PHP很难理解这个功能[关闭]

I have this function written by another programmer, but he quit long ago.

I was trying to understand this function that he wrote, but I don't fully understand it.

It's getting a token from the csv file, and the quantity should depend how much I choose. But what the force_plaform variable does? Also what the $_GET x-parameter and $_COOKIE x-parameter do?

// Get a purchaselink from a given token (if one exists) and a given csv
function getPurchaseLink($token, $csvfile, $force_platform = "", $quantity = 1)
{
$fp = fopen($csvfile, 'r', true);
$columns = fgetcsv($fp, 1024, ',');

while (($row = fgetcsv($fp, 1024, ","))) {
    $row = array_combine($columns, $row);
    if ($row['purchaseToken'] == $token) {
        $purchaseLink = $row;
        break;
    }
}

// Default to pucharse link
$url = http://www.purchase.com//?p1=zzM5X9k4dF%2BDzrTnixoaKw3Fg7wZ8h5pkjp%2BLEidTXBg40xOjcFj5PtPlQniMskLm0W3ti65mE2KafUifZe9dZAcE&ref=purchase.com&style=146&ga=UA-2689090-1&C1=C01507;1;0&C2=C0508;0;0;
if ($url) {     
  // Convert GET x-parameters to cmp, mkey1 and mkey2 if they are present
  $append = "";
  if((isset($_GET["x-source"])) && ($_GET["x-source"] != "")) {
    $append = "&cmp=source_" . $_GET["x-source"];
    $nextParameter = "x-" . $_GET["x-source"];
    $counter = 1;
    $searching = TRUE;
    while(($searching) && ($counter <= 2)) {
      if((!isset($_GET[$nextParameter])) || ($_GET[$nextParameter] == "")) {
        $searching = FALSE;
      }
      else {
        $append .= "&mkey" . $counter . "=" . str_replace("x-", "", $nextParameter) . "_" . $_GET[$nextParameter];
        $nextParameter = "x-" . $_GET[$nextParameter];
    $counter += 1;
      }
    }
  }
  // Convert COOKIE x-parameters to cmp, mkey1 and mkey2 if they are present and there are no GET x-parameters
  if(($append == "") && (isset($_COOKIE["x-source"])) && ($_COOKIE["x-source"] != "")) {
    $append = "&cmp=source_" . $_COOKIE["x-source"];
    $nextParameter = "x-" . $_COOKIE["x-source"];
    $counter = 1;
    $searching = TRUE;
    while(($searching) && ($counter <= 2)) {
      if((!isset($_COOKIE[$nextParameter])) || ($_COOKIE[$nextParameter] == "")) {
        $searching = FALSE;
      }
      else {
        $append .= "&mkey" . $counter . "=" . str_replace("x-", "", $nextParameter) . "_" . $_COOKIE[$nextParameter];
        $nextParameter = "x-" . $_COOKIE[$nextParameter];
    $counter += 1;
      }
    }
  }
  // Return upclick purchase link   
  return $url . $append;
}

if ($quantity != 1) {
    $url .= "&quantity=" . $quantity;
}

// Pass on tracking parameters from URI query and cookies
$append = "";
foreach($_GET as $parameter => $value) {
    if(strpos($parameter, "x-") === 0 || $parameter == "tracking" || $parameter == "serial" || $parameter == "affiliate") {
        $append .= "&" . $parameter . "=" . $value;
    }
}
if (empty($append)) {
    foreach($_COOKIE as $parameter => $value) {
        if(strpos($parameter, "x-") === 0) {
            $append .= "&" . $parameter . "=" . $value;
        }
    }
}

$append = str_replace("x-tracking", "tracking", $append);
$append = str_replace("x-affiliate", "affiliate", $append);
$append = str_replace("&serial=", "&x-serial=", $append);

return $url . $append;
 }

The function is building a query string (URL) and returning it. What the program does once it calls that URL is not up to this code, but the code on the page that gets called. This code just generates a URL. As to force_plaform, it does not appear to be being used in the function at all (just in the function header). It is an unused variable. As to the $_GET and $_COOKIE variables, the code is simply checking if they exist, and appending them to the query string if so.