Next/Previous Product Links On Product Page

<?xml version="1.0"?>
<config>
    <modules>
        <Fc_NextPrevProduct>
            <version>0.1.0</version>
        </Fc_NextPrevProduct>
    </modules>
    <global>
        <helpers>
            <nextprevproduct>
                <class>Fc_NextPrevProduct_Helper</class>
            </nextprevproduct>
        </helpers>
    </global>
    <frontend>
        <layout>
            <updates>
                <Fc_nextprevproduct>
                    <file>fc/newprevproduct.xml</file>
                </fc_nextprevproduct>
            </updates>
        </layout>
    </frontend>
</config>

<?xml version="1.0"?>

<Fc_NextPrevProduct>

</Fc_NextPrevProduct>

</modules>

<class>Fc_NextPrevProduct_Helper</class>

</nextprevproduct>

</helpers>

</global>

<Fc_nextprevproduct>

<file>fc/newprevproduct.xml</file>

</fc_nextprevproduct>

</updates>

</layout>

</frontend>

</config>

<?php

class Fc_NextPrevProduct_Helper_Data extends Mage_Core_Helper_Abstract {

    public function getNextProductUrl($productId, $currentCategory) {


        if($currentCategory){

            $productId = (int)$productId;

            $currentCategory    = $this->_getProductsPosition( $currentCategory ) ;
            $keys               = array_flip(array_keys($currentCategory));
            $values             = array_keys($currentCategory);

            $lastProduct = end($values);
            //make sure that this isn't the last product in the category
            if($lastProduct != $productId) {
                $productId = $values[$keys[$productId]+1];
                $product = Mage::getModel('catalog/product');
                if($productId){
                    $product->load($productId);
                    return $product->getProductUrl();
                }
            } else {
                return false;
            }
        }

        return false;

    }
    
    
    public function _getProductsPosition( $a_category )
    {
        $category   = Mage::getModel('catalog/category')->load( $a_category->getId() );
        $positions  = Mage::getResourceModel('catalog/category')->getProductsPosition( $category );
        
        return $positions ;
    }

    public function getPrevProductUrl($productId, $currentCategory) {


        if($currentCategory){
            $currentCategory    = $this->_getProductsPosition( $currentCategory ) ;
            $keys               = array_flip(array_keys($currentCategory));
            $values             = array_keys($currentCategory);

            $productId = (int)$productId;


            //make sure this isn't the first product in the category
            if($values[0] != $productId) {
                $productId = $values[$keys[$productId]-1];
                $product = Mage::getModel('catalog/product');
                if($productId){
                    $product->load($productId);
                    return $product->getProductUrl();
                }
            } else {
                return false;
            }
        }

        return false;
    }

}

<?php

class Fc_NextPrevProduct_Helper_Data extends Mage_Core_Helper_Abstract {

public function getNextProductUrl($productId, $currentCategory) {

if($currentCategory){

$productId = (int)$productId;

$currentCategory = $this->_getProductsPosition( $currentCategory ) ;

$keys = array_flip(array_keys($currentCategory));

$values = array_keys($currentCategory);

$lastProduct = end($values);

//make sure that this isn't the last product in the category

if($lastProduct != $productId) {

$productId = $values[$keys[$productId]+1];

$product = Mage::getModel('catalog/product');

if($productId){

$product->load($productId);

return $product->getProductUrl();

}

} else {

return false;

}

return false;

}

public function _getProductsPosition( $a_category )

{

$category = Mage::getModel('catalog/category')->load( $a_category->getId() );

$positions = Mage::getResourceModel('catalog/category')->getProductsPosition( $category );

return $positions ;

}

public function getPrevProductUrl($productId, $currentCategory) {

if($currentCategory){

$currentCategory = $this->_getProductsPosition( $currentCategory ) ;

$keys = array_flip(array_keys($currentCategory));

$values = array_keys($currentCategory);

$productId = (int)$productId;

//make sure this isn't the first product in the category

if($values[0] != $productId) {

$productId = $values[$keys[$productId]-1];

$product = Mage::getModel('catalog/product');

if($productId){

$product->load($productId);

return $product->getProductUrl();

}

} else {

return false;

}

return false;

}

<?xml version="1.0"?>
<config>
    <modules>
        <Fc_NextPrevProduct>
            <active>true</active>
            <codePool>local</codePool>
        </Fc_NextPrevProduct>
    </modules>
</config>

<?xml version="1.0"?>

<Fc_NextPrevProduct>

<codePool>local</codePool>

</Fc_NextPrevProduct>

</modules>

</config>

Usage

The below can be used in any template file on a product page.

<?php
    $nextProductUrl = Mage::helper('nextprevproduct')->getNextProductUrl();
    $prevProductUrl = Mage::helper('nextprevproduct')->getPrevProductUrl();
?>
<?php if($prevProductUrl) : ?>
    <a href="<?php echo $prevProductUrl; ?>"><- Previous Product</a>
<?php endif; ?>

<?php if($nextProductUrl) : ?>
    <a href="<?php echo $prevProductUrl; ?>">Next Product --></a>
<?php endif; ?>

<?php

$nextProductUrl = Mage::helper('nextprevproduct')->getNextProductUrl();

$prevProductUrl = Mage::helper('nextprevproduct')->getPrevProductUrl();

<?php if($prevProductUrl) : ?>

<?php endif; ?>

<?php if($nextProductUrl) : ?>

<a href="<?php echo $prevProductUrl; ?>">Next Product --></a>

<?php endif; ?>