Aaron Parecki

<?php /*
 
Affiliate Link Mapping
======================
 
Map affiliate links from the main landing page to individual affiliate links 
for specific stores.
 
Usage
-----
 
Define your affiliate link mapping in the `$AFFILIATES` array. The top-level 
keys are your own affiliate links you make up for your main site. Each 
is an array listing out the query string parameters for the other stores 
affiliate programs.
 
```
$AFFILIATES = [
  'user1' => [
    'store1' => ['p' => '1'],
    'store2' => ['aff' => 'y2'],
    'store3' => ['aff' => '1'],
    'store4' => ['tag' => 'hello-20'],
  ],
  'user2' => [
    'store3' => ['aff' => 'y3'],
  ],
  'user3' => [
    'store1' => ['p' => '3', 'q' => '4'],
  ],
  'user4' => [
    'store2' => ['aff' => 'y8'],
    'store3' => ['aff' => '4'],
  ],
];
```
 
In this example, we create 4 new affiliate codes `user1`, `user2`, etc. 
There are also 4 stores defined, each with their own different set of 
affiliate link parameters.
 
The links from your main website, e.g. `https://example.com/?ref=user1` 
should be turned into links to the individual stores with different 
parameters such as: `https://store1.example/?p=1` and 
`https://store2.example/?aff=y2` etc.
 
When you want to display a link to one of the products, call the 
function `affiliate_link()` with the normal URL to the store and 
the name of the store, e.g.
 
`<?= affiliate_link('https://store1.example/', 'store1'); ?>`
 
The function will add the appropriate query string parameters to 
the store1 link based on the referral code in the URL if present.
 
Note: If you want to persist this across pageloads, you'll need to 
modify the function to store the main affiliate code in the session.
 
 
*/
 
$AFFILIATES = [
  'user1' => [
    'store1' => ['p' => '1'],
    'store2' => ['aff' => 'y2'],
    'store3' => ['aff' => '1'],
    'store4' => ['tag' => 'hello-20'],
  ],
  'user2' => [
    'store3' => ['aff' => 'y3'],
  ],
  'user3' => [
    'store1' => ['p' => '3', 'q' => '4'],
  ],
  'user4' => [
    'store2' => ['aff' => 'y8'],
    'store3' => ['aff' => '4'],
  ],
];
 
function affiliate_link($link, $store) {
  global $AFFILIATES;
 
  // Find current affiliate from query string
  if(isset($_GET['ref'])) {
    $affiliate = $_GET['ref'];
  } else {
    // default to the first affiliate defined
    $affiliate = $AFFILIATES[];
  }
 
  // Check if that affiliate has a tracking code for the given store
  if(isset($AFFILIATES[$affiliate][$store]))
    $params = $AFFILIATES[$affiliate][$store];
  else
    $params = [];
 
  // Add tracking code to the store link
  return add_query_params_to_url($link, $params);
}
 
 
function add_query_params_to_url($url, $add_params) {
  $parts = parse_url($url);
  if(array_key_exists('query', $parts) && $parts['query']) {
    parse_str($parts['query'], $params);
  } else {
    $params = [];
  }
 
  foreach($add_params as $k=>$v) {
    $params[$k] = $v;
  }
 
  $parts['query'] = http_build_query($params);
 
  return build_url($parts);
}
 
// Inverse of parse_url()
// http://php.net/parse_url
function build_url($parsed_url) {
  $scheme   = !empty($parsed_url['scheme']) ? $parsed_url['scheme'] . '://' : '';
  $host     = !empty($parsed_url['host']) ? $parsed_url['host'] : '';
  $port     = !empty($parsed_url['port']) ? ':' . $parsed_url['port'] : '';
  $user     = !empty($parsed_url['user']) ? $parsed_url['user'] : '';
  $pass     = !empty($parsed_url['pass']) ? ':' . $parsed_url['pass']  : '';
  $pass     = ($user || $pass) ? "$pass@" : '';
  $path     = !empty($parsed_url['path']) ? $parsed_url['path'] : '';
  $query    = !empty($parsed_url['query']) ? '?' . $parsed_url['query'] : '';
  $fragment = !empty($parsed_url['fragment']) ? '#' . $parsed_url['fragment'] : '';
  return "$scheme$user$pass$host$port$path$query$fragment";
}