Fix Prev/Next navigator was not pointing to the actual prev/next article (#348)

Signed-off-by: hossainemruz <hossainemruz@gmail.com>

layouts/partials/helpers/get-pages.html

@@ -0,0 +1,10 @@
+{{ $pages:= slice}}
+{{ range . }}
+    {{ if .HasChildren }}
+        {{ $nestedPages:=partial "helpers/get-pages.html" .Children }}
+        {{ $pages = $pages | append $nestedPages }}
+    {{ else }}
+        {{ $pages = $pages | append .Page }}
+    {{ end }}
+{{ end }}
+{{ return $pages}}

layouts/partials/navigators/next-prev-navigator.html

@@ -1,33 +1,39 @@
+{{ $curPage := . }}
+{{ $prevPage := "" }}
+{{ $nextPage := "" }}
+
+<!-- List all the pages. It uses the sidebar menu to discover the page order. -->
+{{ $pages := partial "helpers/get-pages.html" site.Menus.sidebar }}
+
+<!-- Now, find the current page index in the pages list. Then, find previous page and next page. -->
+{{ $idx := 0 }}
+{{ range $pages }}
+  {{ if eq .RelPermalink $curPage.RelPermalink }}
+    {{ $prevPage = index $pages (sub $idx 1) }}
+    {{ $nextPage = index $pages (add $idx 1) }}
+  {{ end }}
+  {{ $idx = add $idx 1 }}
+{{ end }}
+
 <div class="row next-prev-navigator">
-{{ $currentPage := . }}
-{{ range (where site.RegularPages.ByDate "Type" "in" site.Params.mainSections )}}
-  {{ if eq .RelPermalink  $currentPage.RelPermalink }}
-    {{ if .Next }}
-      {{ if (in site.Params.mainSections .Next.Type) }}
-      <div class="col-md-6 previous-article">
-        <a href="{{.Next.RelPermalink}}" title="{{ .Next.Title }}" class="btn btn-outline-info">
-          <div><i class="fas fa-chevron-circle-left"></i> {{ i18n "prev" }}</div>
-          <div class="next-prev-text">{{ .Next.Title }}</div>
+  {{ if $prevPage }}
+    <div class="col-md-6 previous-article">
+      <a href="{{ $prevPage.RelPermalink }}" title="{{ $prevPage.Title }}" class="btn btn-outline-info">
+        <div><i class="fas fa-chevron-circle-left"></i> {{ i18n "prev" }}</div>
+        <div class="next-prev-text">{{ $prevPage.Title }}</div>
+      </a>
+    </div>
+  {{ end }}
+  {{ if $nextPage }}
+      {{ $columnWidth:="col-md-12" }}
+      {{ if $prevPage }}
+        {{ $columnWidth = "col-md-6" }}
+      {{ end}}
+      <div class="{{ $columnWidth }} next-article">
+        <a href="{{ $nextPage.RelPermalink }}" title="{{ $nextPage.Title }}" class="btn btn-outline-info">
+          <div>{{ i18n "next" }} <i class="fas fa-chevron-circle-right"></i></div>
+          <div class="next-prev-text">{{ $nextPage.Title }}</div>
         </a>
       </div>
-      {{ end }}
     {{ end }}
-    {{ if .Prev }}
-      {{ if (in site.Params.mainSections .Prev.Type)  }}
-        {{ $columnWidth:="col-md-12" }}
-        {{ if .Next }}
-          {{ if (in site.Params.mainSections .Next.Type) }}
-              {{ $columnWidth = "col-md-6" }}
-          {{ end }}
-        {{ end}}
-        <div class="{{ $columnWidth }} next-article">
-          <a href="{{ .Prev.RelPermalink }}" title="{{ .Prev.Title }}" class="btn btn-outline-info">
-            <div>{{ i18n "next" }} <i class="fas fa-chevron-circle-right"></i></div>
-            <div class="next-prev-text">{{ .Prev.Title }}</div>
-          </a>
-        </div>
-      {{ end }}
-    {{ end }}
-  {{ end }}
-{{ end }}
 </div>