fix: prev/next navigation links in lessons

/spend 10h

user/plugins/m3-p2/m3-p2.php

@@ -381,18 +381,18 @@ class M3P2Plugin extends Plugin
                         // Found one, let's add it
                         $other_lessons[$page_lesson['slug']] = $page_lesson;
 
-                        // And the prev/next navigation
-                        if ($current_found) {
-                            if ( ! $next_found) {
-                                $next_lesson_slug = $page_lesson['slug'];
-                                $next_found = true;
-                            }
-                        } else {
-                            if ( ! $previous_found) {
-                                $previous_lesson_slug = $page_lesson['slug'];
-                                $previous_found = true;
-                            }
-                        }
+                        // And the prev/next navigation (the old way)
+//                        if ($current_found) {
+//                            if ( ! $next_found) {
+//                                $next_lesson_slug = $page_lesson['slug'];
+//                                $next_found = true;
+//                            }
+//                        } else {
+//                            if ( ! $previous_found) {
+//                                $previous_lesson_slug = $page_lesson['slug'];
+//                                $previous_found = true;
+//                            }
+//                        }
 
                     }
                     continue;
@@ -406,6 +406,24 @@ class M3P2Plugin extends Plugin
             }
         }
 
+        $redirects = array_values($this->getPagesWithRedirects());
+        $amountOfRedirects = count($redirects);
+        $redirect_parent_index = -1;
+        foreach ($redirects as $k => $redirect) {
+            if ($this->endsWith($redirect->redirect(), "/lessons/" . $lesson_slug)) {
+                $redirect_parent_index = $k;
+                break;
+            }
+        }
+        if ($redirect_parent_index > -1) {
+            if ($redirect_parent_index > 0) {
+                $previous_lesson_slug = $this->extractLessonSlug($redirects[$redirect_parent_index - 1]->redirect());
+            }
+            if ($redirect_parent_index < $amountOfRedirects - 1) {
+                $next_lesson_slug = $this->extractLessonSlug($redirects[$redirect_parent_index + 1]->redirect());
+            }
+        }
+
         $translated_lessons = [];  // lang => slug
         $translated_lessons_contenders = [];  // lang => [ slug => likelihood ]
 
@@ -464,4 +482,54 @@ class M3P2Plugin extends Plugin
         $event->page = $page;
         $event->stopPropagation();
     }
+
+    public function getPagesWithRedirects()
+    {
+        /** @var Pages $pages */
+        $pages = $this->grav['pages'];
+        $target_pages = array_filter($pages->instances(), function (Page $p) {
+
+            $page_config = $p->header();
+            if (empty($p->redirect())) {
+                return false;
+            }
+
+            return true;
+        });
+
+        return $target_pages;
+    }
+
+
+    protected function mbEndsWith($haystack, $needle, $case=true): bool
+    {
+        $expectedPosition = mb_strlen($haystack) - mb_strlen($needle);
+
+        if ($case) {
+            return mb_strrpos($haystack, $needle, 0) === $expectedPosition;
+        }
+
+        return mb_strripos($haystack, $needle, 0) === $expectedPosition;
+    }
+
+    protected function endsWith($haystack, $needle, $case=true): bool
+    {
+        $expectedPosition = strlen($haystack) - strlen($needle);
+
+        if ($case) {
+            return strrpos($haystack, $needle, 0) === $expectedPosition;
+        }
+
+        return strripos($haystack, $needle, 0) === $expectedPosition;
+    }
+
+    protected function extractLessonSlug(string $url) : string
+    {
+        $matches = array();
+        if (false !== preg_match("!/lessons/(?P<slug>[^#?&]+)!", $url, $matches)) {
+            return $matches['slug'];
+        }
+
+        return "";
+    }
 }