From 6fc5e535df479382cf08e5ae1f67291ed39faeb5 Mon Sep 17 00:00:00 2001
From: Joseph Milazzo <joseph.v.milazzo@gmail.com>
Date: Mon, 10 May 2021 09:50:26 -0500
Subject: [PATCH] Fixed #206 (#207)

---
 API/Controllers/ReaderController.cs | 62 +++++++++++++++++++++++------
 1 file changed, 50 insertions(+), 12 deletions(-)

diff --git a/API/Controllers/ReaderController.cs b/API/Controllers/ReaderController.cs
index 43197248e..383021408 100644
--- a/API/Controllers/ReaderController.cs
+++ b/API/Controllers/ReaderController.cs
@@ -254,9 +254,10 @@ namespace API.Controllers
             var volumes = await _unitOfWork.SeriesRepository.GetVolumesDtoAsync(seriesId, user.Id);
             var currentVolume = await _unitOfWork.SeriesRepository.GetVolumeAsync(volumeId);
 
-            var next = false;
+            
             if (currentVolume.Number == 0)
             {
+                var next = false;
                 foreach (var chapter in currentVolume.Chapters)
                 {
                     if (next)
@@ -265,11 +266,20 @@ namespace API.Controllers
                     }
                     if (currentChapterId == chapter.Id) next = true;
                 }
+
+                var chapterId = GetNextChapterId(currentVolume.Chapters, currentChapterId);
+                if (chapterId > 0) return Ok(chapterId);
             }
 
             foreach (var volume in volumes)
             {
-                if (volume.Number == currentVolume.Number + 1)
+                if (volume.Number == currentVolume.Number && volume.Chapters.Count > 1)
+                { 
+                    var chapterId = GetNextChapterId(currentVolume.Chapters, currentChapterId);
+                    if (chapterId > 0) return Ok(chapterId);
+                }
+                
+                if (volume.Number == currentVolume.Number)
                 {
                     return Ok(volume.Chapters.FirstOrDefault()?.Id);
                 }
@@ -277,6 +287,36 @@ namespace API.Controllers
             return Ok(-1);
         }
 
+        private int GetNextChapterId(Volume currentVolume, int currentChapterId)
+        {
+            var next = false;
+            foreach (var chapter in currentVolume.Chapters)
+            {
+                if (next)
+                {
+                    return chapter.Id;
+                }
+                if (currentChapterId == chapter.Id) next = true;
+            }
+
+            return -1;
+        }
+        
+        private int GetNextChapterId(IEnumerable<Chapter> chapters, int currentChapterId)
+        {
+            var next = false;
+            foreach (var chapter in chapters)
+            {
+                if (next)
+                {
+                    return chapter.Id;
+                }
+                if (currentChapterId == chapter.Id) next = true;
+            }
+
+            return -1;
+        }
+
         /// <summary>
         /// Returns the previous logical volume from the series.
         /// </summary>
@@ -291,22 +331,20 @@ namespace API.Controllers
             var volumes = await _unitOfWork.SeriesRepository.GetVolumesDtoAsync(seriesId, user.Id);
             var currentVolume = await _unitOfWork.SeriesRepository.GetVolumeAsync(volumeId);
 
-            var next = false;
+            
             if (currentVolume.Number == 0)
             {
-                var chapters = currentVolume.Chapters.Reverse();
-                foreach (var chapter in chapters)
-                {
-                    if (next)
-                    {
-                        return Ok(chapter.Id);
-                    }
-                    if (currentChapterId == chapter.Id) next = true;
-                }
+                var chapterId = GetNextChapterId(currentVolume.Chapters.Reverse(), currentChapterId);
+                if (chapterId > 0) return Ok(chapterId);
             }
 
             foreach (var volume in volumes.Reverse())
             {
+                if (volume.Number == currentVolume.Number)
+                {
+                    var chapterId = GetNextChapterId(currentVolume.Chapters.Reverse(), currentChapterId);
+                    if (chapterId > 0) return Ok(chapterId);
+                }
                 if (volume.Number == currentVolume.Number - 1)
                 {
                     return Ok(volume.Chapters.LastOrDefault()?.Id);