From 4fa01216b1fb8057c3028bead7327b33389ee081 Mon Sep 17 00:00:00 2001
From: huangyuhui <huanghongxun2008@126.com>
Date: Sat, 30 Jun 2018 22:09:35 +0800
Subject: [PATCH] Add debug message for tracing EmptyStackException and
 IllegalStateException

---
 .../hmcl/ui/download/DownloadWizardProvider.java    |  4 ++--
 .../jackhuang/hmcl/ui/wizard/WizardController.java  | 13 +++++++++----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/download/DownloadWizardProvider.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/download/DownloadWizardProvider.java
index 49d540a74..00cb98ed9 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/download/DownloadWizardProvider.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/download/DownloadWizardProvider.java
@@ -102,10 +102,10 @@ public final class DownloadWizardProvider implements WizardProvider {
                     case 1:
                         return new ModpackPage(controller);
                     default:
-                        throw new IllegalStateException("Error step " + step + ", subStep " + subStep + ", settings: " + settings);
+                        throw new IllegalStateException("Error step " + step + ", subStep " + subStep + ", settings: " + settings + ", pages: " + controller.getPages());
                 }
             default:
-                throw new IllegalStateException("error step " + step + ", settings: " + settings);
+                throw new IllegalStateException("error step " + step + ", settings: " + settings + ", pages: " + controller.getPages());
         }
     }
 
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardController.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardController.java
index 85f8725b8..f348e7462 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardController.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardController.java
@@ -20,10 +20,7 @@ package org.jackhuang.hmcl.ui.wizard;
 import javafx.scene.Node;
 import org.jackhuang.hmcl.task.Task;
 
-import java.util.HashMap;
-import java.util.Map;
-import java.util.Objects;
-import java.util.Stack;
+import java.util.*;
 
 public class WizardController implements Navigation {
     private final WizardDisplayer displayer;
@@ -47,6 +44,10 @@ public class WizardController implements Navigation {
         this.provider = provider;
     }
 
+    public List<Node> getPages() {
+        return Collections.unmodifiableList(pages);
+    }
+
     @Override
     public void onStart() {
         Objects.requireNonNull(provider);
@@ -81,6 +82,10 @@ public class WizardController implements Navigation {
 
     @Override
     public void onPrev(boolean cleanUp) {
+        if (!canPrev()) {
+            throw new IllegalStateException("Cannot go backward since this is the back page. Pages: " + pages);
+        }
+        
         Node page = pages.pop();
         if (cleanUp && page instanceof WizardPage)
             ((WizardPage) page).cleanup(settings);