move SearchDescription building into tokens

Moving the logic for extending the SearchDescription into the
token classes splits up the code and makes it more readable.
More importantly: it allows tokenizer to define custom token
classes in the future.

lib-php/TokenCountry.php

@@ -8,9 +8,9 @@ namespace Nominatim\Token;
 class Country
 {
     /// Database word id, if available.
-    public $iId;
+    private $iId;
     /// Two-letter country code (lower-cased).
-    public $sCountryCode;
+    private $sCountryCode;
 
     public function __construct($iId, $sCountryCode)
     {
@@ -18,6 +18,32 @@ class Country
         $this->sCountryCode = $sCountryCode;
     }
 
+    public function getId()
+    {
+        return $this->iId;
+    }
+
+    /**
+     * Derive new searches by adding this token to an existing search.
+     *
+     * @param object  $oSearch      Partial search description derived so far.
+     * @param object  $oPosition    Description of the token position within
+                                    the query.
+     *
+     * @return SearchDescription[] List of derived search descriptions.
+     */
+    public function extendSearch($oSearch, $oPosition)
+    {
+        if ($oSearch->hasCountry() || !$oPosition->maybePhrase('country')) {
+            return array();
+        }
+
+        $oNewSearch = $oSearch->clone($oPosition->isLastToken() ? 1 : 6);
+        $oNewSearch->setCountry($this->sCountryCode);
+
+        return array($oNewSearch);
+    }
+
     public function debugInfo()
     {
         return array(
@@ -26,4 +52,9 @@ class Country
                 'Info' => $this->sCountryCode
                );
     }
+
+    public function debugCode()
+    {
+        return 'C';
+    }
 }