::SQL_DESC),
                sprintf('%s.website_id %s', $tableAlias, Varien_Db_Select::SQL_DESC)
            );
            $attributeSelect->order($order);

            $joinCondition = sprintf('%s.entity_id = %s.entity_id', $table, $quotedTableAlias);
            $select->joinLeft(
                array($tableAlias => $attributeSelect),
                $joinCondition,
                array()
            );
        }
        return $this;
    }

    /**
     * Get empty select object
     *
     * @return Varien_Db_Select
     */
    protected function _getSelect()
    {
        return Mage::getSingleton('weee/tax')->getResource()->getReadConnection()->select();
    }

    /**
     * Add new attribute type to manage attributes interface
     *
     * @param   Varien_Event_Observer $observer
     * @return  Mage_Weee_Model_Observer
     */
    public function addWeeeTaxAttributeType(Varien_Event_Observer $observer)
    {
        // adminhtml_product_attribute_types

        $response = $observer->getEvent()->getResponse();
        $types = $response->getTypes();
        $types[] = array(
            'value' => 'weee',
            'label' => Mage::helper('weee')->__('Fixed Product Tax'),
            'hide_fields' => array(
                'is_unique',
                'is_required',
                'frontend_class',
                'is_configurable',

                '_scope',
                '_default_value',
                '_front_fieldset',
            ),
            'disabled_types' => array(
                Mage_Catalog_Model_Product_Type::TYPE_GROUPED,
            )
        );

        $response->setTypes($types);

        return $this;
    }

    /**
     * Automaticaly assign backend model to weee attributes
     *
     * @param   Varien_Event_Observer $observer
     * @return  Mage_Weee_Model_Observer
     */
    public function assignBackendModelToAttribute(Varien_Event_Observer $observer)
    {
        $backendModel = Mage_Weee_Model_Attribute_Backend_Weee_Tax::getBackendModelName();
        /** @var $object Mage_Eav_Model_Entity_Attribute_Abstract */
        $object = $observer->getEvent()->getAttribute();
        if ($object->getFrontendInput() == 'weee') {
            $object->setBackendModel($backendModel);
            if (!$object->getApplyTo()) {
                $applyTo = array();
                foreach (Mage_Catalog_Model_Product_Type::getOptions() as $option) {
                    if ($option['value'] == Mage_Catalog_Model_Product_Type::TYPE_GROUPED) {
                        continue;
                    }
                    $applyTo[] = $option['value'];
                }
                $object->setApplyTo($applyTo);
            }
        }

        return $this;
    }

    /**
     * Add custom element type for attributes form
     *
     * @param   Varien_Event_Observer $observer
     */
    public function updateElementTypes(Varien_Event_Observer $observer)
    {
        $response = $observer->getEvent()->getResponse();
        $types    = $response->getTypes();
        $types['weee'] = Mage::getConfig()->getBlockClassName('weee/element_weee_tax');
        $response->setTypes($types);
        return $this;
    }

    /**
     * Update WEEE amounts discount percents
     *
     * @param   Varien_Event_Observer $observer
     * @return  Mage_Weee_Model_Observer
     */
    public function updateDiscountPercents(Varien_Event_Observer $observer)
    {
        if (!Mage::helper('weee')->isEnabled()) {
            return $this;
        }

        $productCondition = $observer->getEvent()->getProductCondition();
        if ($productCondition) {
            $eventProduct = $productCondition;
        } else {
            $eventProduct = $observer->getEvent()->getProduct();
        }
        Mage::getModel('weee/tax')->updateProductsDiscountPercent($eventProduct);

        return $this;
    }

    /**
     * Update configurable options of the product view page
     *
     * @param   Varien_Event_Observer $observer
     * @return  Mage_Weee_Model_Observer
     */
    public function updateCofigurableProductOptions(Varien_Event_Observer $observer)
    {
        /* @var $weeeHelper Mage_Weee_Helper_Data */
        $weeeHelper = Mage::helper('weee');
        if (!$weeeHelper->isEnabled()) {
            return $this;
        }

        $response = $observer->getEvent()->getResponseObject();
        $options  = $response->getAdditionalOptions();

        $_product = Mage::registry('current_product');
        if (!$_product) {
            return $this;
        }

        $amount          = $weeeHelper->getAmount($_product);
        $origAmount      = $weeeHelper->getOriginalAmount($_product);
        $attributes      = $weeeHelper->getProductWeeeAttributes($_product, null, null, null, $weeeHelper->isTaxable());
        $amountInclTaxes = $weeeHelper->getAmountInclTaxes($attributes);
        $taxes           = $amountInclTaxes - $amount;

        $options['oldPlusDisposition'] = $origAmount;
        $options['plusDisposition']    = $amount;
        $options['plusDispositionTax'] = ($taxes < 0) ? 0 : $taxes;

        // Exclude Weee amount from excluding tax amount
        if (!$weeeHelper->typeOfDisplay($_product, array(0, 1, 4))) {
            $options['exclDisposition'] = true;
        }

        $response->setAdditionalOptions($options);

        return $this;
    }

    /**
     * Process bundle options selection for prepare view json
     *
     * @param   Varien_Event_Observer $observer
     * @return  Mage_Weee_Model_Observer
     */
    public function updateBundleProductOptions(Varien_Event_Observer $observer)
    {
        /* @var $weeeHelper Mage_Weee_Helper_Data */
        $weeeHelper = Mage::helper('weee');
        if (!$weeeHelper->isEnabled()) {
            return $this;
        }

        $response = $observer->getEvent()->getResponseObject();
        $selection = $observer->getEvent()->getSelection();
        $options = $response->getAdditionalOptions();

        $_product = Mage::registry('current_product');

        $typeDynamic = Mage_Bundle_Block_Adminhtml_Catalog_Product_Edit_Tab_Attributes_Extend::DYNAMIC;
        if (!$_product || $_product->getPriceType() != $typeDynamic) {
            return $this;
        }

        $amount          = $weeeHelper->getAmount($selection);
        $attributes      = $weeeHelper->getProductWeeeAttributes($_product, null, null, null, $weeeHelper->isTaxable());
        $amountInclTaxes = $weeeHelper->getAmountInclTaxes($attributes);
        $taxes           = $amountInclTaxes - $amount;
        $options['plusDisposition']    = $amount;
        $options['plusDispositionTax'] = ($taxes < 0) ? 0 : $taxes;
        // Exclude Weee amount from excluding tax amount
        if (!$weeeHelper->typeOfDisplay($_product, array(0, 1, 4))) {
            $options['exclDisposition'] = true;
        }

        $response->setAdditionalOptions($options);

        return $this;
    }
}