Add feed identifiers

.gitignore

@@ -1,2 +1,3 @@
 vendor
 samples
+test.php

lib/XMLCommonPrimitives.php

@@ -121,4 +121,22 @@ trait XMLCommonPrimitives {
         return $grouped ? ['' => $out] : $out;
 
     }
+
+    /** Primitive to fetch an Atom feed/entry identifier */
+    protected function getIdAtom() {
+        return $this->fetchText("./atom:id");
+    }
+
+    /** Primitive to fetch an RSS feed/entry identifier 
+     * 
+     * Using RSS' <guid> for feed identifiers is non-standard, but harmless
+    */
+    protected function getIdRss2() {
+        return $this->fetchText("./guid");
+    }
+
+    /** Primitive to fetch a Dublin Core feed/entry identifier */
+    protected function getIdDC() {
+        return $this->fetchText("./dc:identifier");
+    }
 }

lib/XMLFeed.php

@@ -61,6 +61,7 @@ class XMLFeed extends XMLCommon {
 
     /** Parses the feed to extract sundry metadata */
     protected function parse() {
+        $this->id = $this->getId();
         $this->link = $this->getLink();
         $this->title = $this->getTitle() ?? $this->link;
         $this->summary = $this->getSummary();
@@ -91,4 +92,9 @@ class XMLFeed extends XMLCommon {
     public function getCategories(bool $grouped = false, bool $humanFriendly = true) {
         return $this->getCategoriesAtom($grouped, $humanFriendly) ?? $this->getCategoriesRss2($grouped, $humanFriendly) ?? $this->getCategoriesDC($grouped, $humanFriendly) ?? $this->getCategoriesApple($grouped, $humanFriendly);
     }
+
+    /** General function to fetch the feed identifier */
+    public function getId() {
+        return $this->getIdAtom() ?? $this->getIdDC() ?? $this->getIdRss2();
+    }
 }